{-
(c) The AQUA Project, Glasgow University, 1993-1998

\section[Simplify]{The main module of the simplifier}
-}


{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE MultiWayIf #-}

{-# OPTIONS_GHC -Wno-incomplete-uni-patterns #-}
module GHC.Core.Opt.Simplify.Iteration ( simplTopBinds, simplExpr, simplImpRules ) where

import GHC.Prelude

import GHC.Platform

import GHC.Driver.Flags

import GHC.Core
import GHC.Core.Opt.Simplify.Monad
import GHC.Core.Type hiding ( substTy, substTyVar, extendTvSubst, extendCvSubst )
import GHC.Core.TyCo.Compare( eqType )
import GHC.Core.Opt.Simplify.Env
import GHC.Core.Opt.Simplify.Utils
import GHC.Core.Opt.OccurAnal ( occurAnalyseExpr, zapLambdaBndrs, scrutBinderSwap_maybe )
import GHC.Core.Make       ( FloatBind, mkImpossibleExpr, castBottomExpr )
import qualified GHC.Core.Make
import GHC.Core.Coercion hiding ( substCo, substCoVar )
import GHC.Core.Reduction
import GHC.Core.Coercion.Opt    ( optCoercion )
import GHC.Core.FamInstEnv      ( FamInstEnv, topNormaliseType_maybe )
import GHC.Core.DataCon
   ( DataCon, dataConWorkId, dataConRepStrictness
   , dataConRepArgTys, isUnboxedTupleDataCon
   , StrictnessMark (..) )
import GHC.Core.Opt.Stats ( Tick(..) )
import GHC.Core.Ppr     ( pprCoreExpr )
import GHC.Core.Unfold
import GHC.Core.Unfold.Make
import GHC.Core.Utils
import GHC.Core.Opt.Arity ( ArityType, exprArity, arityTypeBotSigs_maybe
                          , pushCoTyArg, pushCoValArg, exprIsDeadEnd
                          , typeArity, arityTypeArity, etaExpandAT )
import GHC.Core.SimpleOpt ( exprIsConApp_maybe, joinPointBinding_maybe, joinPointBindings_maybe )
import GHC.Core.FVs     ( mkRuleInfo )
import GHC.Core.Rules   ( lookupRule, getRules )
import GHC.Core.Multiplicity

import GHC.Types.Literal   ( litIsLifted ) --, mkLitInt ) -- temporarily commented out. See #8326
import GHC.Types.SourceText
import GHC.Types.Id
import GHC.Types.Id.Make   ( seqId )
import GHC.Types.Id.Info
import GHC.Types.Name   ( mkSystemVarName, isExternalName, getOccFS )
import GHC.Types.Demand
import GHC.Types.Unique ( hasKey )
import GHC.Types.Basic
import GHC.Types.Tickish
import GHC.Types.Var    ( isTyCoVar )
import GHC.Builtin.PrimOps ( PrimOp (SeqOp) )
import GHC.Builtin.Types.Prim( realWorldStatePrimTy )
import GHC.Builtin.Names( runRWKey )

import GHC.Data.Maybe   ( isNothing, orElse )
import GHC.Data.FastString
import GHC.Unit.Module ( moduleName )
import GHC.Utils.Outputable
import GHC.Utils.Panic
import GHC.Utils.Panic.Plain
import GHC.Utils.Constants (debugIsOn)
import GHC.Utils.Monad  ( mapAccumLM, liftIO )
import GHC.Utils.Logger
import GHC.Utils.Misc

import Control.Monad

{-
The guts of the simplifier is in this module, but the driver loop for
the simplifier is in GHC.Core.Opt.Pipeline

Note [The big picture]
~~~~~~~~~~~~~~~~~~~~~~
The general shape of the simplifier is this:

  simplExpr :: SimplEnv -> InExpr -> SimplCont -> SimplM (SimplFloats, OutExpr)
  simplBind :: SimplEnv -> InBind -> SimplM (SimplFloats, SimplEnv)

 * SimplEnv contains
     - Simplifier mode
     - Ambient substitution
     - InScopeSet

 * SimplFloats contains
     - Let-floats (which includes ok-for-spec case-floats)
     - Join floats
     - InScopeSet (including all the floats)

 * Expressions
      simplExpr :: SimplEnv -> InExpr -> SimplCont
                -> SimplM (SimplFloats, OutExpr)
   The result of simplifying an /expression/ is (floats, expr)
      - A bunch of floats (let bindings, join bindings)
      - A simplified expression.
   The overall result is effectively (let floats in expr)

 * Bindings
      simplBind :: SimplEnv -> InBind -> SimplM (SimplFloats, SimplEnv)
   The result of simplifying a binding is
     - A bunch of floats, the last of which is the simplified binding
       There may be auxiliary bindings too; see prepareRhs
     - An environment suitable for simplifying the scope of the binding

   The floats may also be empty, if the binding is inlined unconditionally;
   in that case the returned SimplEnv will have an augmented substitution.

   The returned floats and env both have an in-scope set, and they are
   guaranteed to be the same.


Note [Shadowing]
~~~~~~~~~~~~~~~~
The simplifier used to guarantee that the output had no shadowing, but
it does not do so any more.   (Actually, it never did!)  The reason is
documented with simplifyArgs.


Eta expansion
~~~~~~~~~~~~~~
For eta expansion, we want to catch things like

        case e of (a,b) -> \x -> case a of (p,q) -> \y -> r

If the \x was on the RHS of a let, we'd eta expand to bring the two
lambdas together.  And in general that's a good thing to do.  Perhaps
we should eta expand wherever we find a (value) lambda?  Then the eta
expansion at a let RHS can concentrate solely on the PAP case.

Note [In-scope set as a substitution]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
As per Note [Lookups in in-scope set], an in-scope set can act as
a substitution. Specifically, it acts as a substitution from variable to
variables /with the same unique/.

Why do we need this? Well, during the course of the simplifier, we may want to
adjust inessential properties of a variable. For instance, when performing a
beta-reduction, we change

    (\x. e) u ==> let x = u in e

We typically want to add an unfolding to `x` so that it inlines to (the
simplification of) `u`.

We do that by adding the unfolding to the binder `x`, which is added to the
in-scope set. When simplifying occurrences of `x` (every occurrence!), they are
replaced by their “updated” version from the in-scope set, hence inherit the
unfolding. This happens in `SimplEnv.substId`.

Another example. Consider

   case x of y { Node a b -> ...y...
               ; Leaf v   -> ...y... }

In the Node branch want y's unfolding to be (Node a b); in the Leaf branch we
want y's unfolding to be (Leaf v). We achieve this by adding the appropriate
unfolding to y, and re-adding it to the in-scope set. See the calls to
`addBinderUnfolding` in `Simplify.addAltUnfoldings` and elsewhere.

It's quite convenient. This way we don't need to manipulate the substitution all
the time: every update to a binder is automatically reflected to its bound
occurrences.

Note [Bangs in the Simplifier]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Both SimplFloats and SimplEnv do *not* generally benefit from making
their fields strict. I don't know if this is because of good use of
laziness or unintended side effects like closures capturing more variables
after WW has run.

But the end result is that we keep these lazy, but force them in some places
where we know it's beneficial to the compiler.

Similarly environments returned from functions aren't *always* beneficial to
force. In some places they would never be demanded so forcing them early
increases allocation. In other places they almost always get demanded so
it's worthwhile to force them early.

Would it be better to through every allocation of e.g. SimplEnv and decide
wether or not to make this one strict? Absolutely! Would be a good use of
someones time? Absolutely not! I made these strict that showed up during
a profiled build or which I noticed while looking at core for one reason
or another.

The result sadly is that we end up with "random" bangs in the simplifier
where we sometimes force e.g. the returned environment from a function and
sometimes we don't for the same function. Depending on the context around
the call. The treatment is also not very consistent. I only added bangs
where I saw it making a difference either in the core or benchmarks. Some
patterns where it would be beneficial aren't convered as a consequence as
I neither have the time to go through all of the core and some cases are
too small to show up in benchmarks.



************************************************************************
*                                                                      *
\subsection{Bindings}
*                                                                      *
************************************************************************
-}

simplTopBinds :: SimplEnv -> [InBind] -> SimplM (SimplFloats, SimplEnv)
-- See Note [The big picture]
simplTopBinds :: SimplEnv -> [InBind] -> SimplM (SimplFloats, SimplEnv)
simplTopBinds SimplEnv
env0 [InBind]
binds0
  = do  {       -- Put all the top-level binders into scope at the start
                -- so that if a rewrite rule has unexpectedly brought
                -- anything into scope, then we don't get a complaint about that.
                -- It's rather as if the top-level binders were imported.
                -- See Note [Glomming] in "GHC.Core.Opt.OccurAnal".
        -- See Note [Bangs in the Simplifier]
        ; !SimplEnv
env1 <- {-#SCC "simplTopBinds-simplRecBndrs" #-} SimplEnv -> [CoreBndr] -> SimplM SimplEnv
simplRecBndrs SimplEnv
env0 ([InBind] -> [CoreBndr]
forall b. [Bind b] -> [b]
bindersOfBinds [InBind]
binds0)
        ; (SimplFloats
floats, SimplEnv
env2) <- {-#SCC "simplTopBinds-simpl_binds" #-} SimplEnv -> [InBind] -> SimplM (SimplFloats, SimplEnv)
simpl_binds SimplEnv
env1 [InBind]
binds0
        ; Tick -> SimplM ()
freeTick Tick
SimplifierDone
        ; (SimplFloats, SimplEnv) -> SimplM (SimplFloats, SimplEnv)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplFloats
floats, SimplEnv
env2) }
  where
        -- We need to track the zapped top-level binders, because
        -- they should have their fragile IdInfo zapped (notably occurrence info)
        -- That's why we run down binds and bndrs' simultaneously.
        --
    simpl_binds :: SimplEnv -> [InBind] -> SimplM (SimplFloats, SimplEnv)
    simpl_binds :: SimplEnv -> [InBind] -> SimplM (SimplFloats, SimplEnv)
simpl_binds SimplEnv
env []           = (SimplFloats, SimplEnv) -> SimplM (SimplFloats, SimplEnv)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplEnv -> SimplFloats
emptyFloats SimplEnv
env, SimplEnv
env)
    simpl_binds SimplEnv
env (InBind
bind:[InBind]
binds) = do { (SimplFloats
float,  SimplEnv
env1) <- SimplEnv -> InBind -> SimplM (SimplFloats, SimplEnv)
simpl_bind SimplEnv
env InBind
bind
                                      ; (SimplFloats
floats, SimplEnv
env2) <- SimplEnv -> [InBind] -> SimplM (SimplFloats, SimplEnv)
simpl_binds SimplEnv
env1 [InBind]
binds
                                      -- See Note [Bangs in the Simplifier]
                                      ; let !floats1 :: SimplFloats
floats1 = SimplFloats
float SimplFloats -> SimplFloats -> SimplFloats
`addFloats` SimplFloats
floats
                                      ; (SimplFloats, SimplEnv) -> SimplM (SimplFloats, SimplEnv)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplFloats
floats1, SimplEnv
env2) }

    simpl_bind :: SimplEnv -> InBind -> SimplM (SimplFloats, SimplEnv)
simpl_bind SimplEnv
env (Rec [(CoreBndr, CoreExpr)]
pairs)
      = SimplEnv
-> BindContext
-> [(CoreBndr, CoreExpr)]
-> SimplM (SimplFloats, SimplEnv)
simplRecBind SimplEnv
env (TopLevelFlag -> RecFlag -> BindContext
BC_Let TopLevelFlag
TopLevel RecFlag
Recursive) [(CoreBndr, CoreExpr)]
pairs
    simpl_bind SimplEnv
env (NonRec CoreBndr
b CoreExpr
r)
      = do { let bind_cxt :: BindContext
bind_cxt = TopLevelFlag -> RecFlag -> BindContext
BC_Let TopLevelFlag
TopLevel RecFlag
NonRecursive
           ; (SimplEnv
env', CoreBndr
b') <- SimplEnv
-> CoreBndr
-> CoreBndr
-> BindContext
-> SimplM (SimplEnv, CoreBndr)
addBndrRules SimplEnv
env CoreBndr
b (SimplEnv -> CoreBndr -> CoreBndr
lookupRecBndr SimplEnv
env CoreBndr
b) BindContext
bind_cxt
           ; SimplEnv
-> BindContext
-> CoreBndr
-> CoreBndr
-> CoreExpr
-> SimplM (SimplFloats, SimplEnv)
simplRecOrTopPair SimplEnv
env' BindContext
bind_cxt CoreBndr
b CoreBndr
b' CoreExpr
r }

{-
************************************************************************
*                                                                      *
        Lazy bindings
*                                                                      *
************************************************************************

simplRecBind is used for
        * recursive bindings only
-}

simplRecBind :: SimplEnv -> BindContext
             -> [(InId, InExpr)]
             -> SimplM (SimplFloats, SimplEnv)
simplRecBind :: SimplEnv
-> BindContext
-> [(CoreBndr, CoreExpr)]
-> SimplM (SimplFloats, SimplEnv)
simplRecBind SimplEnv
env0 BindContext
bind_cxt [(CoreBndr, CoreExpr)]
pairs0
  = do  { (SimplEnv
env1, [(CoreBndr, CoreBndr, CoreExpr)]
triples) <- (SimplEnv
 -> (CoreBndr, CoreExpr)
 -> SimplM (SimplEnv, (CoreBndr, CoreBndr, CoreExpr)))
-> SimplEnv
-> [(CoreBndr, CoreExpr)]
-> SimplM (SimplEnv, [(CoreBndr, CoreBndr, CoreExpr)])
forall (m :: * -> *) (t :: * -> *) acc x y.
(Monad m, Traversable t) =>
(acc -> x -> m (acc, y)) -> acc -> t x -> m (acc, t y)
mapAccumLM SimplEnv
-> (CoreBndr, CoreExpr)
-> SimplM (SimplEnv, (CoreBndr, CoreBndr, CoreExpr))
add_rules SimplEnv
env0 [(CoreBndr, CoreExpr)]
pairs0
        ; let new_bndrs :: [CoreBndr]
new_bndrs = ((CoreBndr, CoreBndr, CoreExpr) -> CoreBndr)
-> [(CoreBndr, CoreBndr, CoreExpr)] -> [CoreBndr]
forall a b. (a -> b) -> [a] -> [b]
map (CoreBndr, CoreBndr, CoreExpr) -> CoreBndr
forall a b c. (a, b, c) -> b
sndOf3 [(CoreBndr, CoreBndr, CoreExpr)]
triples
        ; (SimplFloats
rec_floats, SimplEnv
env2) <- SimplEnv
-> [CoreBndr]
-> (SimplEnv -> SimplM (SimplFloats, SimplEnv))
-> SimplM (SimplFloats, SimplEnv)
forall r.
SimplEnv
-> [CoreBndr]
-> (SimplEnv -> SimplM (r, SimplEnv))
-> SimplM (r, SimplEnv)
enterRecGroupRHSs SimplEnv
env1 [CoreBndr]
new_bndrs ((SimplEnv -> SimplM (SimplFloats, SimplEnv))
 -> SimplM (SimplFloats, SimplEnv))
-> (SimplEnv -> SimplM (SimplFloats, SimplEnv))
-> SimplM (SimplFloats, SimplEnv)
forall a b. (a -> b) -> a -> b
$ \SimplEnv
env ->
            SimplEnv
-> [(CoreBndr, CoreBndr, CoreExpr)]
-> SimplM (SimplFloats, SimplEnv)
go SimplEnv
env [(CoreBndr, CoreBndr, CoreExpr)]
triples
        ; (SimplFloats, SimplEnv) -> SimplM (SimplFloats, SimplEnv)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplFloats -> SimplFloats
mkRecFloats SimplFloats
rec_floats, SimplEnv
env2) }
  where
    add_rules :: SimplEnv -> (InBndr,InExpr) -> SimplM (SimplEnv, (InBndr, OutBndr, InExpr))
        -- Add the (substituted) rules to the binder
    add_rules :: SimplEnv
-> (CoreBndr, CoreExpr)
-> SimplM (SimplEnv, (CoreBndr, CoreBndr, CoreExpr))
add_rules SimplEnv
env (CoreBndr
bndr, CoreExpr
rhs)
        = do { (SimplEnv
env', CoreBndr
bndr') <- SimplEnv
-> CoreBndr
-> CoreBndr
-> BindContext
-> SimplM (SimplEnv, CoreBndr)
addBndrRules SimplEnv
env CoreBndr
bndr (SimplEnv -> CoreBndr -> CoreBndr
lookupRecBndr SimplEnv
env CoreBndr
bndr) BindContext
bind_cxt
             ; (SimplEnv, (CoreBndr, CoreBndr, CoreExpr))
-> SimplM (SimplEnv, (CoreBndr, CoreBndr, CoreExpr))
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplEnv
env', (CoreBndr
bndr, CoreBndr
bndr', CoreExpr
rhs)) }

    go :: SimplEnv
-> [(CoreBndr, CoreBndr, CoreExpr)]
-> SimplM (SimplFloats, SimplEnv)
go SimplEnv
env [] = (SimplFloats, SimplEnv) -> SimplM (SimplFloats, SimplEnv)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplEnv -> SimplFloats
emptyFloats SimplEnv
env, SimplEnv
env)

    go SimplEnv
env ((CoreBndr
old_bndr, CoreBndr
new_bndr, CoreExpr
rhs) : [(CoreBndr, CoreBndr, CoreExpr)]
pairs)
        = do { (SimplFloats
float, SimplEnv
env1) <- SimplEnv
-> BindContext
-> CoreBndr
-> CoreBndr
-> CoreExpr
-> SimplM (SimplFloats, SimplEnv)
simplRecOrTopPair SimplEnv
env BindContext
bind_cxt
                                                  CoreBndr
old_bndr CoreBndr
new_bndr CoreExpr
rhs
             ; (SimplFloats
floats, SimplEnv
env2) <- SimplEnv
-> [(CoreBndr, CoreBndr, CoreExpr)]
-> SimplM (SimplFloats, SimplEnv)
go SimplEnv
env1 [(CoreBndr, CoreBndr, CoreExpr)]
pairs
             ; (SimplFloats, SimplEnv) -> SimplM (SimplFloats, SimplEnv)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplFloats
float SimplFloats -> SimplFloats -> SimplFloats
`addFloats` SimplFloats
floats, SimplEnv
env2) }

{-
simplOrTopPair is used for
        * recursive bindings (whether top level or not)
        * top-level non-recursive bindings

It assumes the binder has already been simplified, but not its IdInfo.
-}

simplRecOrTopPair :: SimplEnv
                  -> BindContext
                  -> InId -> OutBndr -> InExpr  -- Binder and rhs
                  -> SimplM (SimplFloats, SimplEnv)

simplRecOrTopPair :: SimplEnv
-> BindContext
-> CoreBndr
-> CoreBndr
-> CoreExpr
-> SimplM (SimplFloats, SimplEnv)
simplRecOrTopPair SimplEnv
env BindContext
bind_cxt CoreBndr
old_bndr CoreBndr
new_bndr CoreExpr
rhs
  | Just SimplEnv
env' <- SimplEnv
-> TopLevelFlag
-> CoreBndr
-> CoreExpr
-> SimplEnv
-> Maybe SimplEnv
preInlineUnconditionally SimplEnv
env (BindContext -> TopLevelFlag
bindContextLevel BindContext
bind_cxt)
                                          CoreBndr
old_bndr CoreExpr
rhs SimplEnv
env
  = {-#SCC "simplRecOrTopPair-pre-inline-uncond" #-}
    String
-> SDoc
-> SimplM (SimplFloats, SimplEnv)
-> SimplM (SimplFloats, SimplEnv)
forall a. String -> SDoc -> SimplM a -> SimplM a
simplTrace String
"SimplBindr:inline-uncond" (CoreBndr -> SDoc
forall a. Outputable a => a -> SDoc
ppr CoreBndr
old_bndr) (SimplM (SimplFloats, SimplEnv) -> SimplM (SimplFloats, SimplEnv))
-> SimplM (SimplFloats, SimplEnv) -> SimplM (SimplFloats, SimplEnv)
forall a b. (a -> b) -> a -> b
$
    do { Tick -> SimplM ()
tick (CoreBndr -> Tick
PreInlineUnconditionally CoreBndr
old_bndr)
       ; (SimplFloats, SimplEnv) -> SimplM (SimplFloats, SimplEnv)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return ( SimplEnv -> SimplFloats
emptyFloats SimplEnv
env, SimplEnv
env' ) }

  | Bool
otherwise
  = case BindContext
bind_cxt of
      BC_Join RecFlag
is_rec SimplCont
cont -> String
-> SDoc
-> SimplM (SimplFloats, SimplEnv)
-> SimplM (SimplFloats, SimplEnv)
forall a. String -> SDoc -> SimplM a -> SimplM a
simplTrace String
"SimplBind:join" (CoreBndr -> SDoc
forall a. Outputable a => a -> SDoc
ppr CoreBndr
old_bndr) (SimplM (SimplFloats, SimplEnv) -> SimplM (SimplFloats, SimplEnv))
-> SimplM (SimplFloats, SimplEnv) -> SimplM (SimplFloats, SimplEnv)
forall a b. (a -> b) -> a -> b
$
                             SimplEnv
-> RecFlag
-> SimplCont
-> CoreBndr
-> CoreBndr
-> CoreExpr
-> SimplEnv
-> SimplM (SimplFloats, SimplEnv)
simplJoinBind SimplEnv
env RecFlag
is_rec SimplCont
cont CoreBndr
old_bndr CoreBndr
new_bndr CoreExpr
rhs SimplEnv
env

      BC_Let TopLevelFlag
top_lvl RecFlag
is_rec -> String
-> SDoc
-> SimplM (SimplFloats, SimplEnv)
-> SimplM (SimplFloats, SimplEnv)
forall a. String -> SDoc -> SimplM a -> SimplM a
simplTrace String
"SimplBind:normal" (CoreBndr -> SDoc
forall a. Outputable a => a -> SDoc
ppr CoreBndr
old_bndr) (SimplM (SimplFloats, SimplEnv) -> SimplM (SimplFloats, SimplEnv))
-> SimplM (SimplFloats, SimplEnv) -> SimplM (SimplFloats, SimplEnv)
forall a b. (a -> b) -> a -> b
$
                               SimplEnv
-> TopLevelFlag
-> RecFlag
-> CoreBndr
-> CoreBndr
-> CoreExpr
-> SimplEnv
-> SimplM (SimplFloats, SimplEnv)
simplLazyBind SimplEnv
env TopLevelFlag
top_lvl RecFlag
is_rec CoreBndr
old_bndr CoreBndr
new_bndr CoreExpr
rhs SimplEnv
env

simplTrace :: String -> SDoc -> SimplM a -> SimplM a
simplTrace :: forall a. String -> SDoc -> SimplM a -> SimplM a
simplTrace String
herald SDoc
doc SimplM a
thing_inside = do
  Logger
logger <- SimplM Logger
forall (m :: * -> *). HasLogger m => m Logger
getLogger
  if Logger -> DumpFlag -> Bool
logHasDumpFlag Logger
logger DumpFlag
Opt_D_verbose_core2core
    then Logger -> String -> SDoc -> SimplM a -> SimplM a
forall a. Logger -> String -> SDoc -> a -> a
logTraceMsg Logger
logger String
herald SDoc
doc SimplM a
thing_inside
    else SimplM a
thing_inside

--------------------------
simplLazyBind :: SimplEnv
              -> TopLevelFlag -> RecFlag
              -> InId -> OutId          -- Binder, both pre-and post simpl
                                        -- Not a JoinId
                                        -- The OutId has IdInfo (notably RULES),
                                        -- except arity, unfolding
                                        -- Ids only, no TyVars
              -> InExpr -> SimplEnv     -- The RHS and its environment
              -> SimplM (SimplFloats, SimplEnv)
-- Precondition: the OutId is already in the InScopeSet of the incoming 'env'
-- Precondition: not a JoinId
-- Precondition: rhs obeys the let-can-float invariant
simplLazyBind :: SimplEnv
-> TopLevelFlag
-> RecFlag
-> CoreBndr
-> CoreBndr
-> CoreExpr
-> SimplEnv
-> SimplM (SimplFloats, SimplEnv)
simplLazyBind SimplEnv
env TopLevelFlag
top_lvl RecFlag
is_rec CoreBndr
bndr CoreBndr
bndr1 CoreExpr
rhs SimplEnv
rhs_se
  = Bool
-> (Bool
    -> SDoc
    -> SimplM (SimplFloats, SimplEnv)
    -> SimplM (SimplFloats, SimplEnv))
-> Bool
-> SDoc
-> SimplM (SimplFloats, SimplEnv)
-> SimplM (SimplFloats, SimplEnv)
forall a. HasCallStack => Bool -> a -> a
assert (CoreBndr -> Bool
isId CoreBndr
bndr )
    Bool
-> SDoc
-> SimplM (SimplFloats, SimplEnv)
-> SimplM (SimplFloats, SimplEnv)
forall a. HasCallStack => Bool -> SDoc -> a -> a
assertPpr (Bool -> Bool
not (CoreBndr -> Bool
isJoinId CoreBndr
bndr)) (CoreBndr -> SDoc
forall a. Outputable a => a -> SDoc
ppr CoreBndr
bndr) (SimplM (SimplFloats, SimplEnv) -> SimplM (SimplFloats, SimplEnv))
-> SimplM (SimplFloats, SimplEnv) -> SimplM (SimplFloats, SimplEnv)
forall a b. (a -> b) -> a -> b
$
    -- pprTrace "simplLazyBind" ((ppr bndr <+> ppr bndr1) $$ ppr rhs $$ ppr (seIdSubst rhs_se)) $
    do  { let   !rhs_env :: SimplEnv
rhs_env     = SimplEnv
rhs_se SimplEnv -> SimplEnv -> SimplEnv
`setInScopeFromE` SimplEnv
env -- See Note [Bangs in the Simplifier]
                ([CoreBndr]
tvs, CoreExpr
body) = case CoreExpr -> ([CoreBndr], [CoreBndr], CoreExpr)
collectTyAndValBinders CoreExpr
rhs of
                                ([CoreBndr]
tvs, [], CoreExpr
body)
                                  | CoreExpr -> Bool
forall {b}. Expr b -> Bool
surely_not_lam CoreExpr
body -> ([CoreBndr]
tvs, CoreExpr
body)
                                ([CoreBndr], [CoreBndr], CoreExpr)
_                       -> ([], CoreExpr
rhs)

                surely_not_lam :: Expr b -> Bool
surely_not_lam (Lam {})     = Bool
False
                surely_not_lam (Tick CoreTickish
t Expr b
e)
                  | Bool -> Bool
not (CoreTickish -> Bool
forall (pass :: TickishPass). GenTickish pass -> Bool
tickishFloatable CoreTickish
t) = Expr b -> Bool
surely_not_lam Expr b
e
                   -- eta-reduction could float
                surely_not_lam Expr b
_            = Bool
True
                        -- Do not do the "abstract tyvar" thing if there's
                        -- a lambda inside, because it defeats eta-reduction
                        --    f = /\a. \x. g a x
                        -- should eta-reduce.

        ; (SimplEnv
body_env, [CoreBndr]
tvs') <- {-#SCC "simplBinders" #-} SimplEnv -> [CoreBndr] -> SimplM (SimplEnv, [CoreBndr])
simplBinders SimplEnv
rhs_env [CoreBndr]
tvs
                -- See Note [Floating and type abstraction] in GHC.Core.Opt.Simplify.Utils

        -- Simplify the RHS
        ; let rhs_cont :: SimplCont
rhs_cont = Kind -> RecFlag -> Demand -> SimplCont
mkRhsStop ((() :: Constraint) => SimplEnv -> Kind -> Kind
SimplEnv -> Kind -> Kind
substTy SimplEnv
body_env ((() :: Constraint) => CoreExpr -> Kind
CoreExpr -> Kind
exprType CoreExpr
body))
                                   RecFlag
is_rec (CoreBndr -> Demand
idDemandInfo CoreBndr
bndr)
        ; (SimplFloats
body_floats0, CoreExpr
body0) <- {-#SCC "simplExprF" #-} SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF SimplEnv
body_env CoreExpr
body SimplCont
rhs_cont

        -- ANF-ise a constructor or PAP rhs
        ; (SimplFloats
body_floats2, CoreExpr
body2) <- {-#SCC "prepareBinding" #-}
                                   SimplEnv
-> TopLevelFlag
-> RecFlag
-> Bool
-> CoreBndr
-> SimplFloats
-> CoreExpr
-> SimplM (SimplFloats, CoreExpr)
prepareBinding SimplEnv
env TopLevelFlag
top_lvl RecFlag
is_rec
                                                  Bool
False  -- Not strict; this is simplLazyBind
                                                  CoreBndr
bndr1 SimplFloats
body_floats0 CoreExpr
body0
          -- Subtle point: we do not need or want tvs' in the InScope set
          -- of body_floats2, so we pass in 'env' not 'body_env'.
          -- Don't want: if tvs' are in-scope in the scope of this let-binding, we may do
          -- more renaming than necessary => extra work (see !7777 and test T16577).
          -- Don't need: we wrap tvs' around the RHS anyway.

        ; (SimplFloats
rhs_floats, CoreExpr
body3)
            <-  if SimplFloats -> Bool
isEmptyFloats SimplFloats
body_floats2 Bool -> Bool -> Bool
|| [CoreBndr] -> Bool
forall a. [a] -> Bool
forall (t :: * -> *) a. Foldable t => t a -> Bool
null [CoreBndr]
tvs then   -- Simple floating
                     {-#SCC "simplLazyBind-simple-floating" #-}
                     (SimplFloats, CoreExpr) -> SimplM (SimplFloats, CoreExpr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplFloats
body_floats2, CoreExpr
body2)

                else -- Non-empty floats, and non-empty tyvars: do type-abstraction first
                     {-#SCC "simplLazyBind-type-abstraction-first" #-}
                     do { ([InBind]
poly_binds, CoreExpr
body3) <- UnfoldingOpts
-> TopLevelFlag
-> [CoreBndr]
-> SimplFloats
-> CoreExpr
-> SimplM ([InBind], CoreExpr)
abstractFloats (SimplEnv -> UnfoldingOpts
seUnfoldingOpts SimplEnv
env) TopLevelFlag
top_lvl
                                                                [CoreBndr]
tvs' SimplFloats
body_floats2 CoreExpr
body2
                        ; let poly_floats :: SimplFloats
poly_floats = (SimplFloats -> InBind -> SimplFloats)
-> SimplFloats -> [InBind] -> SimplFloats
forall b a. (b -> a -> b) -> b -> [a] -> b
forall (t :: * -> *) b a.
Foldable t =>
(b -> a -> b) -> b -> t a -> b
foldl' SimplFloats -> InBind -> SimplFloats
extendFloats (SimplEnv -> SimplFloats
emptyFloats SimplEnv
env) [InBind]
poly_binds
                        ; (SimplFloats, CoreExpr) -> SimplM (SimplFloats, CoreExpr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplFloats
poly_floats, CoreExpr
body3) }

        ; let env' :: SimplEnv
env' = SimplEnv
env SimplEnv -> SimplFloats -> SimplEnv
`setInScopeFromF` SimplFloats
rhs_floats
        ; CoreExpr
rhs' <- SimplEnv -> [CoreBndr] -> CoreExpr -> SimplCont -> SimplM CoreExpr
rebuildLam SimplEnv
env' [CoreBndr]
tvs' CoreExpr
body3 SimplCont
rhs_cont
        ; (SimplFloats
bind_float, SimplEnv
env2) <- SimplEnv
-> BindContext
-> CoreBndr
-> CoreBndr
-> CoreExpr
-> SimplM (SimplFloats, SimplEnv)
completeBind SimplEnv
env' (TopLevelFlag -> RecFlag -> BindContext
BC_Let TopLevelFlag
top_lvl RecFlag
is_rec) CoreBndr
bndr CoreBndr
bndr1 CoreExpr
rhs'
        ; (SimplFloats, SimplEnv) -> SimplM (SimplFloats, SimplEnv)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplFloats
rhs_floats SimplFloats -> SimplFloats -> SimplFloats
`addFloats` SimplFloats
bind_float, SimplEnv
env2) }

--------------------------
simplJoinBind :: SimplEnv
              -> RecFlag
              -> SimplCont
              -> InId -> OutId          -- Binder, both pre-and post simpl
                                        -- The OutId has IdInfo, except arity,
                                        --   unfolding
              -> InExpr -> SimplEnv     -- The right hand side and its env
              -> SimplM (SimplFloats, SimplEnv)
simplJoinBind :: SimplEnv
-> RecFlag
-> SimplCont
-> CoreBndr
-> CoreBndr
-> CoreExpr
-> SimplEnv
-> SimplM (SimplFloats, SimplEnv)
simplJoinBind SimplEnv
env RecFlag
is_rec SimplCont
cont CoreBndr
old_bndr CoreBndr
new_bndr CoreExpr
rhs SimplEnv
rhs_se
  = do  { let rhs_env :: SimplEnv
rhs_env = SimplEnv
rhs_se SimplEnv -> SimplEnv -> SimplEnv
`setInScopeFromE` SimplEnv
env
        ; CoreExpr
rhs' <- SimplEnv -> CoreBndr -> CoreExpr -> SimplCont -> SimplM CoreExpr
simplJoinRhs SimplEnv
rhs_env CoreBndr
old_bndr CoreExpr
rhs SimplCont
cont
        ; SimplEnv
-> BindContext
-> CoreBndr
-> CoreBndr
-> CoreExpr
-> SimplM (SimplFloats, SimplEnv)
completeBind SimplEnv
env (RecFlag -> SimplCont -> BindContext
BC_Join RecFlag
is_rec SimplCont
cont) CoreBndr
old_bndr CoreBndr
new_bndr CoreExpr
rhs' }

--------------------------
simplAuxBind :: SimplEnv
             -> InId            -- Old binder; not a JoinId
             -> OutExpr         -- Simplified RHS
             -> SimplM (SimplFloats, SimplEnv)
-- A specialised variant of completeBindX used to construct non-recursive
-- auxiliary bindings, notably in knownCon.
--
-- The binder comes from a case expression (case binder or alternative)
-- and so does not have rules, inline pragmas etc.
--
-- Precondition: rhs satisfies the let-can-float invariant

simplAuxBind :: SimplEnv -> CoreBndr -> CoreExpr -> SimplM (SimplFloats, SimplEnv)
simplAuxBind SimplEnv
env CoreBndr
bndr CoreExpr
new_rhs
  | Bool -> SDoc -> Bool -> Bool
forall a. HasCallStack => Bool -> SDoc -> a -> a
assertPpr (CoreBndr -> Bool
isId CoreBndr
bndr Bool -> Bool -> Bool
&& Bool -> Bool
not (CoreBndr -> Bool
isJoinId CoreBndr
bndr)) (CoreBndr -> SDoc
forall a. Outputable a => a -> SDoc
ppr CoreBndr
bndr) (Bool -> Bool) -> Bool -> Bool
forall a b. (a -> b) -> a -> b
$
    CoreBndr -> Bool
isDeadBinder CoreBndr
bndr   -- Not uncommon; e.g. case (a,b) of c { (p,q) -> p }
  = (SimplFloats, SimplEnv) -> SimplM (SimplFloats, SimplEnv)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplEnv -> SimplFloats
emptyFloats SimplEnv
env, SimplEnv
env)    --  Here c is dead, and we avoid
                                     --  creating the binding c = (a,b)

  -- The cases would be inlined unconditionally by completeBind:
  -- but it seems not uncommon, and avoids faff to do it here
  -- This is safe because it's only used for auxiliary bindings, which
  -- have no NOLINE pragmas, nor RULEs
  | CoreExpr -> Bool
exprIsTrivial CoreExpr
new_rhs  -- Short-cut for let x = y in ...
  = (SimplFloats, SimplEnv) -> SimplM (SimplFloats, SimplEnv)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return ( SimplEnv -> SimplFloats
emptyFloats SimplEnv
env
           , case CoreExpr
new_rhs of
                Coercion Coercion
co -> SimplEnv -> CoreBndr -> Coercion -> SimplEnv
extendCvSubst SimplEnv
env CoreBndr
bndr Coercion
co
                CoreExpr
_           -> SimplEnv -> CoreBndr -> SimplSR -> SimplEnv
extendIdSubst SimplEnv
env CoreBndr
bndr (CoreExpr -> Maybe Int -> SimplSR
DoneEx CoreExpr
new_rhs Maybe Int
forall a. Maybe a
Nothing) )

  | Bool
otherwise
  = do  { -- ANF-ise the RHS
          let !occ_fs :: FastString
occ_fs = CoreBndr -> FastString
forall a. NamedThing a => a -> FastString
getOccFS CoreBndr
bndr
        ; (LetFloats
anf_floats, CoreExpr
rhs1) <- (() :: Constraint) =>
SimplEnv
-> TopLevelFlag
-> FastString
-> CoreExpr
-> SimplM (LetFloats, CoreExpr)
SimplEnv
-> TopLevelFlag
-> FastString
-> CoreExpr
-> SimplM (LetFloats, CoreExpr)
prepareRhs SimplEnv
env TopLevelFlag
NotTopLevel FastString
occ_fs CoreExpr
new_rhs
        ; Bool -> SimplM () -> SimplM ()
forall (f :: * -> *). Applicative f => Bool -> f () -> f ()
unless (LetFloats -> Bool
isEmptyLetFloats LetFloats
anf_floats) (Tick -> SimplM ()
tick Tick
LetFloatFromLet)
        ; let rhs_floats :: SimplFloats
rhs_floats = SimplEnv -> SimplFloats
emptyFloats SimplEnv
env SimplFloats -> LetFloats -> SimplFloats
`addLetFloats` LetFloats
anf_floats

          -- Simplify the binder and complete the binding
        ; (SimplEnv
env1, CoreBndr
new_bndr) <- SimplEnv -> CoreBndr -> SimplM (SimplEnv, CoreBndr)
simplBinder (SimplEnv
env SimplEnv -> SimplFloats -> SimplEnv
`setInScopeFromF` SimplFloats
rhs_floats) CoreBndr
bndr
        ; (SimplFloats
bind_float, SimplEnv
env2) <- SimplEnv
-> BindContext
-> CoreBndr
-> CoreBndr
-> CoreExpr
-> SimplM (SimplFloats, SimplEnv)
completeBind SimplEnv
env1 (TopLevelFlag -> RecFlag -> BindContext
BC_Let TopLevelFlag
NotTopLevel RecFlag
NonRecursive)
                                             CoreBndr
bndr CoreBndr
new_bndr CoreExpr
rhs1

        ; (SimplFloats, SimplEnv) -> SimplM (SimplFloats, SimplEnv)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplFloats
rhs_floats SimplFloats -> SimplFloats -> SimplFloats
`addFloats` SimplFloats
bind_float, SimplEnv
env2) }


{- *********************************************************************
*                                                                      *
           Cast worker/wrapper
*                                                                      *
************************************************************************

Note [Cast worker/wrapper]
~~~~~~~~~~~~~~~~~~~~~~~~~~
When we have a binding
   x = e |> co
we want to do something very similar to worker/wrapper:
   $wx = e
   x = $wx |> co

We call this making a cast worker/wrapper in tryCastWorkerWrapper.

The main motivaiton is that x can be inlined freely.  There's a chance
that e will be a constructor application or function, or something
like that, so moving the coercion to the usage site may well cancel
the coercions and lead to further optimisation.  Example:

     data family T a :: *
     data instance T Int = T Int

     foo :: Int -> Int -> Int
     foo m n = ...
        where
          t = T m
          go 0 = 0
          go n = case t of { T m -> go (n-m) }
                -- This case should optimise

A second reason for doing cast worker/wrapper is that the worker/wrapper
pass after strictness analysis can't deal with RHSs like
     f = (\ a b c. blah) |> co
Instead, it relies on cast worker/wrapper to get rid of the cast,
leaving a simpler job for demand-analysis worker/wrapper.  See #19874.

Wrinkles

1. We must /not/ do cast w/w on
     f = g |> co
   otherwise it'll just keep repeating forever! You might think this
   is avoided because the call to tryCastWorkerWrapper is guarded by
   preInlineUnconditinally, but I'm worried that a loop-breaker or an
   exported Id might say False to preInlineUnonditionally.

2. We need to be careful with inline/noinline pragmas:
       rec { {-# NOINLINE f #-}
             f = (...g...) |> co
           ; g = ...f... }
   This is legitimate -- it tells GHC to use f as the loop breaker
   rather than g.  Now we do the cast thing, to get something like
       rec { $wf = ...g...
           ; f = $wf |> co
           ; g = ...f... }
   Where should the NOINLINE pragma go?  If we leave it on f we'll get
     rec { $wf = ...g...
         ; {-# NOINLINE f #-}
           f = $wf |> co
         ; g = ...f... }
   and that is bad: the whole point is that we want to inline that
   cast!  We want to transfer the pagma to $wf:
      rec { {-# NOINLINE $wf #-}
            $wf = ...g...
          ; f = $wf |> co
          ; g = ...f... }
   c.f. Note [Worker/wrapper for NOINLINE functions] in GHC.Core.Opt.WorkWrap.

3. We should still do cast w/w even if `f` is INLINEABLE.  E.g.
      {- f: Stable unfolding = <stable-big> -}
      f = (\xy. <big-body>) |> co
   Then we want to w/w to
      {- $wf: Stable unfolding = <stable-big> |> sym co -}
      $wf = \xy. <big-body>
      f = $wf |> co
   Notice that the stable unfolding moves to the worker!  Now demand analysis
   will work fine on $wf, whereas it has trouble with the original f.
   c.f. Note [Worker/wrapper for INLINABLE functions] in GHC.Core.Opt.WorkWrap.
   This point also applies to strong loopbreakers with INLINE pragmas, see
   wrinkle (4).

4. We should /not/ do cast w/w for non-loop-breaker INLINE functions (hence
   hasInlineUnfolding in tryCastWorkerWrapper, which responds False to
   loop-breakers) because they'll definitely be inlined anyway, cast and
   all. And if we do cast w/w for an INLINE function with arity zero, we get
   something really silly: we inline that "worker" right back into the wrapper!
   Worse than a no-op, because we have then lost the stable unfolding.

All these wrinkles are exactly like worker/wrapper for strictness analysis:
  f is the wrapper and must inline like crazy
  $wf is the worker and must carry f's original pragma
See Note [Worker/wrapper for INLINABLE functions]
and Note [Worker/wrapper for NOINLINE functions] in GHC.Core.Opt.WorkWrap.

See #17673, #18093, #18078, #19890.

Note [Preserve strictness in cast w/w]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In the Note [Cast worker/wrapper] transformation, keep the strictness info.
Eg
        f = e `cast` co    -- f has strictness SSL
When we transform to
        f' = e             -- f' also has strictness SSL
        f = f' `cast` co   -- f still has strictness SSL

Its not wrong to drop it on the floor, but better to keep it.

Note [Preserve RuntimeRep info in cast w/w]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We must not do cast w/w when the presence of the coercion is needed in order
to determine the runtime representation.

Example:

  Suppose we have a type family:

    type F :: RuntimeRep
    type family F where
      F = LiftedRep

  together with a type `ty :: TYPE F` and a top-level binding

    a :: ty |> TYPE F[0]

  The kind of `ty |> TYPE F[0]` is `LiftedRep`, so `a` is a top-level lazy binding.
  However, were we to apply cast w/w, we would get:

    b :: ty
    b = ...

    a :: ty |> TYPE F[0]
    a = b `cast` GRefl (TYPE F[0])

  Now we are in trouble because `ty :: TYPE F` does not have a known runtime
  representation, because we need to be able to reduce the nullary type family
  application `F` to find that out.

Conclusion: only do cast w/w when doing so would not lose the RuntimeRep
information. That is, when handling `Cast rhs co`, don't attempt cast w/w
unless the kind of the type of rhs is concrete, in the sense of
Note [Concrete types] in GHC.Tc.Utils.Concrete.
-}

tryCastWorkerWrapper :: SimplEnv -> BindContext
                     -> InId -> OccInfo
                     -> OutId -> OutExpr
                     -> SimplM (SimplFloats, SimplEnv)
-- See Note [Cast worker/wrapper]
tryCastWorkerWrapper :: SimplEnv
-> BindContext
-> CoreBndr
-> OccInfo
-> CoreBndr
-> CoreExpr
-> SimplM (SimplFloats, SimplEnv)
tryCastWorkerWrapper SimplEnv
env BindContext
bind_cxt CoreBndr
old_bndr OccInfo
occ_info CoreBndr
bndr (Cast CoreExpr
rhs Coercion
co)
  | BC_Let TopLevelFlag
top_lvl RecFlag
is_rec <- BindContext
bind_cxt  -- Not join points
  , Bool -> Bool
not (CoreBndr -> Bool
isDFunId CoreBndr
bndr) -- nor DFuns; cast w/w is no help, and we can't transform
                        --            a DFunUnfolding in mk_worker_unfolding
  , Bool -> Bool
not (CoreExpr -> Bool
exprIsTrivial CoreExpr
rhs)        -- Not x = y |> co; Wrinkle 1
  , Bool -> Bool
not (IdInfo -> Bool
hasInlineUnfolding IdInfo
info)  -- Not INLINE things: Wrinkle 4
  , Kind -> Bool
isConcrete ((() :: Constraint) => Kind -> Kind
Kind -> Kind
typeKind Kind
work_ty)  -- Don't peel off a cast if doing so would
                                   -- lose the underlying runtime representation.
                                   -- See Note [Preserve RuntimeRep info in cast w/w]
  , Bool -> Bool
not (InlinePragma -> Bool
isOpaquePragma (CoreBndr -> InlinePragma
idInlinePragma CoreBndr
old_bndr)) -- Not for OPAQUE bindings
                                                   -- See Note [OPAQUE pragma]
  = do  { Unique
uniq <- SimplM Unique
forall (m :: * -> *). MonadUnique m => m Unique
getUniqueM
        ; let work_name :: Name
work_name = Unique -> FastString -> Name
mkSystemVarName Unique
uniq FastString
occ_fs
              work_id :: CoreBndr
work_id   = (() :: Constraint) => Name -> Kind -> Kind -> IdInfo -> CoreBndr
Name -> Kind -> Kind -> IdInfo -> CoreBndr
mkLocalIdWithInfo Name
work_name Kind
ManyTy Kind
work_ty IdInfo
work_info
              is_strict :: Bool
is_strict = CoreBndr -> Bool
isStrictId CoreBndr
bndr

        ; (SimplFloats
rhs_floats, CoreExpr
work_rhs) <- SimplEnv
-> TopLevelFlag
-> RecFlag
-> Bool
-> CoreBndr
-> SimplFloats
-> CoreExpr
-> SimplM (SimplFloats, CoreExpr)
prepareBinding SimplEnv
env TopLevelFlag
top_lvl RecFlag
is_rec Bool
is_strict
                                                   CoreBndr
work_id (SimplEnv -> SimplFloats
emptyFloats SimplEnv
env) CoreExpr
rhs

        ; Unfolding
work_unf <- TopLevelFlag -> CoreBndr -> CoreExpr -> SimplM Unfolding
mk_worker_unfolding TopLevelFlag
top_lvl CoreBndr
work_id CoreExpr
work_rhs
        ; let  work_id_w_unf :: CoreBndr
work_id_w_unf = CoreBndr
work_id CoreBndr -> Unfolding -> CoreBndr
`setIdUnfolding` Unfolding
work_unf
               floats :: SimplFloats
floats   = SimplFloats
rhs_floats SimplFloats -> LetFloats -> SimplFloats
`addLetFloats`
                          InBind -> LetFloats
unitLetFloat (CoreBndr -> CoreExpr -> InBind
forall b. b -> Expr b -> Bind b
NonRec CoreBndr
work_id_w_unf CoreExpr
work_rhs)

               triv_rhs :: CoreExpr
triv_rhs = CoreExpr -> Coercion -> CoreExpr
forall b. Expr b -> Coercion -> Expr b
Cast (CoreBndr -> CoreExpr
forall b. CoreBndr -> Expr b
Var CoreBndr
work_id_w_unf) Coercion
co

        ; if SimplEnv -> BindContext -> CoreBndr -> OccInfo -> CoreExpr -> Bool
postInlineUnconditionally SimplEnv
env BindContext
bind_cxt CoreBndr
bndr OccInfo
occ_info CoreExpr
triv_rhs
             -- Almost always True, because the RHS is trivial
             -- In that case we want to eliminate the binding fast
             -- We conservatively use postInlineUnconditionally so that we
             -- check all the right things
          then do { Tick -> SimplM ()
tick (CoreBndr -> Tick
PostInlineUnconditionally CoreBndr
bndr)
                  ; (SimplFloats, SimplEnv) -> SimplM (SimplFloats, SimplEnv)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return ( SimplFloats
floats
                           , SimplEnv -> CoreBndr -> SimplSR -> SimplEnv
extendIdSubst (SimplEnv -> SimplFloats -> SimplEnv
setInScopeFromF SimplEnv
env SimplFloats
floats) CoreBndr
old_bndr (SimplSR -> SimplEnv) -> SimplSR -> SimplEnv
forall a b. (a -> b) -> a -> b
$
                             CoreExpr -> Maybe Int -> SimplSR
DoneEx CoreExpr
triv_rhs Maybe Int
forall a. Maybe a
Nothing ) }

          else do { Unfolding
wrap_unf <- UnfoldingOpts
-> TopLevelFlag
-> UnfoldingSource
-> CoreBndr
-> CoreExpr
-> SimplM Unfolding
mkLetUnfolding UnfoldingOpts
uf_opts TopLevelFlag
top_lvl UnfoldingSource
VanillaSrc CoreBndr
bndr CoreExpr
triv_rhs
                  ; let bndr' :: CoreBndr
bndr' = CoreBndr
bndr CoreBndr -> InlinePragma -> CoreBndr
`setInlinePragma` InlinePragma -> InlinePragma
mkCastWrapperInlinePrag (CoreBndr -> InlinePragma
idInlinePragma CoreBndr
bndr)
                                CoreBndr -> Unfolding -> CoreBndr
`setIdUnfolding`  Unfolding
wrap_unf
                        floats' :: SimplFloats
floats' = SimplFloats
floats SimplFloats -> InBind -> SimplFloats
`extendFloats` CoreBndr -> CoreExpr -> InBind
forall b. b -> Expr b -> Bind b
NonRec CoreBndr
bndr' CoreExpr
triv_rhs
                  ; (SimplFloats, SimplEnv) -> SimplM (SimplFloats, SimplEnv)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return ( SimplFloats
floats', SimplEnv -> SimplFloats -> SimplEnv
setInScopeFromF SimplEnv
env SimplFloats
floats' ) } }
  where
    -- Force the occ_fs so that the old Id is not retained in the new Id.
    !occ_fs :: FastString
occ_fs = CoreBndr -> FastString
forall a. NamedThing a => a -> FastString
getOccFS CoreBndr
bndr
    uf_opts :: UnfoldingOpts
uf_opts = SimplEnv -> UnfoldingOpts
seUnfoldingOpts SimplEnv
env
    work_ty :: Kind
work_ty = Coercion -> Kind
coercionLKind Coercion
co
    info :: IdInfo
info   = (() :: Constraint) => CoreBndr -> IdInfo
CoreBndr -> IdInfo
idInfo CoreBndr
bndr
    work_arity :: Int
work_arity = IdInfo -> Int
arityInfo IdInfo
info Int -> Int -> Int
forall a. Ord a => a -> a -> a
`min` Kind -> Int
typeArity Kind
work_ty

    work_info :: IdInfo
work_info = IdInfo
vanillaIdInfo IdInfo -> DmdSig -> IdInfo
`setDmdSigInfo`     IdInfo -> DmdSig
dmdSigInfo IdInfo
info
                              IdInfo -> CprSig -> IdInfo
`setCprSigInfo`     IdInfo -> CprSig
cprSigInfo IdInfo
info
                              IdInfo -> Demand -> IdInfo
`setDemandInfo`     IdInfo -> Demand
demandInfo IdInfo
info
                              IdInfo -> InlinePragma -> IdInfo
`setInlinePragInfo` IdInfo -> InlinePragma
inlinePragInfo IdInfo
info
                              IdInfo -> Int -> IdInfo
`setArityInfo`      Int
work_arity
           -- We do /not/ want to transfer OccInfo, Rules
           -- Note [Preserve strictness in cast w/w]
           -- and Wrinkle 2 of Note [Cast worker/wrapper]

    ----------- Worker unfolding -----------
    -- Stable case: if there is a stable unfolding we have to compose with (Sym co);
    --   the next round of simplification will do the job
    -- Non-stable case: use work_rhs
    -- Wrinkle 3 of Note [Cast worker/wrapper]
    mk_worker_unfolding :: TopLevelFlag -> CoreBndr -> CoreExpr -> SimplM Unfolding
mk_worker_unfolding TopLevelFlag
top_lvl CoreBndr
work_id CoreExpr
work_rhs
      = case IdInfo -> Unfolding
realUnfoldingInfo IdInfo
info of -- NB: the real one, even for loop-breakers
           unf :: Unfolding
unf@(CoreUnfolding { uf_tmpl :: Unfolding -> CoreExpr
uf_tmpl = CoreExpr
unf_rhs, uf_src :: Unfolding -> UnfoldingSource
uf_src = UnfoldingSource
src })
             | UnfoldingSource -> Bool
isStableSource UnfoldingSource
src -> Unfolding -> SimplM Unfolding
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (Unfolding
unf { uf_tmpl = mkCast unf_rhs (mkSymCo co) })
           Unfolding
_ -> UnfoldingOpts
-> TopLevelFlag
-> UnfoldingSource
-> CoreBndr
-> CoreExpr
-> SimplM Unfolding
mkLetUnfolding UnfoldingOpts
uf_opts TopLevelFlag
top_lvl UnfoldingSource
VanillaSrc CoreBndr
work_id CoreExpr
work_rhs

tryCastWorkerWrapper SimplEnv
env BindContext
_ CoreBndr
_ OccInfo
_ CoreBndr
bndr CoreExpr
rhs  -- All other bindings
  = do { String -> SDoc -> SimplM ()
traceSmpl String
"tcww:no" ([SDoc] -> SDoc
forall doc. IsDoc doc => [doc] -> doc
vcat [ String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"bndr:" SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> CoreBndr -> SDoc
forall a. Outputable a => a -> SDoc
ppr CoreBndr
bndr
                                   , String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"rhs:" SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> CoreExpr -> SDoc
forall a. Outputable a => a -> SDoc
ppr CoreExpr
rhs ])
        ; (SimplFloats, SimplEnv) -> SimplM (SimplFloats, SimplEnv)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplEnv -> InBind -> (SimplFloats, SimplEnv)
mkFloatBind SimplEnv
env (CoreBndr -> CoreExpr -> InBind
forall b. b -> Expr b -> Bind b
NonRec CoreBndr
bndr CoreExpr
rhs)) }

mkCastWrapperInlinePrag :: InlinePragma -> InlinePragma
-- See Note [Cast worker/wrapper]
mkCastWrapperInlinePrag :: InlinePragma -> InlinePragma
mkCastWrapperInlinePrag (InlinePragma { inl_inline :: InlinePragma -> InlineSpec
inl_inline = InlineSpec
fn_inl, inl_act :: InlinePragma -> Activation
inl_act = Activation
fn_act, inl_rule :: InlinePragma -> RuleMatchInfo
inl_rule = RuleMatchInfo
rule_info })
  = InlinePragma { inl_src :: SourceText
inl_src    = String -> SourceText
SourceText String
"{-# INLINE"
                 , inl_inline :: InlineSpec
inl_inline = InlineSpec
fn_inl       -- See Note [Worker/wrapper for INLINABLE functions]
                 , inl_sat :: Maybe Int
inl_sat    = Maybe Int
forall a. Maybe a
Nothing      --     in GHC.Core.Opt.WorkWrap
                 , inl_act :: Activation
inl_act    = Activation
wrap_act     -- See Note [Wrapper activation]
                 , inl_rule :: RuleMatchInfo
inl_rule   = RuleMatchInfo
rule_info }  --     in GHC.Core.Opt.WorkWrap
                                -- RuleMatchInfo is (and must be) unaffected
  where
    -- See Note [Wrapper activation] in GHC.Core.Opt.WorkWrap
    -- But simpler, because we don't need to disable during InitialPhase
    wrap_act :: Activation
wrap_act | Activation -> Bool
isNeverActive Activation
fn_act = Activation
activateDuringFinal
             | Bool
otherwise            = Activation
fn_act


{- *********************************************************************
*                                                                      *
           prepareBinding, prepareRhs, makeTrivial
*                                                                      *
********************************************************************* -}

prepareBinding :: SimplEnv -> TopLevelFlag -> RecFlag -> Bool
               -> Id   -- Used only for its OccName; can be InId or OutId
               -> SimplFloats -> OutExpr
               -> SimplM (SimplFloats, OutExpr)
-- In (prepareBinding ... bndr floats rhs), the binding is really just
--    bndr = let floats in rhs
-- Maybe we can ANF-ise this binding and float out; e.g.
--    bndr = let a = f x in K a a (g x)
-- we could float out to give
--    a    = f x
--    tmp  = g x
--    bndr = K a a tmp
-- That's what prepareBinding does
-- Precondition: binder is not a JoinId
-- Postcondition: the returned SimplFloats contains only let-floats
prepareBinding :: SimplEnv
-> TopLevelFlag
-> RecFlag
-> Bool
-> CoreBndr
-> SimplFloats
-> CoreExpr
-> SimplM (SimplFloats, CoreExpr)
prepareBinding SimplEnv
env TopLevelFlag
top_lvl RecFlag
is_rec Bool
strict_bind CoreBndr
bndr SimplFloats
rhs_floats CoreExpr
rhs
  = do { -- Never float join-floats out of a non-join let-binding (which this is)
         -- So wrap the body in the join-floats right now
         -- Hence: rhs_floats1 consists only of let-floats
         let (SimplFloats
rhs_floats1, CoreExpr
rhs1) = SimplFloats -> CoreExpr -> (SimplFloats, CoreExpr)
wrapJoinFloatsX SimplFloats
rhs_floats CoreExpr
rhs

         -- rhs_env: add to in-scope set the binders from rhs_floats
         -- so that prepareRhs knows what is in scope in rhs
       ; let rhs_env :: SimplEnv
rhs_env = SimplEnv
env SimplEnv -> SimplFloats -> SimplEnv
`setInScopeFromF` SimplFloats
rhs_floats1
             -- Force the occ_fs so that the old Id is not retained in the new Id.
             !occ_fs :: FastString
occ_fs = CoreBndr -> FastString
forall a. NamedThing a => a -> FastString
getOccFS CoreBndr
bndr

       -- Now ANF-ise the remaining rhs
       ; (LetFloats
anf_floats, CoreExpr
rhs2) <- (() :: Constraint) =>
SimplEnv
-> TopLevelFlag
-> FastString
-> CoreExpr
-> SimplM (LetFloats, CoreExpr)
SimplEnv
-> TopLevelFlag
-> FastString
-> CoreExpr
-> SimplM (LetFloats, CoreExpr)
prepareRhs SimplEnv
rhs_env TopLevelFlag
top_lvl FastString
occ_fs CoreExpr
rhs1

       -- Finally, decide whether or not to float
       ; let all_floats :: SimplFloats
all_floats = SimplFloats
rhs_floats1 SimplFloats -> LetFloats -> SimplFloats
`addLetFloats` LetFloats
anf_floats
       ; if FloatEnable
-> TopLevelFlag
-> RecFlag
-> Bool
-> SimplFloats
-> CoreExpr
-> Bool
doFloatFromRhs (SimplEnv -> FloatEnable
seFloatEnable SimplEnv
env) TopLevelFlag
top_lvl RecFlag
is_rec Bool
strict_bind SimplFloats
all_floats CoreExpr
rhs2
         then -- Float!
              do { Tick -> SimplM ()
tick Tick
LetFloatFromLet
                 ; (SimplFloats, CoreExpr) -> SimplM (SimplFloats, CoreExpr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplFloats
all_floats, CoreExpr
rhs2) }

         else -- Abandon floating altogether; revert to original rhs
              -- Since we have already built rhs1, we just need to add
              -- rhs_floats1 to it
              (SimplFloats, CoreExpr) -> SimplM (SimplFloats, CoreExpr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplEnv -> SimplFloats
emptyFloats SimplEnv
env, SimplFloats -> CoreExpr -> CoreExpr
wrapFloats SimplFloats
rhs_floats1 CoreExpr
rhs1) }

{- Note [prepareRhs]
~~~~~~~~~~~~~~~~~~~~
prepareRhs takes a putative RHS, checks whether it's a PAP or
constructor application and, if so, converts it to ANF, so that the
resulting thing can be inlined more easily.  Thus
        x = (f a, g b)
becomes
        t1 = f a
        t2 = g b
        x = (t1,t2)

We also want to deal well cases like this
        v = (f e1 `cast` co) e2
Here we want to make e1,e2 trivial and get
        x1 = e1; x2 = e2; v = (f x1 `cast` co) v2
That's what the 'go' loop in prepareRhs does
-}

prepareRhs :: HasDebugCallStack
           => SimplEnv -> TopLevelFlag
           -> FastString    -- Base for any new variables
           -> OutExpr
           -> SimplM (LetFloats, OutExpr)
-- Transforms a RHS into a better RHS by ANF'ing args
-- for expandable RHSs: constructors and PAPs
-- e.g        x = Just e
-- becomes    a = e               -- 'a' is fresh
--            x = Just a
-- See Note [prepareRhs]
prepareRhs :: (() :: Constraint) =>
SimplEnv
-> TopLevelFlag
-> FastString
-> CoreExpr
-> SimplM (LetFloats, CoreExpr)
prepareRhs SimplEnv
env TopLevelFlag
top_lvl FastString
occ CoreExpr
rhs0
  | Bool
is_expandable = CoreExpr -> SimplM (LetFloats, CoreExpr)
anfise CoreExpr
rhs0
  | Bool
otherwise     = (LetFloats, CoreExpr) -> SimplM (LetFloats, CoreExpr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (LetFloats
emptyLetFloats, CoreExpr
rhs0)
  where
    -- We can' use exprIsExpandable because the WHOLE POINT is that
    -- we want to treat (K <big>) as expandable, because we are just
    -- about "anfise" the <big> expression.  exprIsExpandable would
    -- just say no!
    is_expandable :: Bool
is_expandable = CoreExpr -> Int -> Bool
forall {b}. Expr b -> Int -> Bool
go CoreExpr
rhs0 Int
0
       where
         go :: Expr b -> Int -> Bool
go (Var CoreBndr
fun) Int
n_val_args       = CheapAppFun
isExpandableApp CoreBndr
fun Int
n_val_args
         go (App Expr b
fun Expr b
arg) Int
n_val_args
           | Expr b -> Bool
forall {b}. Expr b -> Bool
isTypeArg Expr b
arg             = Expr b -> Int -> Bool
go Expr b
fun Int
n_val_args
           | Bool
otherwise                 = Expr b -> Int -> Bool
go Expr b
fun (Int
n_val_args Int -> Int -> Int
forall a. Num a => a -> a -> a
+ Int
1)
         go (Cast Expr b
rhs Coercion
_)  Int
n_val_args   = Expr b -> Int -> Bool
go Expr b
rhs Int
n_val_args
         go (Tick CoreTickish
_ Expr b
rhs)  Int
n_val_args   = Expr b -> Int -> Bool
go Expr b
rhs Int
n_val_args
         go Expr b
_             Int
_            = Bool
False

    anfise :: OutExpr -> SimplM (LetFloats, OutExpr)
    anfise :: CoreExpr -> SimplM (LetFloats, CoreExpr)
anfise (Cast CoreExpr
rhs Coercion
co)
        = do { (LetFloats
floats, CoreExpr
rhs') <- CoreExpr -> SimplM (LetFloats, CoreExpr)
anfise CoreExpr
rhs
             ; (LetFloats, CoreExpr) -> SimplM (LetFloats, CoreExpr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (LetFloats
floats, CoreExpr -> Coercion -> CoreExpr
forall b. Expr b -> Coercion -> Expr b
Cast CoreExpr
rhs' Coercion
co) }
    anfise (App CoreExpr
fun (Type Kind
ty))
        = do { (LetFloats
floats, CoreExpr
rhs') <- CoreExpr -> SimplM (LetFloats, CoreExpr)
anfise CoreExpr
fun
             ; (LetFloats, CoreExpr) -> SimplM (LetFloats, CoreExpr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (LetFloats
floats, CoreExpr -> CoreExpr -> CoreExpr
forall b. Expr b -> Expr b -> Expr b
App CoreExpr
rhs' (Kind -> CoreExpr
forall b. Kind -> Expr b
Type Kind
ty)) }
    anfise (App CoreExpr
fun CoreExpr
arg)
        = do { (LetFloats
floats1, CoreExpr
fun') <- CoreExpr -> SimplM (LetFloats, CoreExpr)
anfise CoreExpr
fun
             ; (LetFloats
floats2, CoreExpr
arg') <- (() :: Constraint) =>
SimplEnv
-> TopLevelFlag
-> Demand
-> FastString
-> CoreExpr
-> SimplM (LetFloats, CoreExpr)
SimplEnv
-> TopLevelFlag
-> Demand
-> FastString
-> CoreExpr
-> SimplM (LetFloats, CoreExpr)
makeTrivial SimplEnv
env TopLevelFlag
top_lvl Demand
topDmd FastString
occ CoreExpr
arg
             ; (LetFloats, CoreExpr) -> SimplM (LetFloats, CoreExpr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (LetFloats
floats1 LetFloats -> LetFloats -> LetFloats
`addLetFlts` LetFloats
floats2, CoreExpr -> CoreExpr -> CoreExpr
forall b. Expr b -> Expr b -> Expr b
App CoreExpr
fun' CoreExpr
arg') }
    anfise (Var CoreBndr
fun)
        = (LetFloats, CoreExpr) -> SimplM (LetFloats, CoreExpr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (LetFloats
emptyLetFloats, CoreBndr -> CoreExpr
forall b. CoreBndr -> Expr b
Var CoreBndr
fun)

    anfise (Tick CoreTickish
t CoreExpr
rhs)
        -- We want to be able to float bindings past this
        -- tick. Non-scoping ticks don't care.
        | CoreTickish -> TickishScoping
forall (pass :: TickishPass). GenTickish pass -> TickishScoping
tickishScoped CoreTickish
t TickishScoping -> TickishScoping -> Bool
forall a. Eq a => a -> a -> Bool
== TickishScoping
NoScope
        = do { (LetFloats
floats, CoreExpr
rhs') <- CoreExpr -> SimplM (LetFloats, CoreExpr)
anfise CoreExpr
rhs
             ; (LetFloats, CoreExpr) -> SimplM (LetFloats, CoreExpr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (LetFloats
floats, CoreTickish -> CoreExpr -> CoreExpr
forall b. CoreTickish -> Expr b -> Expr b
Tick CoreTickish
t CoreExpr
rhs') }

        -- On the other hand, for scoping ticks we need to be able to
        -- copy them on the floats, which in turn is only allowed if
        -- we can obtain non-counting ticks.
        | (Bool -> Bool
not (CoreTickish -> Bool
forall (pass :: TickishPass). GenTickish pass -> Bool
tickishCounts CoreTickish
t) Bool -> Bool -> Bool
|| CoreTickish -> Bool
forall (pass :: TickishPass). GenTickish pass -> Bool
tickishCanSplit CoreTickish
t)
        = do { (LetFloats
floats, CoreExpr
rhs') <- CoreExpr -> SimplM (LetFloats, CoreExpr)
anfise CoreExpr
rhs
             ; let tickIt :: (CoreBndr, CoreExpr) -> (CoreBndr, CoreExpr)
tickIt (CoreBndr
id, CoreExpr
expr) = (CoreBndr
id, CoreTickish -> CoreExpr -> CoreExpr
mkTick (CoreTickish -> CoreTickish
forall (pass :: TickishPass). GenTickish pass -> GenTickish pass
mkNoCount CoreTickish
t) CoreExpr
expr)
                   floats' :: LetFloats
floats' = LetFloats
-> ((CoreBndr, CoreExpr) -> (CoreBndr, CoreExpr)) -> LetFloats
mapLetFloats LetFloats
floats (CoreBndr, CoreExpr) -> (CoreBndr, CoreExpr)
tickIt
             ; (LetFloats, CoreExpr) -> SimplM (LetFloats, CoreExpr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (LetFloats
floats', CoreTickish -> CoreExpr -> CoreExpr
forall b. CoreTickish -> Expr b -> Expr b
Tick CoreTickish
t CoreExpr
rhs') }

    anfise CoreExpr
other = (LetFloats, CoreExpr) -> SimplM (LetFloats, CoreExpr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (LetFloats
emptyLetFloats, CoreExpr
other)

makeTrivialArg :: HasDebugCallStack => SimplEnv -> ArgSpec -> SimplM (LetFloats, ArgSpec)
makeTrivialArg :: (() :: Constraint) =>
SimplEnv -> ArgSpec -> SimplM (LetFloats, ArgSpec)
makeTrivialArg SimplEnv
env arg :: ArgSpec
arg@(ValArg { as_arg :: ArgSpec -> CoreExpr
as_arg = CoreExpr
e, as_dmd :: ArgSpec -> Demand
as_dmd = Demand
dmd })
  = do { (LetFloats
floats, CoreExpr
e') <- (() :: Constraint) =>
SimplEnv
-> TopLevelFlag
-> Demand
-> FastString
-> CoreExpr
-> SimplM (LetFloats, CoreExpr)
SimplEnv
-> TopLevelFlag
-> Demand
-> FastString
-> CoreExpr
-> SimplM (LetFloats, CoreExpr)
makeTrivial SimplEnv
env TopLevelFlag
NotTopLevel Demand
dmd (String -> FastString
fsLit String
"arg") CoreExpr
e
       ; (LetFloats, ArgSpec) -> SimplM (LetFloats, ArgSpec)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (LetFloats
floats, ArgSpec
arg { as_arg = e' }) }
makeTrivialArg SimplEnv
_ ArgSpec
arg
  = (LetFloats, ArgSpec) -> SimplM (LetFloats, ArgSpec)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (LetFloats
emptyLetFloats, ArgSpec
arg)  -- CastBy, TyArg

makeTrivial :: HasDebugCallStack
            => SimplEnv -> TopLevelFlag -> Demand
            -> FastString  -- ^ A "friendly name" to build the new binder from
            -> OutExpr
            -> SimplM (LetFloats, OutExpr)
-- Binds the expression to a variable, if it's not trivial, returning the variable
-- For the Demand argument, see Note [Keeping demand info in StrictArg Plan A]
makeTrivial :: (() :: Constraint) =>
SimplEnv
-> TopLevelFlag
-> Demand
-> FastString
-> CoreExpr
-> SimplM (LetFloats, CoreExpr)
makeTrivial SimplEnv
env TopLevelFlag
top_lvl Demand
dmd FastString
occ_fs CoreExpr
expr
  | CoreExpr -> Bool
exprIsTrivial CoreExpr
expr                          -- Already trivial
  Bool -> Bool -> Bool
|| Bool -> Bool
not (TopLevelFlag -> CoreExpr -> Kind -> Bool
bindingOk TopLevelFlag
top_lvl CoreExpr
expr Kind
expr_ty)       -- Cannot trivialise
                                                --   See Note [Cannot trivialise]
  = (LetFloats, CoreExpr) -> SimplM (LetFloats, CoreExpr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (LetFloats
emptyLetFloats, CoreExpr
expr)

  | Cast CoreExpr
expr' Coercion
co <- CoreExpr
expr
  = do { (LetFloats
floats, CoreExpr
triv_expr) <- (() :: Constraint) =>
SimplEnv
-> TopLevelFlag
-> Demand
-> FastString
-> CoreExpr
-> SimplM (LetFloats, CoreExpr)
SimplEnv
-> TopLevelFlag
-> Demand
-> FastString
-> CoreExpr
-> SimplM (LetFloats, CoreExpr)
makeTrivial SimplEnv
env TopLevelFlag
top_lvl Demand
dmd FastString
occ_fs CoreExpr
expr'
       ; (LetFloats, CoreExpr) -> SimplM (LetFloats, CoreExpr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (LetFloats
floats, CoreExpr -> Coercion -> CoreExpr
forall b. Expr b -> Coercion -> Expr b
Cast CoreExpr
triv_expr Coercion
co) }

  | Bool
otherwise -- 'expr' is not of form (Cast e co)
  = do  { (LetFloats
floats, CoreExpr
expr1) <- (() :: Constraint) =>
SimplEnv
-> TopLevelFlag
-> FastString
-> CoreExpr
-> SimplM (LetFloats, CoreExpr)
SimplEnv
-> TopLevelFlag
-> FastString
-> CoreExpr
-> SimplM (LetFloats, CoreExpr)
prepareRhs SimplEnv
env TopLevelFlag
top_lvl FastString
occ_fs CoreExpr
expr
        ; Unique
uniq <- SimplM Unique
forall (m :: * -> *). MonadUnique m => m Unique
getUniqueM
        ; let name :: Name
name = Unique -> FastString -> Name
mkSystemVarName Unique
uniq FastString
occ_fs
              var :: CoreBndr
var  = (() :: Constraint) => Name -> Kind -> Kind -> IdInfo -> CoreBndr
Name -> Kind -> Kind -> IdInfo -> CoreBndr
mkLocalIdWithInfo Name
name Kind
ManyTy Kind
expr_ty IdInfo
id_info

        -- Now something very like completeBind,
        -- but without the postInlineUnconditionally part
        ; (ArityType
arity_type, CoreExpr
expr2) <- SimplEnv
-> BindContext
-> CoreBndr
-> CoreExpr
-> SimplM (ArityType, CoreExpr)
tryEtaExpandRhs SimplEnv
env (TopLevelFlag -> RecFlag -> BindContext
BC_Let TopLevelFlag
top_lvl RecFlag
NonRecursive) CoreBndr
var CoreExpr
expr1
          -- Technically we should extend the in-scope set in 'env' with
          -- the 'floats' from prepareRHS; but they are all fresh, so there is
          -- no danger of introducing name shadowig in eta expansion

        ; Unfolding
unf <- UnfoldingOpts
-> TopLevelFlag
-> UnfoldingSource
-> CoreBndr
-> CoreExpr
-> SimplM Unfolding
mkLetUnfolding UnfoldingOpts
uf_opts TopLevelFlag
top_lvl UnfoldingSource
VanillaSrc CoreBndr
var CoreExpr
expr2

        ; let final_id :: CoreBndr
final_id = CoreBndr -> ArityType -> Unfolding -> CoreBndr
addLetBndrInfo CoreBndr
var ArityType
arity_type Unfolding
unf
              bind :: InBind
bind     = CoreBndr -> CoreExpr -> InBind
forall b. b -> Expr b -> Bind b
NonRec CoreBndr
final_id CoreExpr
expr2

        ; String -> SDoc -> SimplM ()
traceSmpl String
"makeTrivial" ([SDoc] -> SDoc
forall doc. IsDoc doc => [doc] -> doc
vcat [String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"final_id" SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> CoreBndr -> SDoc
forall a. Outputable a => a -> SDoc
ppr CoreBndr
final_id, String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"rhs" SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> CoreExpr -> SDoc
forall a. Outputable a => a -> SDoc
ppr CoreExpr
expr2 ])
        ; (LetFloats, CoreExpr) -> SimplM (LetFloats, CoreExpr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return ( LetFloats
floats LetFloats -> LetFloats -> LetFloats
`addLetFlts` InBind -> LetFloats
unitLetFloat InBind
bind, CoreBndr -> CoreExpr
forall b. CoreBndr -> Expr b
Var CoreBndr
final_id ) }
  where
    id_info :: IdInfo
id_info = IdInfo
vanillaIdInfo IdInfo -> Demand -> IdInfo
`setDemandInfo` Demand
dmd
    expr_ty :: Kind
expr_ty = (() :: Constraint) => CoreExpr -> Kind
CoreExpr -> Kind
exprType CoreExpr
expr
    uf_opts :: UnfoldingOpts
uf_opts = SimplEnv -> UnfoldingOpts
seUnfoldingOpts SimplEnv
env

bindingOk :: TopLevelFlag -> CoreExpr -> Type -> Bool
-- True iff we can have a binding of this expression at this level
-- Precondition: the type is the type of the expression
bindingOk :: TopLevelFlag -> CoreExpr -> Kind -> Bool
bindingOk TopLevelFlag
top_lvl CoreExpr
expr Kind
expr_ty
  | TopLevelFlag -> Bool
isTopLevel TopLevelFlag
top_lvl = CoreExpr -> Kind -> Bool
exprIsTopLevelBindable CoreExpr
expr Kind
expr_ty
  | Bool
otherwise          = Bool
True

{- Note [Cannot trivialise]
~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider:
   f :: Int -> Addr#

   foo :: Bar
   foo = Bar (f 3)

Then we can't ANF-ise foo, even though we'd like to, because
we can't make a top-level binding for the Addr# (f 3). And if
so we don't want to turn it into
   foo = let x = f 3 in Bar x
because we'll just end up inlining x back, and that makes the
simplifier loop.  Better not to ANF-ise it at all.

Literal strings are an exception.

   foo = Ptr "blob"#

We want to turn this into:

   foo1 = "blob"#
   foo = Ptr foo1

See Note [Core top-level string literals] in GHC.Core.

************************************************************************
*                                                                      *
          Completing a lazy binding
*                                                                      *
************************************************************************

completeBind
  * deals only with Ids, not TyVars
  * takes an already-simplified binder and RHS
  * is used for both recursive and non-recursive bindings
  * is used for both top-level and non-top-level bindings

It does the following:
  - tries discarding a dead binding
  - tries PostInlineUnconditionally
  - add unfolding [this is the only place we add an unfolding]
  - add arity
  - extend the InScopeSet of the SimplEnv

It does *not* attempt to do let-to-case.  Why?  Because it is used for
  - top-level bindings (when let-to-case is impossible)
  - many situations where the "rhs" is known to be a WHNF
                (so let-to-case is inappropriate).

Nor does it do the atomic-argument thing
-}

completeBind :: SimplEnv
             -> BindContext
             -> InId           -- Old binder
             -> OutId          -- New binder; can be a JoinId
             -> OutExpr        -- New RHS
             -> SimplM (SimplFloats, SimplEnv)
-- completeBind may choose to do its work
--      * by extending the substitution (e.g. let x = y in ...)
--      * or by adding to the floats in the envt
--
-- Binder /can/ be a JoinId
-- Precondition: rhs obeys the let-can-float invariant
completeBind :: SimplEnv
-> BindContext
-> CoreBndr
-> CoreBndr
-> CoreExpr
-> SimplM (SimplFloats, SimplEnv)
completeBind SimplEnv
env BindContext
bind_cxt CoreBndr
old_bndr CoreBndr
new_bndr CoreExpr
new_rhs
 | CoreBndr -> Bool
isCoVar CoreBndr
old_bndr
 = case CoreExpr
new_rhs of
     Coercion Coercion
co -> (SimplFloats, SimplEnv) -> SimplM (SimplFloats, SimplEnv)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplEnv -> SimplFloats
emptyFloats SimplEnv
env, SimplEnv -> CoreBndr -> Coercion -> SimplEnv
extendCvSubst SimplEnv
env CoreBndr
old_bndr Coercion
co)
     CoreExpr
_           -> (SimplFloats, SimplEnv) -> SimplM (SimplFloats, SimplEnv)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplEnv -> InBind -> (SimplFloats, SimplEnv)
mkFloatBind SimplEnv
env (CoreBndr -> CoreExpr -> InBind
forall b. b -> Expr b -> Bind b
NonRec CoreBndr
new_bndr CoreExpr
new_rhs))

 | Bool
otherwise
 = Bool
-> SimplM (SimplFloats, SimplEnv) -> SimplM (SimplFloats, SimplEnv)
forall a. HasCallStack => Bool -> a -> a
assert (CoreBndr -> Bool
isId CoreBndr
new_bndr) (SimplM (SimplFloats, SimplEnv) -> SimplM (SimplFloats, SimplEnv))
-> SimplM (SimplFloats, SimplEnv) -> SimplM (SimplFloats, SimplEnv)
forall a b. (a -> b) -> a -> b
$
   do { let old_info :: IdInfo
old_info = (() :: Constraint) => CoreBndr -> IdInfo
CoreBndr -> IdInfo
idInfo CoreBndr
old_bndr
            old_unf :: Unfolding
old_unf  = IdInfo -> Unfolding
realUnfoldingInfo IdInfo
old_info
            occ_info :: OccInfo
occ_info = IdInfo -> OccInfo
occInfo IdInfo
old_info

         -- Do eta-expansion on the RHS of the binding
         -- See Note [Eta-expanding at let bindings] in GHC.Core.Opt.Simplify.Utils
      ; (ArityType
new_arity, CoreExpr
eta_rhs) <- SimplEnv
-> BindContext
-> CoreBndr
-> CoreExpr
-> SimplM (ArityType, CoreExpr)
tryEtaExpandRhs SimplEnv
env BindContext
bind_cxt CoreBndr
new_bndr CoreExpr
new_rhs

        -- Simplify the unfolding
      ; Unfolding
new_unfolding <- SimplEnv
-> BindContext
-> CoreBndr
-> CoreExpr
-> Kind
-> ArityType
-> Unfolding
-> SimplM Unfolding
simplLetUnfolding SimplEnv
env BindContext
bind_cxt CoreBndr
old_bndr
                         CoreExpr
eta_rhs (CoreBndr -> Kind
idType CoreBndr
new_bndr) ArityType
new_arity Unfolding
old_unf

      ; let new_bndr_w_info :: CoreBndr
new_bndr_w_info = CoreBndr -> ArityType -> Unfolding -> CoreBndr
addLetBndrInfo CoreBndr
new_bndr ArityType
new_arity Unfolding
new_unfolding
        -- See Note [In-scope set as a substitution]

      ; if SimplEnv -> BindContext -> CoreBndr -> OccInfo -> CoreExpr -> Bool
postInlineUnconditionally SimplEnv
env BindContext
bind_cxt CoreBndr
new_bndr_w_info OccInfo
occ_info CoreExpr
eta_rhs

        then -- Inline and discard the binding
             do  { Tick -> SimplM ()
tick (CoreBndr -> Tick
PostInlineUnconditionally CoreBndr
old_bndr)
                 ; let unf_rhs :: CoreExpr
unf_rhs = Unfolding -> Maybe CoreExpr
maybeUnfoldingTemplate Unfolding
new_unfolding Maybe CoreExpr -> CoreExpr -> CoreExpr
forall a. Maybe a -> a -> a
`orElse` CoreExpr
eta_rhs
                          -- See Note [Use occ-anald RHS in postInlineUnconditionally]
                 ; String
-> SDoc
-> SimplM (SimplFloats, SimplEnv)
-> SimplM (SimplFloats, SimplEnv)
forall a. String -> SDoc -> SimplM a -> SimplM a
simplTrace String
"PostInlineUnconditionally" (CoreBndr -> SDoc
forall a. Outputable a => a -> SDoc
ppr CoreBndr
new_bndr SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> CoreExpr -> SDoc
forall a. Outputable a => a -> SDoc
ppr CoreExpr
unf_rhs) (SimplM (SimplFloats, SimplEnv) -> SimplM (SimplFloats, SimplEnv))
-> SimplM (SimplFloats, SimplEnv) -> SimplM (SimplFloats, SimplEnv)
forall a b. (a -> b) -> a -> b
$
                   (SimplFloats, SimplEnv) -> SimplM (SimplFloats, SimplEnv)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return ( SimplEnv -> SimplFloats
emptyFloats SimplEnv
env
                          , SimplEnv -> CoreBndr -> SimplSR -> SimplEnv
extendIdSubst SimplEnv
env CoreBndr
old_bndr (SimplSR -> SimplEnv) -> SimplSR -> SimplEnv
forall a b. (a -> b) -> a -> b
$
                            CoreExpr -> Maybe Int -> SimplSR
DoneEx CoreExpr
unf_rhs (CoreBndr -> Maybe Int
isJoinId_maybe CoreBndr
new_bndr)) }
                -- Use the substitution to make quite, quite sure that the
                -- substitution will happen, since we are going to discard the binding

        else -- Keep the binding; do cast worker/wrapper
             -- pprTrace "Binding" (ppr new_bndr <+> ppr new_unfolding) $
             SimplEnv
-> BindContext
-> CoreBndr
-> OccInfo
-> CoreBndr
-> CoreExpr
-> SimplM (SimplFloats, SimplEnv)
tryCastWorkerWrapper SimplEnv
env BindContext
bind_cxt CoreBndr
old_bndr OccInfo
occ_info CoreBndr
new_bndr_w_info CoreExpr
eta_rhs }

addLetBndrInfo :: OutId -> ArityType -> Unfolding -> OutId
addLetBndrInfo :: CoreBndr -> ArityType -> Unfolding -> CoreBndr
addLetBndrInfo CoreBndr
new_bndr ArityType
new_arity_type Unfolding
new_unf
  = CoreBndr
new_bndr CoreBndr -> IdInfo -> CoreBndr
`setIdInfo` IdInfo
info5
  where
    new_arity :: Int
new_arity = ArityType -> Int
arityTypeArity ArityType
new_arity_type
    info1 :: IdInfo
info1 = (() :: Constraint) => CoreBndr -> IdInfo
CoreBndr -> IdInfo
idInfo CoreBndr
new_bndr IdInfo -> Int -> IdInfo
`setArityInfo` Int
new_arity

    -- Unfolding info: Note [Setting the new unfolding]
    info2 :: IdInfo
info2 = IdInfo
info1 IdInfo -> Unfolding -> IdInfo
`setUnfoldingInfo` Unfolding
new_unf

    -- Demand info: Note [Setting the demand info]
    info3 :: IdInfo
info3 | Unfolding -> Bool
isEvaldUnfolding Unfolding
new_unf
          = IdInfo -> Maybe IdInfo
zapDemandInfo IdInfo
info2 Maybe IdInfo -> IdInfo -> IdInfo
forall a. Maybe a -> a -> a
`orElse` IdInfo
info2
          | Bool
otherwise
          = IdInfo
info2

    -- Bottoming bindings: see Note [Bottoming bindings]
    info4 :: IdInfo
info4 = case ArityType -> Maybe (Int, DmdSig, CprSig)
arityTypeBotSigs_maybe ArityType
new_arity_type of
        Maybe (Int, DmdSig, CprSig)
Nothing -> IdInfo
info3
        Just (Int
ar, DmdSig
str_sig, CprSig
cpr_sig) -> Bool -> IdInfo -> IdInfo
forall a. HasCallStack => Bool -> a -> a
assert (Int
ar Int -> Int -> Bool
forall a. Eq a => a -> a -> Bool
== Int
new_arity) (IdInfo -> IdInfo) -> IdInfo -> IdInfo
forall a b. (a -> b) -> a -> b
$
                                       IdInfo
info3 IdInfo -> DmdSig -> IdInfo
`setDmdSigInfo` DmdSig
str_sig
                                             IdInfo -> CprSig -> IdInfo
`setCprSigInfo` CprSig
cpr_sig

     -- Zap call arity info. We have used it by now (via
     -- `tryEtaExpandRhs`), and the simplifier can invalidate this
     -- information, leading to broken code later (e.g. #13479)
    info5 :: IdInfo
info5 = IdInfo -> IdInfo
zapCallArityInfo IdInfo
info4


{- Note [Bottoming bindings]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Suppose we have
   let x = error "urk"
   in ...(case x of <alts>)...
or
   let f = \y. error (y ++ "urk")
   in ...(case f "foo" of <alts>)...

Then we'd like to drop the dead <alts> immediately.  So it's good to
propagate the info that x's (or f's) RHS is bottom to x's (or f's)
IdInfo as rapidly as possible.

We use tryEtaExpandRhs on every binding, and it turns out that the
arity computation it performs (via GHC.Core.Opt.Arity.findRhsArity) already
does a simple bottoming-expression analysis.  So all we need to do
is propagate that info to the binder's IdInfo.

This showed up in #12150; see comment:16.

There is a second reason for settting  the strictness signature. Consider
   let -- f :: <[S]b>
       f = \x. error "urk"
   in ...(f a b c)...
Then, in GHC.Core.Opt.Arity.findRhsArity we'll use the demand-info on `f`
to eta-expand to
   let f = \x y z. error "urk"
   in ...(f a b c)...

But now f's strictness signature has too short an arity; see
GHC.Core.Opt.DmdAnal Note [idArity varies independently of dmdTypeDepth].
Fortuitously, the same strictness-signature-fixup code
gives the function a new strictness signature with the right number of
arguments.  Example in stranal/should_compile/EtaExpansion.

Note [Setting the demand info]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
If the unfolding is a value, the demand info may
go pear-shaped, so we nuke it.  Example:
     let x = (a,b) in
     case x of (p,q) -> h p q x
Here x is certainly demanded. But after we've nuked
the case, we'll get just
     let x = (a,b) in h a b x
and now x is not demanded (I'm assuming h is lazy)
This really happens.  Similarly
     let f = \x -> e in ...f..f...
After inlining f at some of its call sites the original binding may
(for example) be no longer strictly demanded.
The solution here is a bit ad hoc...

Note [Use occ-anald RHS in postInlineUnconditionally]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Suppose we postInlineUnconditionally 'f in
  let f = \x -> x True in ...(f blah)...
then we'd like to inline the /occ-anald/ RHS for 'f'.  If we
use the non-occ-anald version, we'll end up with a
    ...(let x = blah in x True)...
and hence an extra Simplifier iteration.

We already /have/ the occ-anald version in the Unfolding for
the Id.  Well, maybe not /quite/ always.  If the binder is Dead,
postInlineUnconditionally will return True, but we may not have an
unfolding because it's too big. Hence the belt-and-braces `orElse`
in the defn of unf_rhs.  The Nothing case probably never happens.


************************************************************************
*                                                                      *
\subsection[Simplify-simplExpr]{The main function: simplExpr}
*                                                                      *
************************************************************************

The reason for this OutExprStuff stuff is that we want to float *after*
simplifying a RHS, not before.  If we do so naively we get quadratic
behaviour as things float out.

To see why it's important to do it after, consider this (real) example:

        let t = f x
        in fst t
==>
        let t = let a = e1
                    b = e2
                in (a,b)
        in fst t
==>
        let a = e1
            b = e2
            t = (a,b)
        in
        a       -- Can't inline a this round, cos it appears twice
==>
        e1

Each of the ==> steps is a round of simplification.  We'd save a
whole round if we float first.  This can cascade.  Consider

        let f = g d
        in \x -> ...f...
==>
        let f = let d1 = ..d.. in \y -> e
        in \x -> ...f...
==>
        let d1 = ..d..
        in \x -> ...(\y ->e)...

Only in this second round can the \y be applied, and it
might do the same again.
-}

simplExpr :: SimplEnv -> CoreExpr -> SimplM CoreExpr
simplExpr :: SimplEnv -> CoreExpr -> SimplM CoreExpr
simplExpr !SimplEnv
env (Type Kind
ty) -- See Note [Bangs in the Simplifier]
  = do { Kind
ty' <- SimplEnv -> Kind -> SimplM Kind
simplType SimplEnv
env Kind
ty  -- See Note [Avoiding space leaks in OutType]
       ; CoreExpr -> SimplM CoreExpr
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (Kind -> CoreExpr
forall b. Kind -> Expr b
Type Kind
ty') }

simplExpr SimplEnv
env CoreExpr
expr
  = SimplEnv -> CoreExpr -> SimplCont -> SimplM CoreExpr
simplExprC SimplEnv
env CoreExpr
expr (Kind -> SimplCont
mkBoringStop Kind
expr_out_ty)
  where
    expr_out_ty :: OutType
    expr_out_ty :: Kind
expr_out_ty = (() :: Constraint) => SimplEnv -> Kind -> Kind
SimplEnv -> Kind -> Kind
substTy SimplEnv
env ((() :: Constraint) => CoreExpr -> Kind
CoreExpr -> Kind
exprType CoreExpr
expr)
    -- NB: Since 'expr' is term-valued, not (Type ty), this call
    --     to exprType will succeed.  exprType fails on (Type ty).

simplExprC :: SimplEnv
           -> InExpr     -- A term-valued expression, never (Type ty)
           -> SimplCont
           -> SimplM OutExpr
        -- Simplify an expression, given a continuation
simplExprC :: SimplEnv -> CoreExpr -> SimplCont -> SimplM CoreExpr
simplExprC SimplEnv
env CoreExpr
expr SimplCont
cont
  = -- pprTrace "simplExprC" (ppr expr $$ ppr cont) $
    do  { (SimplFloats
floats, CoreExpr
expr') <- SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF SimplEnv
env CoreExpr
expr SimplCont
cont
        ; -- pprTrace "simplExprC ret" (ppr expr $$ ppr expr') $
          -- pprTrace "simplExprC ret3" (ppr (seInScope env')) $
          -- pprTrace "simplExprC ret4" (ppr (seLetFloats env')) $
          CoreExpr -> SimplM CoreExpr
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplFloats -> CoreExpr -> CoreExpr
wrapFloats SimplFloats
floats CoreExpr
expr') }

--------------------------------------------------
simplExprF :: SimplEnv
           -> InExpr     -- A term-valued expression, never (Type ty)
           -> SimplCont
           -> SimplM (SimplFloats, OutExpr)

simplExprF :: SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF !SimplEnv
env CoreExpr
e !SimplCont
cont -- See Note [Bangs in the Simplifier]
  = {- pprTrace "simplExprF" (vcat
      [ ppr e
      , text "cont =" <+> ppr cont
      , text "inscope =" <+> ppr (seInScope env)
      , text "tvsubst =" <+> ppr (seTvSubst env)
      , text "idsubst =" <+> ppr (seIdSubst env)
      , text "cvsubst =" <+> ppr (seCvSubst env)
      ]) $ -}
    SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF1 SimplEnv
env CoreExpr
e SimplCont
cont

simplExprF1 :: SimplEnv -> InExpr -> SimplCont
            -> SimplM (SimplFloats, OutExpr)

simplExprF1 :: SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF1 SimplEnv
_ (Type Kind
ty) SimplCont
cont
  = String -> SDoc -> SimplM (SimplFloats, CoreExpr)
forall a. HasCallStack => String -> SDoc -> a
pprPanic String
"simplExprF: type" (Kind -> SDoc
forall a. Outputable a => a -> SDoc
ppr Kind
ty SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> String -> SDoc
forall doc. IsLine doc => String -> doc
textString
"cont: " SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> SimplCont -> SDoc
forall a. Outputable a => a -> SDoc
ppr SimplCont
cont)
    -- simplExprF does only with term-valued expressions
    -- The (Type ty) case is handled separately by simplExpr
    -- and by the other callers of simplExprF

simplExprF1 SimplEnv
env (Var CoreBndr
v)        SimplCont
cont = {-#SCC "simplIdF" #-} SimplEnv -> CoreBndr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplIdF SimplEnv
env CoreBndr
v SimplCont
cont
simplExprF1 SimplEnv
env (Lit Literal
lit)      SimplCont
cont = {-#SCC "rebuild" #-} SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
rebuild SimplEnv
env (Literal -> CoreExpr
forall b. Literal -> Expr b
Lit Literal
lit) SimplCont
cont
simplExprF1 SimplEnv
env (Tick CoreTickish
t CoreExpr
expr)  SimplCont
cont = {-#SCC "simplTick" #-} SimplEnv
-> CoreTickish
-> CoreExpr
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
simplTick SimplEnv
env CoreTickish
t CoreExpr
expr SimplCont
cont
simplExprF1 SimplEnv
env (Cast CoreExpr
body Coercion
co) SimplCont
cont = {-#SCC "simplCast" #-} SimplEnv
-> CoreExpr
-> Coercion
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
simplCast SimplEnv
env CoreExpr
body Coercion
co SimplCont
cont
simplExprF1 SimplEnv
env (Coercion Coercion
co)  SimplCont
cont = {-#SCC "simplCoercionF" #-} SimplEnv -> Coercion -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplCoercionF SimplEnv
env Coercion
co SimplCont
cont

simplExprF1 SimplEnv
env (App CoreExpr
fun CoreExpr
arg) SimplCont
cont
  = {-#SCC "simplExprF1-App" #-} case CoreExpr
arg of
      Type Kind
ty -> do { -- The argument type will (almost) certainly be used
                      -- in the output program, so just force it now.
                      -- See Note [Avoiding space leaks in OutType]
                      Kind
arg' <- SimplEnv -> Kind -> SimplM Kind
simplType SimplEnv
env Kind
ty

                      -- But use substTy, not simplType, to avoid forcing
                      -- the hole type; it will likely not be needed.
                      -- See Note [The hole type in ApplyToTy]
                    ; let hole' :: Kind
hole' = (() :: Constraint) => SimplEnv -> Kind -> Kind
SimplEnv -> Kind -> Kind
substTy SimplEnv
env ((() :: Constraint) => CoreExpr -> Kind
CoreExpr -> Kind
exprType CoreExpr
fun)

                    ; SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF SimplEnv
env CoreExpr
fun (SimplCont -> SimplM (SimplFloats, CoreExpr))
-> SimplCont -> SimplM (SimplFloats, CoreExpr)
forall a b. (a -> b) -> a -> b
$
                      ApplyToTy { sc_arg_ty :: Kind
sc_arg_ty  = Kind
arg'
                                , sc_hole_ty :: Kind
sc_hole_ty = Kind
hole'
                                , sc_cont :: SimplCont
sc_cont    = SimplCont
cont } }
      CoreExpr
_       ->
          -- Crucially, sc_hole_ty is a /lazy/ binding.  It will
          -- be forced only if we need to run contHoleType.
          -- When these are forced, we might get quadratic behavior;
          -- this quadratic blowup could be avoided by drilling down
          -- to the function and getting its multiplicities all at once
          -- (instead of one-at-a-time). But in practice, we have not
          -- observed the quadratic behavior, so this extra entanglement
          -- seems not worthwhile.
        SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF SimplEnv
env CoreExpr
fun (SimplCont -> SimplM (SimplFloats, CoreExpr))
-> SimplCont -> SimplM (SimplFloats, CoreExpr)
forall a b. (a -> b) -> a -> b
$
        ApplyToVal { sc_arg :: CoreExpr
sc_arg = CoreExpr
arg, sc_env :: SimplEnv
sc_env = SimplEnv
env
                   , sc_hole_ty :: Kind
sc_hole_ty = (() :: Constraint) => SimplEnv -> Kind -> Kind
SimplEnv -> Kind -> Kind
substTy SimplEnv
env ((() :: Constraint) => CoreExpr -> Kind
CoreExpr -> Kind
exprType CoreExpr
fun)
                   , sc_dup :: DupFlag
sc_dup = DupFlag
NoDup, sc_cont :: SimplCont
sc_cont = SimplCont
cont }

simplExprF1 SimplEnv
env expr :: CoreExpr
expr@(Lam {}) SimplCont
cont
  = {-#SCC "simplExprF1-Lam" #-}
    SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplLam SimplEnv
env (CoreExpr -> Int -> CoreExpr
zapLambdaBndrs CoreExpr
expr Int
n_args) SimplCont
cont
        -- zapLambdaBndrs: the issue here is under-saturated lambdas
        --   (\x1. \x2. e) arg1
        -- Here x1 might have "occurs-once" occ-info, because occ-info
        -- is computed assuming that a group of lambdas is applied
        -- all at once.  If there are too few args, we must zap the
        -- occ-info, UNLESS the remaining binders are one-shot
  where
    n_args :: Int
n_args = SimplCont -> Int
countArgs SimplCont
cont
        -- NB: countArgs counts all the args (incl type args)
        -- and likewise drop counts all binders (incl type lambdas)

simplExprF1 SimplEnv
env (Case CoreExpr
scrut CoreBndr
bndr Kind
_ [Alt CoreBndr]
alts) SimplCont
cont
  = {-#SCC "simplExprF1-Case" #-}
    SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF SimplEnv
env CoreExpr
scrut (Select { sc_dup :: DupFlag
sc_dup = DupFlag
NoDup, sc_bndr :: CoreBndr
sc_bndr = CoreBndr
bndr
                                 , sc_alts :: [Alt CoreBndr]
sc_alts = [Alt CoreBndr]
alts
                                 , sc_env :: SimplEnv
sc_env = SimplEnv
env, sc_cont :: SimplCont
sc_cont = SimplCont
cont })

simplExprF1 SimplEnv
env (Let (Rec [(CoreBndr, CoreExpr)]
pairs) CoreExpr
body) SimplCont
cont
  | Just [(CoreBndr, CoreExpr)]
pairs' <- [(CoreBndr, CoreExpr)] -> Maybe [(CoreBndr, CoreExpr)]
joinPointBindings_maybe [(CoreBndr, CoreExpr)]
pairs
  = {-#SCC "simplRecJoinPoin" #-} SimplEnv
-> [(CoreBndr, CoreExpr)]
-> CoreExpr
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
simplRecJoinPoint SimplEnv
env [(CoreBndr, CoreExpr)]
pairs' CoreExpr
body SimplCont
cont

  | Bool
otherwise
  = {-#SCC "simplRecE" #-} SimplEnv
-> [(CoreBndr, CoreExpr)]
-> CoreExpr
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
simplRecE SimplEnv
env [(CoreBndr, CoreExpr)]
pairs CoreExpr
body SimplCont
cont

simplExprF1 SimplEnv
env (Let (NonRec CoreBndr
bndr CoreExpr
rhs) CoreExpr
body) SimplCont
cont
  | Type Kind
ty <- CoreExpr
rhs    -- First deal with type lets (let a = Type ty in e)
  = {-#SCC "simplExprF1-NonRecLet-Type" #-}
    Bool
-> SimplM (SimplFloats, CoreExpr) -> SimplM (SimplFloats, CoreExpr)
forall a. HasCallStack => Bool -> a -> a
assert (CoreBndr -> Bool
isTyVar CoreBndr
bndr) (SimplM (SimplFloats, CoreExpr) -> SimplM (SimplFloats, CoreExpr))
-> SimplM (SimplFloats, CoreExpr) -> SimplM (SimplFloats, CoreExpr)
forall a b. (a -> b) -> a -> b
$
    do { Kind
ty' <- SimplEnv -> Kind -> SimplM Kind
simplType SimplEnv
env Kind
ty
       ; SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF (SimplEnv -> CoreBndr -> Kind -> SimplEnv
extendTvSubst SimplEnv
env CoreBndr
bndr Kind
ty') CoreExpr
body SimplCont
cont }

  | Just SimplEnv
env' <- SimplEnv
-> TopLevelFlag
-> CoreBndr
-> CoreExpr
-> SimplEnv
-> Maybe SimplEnv
preInlineUnconditionally SimplEnv
env TopLevelFlag
NotTopLevel CoreBndr
bndr CoreExpr
rhs SimplEnv
env
    -- Because of the let-can-float invariant, it's ok to
    -- inline freely, or to drop the binding if it is dead.
  = do { Tick -> SimplM ()
tick (CoreBndr -> Tick
PreInlineUnconditionally CoreBndr
bndr)
       ; SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF SimplEnv
env' CoreExpr
body SimplCont
cont }

  -- Now check for a join point.  It's better to do the preInlineUnconditionally
  -- test first, because joinPointBinding_maybe has to eta-expand, so a trivial
  -- binding like { j = j2 |> co } would first be eta-expanded and then inlined
  -- Better to test preInlineUnconditionally first.
  | Just (CoreBndr
bndr', CoreExpr
rhs') <- CoreBndr -> CoreExpr -> Maybe (CoreBndr, CoreExpr)
joinPointBinding_maybe CoreBndr
bndr CoreExpr
rhs
  = {-#SCC "simplNonRecJoinPoint" #-}
    SimplEnv
-> CoreBndr
-> CoreExpr
-> CoreExpr
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
simplNonRecJoinPoint SimplEnv
env CoreBndr
bndr' CoreExpr
rhs' CoreExpr
body SimplCont
cont

  | Bool
otherwise
  = {-#SCC "simplNonRecE" #-}
    SimplEnv
-> FromWhat
-> CoreBndr
-> (CoreExpr, SimplEnv)
-> CoreExpr
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
simplNonRecE SimplEnv
env FromWhat
FromLet CoreBndr
bndr (CoreExpr
rhs, SimplEnv
env) CoreExpr
body SimplCont
cont

{- Note [Avoiding space leaks in OutType]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Since the simplifier is run for multiple iterations, we need to ensure
that any thunks in the output of one simplifier iteration are forced
by the evaluation of the next simplifier iteration. Otherwise we may
retain multiple copies of the Core program and leak a terrible amount
of memory (as in #13426).

The simplifier is naturally strict in the entire "Expr part" of the
input Core program, because any expression may contain binders, which
we must find in order to extend the SimplEnv accordingly. But types
do not contain binders and so it is tempting to write things like

    simplExpr env (Type ty) = return (Type (substTy env ty))   -- Bad!

This is Bad because the result includes a thunk (substTy env ty) which
retains a reference to the whole simplifier environment; and the next
simplifier iteration will not force this thunk either, because the
line above is not strict in ty.

So instead our strategy is for the simplifier to fully evaluate
OutTypes when it emits them into the output Core program, for example

    simplExpr env (Type ty) = do { ty' <- simplType env ty     -- Good
                                 ; return (Type ty') }

where the only difference from above is that simplType calls seqType
on the result of substTy.

However, SimplCont can also contain OutTypes and it's not necessarily
a good idea to force types on the way in to SimplCont, because they
may end up not being used and forcing them could be a lot of wasted
work. T5631 is a good example of this.

- For ApplyToTy's sc_arg_ty, we force the type on the way in because
  the type will almost certainly appear as a type argument in the
  output program.

- For the hole types in Stop and ApplyToTy, we force the type when we
  emit it into the output program, after obtaining it from
  contResultType. (The hole type in ApplyToTy is only directly used
  to form the result type in a new Stop continuation.)
-}

---------------------------------
-- Simplify a join point, adding the context.
-- Context goes *inside* the lambdas. IOW, if the join point has arity n, we do:
--   \x1 .. xn -> e => \x1 .. xn -> E[e]
-- Note that we need the arity of the join point, since e may be a lambda
-- (though this is unlikely). See Note [Join points and case-of-case].
simplJoinRhs :: SimplEnv -> InId -> InExpr -> SimplCont
             -> SimplM OutExpr
simplJoinRhs :: SimplEnv -> CoreBndr -> CoreExpr -> SimplCont -> SimplM CoreExpr
simplJoinRhs SimplEnv
env CoreBndr
bndr CoreExpr
expr SimplCont
cont
  | Just Int
arity <- CoreBndr -> Maybe Int
isJoinId_maybe CoreBndr
bndr
  =  do { let ([CoreBndr]
join_bndrs, CoreExpr
join_body) = Int -> CoreExpr -> ([CoreBndr], CoreExpr)
forall b. Int -> Expr b -> ([b], Expr b)
collectNBinders Int
arity CoreExpr
expr
              mult :: Kind
mult = SimplCont -> Kind
contHoleScaling SimplCont
cont
        ; (SimplEnv
env', [CoreBndr]
join_bndrs') <- SimplEnv -> [CoreBndr] -> SimplM (SimplEnv, [CoreBndr])
simplLamBndrs SimplEnv
env ((CoreBndr -> CoreBndr) -> [CoreBndr] -> [CoreBndr]
forall a b. (a -> b) -> [a] -> [b]
map (Kind -> CoreBndr -> CoreBndr
scaleVarBy Kind
mult) [CoreBndr]
join_bndrs)
        ; CoreExpr
join_body' <- SimplEnv -> CoreExpr -> SimplCont -> SimplM CoreExpr
simplExprC SimplEnv
env' CoreExpr
join_body SimplCont
cont
        ; CoreExpr -> SimplM CoreExpr
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (CoreExpr -> SimplM CoreExpr) -> CoreExpr -> SimplM CoreExpr
forall a b. (a -> b) -> a -> b
$ [CoreBndr] -> CoreExpr -> CoreExpr
forall b. [b] -> Expr b -> Expr b
mkLams [CoreBndr]
join_bndrs' CoreExpr
join_body' }

  | Bool
otherwise
  = String -> SDoc -> SimplM CoreExpr
forall a. HasCallStack => String -> SDoc -> a
pprPanic String
"simplJoinRhs" (CoreBndr -> SDoc
forall a. Outputable a => a -> SDoc
ppr CoreBndr
bndr)

---------------------------------
simplType :: SimplEnv -> InType -> SimplM OutType
        -- Kept monadic just so we can do the seqType
        -- See Note [Avoiding space leaks in OutType]
simplType :: SimplEnv -> Kind -> SimplM Kind
simplType SimplEnv
env Kind
ty
  = -- pprTrace "simplType" (ppr ty $$ ppr (seTvSubst env)) $
    Kind -> ()
seqType Kind
new_ty () -> SimplM Kind -> SimplM Kind
forall a b. a -> b -> b
`seq` Kind -> SimplM Kind
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return Kind
new_ty
  where
    new_ty :: Kind
new_ty = (() :: Constraint) => SimplEnv -> Kind -> Kind
SimplEnv -> Kind -> Kind
substTy SimplEnv
env Kind
ty

---------------------------------
simplCoercionF :: SimplEnv -> InCoercion -> SimplCont
               -> SimplM (SimplFloats, OutExpr)
simplCoercionF :: SimplEnv -> Coercion -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplCoercionF SimplEnv
env Coercion
co SimplCont
cont
  = do { Coercion
co' <- SimplEnv -> Coercion -> SimplM Coercion
simplCoercion SimplEnv
env Coercion
co
       ; SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
rebuild SimplEnv
env (Coercion -> CoreExpr
forall b. Coercion -> Expr b
Coercion Coercion
co') SimplCont
cont }

simplCoercion :: SimplEnv -> InCoercion -> SimplM OutCoercion
simplCoercion :: SimplEnv -> Coercion -> SimplM Coercion
simplCoercion SimplEnv
env Coercion
co
  = do { let opt_co :: Coercion
opt_co = OptCoercionOpts -> Subst -> Coercion -> Coercion
optCoercion OptCoercionOpts
opts (SimplEnv -> Subst
getSubst SimplEnv
env) Coercion
co
       ; Coercion -> ()
seqCo Coercion
opt_co () -> SimplM Coercion -> SimplM Coercion
forall a b. a -> b -> b
`seq` Coercion -> SimplM Coercion
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return Coercion
opt_co }
  where
    opts :: OptCoercionOpts
opts = SimplEnv -> OptCoercionOpts
seOptCoercionOpts SimplEnv
env

-----------------------------------
-- | Push a TickIt context outwards past applications and cases, as
-- long as this is a non-scoping tick, to let case and application
-- optimisations apply.

simplTick :: SimplEnv -> CoreTickish -> InExpr -> SimplCont
          -> SimplM (SimplFloats, OutExpr)
simplTick :: SimplEnv
-> CoreTickish
-> CoreExpr
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
simplTick SimplEnv
env CoreTickish
tickish CoreExpr
expr SimplCont
cont
  -- A scoped tick turns into a continuation, so that we can spot
  -- (scc t (\x . e)) in simplLam and eliminate the scc.  If we didn't do
  -- it this way, then it would take two passes of the simplifier to
  -- reduce ((scc t (\x . e)) e').
  -- NB, don't do this with counting ticks, because if the expr is
  -- bottom, then rebuildCall will discard the continuation.

-- XXX: we cannot do this, because the simplifier assumes that
-- the context can be pushed into a case with a single branch. e.g.
--    scc<f>  case expensive of p -> e
-- becomes
--    case expensive of p -> scc<f> e
--
-- So I'm disabling this for now.  It just means we will do more
-- simplifier iterations that necessary in some cases.

--  | tickishScoped tickish && not (tickishCounts tickish)
--  = simplExprF env expr (TickIt tickish cont)

  -- For unscoped or soft-scoped ticks, we are allowed to float in new
  -- cost, so we simply push the continuation inside the tick.  This
  -- has the effect of moving the tick to the outside of a case or
  -- application context, allowing the normal case and application
  -- optimisations to fire.
  | CoreTickish
tickish CoreTickish -> TickishScoping -> Bool
forall (pass :: TickishPass).
GenTickish pass -> TickishScoping -> Bool
`tickishScopesLike` TickishScoping
SoftScope
  = do { (SimplFloats
floats, CoreExpr
expr') <- SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF SimplEnv
env CoreExpr
expr SimplCont
cont
       ; (SimplFloats, CoreExpr) -> SimplM (SimplFloats, CoreExpr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplFloats
floats, CoreTickish -> CoreExpr -> CoreExpr
mkTick CoreTickish
tickish CoreExpr
expr')
       }

  -- Push tick inside if the context looks like this will allow us to
  -- do a case-of-case - see Note [case-of-scc-of-case]
  | Select {} <- SimplCont
cont, Just CoreExpr
expr' <- Maybe CoreExpr
push_tick_inside
  = SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF SimplEnv
env CoreExpr
expr' SimplCont
cont

  -- We don't want to move the tick, but we might still want to allow
  -- floats to pass through with appropriate wrapping (or not, see
  -- wrap_floats below)
  --- | not (tickishCounts tickish) || tickishCanSplit tickish
  -- = wrap_floats

  | Bool
otherwise
  = SimplM (SimplFloats, CoreExpr)
no_floating_past_tick

 where

  -- Try to push tick inside a case, see Note [case-of-scc-of-case].
  push_tick_inside :: Maybe CoreExpr
push_tick_inside =
    case CoreExpr
expr0 of
      Case CoreExpr
scrut CoreBndr
bndr Kind
ty [Alt CoreBndr]
alts
             -> CoreExpr -> Maybe CoreExpr
forall a. a -> Maybe a
Just (CoreExpr -> Maybe CoreExpr) -> CoreExpr -> Maybe CoreExpr
forall a b. (a -> b) -> a -> b
$ CoreExpr -> CoreBndr -> Kind -> [Alt CoreBndr] -> CoreExpr
forall b. Expr b -> b -> Kind -> [Alt b] -> Expr b
Case (CoreExpr -> CoreExpr
tickScrut CoreExpr
scrut) CoreBndr
bndr Kind
ty ((Alt CoreBndr -> Alt CoreBndr) -> [Alt CoreBndr] -> [Alt CoreBndr]
forall a b. (a -> b) -> [a] -> [b]
map Alt CoreBndr -> Alt CoreBndr
tickAlt [Alt CoreBndr]
alts)
      CoreExpr
_other -> Maybe CoreExpr
forall a. Maybe a
Nothing
   where ([CoreTickish]
ticks, CoreExpr
expr0) = (CoreTickish -> Bool) -> CoreExpr -> ([CoreTickish], CoreExpr)
forall b.
(CoreTickish -> Bool) -> Expr b -> ([CoreTickish], Expr b)
stripTicksTop CoreTickish -> Bool
forall (pass :: TickishPass). GenTickish pass -> Bool
movable (CoreTickish -> CoreExpr -> CoreExpr
forall b. CoreTickish -> Expr b -> Expr b
Tick CoreTickish
tickish CoreExpr
expr)
         movable :: GenTickish pass -> Bool
movable GenTickish pass
t      = Bool -> Bool
not (GenTickish pass -> Bool
forall (pass :: TickishPass). GenTickish pass -> Bool
tickishCounts GenTickish pass
t) Bool -> Bool -> Bool
||
                          GenTickish pass
t GenTickish pass -> TickishScoping -> Bool
forall (pass :: TickishPass).
GenTickish pass -> TickishScoping -> Bool
`tickishScopesLike` TickishScoping
NoScope Bool -> Bool -> Bool
||
                          GenTickish pass -> Bool
forall (pass :: TickishPass). GenTickish pass -> Bool
tickishCanSplit GenTickish pass
t
         tickScrut :: CoreExpr -> CoreExpr
tickScrut CoreExpr
e    = (CoreTickish -> CoreExpr -> CoreExpr)
-> CoreExpr -> [CoreTickish] -> CoreExpr
forall a b. (a -> b -> b) -> b -> [a] -> b
forall (t :: * -> *) a b.
Foldable t =>
(a -> b -> b) -> b -> t a -> b
foldr CoreTickish -> CoreExpr -> CoreExpr
mkTick CoreExpr
e [CoreTickish]
ticks
         -- Alternatives get annotated with all ticks that scope in some way,
         -- but we don't want to count entries.
         tickAlt :: Alt CoreBndr -> Alt CoreBndr
tickAlt (Alt AltCon
c [CoreBndr]
bs CoreExpr
e) = AltCon -> [CoreBndr] -> CoreExpr -> Alt CoreBndr
forall b. AltCon -> [b] -> Expr b -> Alt b
Alt AltCon
c [CoreBndr]
bs ((CoreTickish -> CoreExpr -> CoreExpr)
-> CoreExpr -> [CoreTickish] -> CoreExpr
forall a b. (a -> b -> b) -> b -> [a] -> b
forall (t :: * -> *) a b.
Foldable t =>
(a -> b -> b) -> b -> t a -> b
foldr CoreTickish -> CoreExpr -> CoreExpr
mkTick CoreExpr
e [CoreTickish]
ts_scope)
         ts_scope :: [CoreTickish]
ts_scope         = (CoreTickish -> CoreTickish) -> [CoreTickish] -> [CoreTickish]
forall a b. (a -> b) -> [a] -> [b]
map CoreTickish -> CoreTickish
forall (pass :: TickishPass). GenTickish pass -> GenTickish pass
mkNoCount ([CoreTickish] -> [CoreTickish]) -> [CoreTickish] -> [CoreTickish]
forall a b. (a -> b) -> a -> b
$
                            (CoreTickish -> Bool) -> [CoreTickish] -> [CoreTickish]
forall a. (a -> Bool) -> [a] -> [a]
filter (Bool -> Bool
not (Bool -> Bool) -> (CoreTickish -> Bool) -> CoreTickish -> Bool
forall b c a. (b -> c) -> (a -> b) -> a -> c
. (CoreTickish -> TickishScoping -> Bool
forall (pass :: TickishPass).
GenTickish pass -> TickishScoping -> Bool
`tickishScopesLike` TickishScoping
NoScope)) [CoreTickish]
ticks

  no_floating_past_tick :: SimplM (SimplFloats, CoreExpr)
no_floating_past_tick =
    do { let (SimplCont
inc,SimplCont
outc) = SimplCont -> (SimplCont, SimplCont)
splitCont SimplCont
cont
       ; (SimplFloats
floats, CoreExpr
expr1) <- SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF SimplEnv
env CoreExpr
expr SimplCont
inc
       ; let expr2 :: CoreExpr
expr2    = SimplFloats -> CoreExpr -> CoreExpr
wrapFloats SimplFloats
floats CoreExpr
expr1
             tickish' :: CoreTickish
tickish' = SimplEnv -> CoreTickish -> CoreTickish
forall {pass :: TickishPass}.
(XTickishId pass ~ CoreBndr) =>
SimplEnv -> GenTickish pass -> GenTickish pass
simplTickish SimplEnv
env CoreTickish
tickish
       ; SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
rebuild SimplEnv
env (CoreTickish -> CoreExpr -> CoreExpr
mkTick CoreTickish
tickish' CoreExpr
expr2) SimplCont
outc
       }

-- Alternative version that wraps outgoing floats with the tick.  This
-- results in ticks being duplicated, as we don't make any attempt to
-- eliminate the tick if we re-inline the binding (because the tick
-- semantics allows unrestricted inlining of HNFs), so I'm not doing
-- this any more.  FloatOut will catch any real opportunities for
-- floating.
--
--  wrap_floats =
--    do { let (inc,outc) = splitCont cont
--       ; (env', expr') <- simplExprF (zapFloats env) expr inc
--       ; let tickish' = simplTickish env tickish
--       ; let wrap_float (b,rhs) = (zapIdDmdSig (setIdArity b 0),
--                                   mkTick (mkNoCount tickish') rhs)
--              -- when wrapping a float with mkTick, we better zap the Id's
--              -- strictness info and arity, because it might be wrong now.
--       ; let env'' = addFloats env (mapFloats env' wrap_float)
--       ; rebuild env'' expr' (TickIt tickish' outc)
--       }


  simplTickish :: SimplEnv -> GenTickish pass -> GenTickish pass
simplTickish SimplEnv
env GenTickish pass
tickish
    | Breakpoint XBreakpoint pass
ext Int
n [XTickishId pass]
ids <- GenTickish pass
tickish
          = XBreakpoint pass -> Int -> [XTickishId pass] -> GenTickish pass
forall (pass :: TickishPass).
XBreakpoint pass -> Int -> [XTickishId pass] -> GenTickish pass
Breakpoint XBreakpoint pass
ext Int
n ((CoreBndr -> CoreBndr) -> [CoreBndr] -> [CoreBndr]
forall a b. (a -> b) -> [a] -> [b]
map (SimplSR -> CoreBndr
getDoneId (SimplSR -> CoreBndr)
-> (CoreBndr -> SimplSR) -> CoreBndr -> CoreBndr
forall b c a. (b -> c) -> (a -> b) -> a -> c
. SimplEnv -> CoreBndr -> SimplSR
substId SimplEnv
env) [CoreBndr]
[XTickishId pass]
ids)
    | Bool
otherwise = GenTickish pass
tickish

  -- Push type application and coercion inside a tick
  splitCont :: SimplCont -> (SimplCont, SimplCont)
  splitCont :: SimplCont -> (SimplCont, SimplCont)
splitCont cont :: SimplCont
cont@(ApplyToTy { sc_cont :: SimplCont -> SimplCont
sc_cont = SimplCont
tail }) = (SimplCont
cont { sc_cont = inc }, SimplCont
outc)
    where (SimplCont
inc,SimplCont
outc) = SimplCont -> (SimplCont, SimplCont)
splitCont SimplCont
tail
  splitCont (CastIt Coercion
co SimplCont
c) = (Coercion -> SimplCont -> SimplCont
CastIt Coercion
co SimplCont
inc, SimplCont
outc)
    where (SimplCont
inc,SimplCont
outc) = SimplCont -> (SimplCont, SimplCont)
splitCont SimplCont
c
  splitCont SimplCont
other = (Kind -> SimplCont
mkBoringStop (SimplCont -> Kind
contHoleType SimplCont
other), SimplCont
other)

  getDoneId :: SimplSR -> CoreBndr
getDoneId (DoneId CoreBndr
id)  = CoreBndr
id
  getDoneId (DoneEx CoreExpr
e Maybe Int
_) = (() :: Constraint) => CoreExpr -> CoreBndr
CoreExpr -> CoreBndr
getIdFromTrivialExpr CoreExpr
e -- Note [substTickish] in GHC.Core.Subst
  getDoneId SimplSR
other = String -> SDoc -> CoreBndr
forall a. HasCallStack => String -> SDoc -> a
pprPanic String
"getDoneId" (SimplSR -> SDoc
forall a. Outputable a => a -> SDoc
ppr SimplSR
other)

-- Note [case-of-scc-of-case]
-- ~~~~~~~~~~~~~~~~~~~~~~~~~~
-- It's pretty important to be able to transform case-of-case when
-- there's an SCC in the way.  For example, the following comes up
-- in nofib/real/compress/Encode.hs:
--
--        case scctick<code_string.r1>
--             case $wcode_string_r13s wild_XC w1_s137 w2_s138 l_aje
--             of _ { (# ww1_s13f, ww2_s13g, ww3_s13h #) ->
--             (ww1_s13f, ww2_s13g, ww3_s13h)
--             }
--        of _ { (ww_s12Y, ww1_s12Z, ww2_s130) ->
--        tick<code_string.f1>
--        (ww_s12Y,
--         ww1_s12Z,
--         PTTrees.PT
--           @ GHC.Types.Char @ GHC.Types.Int wild2_Xj ww2_s130 r_ajf)
--        }
--
-- We really want this case-of-case to fire, because then the 3-tuple
-- will go away (indeed, the CPR optimisation is relying on this
-- happening).  But the scctick is in the way - we need to push it
-- inside to expose the case-of-case.  So we perform this
-- transformation on the inner case:
--
--   scctick c (case e of { p1 -> e1; ...; pn -> en })
--    ==>
--   case (scctick c e) of { p1 -> scc c e1; ...; pn -> scc c en }
--
-- So we've moved a constant amount of work out of the scc to expose
-- the case.  We only do this when the continuation is interesting: in
-- for now, it has to be another Case (maybe generalise this later).

{-
************************************************************************
*                                                                      *
\subsection{The main rebuilder}
*                                                                      *
************************************************************************
-}

rebuild :: SimplEnv -> OutExpr -> SimplCont -> SimplM (SimplFloats, OutExpr)
-- At this point the substitution in the SimplEnv should be irrelevant;
-- only the in-scope set matters
rebuild :: SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
rebuild SimplEnv
env CoreExpr
expr SimplCont
cont
  = case SimplCont
cont of
      Stop {}          -> (SimplFloats, CoreExpr) -> SimplM (SimplFloats, CoreExpr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplEnv -> SimplFloats
emptyFloats SimplEnv
env, CoreExpr
expr)
      TickIt CoreTickish
t SimplCont
cont    -> SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
rebuild SimplEnv
env (CoreTickish -> CoreExpr -> CoreExpr
mkTick CoreTickish
t CoreExpr
expr) SimplCont
cont
      CastIt Coercion
co SimplCont
cont   -> SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
rebuild SimplEnv
env ((() :: Constraint) => CoreExpr -> Coercion -> CoreExpr
CoreExpr -> Coercion -> CoreExpr
mkCast CoreExpr
expr Coercion
co) SimplCont
cont
                       -- NB: mkCast implements the (Coercion co |> g) optimisation

      Select { sc_bndr :: SimplCont -> CoreBndr
sc_bndr = CoreBndr
bndr, sc_alts :: SimplCont -> [Alt CoreBndr]
sc_alts = [Alt CoreBndr]
alts, sc_env :: SimplCont -> SimplEnv
sc_env = SimplEnv
se, sc_cont :: SimplCont -> SimplCont
sc_cont = SimplCont
cont }
        -> SimplEnv
-> CoreExpr
-> CoreBndr
-> [Alt CoreBndr]
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
rebuildCase (SimplEnv
se SimplEnv -> SimplEnv -> SimplEnv
`setInScopeFromE` SimplEnv
env) CoreExpr
expr CoreBndr
bndr [Alt CoreBndr]
alts SimplCont
cont

      StrictArg { sc_fun :: SimplCont -> ArgInfo
sc_fun = ArgInfo
fun, sc_cont :: SimplCont -> SimplCont
sc_cont = SimplCont
cont, sc_fun_ty :: SimplCont -> Kind
sc_fun_ty = Kind
fun_ty }
        -> SimplEnv -> ArgInfo -> SimplCont -> SimplM (SimplFloats, CoreExpr)
rebuildCall SimplEnv
env (ArgInfo -> CoreExpr -> Kind -> ArgInfo
addValArgTo ArgInfo
fun CoreExpr
expr Kind
fun_ty ) SimplCont
cont

      StrictBind { sc_bndr :: SimplCont -> CoreBndr
sc_bndr = CoreBndr
b, sc_body :: SimplCont -> CoreExpr
sc_body = CoreExpr
body, sc_env :: SimplCont -> SimplEnv
sc_env = SimplEnv
se
                 , sc_cont :: SimplCont -> SimplCont
sc_cont = SimplCont
cont, sc_from :: SimplCont -> FromWhat
sc_from = FromWhat
from_what }
        -> SimplEnv
-> FromWhat
-> CoreBndr
-> CoreExpr
-> CoreExpr
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
completeBindX (SimplEnv
se SimplEnv -> SimplEnv -> SimplEnv
`setInScopeFromE` SimplEnv
env) FromWhat
from_what CoreBndr
b CoreExpr
expr CoreExpr
body SimplCont
cont

      ApplyToTy  { sc_arg_ty :: SimplCont -> Kind
sc_arg_ty = Kind
ty, sc_cont :: SimplCont -> SimplCont
sc_cont = SimplCont
cont}
        -> SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
rebuild SimplEnv
env (CoreExpr -> CoreExpr -> CoreExpr
forall b. Expr b -> Expr b -> Expr b
App CoreExpr
expr (Kind -> CoreExpr
forall b. Kind -> Expr b
Type Kind
ty)) SimplCont
cont

      ApplyToVal { sc_arg :: SimplCont -> CoreExpr
sc_arg = CoreExpr
arg, sc_env :: SimplCont -> SimplEnv
sc_env = SimplEnv
se, sc_dup :: SimplCont -> DupFlag
sc_dup = DupFlag
dup_flag
                 , sc_cont :: SimplCont -> SimplCont
sc_cont = SimplCont
cont, sc_hole_ty :: SimplCont -> Kind
sc_hole_ty = Kind
fun_ty }
        -- See Note [Avoid redundant simplification]
        -> do { (DupFlag
_, SimplEnv
_, CoreExpr
arg') <- SimplEnv
-> DupFlag
-> Kind
-> SimplEnv
-> CoreExpr
-> SimplM (DupFlag, SimplEnv, CoreExpr)
simplArg SimplEnv
env DupFlag
dup_flag Kind
fun_ty SimplEnv
se CoreExpr
arg
              ; SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
rebuild SimplEnv
env (CoreExpr -> CoreExpr -> CoreExpr
forall b. Expr b -> Expr b -> Expr b
App CoreExpr
expr CoreExpr
arg') SimplCont
cont }

completeBindX :: SimplEnv
              -> FromWhat
              -> InId -> OutExpr   -- Bind this Id to this (simplified) expression
                                   -- (the let-can-float invariant may not be satisfied)
              -> InExpr            -- In this body
              -> SimplCont         -- Consumed by this continuation
              -> SimplM (SimplFloats, OutExpr)
completeBindX :: SimplEnv
-> FromWhat
-> CoreBndr
-> CoreExpr
-> CoreExpr
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
completeBindX SimplEnv
env FromWhat
from_what CoreBndr
bndr CoreExpr
rhs CoreExpr
body SimplCont
cont
  | FromBeta Kind
arg_ty <- FromWhat
from_what
  , Kind -> CoreExpr -> Bool
needsCaseBinding Kind
arg_ty CoreExpr
rhs -- Enforcing the let-can-float-invariant
  = do { (SimplEnv
env1, CoreBndr
bndr1)   <- SimplEnv -> CoreBndr -> SimplM (SimplEnv, CoreBndr)
simplNonRecBndr SimplEnv
env CoreBndr
bndr  -- Lambda binders don't have rules
       ; (SimplFloats
floats, CoreExpr
expr') <- SimplEnv
-> FromWhat
-> CoreExpr
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
simplNonRecBody SimplEnv
env1 FromWhat
from_what CoreExpr
body SimplCont
cont
       -- Do not float floats past the Case binder below
       ; let expr'' :: CoreExpr
expr'' = SimplFloats -> CoreExpr -> CoreExpr
wrapFloats SimplFloats
floats CoreExpr
expr'
             case_expr :: CoreExpr
case_expr = CoreExpr -> CoreBndr -> Kind -> [Alt CoreBndr] -> CoreExpr
forall b. Expr b -> b -> Kind -> [Alt b] -> Expr b
Case CoreExpr
rhs CoreBndr
bndr1 (SimplCont -> Kind
contResultType SimplCont
cont) [AltCon -> [CoreBndr] -> CoreExpr -> Alt CoreBndr
forall b. AltCon -> [b] -> Expr b -> Alt b
Alt AltCon
DEFAULT [] CoreExpr
expr'']
       ; (SimplFloats, CoreExpr) -> SimplM (SimplFloats, CoreExpr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplEnv -> SimplFloats
emptyFloats SimplEnv
env, CoreExpr
case_expr) }

  | Bool
otherwise -- Make a let-binding
  = do  { (SimplEnv
env1, CoreBndr
bndr1) <- SimplEnv -> CoreBndr -> SimplM (SimplEnv, CoreBndr)
simplNonRecBndr SimplEnv
env CoreBndr
bndr
        ; (SimplEnv
env2, CoreBndr
bndr2) <- SimplEnv
-> CoreBndr
-> CoreBndr
-> BindContext
-> SimplM (SimplEnv, CoreBndr)
addBndrRules SimplEnv
env1 CoreBndr
bndr CoreBndr
bndr1 (TopLevelFlag -> RecFlag -> BindContext
BC_Let TopLevelFlag
NotTopLevel RecFlag
NonRecursive)

        ; let is_strict :: Bool
is_strict = CoreBndr -> Bool
isStrictId CoreBndr
bndr2
              -- isStrictId: use simplified binder because the InId bndr might not have
              -- a fixed runtime representation, which isStrictId doesn't expect
              -- c.f. Note [Dark corner with representation polymorphism]

        ; (SimplFloats
rhs_floats, CoreExpr
rhs1) <- SimplEnv
-> TopLevelFlag
-> RecFlag
-> Bool
-> CoreBndr
-> SimplFloats
-> CoreExpr
-> SimplM (SimplFloats, CoreExpr)
prepareBinding SimplEnv
env TopLevelFlag
NotTopLevel RecFlag
NonRecursive Bool
is_strict
                                               CoreBndr
bndr2 (SimplEnv -> SimplFloats
emptyFloats SimplEnv
env) CoreExpr
rhs
              -- NB: it makes a surprisingly big difference (5% in compiler allocation
              -- in T9630) to pass 'env' rather than 'env1'.  It's fine to pass 'env',
              -- because this is simplNonRecX, so bndr is not in scope in the RHS.

        ; (SimplFloats
bind_float, SimplEnv
env2) <- SimplEnv
-> BindContext
-> CoreBndr
-> CoreBndr
-> CoreExpr
-> SimplM (SimplFloats, SimplEnv)
completeBind (SimplEnv
env2 SimplEnv -> SimplFloats -> SimplEnv
`setInScopeFromF` SimplFloats
rhs_floats)
                                             (TopLevelFlag -> RecFlag -> BindContext
BC_Let TopLevelFlag
NotTopLevel RecFlag
NonRecursive)
                                             CoreBndr
bndr CoreBndr
bndr2 CoreExpr
rhs1
              -- Must pass env1 to completeBind in case simplBinder had to clone,
              -- and extended the substitution with [bndr :-> new_bndr]

        -- Simplify the body
        ; (SimplFloats
body_floats, CoreExpr
body') <- SimplEnv
-> FromWhat
-> CoreExpr
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
simplNonRecBody SimplEnv
env2 FromWhat
from_what CoreExpr
body SimplCont
cont

        ; let all_floats :: SimplFloats
all_floats = SimplFloats
rhs_floats SimplFloats -> SimplFloats -> SimplFloats
`addFloats` SimplFloats
bind_float SimplFloats -> SimplFloats -> SimplFloats
`addFloats` SimplFloats
body_floats
        ; (SimplFloats, CoreExpr) -> SimplM (SimplFloats, CoreExpr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return ( SimplFloats
all_floats, CoreExpr
body' ) }

{-
************************************************************************
*                                                                      *
\subsection{Lambdas}
*                                                                      *
************************************************************************
-}

{- Note [Optimising reflexivity]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
It's important (for compiler performance) to get rid of reflexivity as soon
as it appears.  See #11735, #14737, and #15019.

In particular, we want to behave well on

 *  e |> co1 |> co2
    where the two happen to cancel out entirely. That is quite common;
    e.g. a newtype wrapping and unwrapping cancel.


 * (f |> co) @t1 @t2 ... @tn x1 .. xm
   Here we will use pushCoTyArg and pushCoValArg successively, which
   build up SelCo stacks.  Silly to do that if co is reflexive.

However, we don't want to call isReflexiveCo too much, because it uses
type equality which is expensive on big types (#14737 comment:7).

A good compromise (determined experimentally) seems to be to call
isReflexiveCo
 * when composing casts, and
 * at the end

In investigating this I saw missed opportunities for on-the-fly
coercion shrinkage. See #15090.
-}


simplCast :: SimplEnv -> InExpr -> Coercion -> SimplCont
          -> SimplM (SimplFloats, OutExpr)
simplCast :: SimplEnv
-> CoreExpr
-> Coercion
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
simplCast SimplEnv
env CoreExpr
body Coercion
co0 SimplCont
cont0
  = do  { Coercion
co1   <- {-#SCC "simplCast-simplCoercion" #-} SimplEnv -> Coercion -> SimplM Coercion
simplCoercion SimplEnv
env Coercion
co0
        ; SimplCont
cont1 <- {-#SCC "simplCast-addCoerce" #-}
                   if Coercion -> Bool
isReflCo Coercion
co1
                   then SimplCont -> SimplM SimplCont
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return SimplCont
cont0  -- See Note [Optimising reflexivity]
                   else Coercion -> SimplCont -> SimplM SimplCont
addCoerce Coercion
co1 SimplCont
cont0
        ; {-#SCC "simplCast-simplExprF" #-} SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF SimplEnv
env CoreExpr
body SimplCont
cont1 }
  where
        -- If the first parameter is MRefl, then simplifying revealed a
        -- reflexive coercion. Omit.
        addCoerceM :: MOutCoercion -> SimplCont -> SimplM SimplCont
        addCoerceM :: MOutCoercion -> SimplCont -> SimplM SimplCont
addCoerceM MOutCoercion
MRefl   SimplCont
cont = SimplCont -> SimplM SimplCont
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return SimplCont
cont
        addCoerceM (MCo Coercion
co) SimplCont
cont = Coercion -> SimplCont -> SimplM SimplCont
addCoerce Coercion
co SimplCont
cont

        addCoerce :: OutCoercion -> SimplCont -> SimplM SimplCont
        addCoerce :: Coercion -> SimplCont -> SimplM SimplCont
addCoerce Coercion
co1 (CastIt Coercion
co2 SimplCont
cont)  -- See Note [Optimising reflexivity]
          | Coercion -> Bool
isReflexiveCo Coercion
co' = SimplCont -> SimplM SimplCont
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return SimplCont
cont
          | Bool
otherwise         = Coercion -> SimplCont -> SimplM SimplCont
addCoerce Coercion
co' SimplCont
cont
          where
            co' :: Coercion
co' = Coercion -> Coercion -> Coercion
mkTransCo Coercion
co1 Coercion
co2

        addCoerce Coercion
co (ApplyToTy { sc_arg_ty :: SimplCont -> Kind
sc_arg_ty = Kind
arg_ty, sc_cont :: SimplCont -> SimplCont
sc_cont = SimplCont
tail })
          | Just (Kind
arg_ty', MOutCoercion
m_co') <- Coercion -> Kind -> Maybe (Kind, MOutCoercion)
pushCoTyArg Coercion
co Kind
arg_ty
          = {-#SCC "addCoerce-pushCoTyArg" #-}
            do { SimplCont
tail' <- MOutCoercion -> SimplCont -> SimplM SimplCont
addCoerceM MOutCoercion
m_co' SimplCont
tail
               ; SimplCont -> SimplM SimplCont
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (ApplyToTy { sc_arg_ty :: Kind
sc_arg_ty  = Kind
arg_ty'
                                   , sc_cont :: SimplCont
sc_cont    = SimplCont
tail'
                                   , sc_hole_ty :: Kind
sc_hole_ty = Coercion -> Kind
coercionLKind Coercion
co }) }
                                        -- NB!  As the cast goes past, the
                                        -- type of the hole changes (#16312)

        -- (f |> co) e   ===>   (f (e |> co1)) |> co2
        -- where   co :: (s1->s2) ~ (t1->t2)
        --         co1 :: t1 ~ s1
        --         co2 :: s2 ~ t2
        addCoerce Coercion
co cont :: SimplCont
cont@(ApplyToVal { sc_arg :: SimplCont -> CoreExpr
sc_arg = CoreExpr
arg, sc_env :: SimplCont -> SimplEnv
sc_env = SimplEnv
arg_se
                                      , sc_dup :: SimplCont -> DupFlag
sc_dup = DupFlag
dup, sc_cont :: SimplCont -> SimplCont
sc_cont = SimplCont
tail
                                      , sc_hole_ty :: SimplCont -> Kind
sc_hole_ty = Kind
fun_ty })
          | Just (MOutCoercion
m_co1, MOutCoercion
m_co2) <- Coercion -> Maybe (MOutCoercion, MOutCoercion)
pushCoValArg Coercion
co
          , MOutCoercion -> Bool
fixed_rep MOutCoercion
m_co1
          = {-#SCC "addCoerce-pushCoValArg" #-}
            do { SimplCont
tail' <- MOutCoercion -> SimplCont -> SimplM SimplCont
addCoerceM MOutCoercion
m_co2 SimplCont
tail
               ; case MOutCoercion
m_co1 of {
                   MOutCoercion
MRefl -> SimplCont -> SimplM SimplCont
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplCont
cont { sc_cont = tail'
                                         , sc_hole_ty = coercionLKind co }) ;
                      -- Avoid simplifying if possible;
                      -- See Note [Avoiding exponential behaviour]

                   MCo Coercion
co1 ->
            do { (DupFlag
dup', SimplEnv
arg_se', CoreExpr
arg') <- SimplEnv
-> DupFlag
-> Kind
-> SimplEnv
-> CoreExpr
-> SimplM (DupFlag, SimplEnv, CoreExpr)
simplArg SimplEnv
env DupFlag
dup Kind
fun_ty SimplEnv
arg_se CoreExpr
arg
                    -- When we build the ApplyTo we can't mix the OutCoercion
                    -- 'co' with the InExpr 'arg', so we simplify
                    -- to make it all consistent.  It's a bit messy.
                    -- But it isn't a common case.
                    -- Example of use: #995
               ; SimplCont -> SimplM SimplCont
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (ApplyToVal { sc_arg :: CoreExpr
sc_arg  = (() :: Constraint) => CoreExpr -> Coercion -> CoreExpr
CoreExpr -> Coercion -> CoreExpr
mkCast CoreExpr
arg' Coercion
co1
                                    , sc_env :: SimplEnv
sc_env  = SimplEnv
arg_se'
                                    , sc_dup :: DupFlag
sc_dup  = DupFlag
dup'
                                    , sc_cont :: SimplCont
sc_cont = SimplCont
tail'
                                    , sc_hole_ty :: Kind
sc_hole_ty = Coercion -> Kind
coercionLKind Coercion
co }) } } }

        addCoerce Coercion
co SimplCont
cont
          | Coercion -> Bool
isReflexiveCo Coercion
co = SimplCont -> SimplM SimplCont
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return SimplCont
cont  -- Having this at the end makes a huge
                                            -- difference in T12227, for some reason
                                            -- See Note [Optimising reflexivity]
          | Bool
otherwise        = SimplCont -> SimplM SimplCont
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (Coercion -> SimplCont -> SimplCont
CastIt Coercion
co SimplCont
cont)

        fixed_rep :: MCoercionR -> Bool
        fixed_rep :: MOutCoercion -> Bool
fixed_rep MOutCoercion
MRefl    = Bool
True
        fixed_rep (MCo Coercion
co) = (() :: Constraint) => Kind -> Bool
Kind -> Bool
typeHasFixedRuntimeRep (Kind -> Bool) -> Kind -> Bool
forall a b. (a -> b) -> a -> b
$ Coercion -> Kind
coercionRKind Coercion
co
          -- Without this check, we can get an argument which does not
          -- have a fixed runtime representation.
          -- See Note [Representation polymorphism invariants] in GHC.Core
          -- test: typecheck/should_run/EtaExpandLevPoly

simplArg :: SimplEnv -> DupFlag
         -> OutType                 -- Type of the function applied to this arg
         -> StaticEnv -> CoreExpr   -- Expression with its static envt
         -> SimplM (DupFlag, StaticEnv, OutExpr)
simplArg :: SimplEnv
-> DupFlag
-> Kind
-> SimplEnv
-> CoreExpr
-> SimplM (DupFlag, SimplEnv, CoreExpr)
simplArg SimplEnv
env DupFlag
dup_flag Kind
fun_ty SimplEnv
arg_env CoreExpr
arg
  | DupFlag -> Bool
isSimplified DupFlag
dup_flag
  = (DupFlag, SimplEnv, CoreExpr)
-> SimplM (DupFlag, SimplEnv, CoreExpr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (DupFlag
dup_flag, SimplEnv
arg_env, CoreExpr
arg)
  | Bool
otherwise
  = do { let arg_env' :: SimplEnv
arg_env' = SimplEnv
arg_env SimplEnv -> SimplEnv -> SimplEnv
`setInScopeFromE` SimplEnv
env
       ; CoreExpr
arg' <- SimplEnv -> CoreExpr -> SimplCont -> SimplM CoreExpr
simplExprC SimplEnv
arg_env' CoreExpr
arg (Kind -> SimplCont
mkBoringStop (Kind -> Kind
funArgTy Kind
fun_ty))
       ; (DupFlag, SimplEnv, CoreExpr)
-> SimplM (DupFlag, SimplEnv, CoreExpr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (DupFlag
Simplified, SimplEnv -> SimplEnv
zapSubstEnv SimplEnv
arg_env', CoreExpr
arg') }
         -- Return a StaticEnv that includes the in-scope set from 'env',
         -- because arg' may well mention those variables (#20639)

{-
************************************************************************
*                                                                      *
\subsection{Lambdas}
*                                                                      *
************************************************************************
-}

simplNonRecBody :: SimplEnv -> FromWhat
                -> InExpr -> SimplCont
                -> SimplM (SimplFloats, OutExpr)
simplNonRecBody :: SimplEnv
-> FromWhat
-> CoreExpr
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
simplNonRecBody SimplEnv
env FromWhat
from_what CoreExpr
body SimplCont
cont
  = case FromWhat
from_what of
      FromWhat
FromLet     -> SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF SimplEnv
env CoreExpr
body SimplCont
cont
      FromBeta {} -> SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplLam   SimplEnv
env CoreExpr
body SimplCont
cont

simplLam :: SimplEnv -> InExpr -> SimplCont
         -> SimplM (SimplFloats, OutExpr)

simplLam :: SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplLam SimplEnv
env (Lam CoreBndr
bndr CoreExpr
body) SimplCont
cont = SimplEnv
-> CoreBndr
-> CoreExpr
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
simpl_lam SimplEnv
env CoreBndr
bndr CoreExpr
body SimplCont
cont
simplLam SimplEnv
env CoreExpr
expr            SimplCont
cont = SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF SimplEnv
env CoreExpr
expr SimplCont
cont

simpl_lam :: SimplEnv -> InBndr -> InExpr -> SimplCont
          -> SimplM (SimplFloats, OutExpr)

-- Type beta-reduction
simpl_lam :: SimplEnv
-> CoreBndr
-> CoreExpr
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
simpl_lam SimplEnv
env CoreBndr
bndr CoreExpr
body (ApplyToTy { sc_arg_ty :: SimplCont -> Kind
sc_arg_ty = Kind
arg_ty, sc_cont :: SimplCont -> SimplCont
sc_cont = SimplCont
cont })
  = do { Tick -> SimplM ()
tick (CoreBndr -> Tick
BetaReduction CoreBndr
bndr)
       ; SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplLam (SimplEnv -> CoreBndr -> Kind -> SimplEnv
extendTvSubst SimplEnv
env CoreBndr
bndr Kind
arg_ty) CoreExpr
body SimplCont
cont }

-- Value beta-reduction
simpl_lam SimplEnv
env CoreBndr
bndr CoreExpr
body (ApplyToVal { sc_arg :: SimplCont -> CoreExpr
sc_arg = CoreExpr
arg, sc_env :: SimplCont -> SimplEnv
sc_env = SimplEnv
arg_se
                                    , sc_cont :: SimplCont -> SimplCont
sc_cont = SimplCont
cont, sc_dup :: SimplCont -> DupFlag
sc_dup = DupFlag
dup
                                    , sc_hole_ty :: SimplCont -> Kind
sc_hole_ty = Kind
fun_ty})
  = do { Tick -> SimplM ()
tick (CoreBndr -> Tick
BetaReduction CoreBndr
bndr)
       ; let arg_ty :: Kind
arg_ty = Kind -> Kind
funArgTy Kind
fun_ty
       ; if | DupFlag -> Bool
isSimplified DupFlag
dup  -- Don't re-simplify if we've simplified it once
                                -- Including don't preInlineUnconditionally
                                -- See Note [Avoiding exponential behaviour]
            -> SimplEnv
-> FromWhat
-> CoreBndr
-> CoreExpr
-> CoreExpr
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
completeBindX SimplEnv
env (Kind -> FromWhat
FromBeta Kind
arg_ty) CoreBndr
bndr CoreExpr
arg CoreExpr
body SimplCont
cont

            | Just SimplEnv
env' <- SimplEnv
-> TopLevelFlag
-> CoreBndr
-> CoreExpr
-> SimplEnv
-> Maybe SimplEnv
preInlineUnconditionally SimplEnv
env TopLevelFlag
NotTopLevel CoreBndr
bndr CoreExpr
arg SimplEnv
arg_se
            , Bool -> Bool
not (Kind -> CoreExpr -> Bool
needsCaseBinding Kind
arg_ty CoreExpr
arg)
              -- Ok to test arg::InExpr in needsCaseBinding because
              -- exprOkForSpeculation is stable under simplification
            -> do { Tick -> SimplM ()
tick (CoreBndr -> Tick
PreInlineUnconditionally CoreBndr
bndr)
                  ; SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplLam SimplEnv
env' CoreExpr
body SimplCont
cont }

            | Bool
otherwise
            -> SimplEnv
-> FromWhat
-> CoreBndr
-> (CoreExpr, SimplEnv)
-> CoreExpr
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
simplNonRecE SimplEnv
env (Kind -> FromWhat
FromBeta Kind
arg_ty) CoreBndr
bndr (CoreExpr
arg, SimplEnv
arg_se) CoreExpr
body SimplCont
cont }

-- Discard a non-counting tick on a lambda.  This may change the
-- cost attribution slightly (moving the allocation of the
-- lambda elsewhere), but we don't care: optimisation changes
-- cost attribution all the time.
simpl_lam SimplEnv
env CoreBndr
bndr CoreExpr
body (TickIt CoreTickish
tickish SimplCont
cont)
  | Bool -> Bool
not (CoreTickish -> Bool
forall (pass :: TickishPass). GenTickish pass -> Bool
tickishCounts CoreTickish
tickish)
  = SimplEnv
-> CoreBndr
-> CoreExpr
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
simpl_lam SimplEnv
env CoreBndr
bndr CoreExpr
body SimplCont
cont

-- Not enough args, so there are real lambdas left to put in the result
simpl_lam SimplEnv
env CoreBndr
bndr CoreExpr
body SimplCont
cont
  = do  { let ([CoreBndr]
inner_bndrs, CoreExpr
inner_body) = CoreExpr -> ([CoreBndr], CoreExpr)
forall b. Expr b -> ([b], Expr b)
collectBinders CoreExpr
body
        ; (SimplEnv
env', [CoreBndr]
bndrs') <- SimplEnv -> [CoreBndr] -> SimplM (SimplEnv, [CoreBndr])
simplLamBndrs SimplEnv
env (CoreBndr
bndrCoreBndr -> [CoreBndr] -> [CoreBndr]
forall a. a -> [a] -> [a]
:[CoreBndr]
inner_bndrs)
        ; CoreExpr
body'   <- SimplEnv -> CoreExpr -> SimplM CoreExpr
simplExpr SimplEnv
env' CoreExpr
inner_body
        ; CoreExpr
new_lam <- SimplEnv -> [CoreBndr] -> CoreExpr -> SimplCont -> SimplM CoreExpr
rebuildLam SimplEnv
env' [CoreBndr]
bndrs' CoreExpr
body' SimplCont
cont
        ; SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
rebuild SimplEnv
env' CoreExpr
new_lam SimplCont
cont }

-------------
simplLamBndr :: SimplEnv -> InBndr -> SimplM (SimplEnv, OutBndr)
-- Historically this had a special case for when a lambda-binder
-- could have a stable unfolding;
-- see Historical Note [Case binders and join points]
-- But now it is much simpler! We now only remove unfoldings.
-- See Note [Never put `OtherCon` unfoldings on lambda binders]
simplLamBndr :: SimplEnv -> CoreBndr -> SimplM (SimplEnv, CoreBndr)
simplLamBndr SimplEnv
env CoreBndr
bndr = SimplEnv -> CoreBndr -> SimplM (SimplEnv, CoreBndr)
simplBinder SimplEnv
env (CoreBndr -> CoreBndr
zapIdUnfolding CoreBndr
bndr)

simplLamBndrs :: SimplEnv -> [InBndr] -> SimplM (SimplEnv, [OutBndr])
simplLamBndrs :: SimplEnv -> [CoreBndr] -> SimplM (SimplEnv, [CoreBndr])
simplLamBndrs SimplEnv
env [CoreBndr]
bndrs = (SimplEnv -> CoreBndr -> SimplM (SimplEnv, CoreBndr))
-> SimplEnv -> [CoreBndr] -> SimplM (SimplEnv, [CoreBndr])
forall (m :: * -> *) (t :: * -> *) acc x y.
(Monad m, Traversable t) =>
(acc -> x -> m (acc, y)) -> acc -> t x -> m (acc, t y)
mapAccumLM SimplEnv -> CoreBndr -> SimplM (SimplEnv, CoreBndr)
simplLamBndr SimplEnv
env [CoreBndr]
bndrs

------------------
simplNonRecE :: SimplEnv
             -> FromWhat
             -> InId                    -- The binder, always an Id
                                        -- Never a join point
             -> (InExpr, SimplEnv)      -- Rhs of binding (or arg of lambda)
             -> InExpr                  -- Body of the let/lambda
             -> SimplCont
             -> SimplM (SimplFloats, OutExpr)

-- simplNonRecE is used for
--  * from=FromLet:  a non-top-level non-recursive non-join-point let-expression
--  * from=FromBeta: a binding arising from a beta reduction
--
-- simplNonRecE env b (rhs, rhs_se) body k
--   = let env in
--     cont< let b = rhs_se(rhs) in body >
--
-- It deals with strict bindings, via the StrictBind continuation,
-- which may abort the whole process.
--
-- from_what=FromLet => the RHS satisfies the let-can-float invariant
-- Otherwise it may or may not satisfy it.

simplNonRecE :: SimplEnv
-> FromWhat
-> CoreBndr
-> (CoreExpr, SimplEnv)
-> CoreExpr
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
simplNonRecE SimplEnv
env FromWhat
from_what CoreBndr
bndr (CoreExpr
rhs, SimplEnv
rhs_se) CoreExpr
body SimplCont
cont
  | Bool -> Bool -> Bool
forall a. HasCallStack => Bool -> a -> a
assert (CoreBndr -> Bool
isId CoreBndr
bndr Bool -> Bool -> Bool
&& Bool -> Bool
not (CoreBndr -> Bool
isJoinId CoreBndr
bndr) ) (Bool -> Bool) -> Bool -> Bool
forall a b. (a -> b) -> a -> b
$
    Bool
is_strict_bind
  = -- Evaluate RHS strictly
    SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF (SimplEnv
rhs_se SimplEnv -> SimplEnv -> SimplEnv
`setInScopeFromE` SimplEnv
env) CoreExpr
rhs
               (StrictBind { sc_bndr :: CoreBndr
sc_bndr = CoreBndr
bndr, sc_body :: CoreExpr
sc_body = CoreExpr
body, sc_from :: FromWhat
sc_from = FromWhat
from_what
                           , sc_env :: SimplEnv
sc_env = SimplEnv
env, sc_cont :: SimplCont
sc_cont = SimplCont
cont, sc_dup :: DupFlag
sc_dup = DupFlag
NoDup })

  | Bool
otherwise  -- Evaluate RHS lazily
  = do { (SimplEnv
env1, CoreBndr
bndr1)    <- SimplEnv -> CoreBndr -> SimplM (SimplEnv, CoreBndr)
simplNonRecBndr SimplEnv
env CoreBndr
bndr
       ; (SimplEnv
env2, CoreBndr
bndr2)    <- SimplEnv
-> CoreBndr
-> CoreBndr
-> BindContext
-> SimplM (SimplEnv, CoreBndr)
addBndrRules SimplEnv
env1 CoreBndr
bndr CoreBndr
bndr1 (TopLevelFlag -> RecFlag -> BindContext
BC_Let TopLevelFlag
NotTopLevel RecFlag
NonRecursive)
       ; (SimplFloats
floats1, SimplEnv
env3)  <- SimplEnv
-> TopLevelFlag
-> RecFlag
-> CoreBndr
-> CoreBndr
-> CoreExpr
-> SimplEnv
-> SimplM (SimplFloats, SimplEnv)
simplLazyBind SimplEnv
env2 TopLevelFlag
NotTopLevel RecFlag
NonRecursive
                                           CoreBndr
bndr CoreBndr
bndr2 CoreExpr
rhs SimplEnv
rhs_se
       ; (SimplFloats
floats2, CoreExpr
expr') <- SimplEnv
-> FromWhat
-> CoreExpr
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
simplNonRecBody SimplEnv
env3 FromWhat
from_what CoreExpr
body SimplCont
cont
       ; (SimplFloats, CoreExpr) -> SimplM (SimplFloats, CoreExpr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplFloats
floats1 SimplFloats -> SimplFloats -> SimplFloats
`addFloats` SimplFloats
floats2, CoreExpr
expr') }

  where
    is_strict_bind :: Bool
is_strict_bind = case FromWhat
from_what of
       FromBeta Kind
arg_ty | (() :: Constraint) => Kind -> Bool
Kind -> Bool
isUnliftedType Kind
arg_ty -> Bool
True
         -- If we are coming from a beta-reduction (FromBeta) we must
         -- establish the let-can-float invariant, so go via StrictBind
         -- If not, the invariant holds already, and it's optional.
         -- Using arg_ty: see Note [Dark corner with representation polymorphism]
         -- e.g  (\r \(a::TYPE r) \(x::a). blah) @LiftedRep @Int arg
         --      When we come to `x=arg` we myst choose lazy/strict correctly
         --      It's wrong to err in either directly

       FromWhat
_ -> SimplEnv -> Bool
seCaseCase SimplEnv
env Bool -> Bool -> Bool
&& Demand -> Bool
isStrUsedDmd (CoreBndr -> Demand
idDemandInfo CoreBndr
bndr)


------------------
simplRecE :: SimplEnv
          -> [(InId, InExpr)]
          -> InExpr
          -> SimplCont
          -> SimplM (SimplFloats, OutExpr)

-- simplRecE is used for
--  * non-top-level recursive lets in expressions
-- Precondition: not a join-point binding
simplRecE :: SimplEnv
-> [(CoreBndr, CoreExpr)]
-> CoreExpr
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
simplRecE SimplEnv
env [(CoreBndr, CoreExpr)]
pairs CoreExpr
body SimplCont
cont
  = do  { let bndrs :: [CoreBndr]
bndrs = ((CoreBndr, CoreExpr) -> CoreBndr)
-> [(CoreBndr, CoreExpr)] -> [CoreBndr]
forall a b. (a -> b) -> [a] -> [b]
map (CoreBndr, CoreExpr) -> CoreBndr
forall a b. (a, b) -> a
fst [(CoreBndr, CoreExpr)]
pairs
        ; Bool -> SimplM ()
forall (m :: * -> *). (HasCallStack, Applicative m) => Bool -> m ()
massert ((CoreBndr -> Bool) -> [CoreBndr] -> Bool
forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
all (Bool -> Bool
not (Bool -> Bool) -> (CoreBndr -> Bool) -> CoreBndr -> Bool
forall b c a. (b -> c) -> (a -> b) -> a -> c
. CoreBndr -> Bool
isJoinId) [CoreBndr]
bndrs)
        ; SimplEnv
env1 <- SimplEnv -> [CoreBndr] -> SimplM SimplEnv
simplRecBndrs SimplEnv
env [CoreBndr]
bndrs
                -- NB: bndrs' don't have unfoldings or rules
                -- We add them as we go down
        ; (SimplFloats
floats1, SimplEnv
env2)  <- SimplEnv
-> BindContext
-> [(CoreBndr, CoreExpr)]
-> SimplM (SimplFloats, SimplEnv)
simplRecBind SimplEnv
env1 (TopLevelFlag -> RecFlag -> BindContext
BC_Let TopLevelFlag
NotTopLevel RecFlag
Recursive) [(CoreBndr, CoreExpr)]
pairs
        ; (SimplFloats
floats2, CoreExpr
expr') <- SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF SimplEnv
env2 CoreExpr
body SimplCont
cont
        ; (SimplFloats, CoreExpr) -> SimplM (SimplFloats, CoreExpr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplFloats
floats1 SimplFloats -> SimplFloats -> SimplFloats
`addFloats` SimplFloats
floats2, CoreExpr
expr') }

{- Note [Dark corner with representation polymorphism]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In `simplNonRecE`, the call to `needsCaseBinding` or to `isStrictId` will fail
if the binder does not have a fixed runtime representation, e.g. if it is of kind (TYPE r).
So we are careful to call `isStrictId` on the OutId, not the InId, in case we have
     ((\(r::RuntimeRep) \(x::TYPE r). blah) Lifted arg)
That will lead to `simplNonRecE env (x::TYPE r) arg`, and we can't tell
if x is lifted or unlifted from that.

We only get such redexes from the compulsory inlining of a wired-in,
representation-polymorphic function like `rightSection` (see
GHC.Types.Id.Make).  Mind you, SimpleOpt should probably have inlined
such compulsory inlinings already, but belt and braces does no harm.

Plus, it turns out that GHC.Driver.Main.hscCompileCoreExpr calls the
Simplifier without first calling SimpleOpt, so anything involving
GHCi or TH and operator sections will fall over if we don't take
care here.

Note [Avoiding exponential behaviour]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
One way in which we can get exponential behaviour is if we simplify a
big expression, and then re-simplify it -- and then this happens in a
deeply-nested way.  So we must be jolly careful about re-simplifying
an expression (#13379).  That is why simplNonRecX does not try
preInlineUnconditionally (unlike simplNonRecE).

Example:
  f BIG, where f has a RULE
Then
 * We simplify BIG before trying the rule; but the rule does not fire
 * We inline f = \x. x True
 * So if we did preInlineUnconditionally we'd re-simplify (BIG True)

However, if BIG has /not/ already been simplified, we'd /like/ to
simplify BIG True; maybe good things happen.  That is why

* simplLam has
    - a case for (isSimplified dup), which goes via simplNonRecX, and
    - a case for the un-simplified case, which goes via simplNonRecE

* We go to some efforts to avoid unnecessarily simplifying ApplyToVal,
  in at least two places
    - In simplCast/addCoerce, where we check for isReflCo
    - In rebuildCall we avoid simplifying arguments before we have to
      (see Note [Trying rewrite rules])


************************************************************************
*                                                                      *
                     Join points
*                                                                      *
********************************************************************* -}

{- Note [Rules and unfolding for join points]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Suppose we have

   simplExpr (join j x = rhs                         ) cont
             (      {- RULE j (p:ps) = blah -}       )
             (      {- StableUnfolding j = blah -}   )
             (in blah                                )

Then we will push 'cont' into the rhs of 'j'.  But we should *also* push
'cont' into the RHS of
  * Any RULEs for j, e.g. generated by SpecConstr
  * Any stable unfolding for j, e.g. the result of an INLINE pragma

Simplifying rules and stable-unfoldings happens a bit after
simplifying the right-hand side, so we remember whether or not it
is a join point, and what 'cont' is, in a value of type MaybeJoinCont

#13900 was caused by forgetting to push 'cont' into the RHS
of a SpecConstr-generated RULE for a join point.
-}

simplNonRecJoinPoint :: SimplEnv -> InId -> InExpr
                     -> InExpr -> SimplCont
                     -> SimplM (SimplFloats, OutExpr)
simplNonRecJoinPoint :: SimplEnv
-> CoreBndr
-> CoreExpr
-> CoreExpr
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
simplNonRecJoinPoint SimplEnv
env CoreBndr
bndr CoreExpr
rhs CoreExpr
body SimplCont
cont
   = Bool
-> SimplM (SimplFloats, CoreExpr) -> SimplM (SimplFloats, CoreExpr)
forall a. HasCallStack => Bool -> a -> a
assert (CoreBndr -> Bool
isJoinId CoreBndr
bndr ) (SimplM (SimplFloats, CoreExpr) -> SimplM (SimplFloats, CoreExpr))
-> SimplM (SimplFloats, CoreExpr) -> SimplM (SimplFloats, CoreExpr)
forall a b. (a -> b) -> a -> b
$
     SimplEnv
-> SimplCont
-> (SimplEnv -> SimplCont -> SimplM (SimplFloats, CoreExpr))
-> SimplM (SimplFloats, CoreExpr)
wrapJoinCont SimplEnv
env SimplCont
cont ((SimplEnv -> SimplCont -> SimplM (SimplFloats, CoreExpr))
 -> SimplM (SimplFloats, CoreExpr))
-> (SimplEnv -> SimplCont -> SimplM (SimplFloats, CoreExpr))
-> SimplM (SimplFloats, CoreExpr)
forall a b. (a -> b) -> a -> b
$ \ SimplEnv
env SimplCont
cont ->
     do { -- We push join_cont into the join RHS and the body;
          -- and wrap wrap_cont around the whole thing
        ; let mult :: Kind
mult   = SimplCont -> Kind
contHoleScaling SimplCont
cont
              res_ty :: Kind
res_ty = SimplCont -> Kind
contResultType SimplCont
cont
        ; (SimplEnv
env1, CoreBndr
bndr1)    <- SimplEnv -> CoreBndr -> Kind -> Kind -> SimplM (SimplEnv, CoreBndr)
simplNonRecJoinBndr SimplEnv
env CoreBndr
bndr Kind
mult Kind
res_ty
        ; (SimplEnv
env2, CoreBndr
bndr2)    <- SimplEnv
-> CoreBndr
-> CoreBndr
-> BindContext
-> SimplM (SimplEnv, CoreBndr)
addBndrRules SimplEnv
env1 CoreBndr
bndr CoreBndr
bndr1 (RecFlag -> SimplCont -> BindContext
BC_Join RecFlag
NonRecursive SimplCont
cont)
        ; (SimplFloats
floats1, SimplEnv
env3)  <- SimplEnv
-> RecFlag
-> SimplCont
-> CoreBndr
-> CoreBndr
-> CoreExpr
-> SimplEnv
-> SimplM (SimplFloats, SimplEnv)
simplJoinBind SimplEnv
env2 RecFlag
NonRecursive SimplCont
cont CoreBndr
bndr CoreBndr
bndr2 CoreExpr
rhs SimplEnv
env
        ; (SimplFloats
floats2, CoreExpr
body') <- SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF SimplEnv
env3 CoreExpr
body SimplCont
cont
        ; (SimplFloats, CoreExpr) -> SimplM (SimplFloats, CoreExpr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplFloats
floats1 SimplFloats -> SimplFloats -> SimplFloats
`addFloats` SimplFloats
floats2, CoreExpr
body') }


------------------
simplRecJoinPoint :: SimplEnv -> [(InId, InExpr)]
                  -> InExpr -> SimplCont
                  -> SimplM (SimplFloats, OutExpr)
simplRecJoinPoint :: SimplEnv
-> [(CoreBndr, CoreExpr)]
-> CoreExpr
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
simplRecJoinPoint SimplEnv
env [(CoreBndr, CoreExpr)]
pairs CoreExpr
body SimplCont
cont
  = SimplEnv
-> SimplCont
-> (SimplEnv -> SimplCont -> SimplM (SimplFloats, CoreExpr))
-> SimplM (SimplFloats, CoreExpr)
wrapJoinCont SimplEnv
env SimplCont
cont ((SimplEnv -> SimplCont -> SimplM (SimplFloats, CoreExpr))
 -> SimplM (SimplFloats, CoreExpr))
-> (SimplEnv -> SimplCont -> SimplM (SimplFloats, CoreExpr))
-> SimplM (SimplFloats, CoreExpr)
forall a b. (a -> b) -> a -> b
$ \ SimplEnv
env SimplCont
cont ->
    do { let bndrs :: [CoreBndr]
bndrs  = ((CoreBndr, CoreExpr) -> CoreBndr)
-> [(CoreBndr, CoreExpr)] -> [CoreBndr]
forall a b. (a -> b) -> [a] -> [b]
map (CoreBndr, CoreExpr) -> CoreBndr
forall a b. (a, b) -> a
fst [(CoreBndr, CoreExpr)]
pairs
             mult :: Kind
mult   = SimplCont -> Kind
contHoleScaling SimplCont
cont
             res_ty :: Kind
res_ty = SimplCont -> Kind
contResultType SimplCont
cont
       ; SimplEnv
env1 <- SimplEnv -> [CoreBndr] -> Kind -> Kind -> SimplM SimplEnv
simplRecJoinBndrs SimplEnv
env [CoreBndr]
bndrs Kind
mult Kind
res_ty
               -- NB: bndrs' don't have unfoldings or rules
               -- We add them as we go down
       ; (SimplFloats
floats1, SimplEnv
env2)  <- SimplEnv
-> BindContext
-> [(CoreBndr, CoreExpr)]
-> SimplM (SimplFloats, SimplEnv)
simplRecBind SimplEnv
env1 (RecFlag -> SimplCont -> BindContext
BC_Join RecFlag
Recursive SimplCont
cont) [(CoreBndr, CoreExpr)]
pairs
       ; (SimplFloats
floats2, CoreExpr
body') <- SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF SimplEnv
env2 CoreExpr
body SimplCont
cont
       ; (SimplFloats, CoreExpr) -> SimplM (SimplFloats, CoreExpr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplFloats
floats1 SimplFloats -> SimplFloats -> SimplFloats
`addFloats` SimplFloats
floats2, CoreExpr
body') }

--------------------
wrapJoinCont :: SimplEnv -> SimplCont
             -> (SimplEnv -> SimplCont -> SimplM (SimplFloats, OutExpr))
             -> SimplM (SimplFloats, OutExpr)
-- Deal with making the continuation duplicable if necessary,
-- and with the no-case-of-case situation.
wrapJoinCont :: SimplEnv
-> SimplCont
-> (SimplEnv -> SimplCont -> SimplM (SimplFloats, CoreExpr))
-> SimplM (SimplFloats, CoreExpr)
wrapJoinCont SimplEnv
env SimplCont
cont SimplEnv -> SimplCont -> SimplM (SimplFloats, CoreExpr)
thing_inside
  | SimplCont -> Bool
contIsStop SimplCont
cont        -- Common case; no need for fancy footwork
  = SimplEnv -> SimplCont -> SimplM (SimplFloats, CoreExpr)
thing_inside SimplEnv
env SimplCont
cont

  | Bool -> Bool
not (SimplEnv -> Bool
seCaseCase SimplEnv
env)
    -- See Note [Join points with -fno-case-of-case]
  = do { (SimplFloats
floats1, CoreExpr
expr1) <- SimplEnv -> SimplCont -> SimplM (SimplFloats, CoreExpr)
thing_inside SimplEnv
env (Kind -> SimplCont
mkBoringStop (SimplCont -> Kind
contHoleType SimplCont
cont))
       ; let (SimplFloats
floats2, CoreExpr
expr2) = SimplFloats -> CoreExpr -> (SimplFloats, CoreExpr)
wrapJoinFloatsX SimplFloats
floats1 CoreExpr
expr1
       ; (SimplFloats
floats3, CoreExpr
expr3) <- SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
rebuild (SimplEnv
env SimplEnv -> SimplFloats -> SimplEnv
`setInScopeFromF` SimplFloats
floats2) CoreExpr
expr2 SimplCont
cont
       ; (SimplFloats, CoreExpr) -> SimplM (SimplFloats, CoreExpr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplFloats
floats2 SimplFloats -> SimplFloats -> SimplFloats
`addFloats` SimplFloats
floats3, CoreExpr
expr3) }

  | Bool
otherwise
    -- Normal case; see Note [Join points and case-of-case]
  = do { (SimplFloats
floats1, SimplCont
cont')  <- SimplEnv -> SimplCont -> SimplM (SimplFloats, SimplCont)
mkDupableCont SimplEnv
env SimplCont
cont
       ; (SimplFloats
floats2, CoreExpr
result) <- SimplEnv -> SimplCont -> SimplM (SimplFloats, CoreExpr)
thing_inside (SimplEnv
env SimplEnv -> SimplFloats -> SimplEnv
`setInScopeFromF` SimplFloats
floats1) SimplCont
cont'
       ; (SimplFloats, CoreExpr) -> SimplM (SimplFloats, CoreExpr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplFloats
floats1 SimplFloats -> SimplFloats -> SimplFloats
`addFloats` SimplFloats
floats2, CoreExpr
result) }


--------------------
trimJoinCont :: Id         -- Used only in error message
             -> Maybe JoinArity
             -> SimplCont -> SimplCont
-- Drop outer context from join point invocation (jump)
-- See Note [Join points and case-of-case]

trimJoinCont :: CoreBndr -> Maybe Int -> SimplCont -> SimplCont
trimJoinCont CoreBndr
_ Maybe Int
Nothing SimplCont
cont
  = SimplCont
cont -- Not a jump
trimJoinCont CoreBndr
var (Just Int
arity) SimplCont
cont
  = Int -> SimplCont -> SimplCont
trim Int
arity SimplCont
cont
  where
    trim :: Int -> SimplCont -> SimplCont
trim Int
0 cont :: SimplCont
cont@(Stop {})
      = SimplCont
cont
    trim Int
0 SimplCont
cont
      = Kind -> SimplCont
mkBoringStop (SimplCont -> Kind
contResultType SimplCont
cont)
    trim Int
n cont :: SimplCont
cont@(ApplyToVal { sc_cont :: SimplCont -> SimplCont
sc_cont = SimplCont
k })
      = SimplCont
cont { sc_cont = trim (n-1) k }
    trim Int
n cont :: SimplCont
cont@(ApplyToTy { sc_cont :: SimplCont -> SimplCont
sc_cont = SimplCont
k })
      = SimplCont
cont { sc_cont = trim (n-1) k } -- join arity counts types!
    trim Int
_ SimplCont
cont
      = String -> SDoc -> SimplCont
forall a. HasCallStack => String -> SDoc -> a
pprPanic String
"completeCall" (SDoc -> SimplCont) -> SDoc -> SimplCont
forall a b. (a -> b) -> a -> b
$ CoreBndr -> SDoc
forall a. Outputable a => a -> SDoc
ppr CoreBndr
var SDoc -> SDoc -> SDoc
forall doc. IsDoc doc => doc -> doc -> doc
$$ SimplCont -> SDoc
forall a. Outputable a => a -> SDoc
ppr SimplCont
cont


{- Note [Join points and case-of-case]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
When we perform the case-of-case transform (or otherwise push continuations
inward), we want to treat join points specially. Since they're always
tail-called and we want to maintain this invariant, we can do this (for any
evaluation context E):

  E[join j = e
    in case ... of
         A -> jump j 1
         B -> jump j 2
         C -> f 3]

    -->

  join j = E[e]
  in case ... of
       A -> jump j 1
       B -> jump j 2
       C -> E[f 3]

As is evident from the example, there are two components to this behavior:

  1. When entering the RHS of a join point, copy the context inside.
  2. When a join point is invoked, discard the outer context.

We need to be very careful here to remain consistent---neither part is
optional!

We need do make the continuation E duplicable (since we are duplicating it)
with mkDupableCont.


Note [Join points with -fno-case-of-case]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Supose case-of-case is switched off, and we are simplifying

    case (join j x = <j-rhs> in
          case y of
             A -> j 1
             B -> j 2
             C -> e) of <outer-alts>

Usually, we'd push the outer continuation (case . of <outer-alts>) into
both the RHS and the body of the join point j.  But since we aren't doing
case-of-case we may then end up with this totally bogus result

    join x = case <j-rhs> of <outer-alts> in
    case (case y of
             A -> j 1
             B -> j 2
             C -> e) of <outer-alts>

This would be OK in the language of the paper, but not in GHC: j is no longer
a join point.  We can only do the "push continuation into the RHS of the
join point j" if we also push the continuation right down to the /jumps/ to
j, so that it can evaporate there.  If we are doing case-of-case, we'll get to

    join x = case <j-rhs> of <outer-alts> in
    case y of
      A -> j 1
      B -> j 2
      C -> case e of <outer-alts>

which is great.

Bottom line: if case-of-case is off, we must stop pushing the continuation
inwards altogether at any join point.  Instead simplify the (join ... in ...)
with a Stop continuation, and wrap the original continuation around the
outside.  Surprisingly tricky!


************************************************************************
*                                                                      *
                     Variables
*                                                                      *
************************************************************************

Note [zapSubstEnv]
~~~~~~~~~~~~~~~~~~
When simplifying something that has already been simplified, be sure to
zap the SubstEnv.  This is VITAL.  Consider
     let x = e in
     let y = \z -> ...x... in
     \ x -> ...y...

We'll clone the inner \x, adding x->x' in the id_subst Then when we
inline y, we must *not* replace x by x' in the inlined copy!!

Note [Fast path for data constructors]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
For applications of a data constructor worker, the full glory of
rebuildCall is a waste of effort;
* They never inline, obviously
* They have no rewrite rules
* They are not strict (see Note [Data-con worker strictness]
  in GHC.Core.DataCon)
So it's fine to zoom straight to `rebuild` which just rebuilds the
call in a very straightforward way.

Some programs have a /lot/ of data constructors in the source program
(compiler/perf/T9961 is an example), so this fast path can be very
valuable.
-}

simplVar :: SimplEnv -> InVar -> SimplM OutExpr
-- Look up an InVar in the environment
simplVar :: SimplEnv -> CoreBndr -> SimplM CoreExpr
simplVar SimplEnv
env CoreBndr
var
  -- Why $! ? See Note [Bangs in the Simplifier]
  | CoreBndr -> Bool
isTyVar CoreBndr
var = CoreExpr -> SimplM CoreExpr
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (CoreExpr -> SimplM CoreExpr) -> CoreExpr -> SimplM CoreExpr
forall a b. (a -> b) -> a -> b
$! Kind -> CoreExpr
forall b. Kind -> Expr b
Type (Kind -> CoreExpr) -> Kind -> CoreExpr
forall a b. (a -> b) -> a -> b
$! (SimplEnv -> CoreBndr -> Kind
substTyVar SimplEnv
env CoreBndr
var)
  | CoreBndr -> Bool
isCoVar CoreBndr
var = CoreExpr -> SimplM CoreExpr
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (CoreExpr -> SimplM CoreExpr) -> CoreExpr -> SimplM CoreExpr
forall a b. (a -> b) -> a -> b
$! Coercion -> CoreExpr
forall b. Coercion -> Expr b
Coercion (Coercion -> CoreExpr) -> Coercion -> CoreExpr
forall a b. (a -> b) -> a -> b
$! (SimplEnv -> CoreBndr -> Coercion
substCoVar SimplEnv
env CoreBndr
var)
  | Bool
otherwise
  = case SimplEnv -> CoreBndr -> SimplSR
substId SimplEnv
env CoreBndr
var of
        ContEx TvSubstEnv
tvs CvSubstEnv
cvs SimplIdSubst
ids CoreExpr
e -> let env' :: SimplEnv
env' = SimplEnv -> TvSubstEnv -> CvSubstEnv -> SimplIdSubst -> SimplEnv
setSubstEnv SimplEnv
env TvSubstEnv
tvs CvSubstEnv
cvs SimplIdSubst
ids
                                in SimplEnv -> CoreExpr -> SimplM CoreExpr
simplExpr SimplEnv
env' CoreExpr
e
        DoneId CoreBndr
var1          -> CoreExpr -> SimplM CoreExpr
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (CoreBndr -> CoreExpr
forall b. CoreBndr -> Expr b
Var CoreBndr
var1)
        DoneEx CoreExpr
e Maybe Int
_           -> CoreExpr -> SimplM CoreExpr
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return CoreExpr
e

simplIdF :: SimplEnv -> InId -> SimplCont -> SimplM (SimplFloats, OutExpr)
simplIdF :: SimplEnv -> CoreBndr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplIdF SimplEnv
env CoreBndr
var SimplCont
cont
  | CoreBndr -> Bool
isDataConWorkId CoreBndr
var         -- See Note [Fast path for data constructors]
  = SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
rebuild SimplEnv
env (CoreBndr -> CoreExpr
forall b. CoreBndr -> Expr b
Var CoreBndr
var) SimplCont
cont
  | Bool
otherwise
  = case SimplEnv -> CoreBndr -> SimplSR
substId SimplEnv
env CoreBndr
var of
      ContEx TvSubstEnv
tvs CvSubstEnv
cvs SimplIdSubst
ids CoreExpr
e -> SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF SimplEnv
env' CoreExpr
e SimplCont
cont
        -- Don't trimJoinCont; haven't already simplified e,
        -- so the cont is not embodied in e
        where
          env' :: SimplEnv
env' = SimplEnv -> TvSubstEnv -> CvSubstEnv -> SimplIdSubst -> SimplEnv
setSubstEnv SimplEnv
env TvSubstEnv
tvs CvSubstEnv
cvs SimplIdSubst
ids

      DoneId CoreBndr
var1 ->
        do { RuleEnv
rule_base <- SimplM RuleEnv
getSimplRules
           ; let cont' :: SimplCont
cont' = CoreBndr -> Maybe Int -> SimplCont -> SimplCont
trimJoinCont CoreBndr
var1 (CoreBndr -> Maybe Int
isJoinId_maybe CoreBndr
var1) SimplCont
cont
                 info :: ArgInfo
info  = SimplEnv -> RuleEnv -> CoreBndr -> SimplCont -> ArgInfo
mkArgInfo SimplEnv
env RuleEnv
rule_base CoreBndr
var1 SimplCont
cont'
           ; SimplEnv -> ArgInfo -> SimplCont -> SimplM (SimplFloats, CoreExpr)
rebuildCall SimplEnv
env ArgInfo
info SimplCont
cont' }

      DoneEx CoreExpr
e Maybe Int
mb_join -> SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF SimplEnv
env' CoreExpr
e SimplCont
cont'
        where
          cont' :: SimplCont
cont' = CoreBndr -> Maybe Int -> SimplCont -> SimplCont
trimJoinCont CoreBndr
var Maybe Int
mb_join SimplCont
cont
          env' :: SimplEnv
env'  = SimplEnv -> SimplEnv
zapSubstEnv SimplEnv
env  -- See Note [zapSubstEnv]

---------------------------------------------------------
--      Dealing with a call site

rebuildCall :: SimplEnv -> ArgInfo -> SimplCont
            -> SimplM (SimplFloats, OutExpr)

---------- Bottoming applications --------------
rebuildCall :: SimplEnv -> ArgInfo -> SimplCont -> SimplM (SimplFloats, CoreExpr)
rebuildCall SimplEnv
env (ArgInfo { ai_fun :: ArgInfo -> CoreBndr
ai_fun = CoreBndr
fun, ai_args :: ArgInfo -> [ArgSpec]
ai_args = [ArgSpec]
rev_args, ai_dmds :: ArgInfo -> [Demand]
ai_dmds = [] }) SimplCont
cont
  -- When we run out of strictness args, it means
  -- that the call is definitely bottom; see GHC.Core.Opt.Simplify.Utils.mkArgInfo
  -- Then we want to discard the entire strict continuation.  E.g.
  --    * case (error "hello") of { ... }
  --    * (error "Hello") arg
  --    * f (error "Hello") where f is strict
  --    etc
  -- Then, especially in the first of these cases, we'd like to discard
  -- the continuation, leaving just the bottoming expression.  But the
  -- type might not be right, so we may have to add a coerce.
  | Bool -> Bool
not (SimplCont -> Bool
contIsTrivial SimplCont
cont)     -- Only do this if there is a non-trivial
                                 -- continuation to discard, else we do it
                                 -- again and again!
  = Kind -> ()
seqType Kind
cont_ty ()
-> SimplM (SimplFloats, CoreExpr) -> SimplM (SimplFloats, CoreExpr)
forall a b. a -> b -> b
`seq`        -- See Note [Avoiding space leaks in OutType]
    (SimplFloats, CoreExpr) -> SimplM (SimplFloats, CoreExpr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplEnv -> SimplFloats
emptyFloats SimplEnv
env, CoreExpr -> Kind -> CoreExpr
castBottomExpr CoreExpr
res Kind
cont_ty)
  where
    res :: CoreExpr
res     = CoreBndr -> [ArgSpec] -> CoreExpr
argInfoExpr CoreBndr
fun [ArgSpec]
rev_args
    cont_ty :: Kind
cont_ty = SimplCont -> Kind
contResultType SimplCont
cont

---------- Try inlining, if ai_rewrite = TryInlining --------
-- In the TryInlining case we try inlining immediately, before simplifying
-- any (more) arguments. Why?  See Note [Rewrite rules and inlining].
--
-- If there are rewrite rules we'll skip this case until we have
-- simplified enough args to satisfy nr_wanted==0 in the TryRules case below
-- Then we'll try the rules, and if that fails, we'll do TryInlining
rebuildCall SimplEnv
env info :: ArgInfo
info@(ArgInfo { ai_fun :: ArgInfo -> CoreBndr
ai_fun = CoreBndr
fun, ai_args :: ArgInfo -> [ArgSpec]
ai_args = [ArgSpec]
rev_args
                              , ai_rewrite :: ArgInfo -> RewriteCall
ai_rewrite = RewriteCall
TryInlining }) SimplCont
cont
  = do { Logger
logger <- SimplM Logger
forall (m :: * -> *). HasLogger m => m Logger
getLogger
       ; let full_cont :: SimplCont
full_cont = SimplEnv -> [ArgSpec] -> SimplCont -> SimplCont
pushSimplifiedRevArgs SimplEnv
env [ArgSpec]
rev_args SimplCont
cont
       ; Maybe CoreExpr
mb_inline <- SimplEnv
-> Logger -> CoreBndr -> SimplCont -> SimplM (Maybe CoreExpr)
tryInlining SimplEnv
env Logger
logger CoreBndr
fun SimplCont
full_cont
       ; case Maybe CoreExpr
mb_inline of
            Just CoreExpr
expr -> do { Tick -> SimplM ()
checkedTick (CoreBndr -> Tick
UnfoldingDone CoreBndr
fun)
                            ; let env1 :: SimplEnv
env1 = SimplEnv -> SimplEnv
zapSubstEnv SimplEnv
env
                            ; SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF SimplEnv
env1 CoreExpr
expr SimplCont
full_cont }
            Maybe CoreExpr
Nothing -> SimplEnv -> ArgInfo -> SimplCont -> SimplM (SimplFloats, CoreExpr)
rebuildCall SimplEnv
env (ArgInfo
info { ai_rewrite = TryNothing }) SimplCont
cont
       }

---------- Try rewrite RULES, if ai_rewrite = TryRules --------------
-- See Note [Rewrite rules and inlining]
-- See also Note [Trying rewrite rules]
rebuildCall SimplEnv
env info :: ArgInfo
info@(ArgInfo { ai_fun :: ArgInfo -> CoreBndr
ai_fun = CoreBndr
fun, ai_args :: ArgInfo -> [ArgSpec]
ai_args = [ArgSpec]
rev_args
                              , ai_rewrite :: ArgInfo -> RewriteCall
ai_rewrite = TryRules Int
nr_wanted [CoreRule]
rules }) SimplCont
cont
  | Int
nr_wanted Int -> Int -> Bool
forall a. Eq a => a -> a -> Bool
== Int
0 Bool -> Bool -> Bool
|| Bool
no_more_args
  = -- We've accumulated a simplified call in <fun,rev_args>
    -- so try rewrite rules; see Note [RULES apply to simplified arguments]
    -- See also Note [Rules for recursive functions]
    do { Maybe (SimplEnv, CoreExpr, SimplCont)
mb_match <- SimplEnv
-> [CoreRule]
-> CoreBndr
-> [ArgSpec]
-> SimplCont
-> SimplM (Maybe (SimplEnv, CoreExpr, SimplCont))
tryRules SimplEnv
env [CoreRule]
rules CoreBndr
fun ([ArgSpec] -> [ArgSpec]
forall a. [a] -> [a]
reverse [ArgSpec]
rev_args) SimplCont
cont
       ; case Maybe (SimplEnv, CoreExpr, SimplCont)
mb_match of
             Just (SimplEnv
env', CoreExpr
rhs, SimplCont
cont') -> SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF SimplEnv
env' CoreExpr
rhs SimplCont
cont'
             Maybe (SimplEnv, CoreExpr, SimplCont)
Nothing -> SimplEnv -> ArgInfo -> SimplCont -> SimplM (SimplFloats, CoreExpr)
rebuildCall SimplEnv
env (ArgInfo
info { ai_rewrite = TryInlining }) SimplCont
cont }
  where
    -- If we have run out of arguments, just try the rules; there might
    -- be some with lower arity.  Casts get in the way -- they aren't
    -- allowed on rule LHSs
    no_more_args :: Bool
no_more_args = case SimplCont
cont of
                      ApplyToTy  {} -> Bool
False
                      ApplyToVal {} -> Bool
False
                      SimplCont
_             -> Bool
True

---------- Simplify type applications and casts --------------
rebuildCall SimplEnv
env ArgInfo
info (CastIt Coercion
co SimplCont
cont)
  = SimplEnv -> ArgInfo -> SimplCont -> SimplM (SimplFloats, CoreExpr)
rebuildCall SimplEnv
env (ArgInfo -> Coercion -> ArgInfo
addCastTo ArgInfo
info Coercion
co) SimplCont
cont

rebuildCall SimplEnv
env ArgInfo
info (ApplyToTy { sc_arg_ty :: SimplCont -> Kind
sc_arg_ty = Kind
arg_ty, sc_hole_ty :: SimplCont -> Kind
sc_hole_ty = Kind
hole_ty, sc_cont :: SimplCont -> SimplCont
sc_cont = SimplCont
cont })
  = SimplEnv -> ArgInfo -> SimplCont -> SimplM (SimplFloats, CoreExpr)
rebuildCall SimplEnv
env (ArgInfo -> Kind -> Kind -> ArgInfo
addTyArgTo ArgInfo
info Kind
arg_ty Kind
hole_ty) SimplCont
cont

---------- The runRW# rule. Do this after absorbing all arguments ------
-- See Note [Simplification of runRW#] in GHC.CoreToSTG.Prep.
--
-- runRW# :: forall (r :: RuntimeRep) (o :: TYPE r). (State# RealWorld -> o) -> o
-- K[ runRW# rr ty body ]   -->   runRW rr' ty' (\s. K[ body s ])
rebuildCall SimplEnv
env (ArgInfo { ai_fun :: ArgInfo -> CoreBndr
ai_fun = CoreBndr
fun_id, ai_args :: ArgInfo -> [ArgSpec]
ai_args = [ArgSpec]
rev_args })
            (ApplyToVal { sc_arg :: SimplCont -> CoreExpr
sc_arg = CoreExpr
arg, sc_env :: SimplCont -> SimplEnv
sc_env = SimplEnv
arg_se
                        , sc_cont :: SimplCont -> SimplCont
sc_cont = SimplCont
cont, sc_hole_ty :: SimplCont -> Kind
sc_hole_ty = Kind
fun_ty })
  | CoreBndr
fun_id CoreBndr -> Unique -> Bool
forall a. Uniquable a => a -> Unique -> Bool
`hasKey` Unique
runRWKey
  , [ TyArg {}, TyArg {} ] <- [ArgSpec]
rev_args
  -- Do this even if (contIsStop cont)
  -- See Note [No eta-expansion in runRW#]
  = do { let arg_env :: SimplEnv
arg_env = SimplEnv
arg_se SimplEnv -> SimplEnv -> SimplEnv
`setInScopeFromE` SimplEnv
env
             ty' :: Kind
ty'   = SimplCont -> Kind
contResultType SimplCont
cont

       -- If the argument is a literal lambda already, take a short cut
       -- This isn't just efficiency; if we don't do this we get a beta-redex
       -- every time, so the simplifier keeps doing more iterations.
       ; CoreExpr
arg' <- case CoreExpr
arg of
           Lam CoreBndr
s CoreExpr
body -> do { (SimplEnv
env', CoreBndr
s') <- SimplEnv -> CoreBndr -> SimplM (SimplEnv, CoreBndr)
simplBinder SimplEnv
arg_env CoreBndr
s
                            ; CoreExpr
body' <- SimplEnv -> CoreExpr -> SimplCont -> SimplM CoreExpr
simplExprC SimplEnv
env' CoreExpr
body SimplCont
cont
                            ; CoreExpr -> SimplM CoreExpr
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (CoreBndr -> CoreExpr -> CoreExpr
forall b. b -> Expr b -> Expr b
Lam CoreBndr
s' CoreExpr
body') }
                            -- Important: do not try to eta-expand this lambda
                            -- See Note [No eta-expansion in runRW#]
           CoreExpr
_ -> do { CoreBndr
s' <- FastString -> Kind -> Kind -> SimplM CoreBndr
newId (String -> FastString
fsLit String
"s") Kind
ManyTy Kind
realWorldStatePrimTy
                   ; let (Kind
m,Kind
_,Kind
_) = Kind -> (Kind, Kind, Kind)
splitFunTy Kind
fun_ty
                         env' :: SimplEnv
env'  = SimplEnv
arg_env SimplEnv -> [CoreBndr] -> SimplEnv
`addNewInScopeIds` [CoreBndr
s']
                         cont' :: SimplCont
cont' = ApplyToVal { sc_dup :: DupFlag
sc_dup = DupFlag
Simplified, sc_arg :: CoreExpr
sc_arg = CoreBndr -> CoreExpr
forall b. CoreBndr -> Expr b
Var CoreBndr
s'
                                            , sc_env :: SimplEnv
sc_env = SimplEnv
env', sc_cont :: SimplCont
sc_cont = SimplCont
cont
                                            , sc_hole_ty :: Kind
sc_hole_ty = (() :: Constraint) => Kind -> Kind -> Kind -> Kind
Kind -> Kind -> Kind -> Kind
mkVisFunTy Kind
m Kind
realWorldStatePrimTy Kind
ty' }
                                -- cont' applies to s', then K
                   ; CoreExpr
body' <- SimplEnv -> CoreExpr -> SimplCont -> SimplM CoreExpr
simplExprC SimplEnv
env' CoreExpr
arg SimplCont
cont'
                   ; CoreExpr -> SimplM CoreExpr
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (CoreBndr -> CoreExpr -> CoreExpr
forall b. b -> Expr b -> Expr b
Lam CoreBndr
s' CoreExpr
body') }

       ; let rr' :: Kind
rr'   = (() :: Constraint) => Kind -> Kind
Kind -> Kind
getRuntimeRep Kind
ty'
             call' :: CoreExpr
call' = CoreExpr -> [CoreExpr] -> CoreExpr
forall b. Expr b -> [Expr b] -> Expr b
mkApps (CoreBndr -> CoreExpr
forall b. CoreBndr -> Expr b
Var CoreBndr
fun_id) [Kind -> CoreExpr
forall b. Kind -> Expr b
mkTyArg Kind
rr', Kind -> CoreExpr
forall b. Kind -> Expr b
mkTyArg Kind
ty', CoreExpr
arg']
       ; (SimplFloats, CoreExpr) -> SimplM (SimplFloats, CoreExpr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplEnv -> SimplFloats
emptyFloats SimplEnv
env, CoreExpr
call') }

---------- Simplify value arguments --------------------
rebuildCall SimplEnv
env ArgInfo
fun_info
            (ApplyToVal { sc_arg :: SimplCont -> CoreExpr
sc_arg = CoreExpr
arg, sc_env :: SimplCont -> SimplEnv
sc_env = SimplEnv
arg_se
                        , sc_dup :: SimplCont -> DupFlag
sc_dup = DupFlag
dup_flag, sc_hole_ty :: SimplCont -> Kind
sc_hole_ty = Kind
fun_ty
                        , sc_cont :: SimplCont -> SimplCont
sc_cont = SimplCont
cont })
  -- Argument is already simplified
  | DupFlag -> Bool
isSimplified DupFlag
dup_flag     -- See Note [Avoid redundant simplification]
  = SimplEnv -> ArgInfo -> SimplCont -> SimplM (SimplFloats, CoreExpr)
rebuildCall SimplEnv
env (ArgInfo -> CoreExpr -> Kind -> ArgInfo
addValArgTo ArgInfo
fun_info CoreExpr
arg Kind
fun_ty) SimplCont
cont

  -- Strict arguments
  | ArgInfo -> Bool
isStrictArgInfo ArgInfo
fun_info
  , SimplEnv -> Bool
seCaseCase SimplEnv
env
  = -- pprTrace "Strict Arg" (ppr arg $$ ppr (seIdSubst env) $$ ppr (seInScope env)) $
    SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF (SimplEnv
arg_se SimplEnv -> SimplEnv -> SimplEnv
`setInScopeFromE` SimplEnv
env) CoreExpr
arg
               (StrictArg { sc_fun :: ArgInfo
sc_fun = ArgInfo
fun_info, sc_fun_ty :: Kind
sc_fun_ty = Kind
fun_ty
                          , sc_dup :: DupFlag
sc_dup = DupFlag
Simplified
                          , sc_cont :: SimplCont
sc_cont = SimplCont
cont })
                -- Note [Shadowing]

  -- Lazy arguments
  | Bool
otherwise
        -- DO NOT float anything outside, hence simplExprC
        -- There is no benefit (unlike in a let-binding), and we'd
        -- have to be very careful about bogus strictness through
        -- floating a demanded let.
  = do  { CoreExpr
arg' <- SimplEnv -> CoreExpr -> SimplCont -> SimplM CoreExpr
simplExprC (SimplEnv
arg_se SimplEnv -> SimplEnv -> SimplEnv
`setInScopeFromE` SimplEnv
env) CoreExpr
arg
                             (Kind -> ArgInfo -> SimplCont
mkLazyArgStop Kind
arg_ty ArgInfo
fun_info)
        ; SimplEnv -> ArgInfo -> SimplCont -> SimplM (SimplFloats, CoreExpr)
rebuildCall SimplEnv
env (ArgInfo -> CoreExpr -> Kind -> ArgInfo
addValArgTo ArgInfo
fun_info  CoreExpr
arg' Kind
fun_ty) SimplCont
cont }
  where
    arg_ty :: Kind
arg_ty = Kind -> Kind
funArgTy Kind
fun_ty


---------- No further useful info, revert to generic rebuild ------------
rebuildCall SimplEnv
env (ArgInfo { ai_fun :: ArgInfo -> CoreBndr
ai_fun = CoreBndr
fun, ai_args :: ArgInfo -> [ArgSpec]
ai_args = [ArgSpec]
rev_args }) SimplCont
cont
  = SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
rebuild SimplEnv
env (CoreBndr -> [ArgSpec] -> CoreExpr
argInfoExpr CoreBndr
fun [ArgSpec]
rev_args) SimplCont
cont

-----------------------------------
tryInlining :: SimplEnv -> Logger -> OutId -> SimplCont -> SimplM (Maybe OutExpr)
tryInlining :: SimplEnv
-> Logger -> CoreBndr -> SimplCont -> SimplM (Maybe CoreExpr)
tryInlining SimplEnv
env Logger
logger CoreBndr
var SimplCont
cont
  | Just CoreExpr
expr <- Logger
-> UnfoldingOpts
-> Int
-> CoreBndr
-> Bool
-> Bool
-> [ArgSummary]
-> CallCtxt
-> Maybe CoreExpr
callSiteInline Logger
logger UnfoldingOpts
uf_opts Int
case_depth CoreBndr
var Bool
active_unf
                                Bool
lone_variable [ArgSummary]
arg_infos CallCtxt
interesting_cont
  = do { CoreExpr -> SimplCont -> SimplM ()
dump_inline CoreExpr
expr SimplCont
cont
       ; Maybe CoreExpr -> SimplM (Maybe CoreExpr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (CoreExpr -> Maybe CoreExpr
forall a. a -> Maybe a
Just CoreExpr
expr) }

  | Bool
otherwise
  = Maybe CoreExpr -> SimplM (Maybe CoreExpr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return Maybe CoreExpr
forall a. Maybe a
Nothing

  where
    uf_opts :: UnfoldingOpts
uf_opts    = SimplEnv -> UnfoldingOpts
seUnfoldingOpts SimplEnv
env
    case_depth :: Int
case_depth = SimplEnv -> Int
seCaseDepth SimplEnv
env
    (Bool
lone_variable, [ArgSummary]
arg_infos, SimplCont
call_cont) = SimplCont -> (Bool, [ArgSummary], SimplCont)
contArgs SimplCont
cont
    interesting_cont :: CallCtxt
interesting_cont = SimplEnv -> SimplCont -> CallCtxt
interestingCallContext SimplEnv
env SimplCont
call_cont
    active_unf :: Bool
active_unf       = SimplMode -> CoreBndr -> Bool
activeUnfolding (SimplEnv -> SimplMode
seMode SimplEnv
env) CoreBndr
var

    log_inlining :: SDoc -> SimplM ()
log_inlining SDoc
doc
      = IO () -> SimplM ()
forall a. IO a -> SimplM a
forall (m :: * -> *) a. MonadIO m => IO a -> m a
liftIO (IO () -> SimplM ()) -> IO () -> SimplM ()
forall a b. (a -> b) -> a -> b
$ Logger
-> PprStyle -> DumpFlag -> String -> DumpFormat -> SDoc -> IO ()
logDumpFile Logger
logger (NamePprCtx -> PprStyle
mkDumpStyle NamePprCtx
alwaysQualify)
           DumpFlag
Opt_D_dump_inlinings
           String
"" DumpFormat
FormatText SDoc
doc

    dump_inline :: CoreExpr -> SimplCont -> SimplM ()
dump_inline CoreExpr
unfolding SimplCont
cont
      | Bool -> Bool
not (Logger -> DumpFlag -> Bool
logHasDumpFlag Logger
logger DumpFlag
Opt_D_dump_inlinings) = () -> SimplM ()
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return ()
      | Bool -> Bool
not (Logger -> DumpFlag -> Bool
logHasDumpFlag Logger
logger DumpFlag
Opt_D_verbose_core2core)
      = Bool -> SimplM () -> SimplM ()
forall (f :: * -> *). Applicative f => Bool -> f () -> f ()
when (Name -> Bool
isExternalName (CoreBndr -> Name
idName CoreBndr
var)) (SimplM () -> SimplM ()) -> SimplM () -> SimplM ()
forall a b. (a -> b) -> a -> b
$
            SDoc -> SimplM ()
log_inlining (SDoc -> SimplM ()) -> SDoc -> SimplM ()
forall a b. (a -> b) -> a -> b
$
                [SDoc] -> SDoc
forall doc. IsLine doc => [doc] -> doc
sep [String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"Inlining done:", Int -> SDoc -> SDoc
nest Int
4 (CoreBndr -> SDoc
forall a. Outputable a => a -> SDoc
ppr CoreBndr
var)]
      | Bool
otherwise
      = SDoc -> SimplM ()
log_inlining (SDoc -> SimplM ()) -> SDoc -> SimplM ()
forall a b. (a -> b) -> a -> b
$
           [SDoc] -> SDoc
forall doc. IsLine doc => [doc] -> doc
sep [String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"Inlining done: " SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<> CoreBndr -> SDoc
forall a. Outputable a => a -> SDoc
ppr CoreBndr
var,
                Int -> SDoc -> SDoc
nest Int
4 ([SDoc] -> SDoc
forall doc. IsDoc doc => [doc] -> doc
vcat [String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"Inlined fn: " SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> Int -> SDoc -> SDoc
nest Int
2 (CoreExpr -> SDoc
forall a. Outputable a => a -> SDoc
ppr CoreExpr
unfolding),
                              String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"Cont:  " SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> SimplCont -> SDoc
forall a. Outputable a => a -> SDoc
ppr SimplCont
cont])]


{- Note [Trying rewrite rules]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider an application (f e1 e2 e3) where the e1,e2,e3 are not yet
simplified.  We want to simplify enough arguments to allow the rules
to apply, but it's more efficient to avoid simplifying e2,e3 if e1 alone
is sufficient.  Example: class ops
   (+) dNumInt e2 e3
If we rewrite ((+) dNumInt) to plusInt, we can take advantage of the
latter's strictness when simplifying e2, e3.  Moreover, suppose we have
  RULE  f Int = \x. x True

Then given (f Int e1) we rewrite to
   (\x. x True) e1
without simplifying e1.  Now we can inline x into its unique call site,
and absorb the True into it all in the same pass.  If we simplified
e1 first, we couldn't do that; see Note [Avoiding exponential behaviour].

So we try to apply rules if either
  (a) no_more_args: we've run out of argument that the rules can "see"
  (b) nr_wanted: none of the rules wants any more arguments


Note [RULES apply to simplified arguments]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
It's very desirable to try RULES once the arguments have been simplified, because
doing so ensures that rule cascades work in one pass.  Consider
   {-# RULES g (h x) = k x
             f (k x) = x #-}
   ...f (g (h x))...
Then we want to rewrite (g (h x)) to (k x) and only then try f's rules. If
we match f's rules against the un-simplified RHS, it won't match.  This
makes a particularly big difference when superclass selectors are involved:
        op ($p1 ($p2 (df d)))
We want all this to unravel in one sweep.

Note [Rewrite rules and inlining]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In general we try to arrange that inlining is disabled (via a pragma) if
a rewrite rule should apply, so that the rule has a decent chance to fire
before we inline the function.

But it turns out that (especially when type-class specialisation or
SpecConstr is involved) it is very helpful for the the rewrite rule to
"win" over inlining when both are active at once: see #21851, #22097.

The simplifier arranges to do this, as follows. In effect, the ai_rewrite
field of the ArgInfo record is the state of a little state-machine:

* mkArgInfo sets the ai_rewrite field to TryRules if there are any rewrite
  rules avaialable for that function.

* rebuildCall simplifies arguments until enough are simplified to match the
  rule with greatest arity.  See Note [RULES apply to simplified arguments]
  and the first field of `TryRules`.

  But no more! As soon as we have simplified enough arguments to satisfy the
  maximum-arity rules, we try the rules; see Note [Trying rewrite rules].

* Once we have tried rules (or immediately if there are no rules) set
  ai_rewrite to TryInlining, and the Simplifier will try to inline the
  function.  We want to try this immediately (before simplifying any (more)
  arguments). Why? Consider
      f BIG      where   f = \x{OneOcc}. ...x...
  If we inline `f` before simplifying `BIG` well use preInlineUnconditionally,
  and we'll simplify BIG once, at x's occurrence, rather than twice.

* GHC.Core.Opt.Simplify.Utils. mkRewriteCall: if there are no rules, and no
  unfolding, we can skip both TryRules and TryInlining, which saves work.

Note [Avoid redundant simplification]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Because RULES apply to simplified arguments, there's a danger of repeatedly
simplifying already-simplified arguments.  An important example is that of
        (>>=) d e1 e2
Here e1, e2 are simplified before the rule is applied, but don't really
participate in the rule firing. So we mark them as Simplified to avoid
re-simplifying them.

Note [Shadowing]
~~~~~~~~~~~~~~~~
This part of the simplifier may break the no-shadowing invariant
Consider
        f (...(\a -> e)...) (case y of (a,b) -> e')
where f is strict in its second arg
If we simplify the innermost one first we get (...(\a -> e)...)
Simplifying the second arg makes us float the case out, so we end up with
        case y of (a,b) -> f (...(\a -> e)...) e'
So the output does not have the no-shadowing invariant.  However, there is
no danger of getting name-capture, because when the first arg was simplified
we used an in-scope set that at least mentioned all the variables free in its
static environment, and that is enough.

We can't just do innermost first, or we'd end up with a dual problem:
        case x of (a,b) -> f e (...(\a -> e')...)

I spent hours trying to recover the no-shadowing invariant, but I just could
not think of an elegant way to do it.  The simplifier is already knee-deep in
continuations.  We have to keep the right in-scope set around; AND we have
to get the effect that finding (error "foo") in a strict arg position will
discard the entire application and replace it with (error "foo").  Getting
all this at once is TOO HARD!

Note [No eta-expansion in runRW#]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
When we see `runRW# (\s. blah)` we must not attempt to eta-expand that
lambda.  Why not?  Because
* `blah` can mention join points bound outside the runRW#
* eta-expansion uses arityType, and
* `arityType` cannot cope with free join Ids:

So the simplifier spots the literal lambda, and simplifies inside it.
It's a very special lambda, because it is the one the OccAnal spots and
allows join points bound /outside/ to be called /inside/.

See Note [No free join points in arityType] in GHC.Core.Opt.Arity

************************************************************************
*                                                                      *
                Rewrite rules
*                                                                      *
************************************************************************
-}

tryRules :: SimplEnv -> [CoreRule]
         -> Id
         -> [ArgSpec]   -- In /normal, forward/ order
         -> SimplCont
         -> SimplM (Maybe (SimplEnv, CoreExpr, SimplCont))

tryRules :: SimplEnv
-> [CoreRule]
-> CoreBndr
-> [ArgSpec]
-> SimplCont
-> SimplM (Maybe (SimplEnv, CoreExpr, SimplCont))
tryRules SimplEnv
env [CoreRule]
rules CoreBndr
fn [ArgSpec]
args SimplCont
call_cont
  | [CoreRule] -> Bool
forall a. [a] -> Bool
forall (t :: * -> *) a. Foldable t => t a -> Bool
null [CoreRule]
rules
  = Maybe (SimplEnv, CoreExpr, SimplCont)
-> SimplM (Maybe (SimplEnv, CoreExpr, SimplCont))
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return Maybe (SimplEnv, CoreExpr, SimplCont)
forall a. Maybe a
Nothing

{- Disabled until we fix #8326
  | fn `hasKey` tagToEnumKey   -- See Note [Optimising tagToEnum#]
  , [_type_arg, val_arg] <- args
  , Select dup bndr ((_,[],rhs1) : rest_alts) se cont <- call_cont
  , isDeadBinder bndr
  = do { let enum_to_tag :: CoreAlt -> CoreAlt
                -- Takes   K -> e  into   tagK# -> e
                -- where tagK# is the tag of constructor K
             enum_to_tag (DataAlt con, [], rhs)
               = assert (isEnumerationTyCon (dataConTyCon con) )
                (LitAlt tag, [], rhs)
              where
                tag = mkLitInt (sePlatform env) (toInteger (dataConTag con - fIRST_TAG))
             enum_to_tag alt = pprPanic "tryRules: tagToEnum" (ppr alt)

             new_alts = (DEFAULT, [], rhs1) : map enum_to_tag rest_alts
             new_bndr = setIdType bndr intPrimTy
                 -- The binder is dead, but should have the right type
      ; return (Just (val_arg, Select dup new_bndr new_alts se cont)) }
-}

  | Just (CoreRule
rule, CoreExpr
rule_rhs) <- RuleOpts
-> InScopeEnv
-> (Activation -> Bool)
-> CoreBndr
-> [CoreExpr]
-> [CoreRule]
-> Maybe (CoreRule, CoreExpr)
lookupRule RuleOpts
ropts (SimplEnv -> InScopeEnv
getUnfoldingInRuleMatch SimplEnv
env)
                                        (SimplMode -> Activation -> Bool
activeRule (SimplEnv -> SimplMode
seMode SimplEnv
env)) CoreBndr
fn
                                        ([ArgSpec] -> [CoreExpr]
argInfoAppArgs [ArgSpec]
args) [CoreRule]
rules
  -- Fire a rule for the function
  = do { Logger
logger <- SimplM Logger
forall (m :: * -> *). HasLogger m => m Logger
getLogger
       ; Tick -> SimplM ()
checkedTick (FastString -> Tick
RuleFired (CoreRule -> FastString
ruleName CoreRule
rule))
       ; let cont' :: SimplCont
cont' = SimplEnv -> [ArgSpec] -> SimplCont -> SimplCont
pushSimplifiedArgs SimplEnv
zapped_env
                                        (Int -> [ArgSpec] -> [ArgSpec]
forall a. Int -> [a] -> [a]
drop (CoreRule -> Int
ruleArity CoreRule
rule) [ArgSpec]
args)
                                        SimplCont
call_cont
                     -- (ruleArity rule) says how
                     -- many args the rule consumed

             occ_anald_rhs :: CoreExpr
occ_anald_rhs = CoreExpr -> CoreExpr
occurAnalyseExpr CoreExpr
rule_rhs
                 -- See Note [Occurrence-analyse after rule firing]
       ; Logger -> CoreRule -> CoreExpr -> SimplM ()
dump Logger
logger CoreRule
rule CoreExpr
rule_rhs
       ; Maybe (SimplEnv, CoreExpr, SimplCont)
-> SimplM (Maybe (SimplEnv, CoreExpr, SimplCont))
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return ((SimplEnv, CoreExpr, SimplCont)
-> Maybe (SimplEnv, CoreExpr, SimplCont)
forall a. a -> Maybe a
Just (SimplEnv
zapped_env, CoreExpr
occ_anald_rhs, SimplCont
cont')) }
            -- The occ_anald_rhs and cont' are all Out things
            -- hence zapping the environment

  | Bool
otherwise  -- No rule fires
  = do { Logger
logger <- SimplM Logger
forall (m :: * -> *). HasLogger m => m Logger
getLogger
       ; Logger -> SimplM ()
forall {m :: * -> *}. MonadIO m => Logger -> m ()
nodump Logger
logger  -- This ensures that an empty file is written
       ; Maybe (SimplEnv, CoreExpr, SimplCont)
-> SimplM (Maybe (SimplEnv, CoreExpr, SimplCont))
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return Maybe (SimplEnv, CoreExpr, SimplCont)
forall a. Maybe a
Nothing }

  where
    ropts :: RuleOpts
ropts      = SimplEnv -> RuleOpts
seRuleOpts SimplEnv
env
    zapped_env :: SimplEnv
zapped_env = SimplEnv -> SimplEnv
zapSubstEnv SimplEnv
env  -- See Note [zapSubstEnv]

    printRuleModule :: CoreRule -> doc
printRuleModule CoreRule
rule
      = doc -> doc
forall doc. IsLine doc => doc -> doc
parens (doc -> (GenModule Unit -> doc) -> Maybe (GenModule Unit) -> doc
forall b a. b -> (a -> b) -> Maybe a -> b
maybe (String -> doc
forall doc. IsLine doc => String -> doc
text String
"BUILTIN")
                      (ModuleName -> doc
forall doc. IsLine doc => ModuleName -> doc
pprModuleName (ModuleName -> doc)
-> (GenModule Unit -> ModuleName) -> GenModule Unit -> doc
forall b c a. (b -> c) -> (a -> b) -> a -> c
. GenModule Unit -> ModuleName
forall unit. GenModule unit -> ModuleName
moduleName)
                      (CoreRule -> Maybe (GenModule Unit)
ruleModule CoreRule
rule))

    dump :: Logger -> CoreRule -> CoreExpr -> SimplM ()
dump Logger
logger CoreRule
rule CoreExpr
rule_rhs
      | Logger -> DumpFlag -> Bool
logHasDumpFlag Logger
logger DumpFlag
Opt_D_dump_rule_rewrites
      = DumpFlag -> String -> SDoc -> SimplM ()
forall {m :: * -> *}.
(HasLogger m, MonadIO m) =>
DumpFlag -> String -> SDoc -> m ()
log_rule DumpFlag
Opt_D_dump_rule_rewrites String
"Rule fired" (SDoc -> SimplM ()) -> SDoc -> SimplM ()
forall a b. (a -> b) -> a -> b
$ [SDoc] -> SDoc
forall doc. IsDoc doc => [doc] -> doc
vcat
          [ String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"Rule:" SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> FastString -> SDoc
forall doc. IsLine doc => FastString -> doc
ftext (CoreRule -> FastString
ruleName CoreRule
rule)
          , String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"Module:" SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+>  CoreRule -> SDoc
forall {doc}. IsLine doc => CoreRule -> doc
printRuleModule CoreRule
rule
          , String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"Before:" SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> SDoc -> Int -> SDoc -> SDoc
hang (CoreBndr -> SDoc
forall a. Outputable a => a -> SDoc
ppr CoreBndr
fn) Int
2 ([SDoc] -> SDoc
forall doc. IsLine doc => [doc] -> doc
sep ((ArgSpec -> SDoc) -> [ArgSpec] -> [SDoc]
forall a b. (a -> b) -> [a] -> [b]
map ArgSpec -> SDoc
forall a. Outputable a => a -> SDoc
ppr [ArgSpec]
args))
          , String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"After: " SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> SDoc -> Int -> SDoc -> SDoc
hang (CoreExpr -> SDoc
forall b. OutputableBndr b => Expr b -> SDoc
pprCoreExpr CoreExpr
rule_rhs) Int
2
                               ([SDoc] -> SDoc
forall doc. IsLine doc => [doc] -> doc
sep ([SDoc] -> SDoc) -> [SDoc] -> SDoc
forall a b. (a -> b) -> a -> b
$ (ArgSpec -> SDoc) -> [ArgSpec] -> [SDoc]
forall a b. (a -> b) -> [a] -> [b]
map ArgSpec -> SDoc
forall a. Outputable a => a -> SDoc
ppr ([ArgSpec] -> [SDoc]) -> [ArgSpec] -> [SDoc]
forall a b. (a -> b) -> a -> b
$ Int -> [ArgSpec] -> [ArgSpec]
forall a. Int -> [a] -> [a]
drop (CoreRule -> Int
ruleArity CoreRule
rule) [ArgSpec]
args)
          , String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"Cont:  " SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> SimplCont -> SDoc
forall a. Outputable a => a -> SDoc
ppr SimplCont
call_cont ]

      | Logger -> DumpFlag -> Bool
logHasDumpFlag Logger
logger DumpFlag
Opt_D_dump_rule_firings
      = DumpFlag -> String -> SDoc -> SimplM ()
forall {m :: * -> *}.
(HasLogger m, MonadIO m) =>
DumpFlag -> String -> SDoc -> m ()
log_rule DumpFlag
Opt_D_dump_rule_firings String
"Rule fired:" (SDoc -> SimplM ()) -> SDoc -> SimplM ()
forall a b. (a -> b) -> a -> b
$
          FastString -> SDoc
forall doc. IsLine doc => FastString -> doc
ftext (CoreRule -> FastString
ruleName CoreRule
rule)
            SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> CoreRule -> SDoc
forall {doc}. IsLine doc => CoreRule -> doc
printRuleModule CoreRule
rule

      | Bool
otherwise
      = () -> SimplM ()
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return ()

    nodump :: Logger -> m ()
nodump Logger
logger
      | Logger -> DumpFlag -> Bool
logHasDumpFlag Logger
logger DumpFlag
Opt_D_dump_rule_rewrites
      = IO () -> m ()
forall a. IO a -> m a
forall (m :: * -> *) a. MonadIO m => IO a -> m a
liftIO (IO () -> m ()) -> IO () -> m ()
forall a b. (a -> b) -> a -> b
$
          Logger -> DumpFlag -> IO ()
touchDumpFile Logger
logger DumpFlag
Opt_D_dump_rule_rewrites

      | Logger -> DumpFlag -> Bool
logHasDumpFlag Logger
logger DumpFlag
Opt_D_dump_rule_firings
      = IO () -> m ()
forall a. IO a -> m a
forall (m :: * -> *) a. MonadIO m => IO a -> m a
liftIO (IO () -> m ()) -> IO () -> m ()
forall a b. (a -> b) -> a -> b
$
          Logger -> DumpFlag -> IO ()
touchDumpFile Logger
logger DumpFlag
Opt_D_dump_rule_firings

      | Bool
otherwise
      = () -> m ()
forall a. a -> m a
forall (m :: * -> *) a. Monad m => a -> m a
return ()

    log_rule :: DumpFlag -> String -> SDoc -> m ()
log_rule DumpFlag
flag String
hdr SDoc
details
      = do
      { Logger
logger <- m Logger
forall (m :: * -> *). HasLogger m => m Logger
getLogger
      ; IO () -> m ()
forall a. IO a -> m a
forall (m :: * -> *) a. MonadIO m => IO a -> m a
liftIO (IO () -> m ()) -> IO () -> m ()
forall a b. (a -> b) -> a -> b
$ Logger
-> PprStyle -> DumpFlag -> String -> DumpFormat -> SDoc -> IO ()
logDumpFile Logger
logger (NamePprCtx -> PprStyle
mkDumpStyle NamePprCtx
alwaysQualify) DumpFlag
flag String
"" DumpFormat
FormatText
               (SDoc -> IO ()) -> SDoc -> IO ()
forall a b. (a -> b) -> a -> b
$ [SDoc] -> SDoc
forall doc. IsLine doc => [doc] -> doc
sep [String -> SDoc
forall doc. IsLine doc => String -> doc
text String
hdr, Int -> SDoc -> SDoc
nest Int
4 SDoc
details]
      }

trySeqRules :: SimplEnv
            -> OutExpr -> InExpr   -- Scrutinee and RHS
            -> SimplCont
            -> SimplM (Maybe (SimplEnv, CoreExpr, SimplCont))
-- See Note [User-defined RULES for seq]
trySeqRules :: SimplEnv
-> CoreExpr
-> CoreExpr
-> SimplCont
-> SimplM (Maybe (SimplEnv, CoreExpr, SimplCont))
trySeqRules SimplEnv
in_env CoreExpr
scrut CoreExpr
rhs SimplCont
cont
  = do { RuleEnv
rule_base <- SimplM RuleEnv
getSimplRules
       ; SimplEnv
-> [CoreRule]
-> CoreBndr
-> [ArgSpec]
-> SimplCont
-> SimplM (Maybe (SimplEnv, CoreExpr, SimplCont))
tryRules SimplEnv
in_env (RuleEnv -> CoreBndr -> [CoreRule]
getRules RuleEnv
rule_base CoreBndr
seqId) CoreBndr
seqId [ArgSpec]
out_args SimplCont
rule_cont }
  where
    no_cast_scrut :: CoreExpr
no_cast_scrut = CoreExpr -> CoreExpr
forall {b}. Expr b -> Expr b
drop_casts CoreExpr
scrut
    scrut_ty :: Kind
scrut_ty  = (() :: Constraint) => CoreExpr -> Kind
CoreExpr -> Kind
exprType CoreExpr
no_cast_scrut
    seq_id_ty :: Kind
seq_id_ty = CoreBndr -> Kind
idType CoreBndr
seqId                    -- forall r a (b::TYPE r). a -> b -> b
    res1_ty :: Kind
res1_ty   = (() :: Constraint) => Kind -> Kind -> Kind
Kind -> Kind -> Kind
piResultTy Kind
seq_id_ty Kind
rhs_rep    -- forall a (b::TYPE rhs_rep). a -> b -> b
    res2_ty :: Kind
res2_ty   = (() :: Constraint) => Kind -> Kind -> Kind
Kind -> Kind -> Kind
piResultTy Kind
res1_ty   Kind
scrut_ty   -- forall (b::TYPE rhs_rep). scrut_ty -> b -> b
    res3_ty :: Kind
res3_ty   = (() :: Constraint) => Kind -> Kind -> Kind
Kind -> Kind -> Kind
piResultTy Kind
res2_ty   Kind
rhs_ty     -- scrut_ty -> rhs_ty -> rhs_ty
    res4_ty :: Kind
res4_ty   = (() :: Constraint) => Kind -> Kind
Kind -> Kind
funResultTy Kind
res3_ty             -- rhs_ty -> rhs_ty
    rhs_ty :: Kind
rhs_ty    = (() :: Constraint) => SimplEnv -> Kind -> Kind
SimplEnv -> Kind -> Kind
substTy SimplEnv
in_env ((() :: Constraint) => CoreExpr -> Kind
CoreExpr -> Kind
exprType CoreExpr
rhs)
    rhs_rep :: Kind
rhs_rep   = (() :: Constraint) => Kind -> Kind
Kind -> Kind
getRuntimeRep Kind
rhs_ty
    out_args :: [ArgSpec]
out_args  = [ TyArg { as_arg_ty :: Kind
as_arg_ty  = Kind
rhs_rep
                        , as_hole_ty :: Kind
as_hole_ty = Kind
seq_id_ty }
                , TyArg { as_arg_ty :: Kind
as_arg_ty  = Kind
scrut_ty
                        , as_hole_ty :: Kind
as_hole_ty = Kind
res1_ty }
                , TyArg { as_arg_ty :: Kind
as_arg_ty  = Kind
rhs_ty
                        , as_hole_ty :: Kind
as_hole_ty = Kind
res2_ty }
                , ValArg { as_arg :: CoreExpr
as_arg = CoreExpr
no_cast_scrut
                         , as_dmd :: Demand
as_dmd = Demand
seqDmd
                         , as_hole_ty :: Kind
as_hole_ty = Kind
res3_ty } ]
    rule_cont :: SimplCont
rule_cont = ApplyToVal { sc_dup :: DupFlag
sc_dup = DupFlag
NoDup, sc_arg :: CoreExpr
sc_arg = CoreExpr
rhs
                           , sc_env :: SimplEnv
sc_env = SimplEnv
in_env, sc_cont :: SimplCont
sc_cont = SimplCont
cont
                           , sc_hole_ty :: Kind
sc_hole_ty = Kind
res4_ty }

    -- Lazily evaluated, so we don't do most of this

    drop_casts :: Expr b -> Expr b
drop_casts (Cast Expr b
e Coercion
_) = Expr b -> Expr b
drop_casts Expr b
e
    drop_casts Expr b
e          = Expr b
e

{- Note [User-defined RULES for seq]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Given
   case (scrut |> co) of _ -> rhs
look for rules that match the expression
   seq @t1 @t2 scrut
where scrut :: t1
      rhs   :: t2

If you find a match, rewrite it, and apply to 'rhs'.

Notice that we can simply drop casts on the fly here, which
makes it more likely that a rule will match.

See Note [User-defined RULES for seq] in GHC.Types.Id.Make.

Note [Occurrence-analyse after rule firing]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
After firing a rule, we occurrence-analyse the instantiated RHS before
simplifying it.  Usually this doesn't make much difference, but it can
be huge.  Here's an example (simplCore/should_compile/T7785)

  map f (map f (map f xs)

= -- Use build/fold form of map, twice
  map f (build (\cn. foldr (mapFB c f) n
                           (build (\cn. foldr (mapFB c f) n xs))))

= -- Apply fold/build rule
  map f (build (\cn. (\cn. foldr (mapFB c f) n xs) (mapFB c f) n))

= -- Beta-reduce
  -- Alas we have no occurrence-analysed, so we don't know
  -- that c is used exactly once
  map f (build (\cn. let c1 = mapFB c f in
                     foldr (mapFB c1 f) n xs))

= -- Use mapFB rule:   mapFB (mapFB c f) g = mapFB c (f.g)
  -- We can do this because (mapFB c n) is a PAP and hence expandable
  map f (build (\cn. let c1 = mapFB c n in
                     foldr (mapFB c (f.f)) n x))

This is not too bad.  But now do the same with the outer map, and
we get another use of mapFB, and t can interact with /both/ remaining
mapFB calls in the above expression.  This is stupid because actually
that 'c1' binding is dead.  The outer map introduces another c2. If
there is a deep stack of maps we get lots of dead bindings, and lots
of redundant work as we repeatedly simplify the result of firing rules.

The easy thing to do is simply to occurrence analyse the result of
the rule firing.  Note that this occ-anals not only the RHS of the
rule, but also the function arguments, which by now are OutExprs.
E.g.
      RULE f (g x) = x+1

Call   f (g BIG)  -->   (\x. x+1) BIG

The rule binders are lambda-bound and applied to the OutExpr arguments
(here BIG) which lack all internal occurrence info.

Is this inefficient?  Not really: we are about to walk over the result
of the rule firing to simplify it, so occurrence analysis is at most
a constant factor.

Note, however, that the rule RHS is /already/ occ-analysed; see
Note [OccInfo in unfoldings and rules] in GHC.Core.  There is something
unsatisfactory about doing it twice; but the rule RHS is usually very
small, and this is simple.

Note [Optimising tagToEnum#]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
If we have an enumeration data type:

  data Foo = A | B | C

Then we want to transform

   case tagToEnum# x of   ==>    case x of
     A -> e1                       DEFAULT -> e1
     B -> e2                       1#      -> e2
     C -> e3                       2#      -> e3

thereby getting rid of the tagToEnum# altogether.  If there was a DEFAULT
alternative we retain it (remember it comes first).  If not the case must
be exhaustive, and we reflect that in the transformed version by adding
a DEFAULT.  Otherwise Lint complains that the new case is not exhaustive.
See #8317.

Note [Rules for recursive functions]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
You might think that we shouldn't apply rules for a loop breaker:
doing so might give rise to an infinite loop, because a RULE is
rather like an extra equation for the function:
     RULE:           f (g x) y = x+y
     Eqn:            f a     y = a-y

But it's too drastic to disable rules for loop breakers.
Even the foldr/build rule would be disabled, because foldr
is recursive, and hence a loop breaker:
     foldr k z (build g) = g k z
So it's up to the programmer: rules can cause divergence


************************************************************************
*                                                                      *
                Rebuilding a case expression
*                                                                      *
************************************************************************

Note [Case elimination]
~~~~~~~~~~~~~~~~~~~~~~~
The case-elimination transformation discards redundant case expressions.
Start with a simple situation:

        case x# of      ===>   let y# = x# in e
          y# -> e

(when x#, y# are of primitive type, of course).  We can't (in general)
do this for algebraic cases, because we might turn bottom into
non-bottom!

The code in GHC.Core.Opt.Simplify.Utils.prepareAlts has the effect of generalise
this idea to look for a case where we're scrutinising a variable, and we know
that only the default case can match.  For example:

        case x of
          0#      -> ...
          DEFAULT -> ...(case x of
                         0#      -> ...
                         DEFAULT -> ...) ...

Here the inner case is first trimmed to have only one alternative, the
DEFAULT, after which it's an instance of the previous case.  This
really only shows up in eliminating error-checking code.

Note that GHC.Core.Opt.Simplify.Utils.mkCase combines identical RHSs.  So

        case e of       ===> case e of DEFAULT -> r
           True  -> r
           False -> r

Now again the case may be eliminated by the CaseElim transformation.
This includes things like (==# a# b#)::Bool so that we simplify
      case ==# a# b# of { True -> x; False -> x }
to just
      x
This particular example shows up in default methods for
comparison operations (e.g. in (>=) for Int.Int32)

Note [Case to let transformation]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
If a case over a lifted type has a single alternative, and is being
used as a strict 'let' (all isDeadBinder bndrs), we may want to do
this transformation:

    case e of r       ===>   let r = e in ...r...
      _ -> ...r...

We treat the unlifted and lifted cases separately:

* Unlifted case: 'e' satisfies exprOkForSpeculation
  (ok-for-spec is needed to satisfy the let-can-float invariant).
  This turns     case a +# b of r -> ...r...
  into           let r = a +# b in ...r...
  and thence     .....(a +# b)....

  However, if we have
      case indexArray# a i of r -> ...r...
  we might like to do the same, and inline the (indexArray# a i).
  But indexArray# is not okForSpeculation, so we don't build a let
  in rebuildCase (lest it get floated *out*), so the inlining doesn't
  happen either.  Annoying.

* Lifted case: we need to be sure that the expression is already
  evaluated (exprIsHNF).  If it's not already evaluated
      - we risk losing exceptions, divergence or
        user-specified thunk-forcing
      - even if 'e' is guaranteed to converge, we don't want to
        create a thunk (call by need) instead of evaluating it
        right away (call by value)

  However, we can turn the case into a /strict/ let if the 'r' is
  used strictly in the body.  Then we won't lose divergence; and
  we won't build a thunk because the let is strict.
  See also Note [Case-to-let for strictly-used binders]

Note [Case-to-let for strictly-used binders]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
If we have this:
   case <scrut> of r { _ -> ..r.. }

where 'r' is used strictly in (..r..), we can safely transform to
   let r = <scrut> in ...r...

This is a Good Thing, because 'r' might be dead (if the body just
calls error), or might be used just once (in which case it can be
inlined); or we might be able to float the let-binding up or down.
E.g. #15631 has an example.

Note that this can change the error behaviour.  For example, we might
transform
    case x of { _ -> error "bad" }
    --> error "bad"
which is might be puzzling if 'x' currently lambda-bound, but later gets
let-bound to (error "good").

Nevertheless, the paper "A semantics for imprecise exceptions" allows
this transformation. If you want to fix the evaluation order, use
'pseq'.  See #8900 for an example where the loss of this
transformation bit us in practice.

See also Note [Empty case alternatives] in GHC.Core.

Historical notes

There have been various earlier versions of this patch:

* By Sept 18 the code looked like this:
     || scrut_is_demanded_var scrut

    scrut_is_demanded_var :: CoreExpr -> Bool
    scrut_is_demanded_var (Cast s _) = scrut_is_demanded_var s
    scrut_is_demanded_var (Var _)    = isStrUsedDmd (idDemandInfo case_bndr)
    scrut_is_demanded_var _          = False

  This only fired if the scrutinee was a /variable/, which seems
  an unnecessary restriction. So in #15631 I relaxed it to allow
  arbitrary scrutinees.  Less code, less to explain -- but the change
  had 0.00% effect on nofib.

* Previously, in Jan 13 the code looked like this:
     || case_bndr_evald_next rhs

    case_bndr_evald_next :: CoreExpr -> Bool
      -- See Note [Case binder next]
    case_bndr_evald_next (Var v)         = v == case_bndr
    case_bndr_evald_next (Cast e _)      = case_bndr_evald_next e
    case_bndr_evald_next (App e _)       = case_bndr_evald_next e
    case_bndr_evald_next (Case e _ _ _)  = case_bndr_evald_next e
    case_bndr_evald_next _               = False

  This patch was part of fixing #7542. See also
  Note [Eta reduction soundness], criterion (E) in GHC.Core.Utils.)


Further notes about case elimination
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider:       test :: Integer -> IO ()
                test = print

Turns out that this compiles to:
    Print.test
      = \ eta :: Integer
          eta1 :: Void# ->
          case PrelNum.< eta PrelNum.zeroInteger of wild { __DEFAULT ->
          case hPutStr stdout
                 (PrelNum.jtos eta ($w[] @ Char))
                 eta1
          of wild1 { (# new_s, a4 #) -> PrelIO.lvl23 new_s  }}

Notice the strange '<' which has no effect at all. This is a funny one.
It started like this:

f x y = if x < 0 then jtos x
          else if y==0 then "" else jtos x

At a particular call site we have (f v 1).  So we inline to get

        if v < 0 then jtos x
        else if 1==0 then "" else jtos x

Now simplify the 1==0 conditional:

        if v<0 then jtos v else jtos v

Now common-up the two branches of the case:

        case (v<0) of DEFAULT -> jtos v

Why don't we drop the case?  Because it's strict in v.  It's technically
wrong to drop even unnecessary evaluations, and in practice they
may be a result of 'seq' so we *definitely* don't want to drop those.
I don't really know how to improve this situation.


Note [FloatBinds from constructor wrappers]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
If we have FloatBinds coming from the constructor wrapper
(as in Note [exprIsConApp_maybe on data constructors with wrappers]),
we cannot float past them. We'd need to float the FloatBind
together with the simplify floats, unfortunately the
simplifier doesn't have case-floats. The simplest thing we can
do is to wrap all the floats here. The next iteration of the
simplifier will take care of all these cases and lets.

Given data T = MkT !Bool, this allows us to simplify
case $WMkT b of { MkT x -> f x }
to
case b of { b' -> f b' }.

We could try and be more clever (like maybe wfloats only contain
let binders, so we could float them). But the need for the
extra complication is not clear.

Note [Do not duplicate constructor applications]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider this (#20125)
   let x = (a,b)
   in ...(case x of x' -> blah)...x...x...

We want that `case` to vanish (since `x` is bound to a data con) leaving
   let x = (a,b)
   in ...(let x'=x in blah)...x..x...

In rebuildCase, `exprIsConApp_maybe` will succeed on the scrutinee `x`,
since is bound to (a,b).  But in eliminating the case, if the scrutinee
is trivial, we want to bind the case-binder to the scrutinee, /not/ to
the constructor application.  Hence the case_bndr_rhs in rebuildCase.

This applies equally to a non-DEFAULT case alternative, say
   let x = (a,b) in ...(case x of x' { (p,q) -> blah })...
This variant is handled by bind_case_bndr in knownCon.

We want to bind x' to x, and not to a duplicated (a,b)).
-}

---------------------------------------------------------
--      Eliminate the case if possible

rebuildCase, reallyRebuildCase
   :: SimplEnv
   -> OutExpr          -- Scrutinee
   -> InId             -- Case binder
   -> [InAlt]          -- Alternatives (increasing order)
   -> SimplCont
   -> SimplM (SimplFloats, OutExpr)

--------------------------------------------------
--      1. Eliminate the case if there's a known constructor
--------------------------------------------------

rebuildCase :: SimplEnv
-> CoreExpr
-> CoreBndr
-> [Alt CoreBndr]
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
rebuildCase SimplEnv
env CoreExpr
scrut CoreBndr
case_bndr [Alt CoreBndr]
alts SimplCont
cont
  | Lit Literal
lit <- CoreExpr
scrut    -- No need for same treatment as constructors
                        -- because literals are inlined more vigorously
  , Bool -> Bool
not (Literal -> Bool
litIsLifted Literal
lit)
  = do  { Tick -> SimplM ()
tick (CoreBndr -> Tick
KnownBranch CoreBndr
case_bndr)
        ; case AltCon -> [Alt CoreBndr] -> Maybe (Alt CoreBndr)
forall b. AltCon -> [Alt b] -> Maybe (Alt b)
findAlt (Literal -> AltCon
LitAlt Literal
lit) [Alt CoreBndr]
alts of
            Maybe (Alt CoreBndr)
Nothing             -> SimplEnv
-> CoreBndr
-> [Alt CoreBndr]
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
missingAlt SimplEnv
env CoreBndr
case_bndr [Alt CoreBndr]
alts SimplCont
cont
            Just (Alt AltCon
_ [CoreBndr]
bs CoreExpr
rhs) -> SimplEnv
-> [FloatBind]
-> CoreExpr
-> [CoreBndr]
-> CoreExpr
-> SimplM (SimplFloats, CoreExpr)
simple_rhs SimplEnv
env [] CoreExpr
scrut [CoreBndr]
bs CoreExpr
rhs }

  | Just (InScopeSet
in_scope', [FloatBind]
wfloats, DataCon
con, [Kind]
ty_args, [CoreExpr]
other_args)
      <- (() :: Constraint) =>
InScopeEnv
-> CoreExpr
-> Maybe (InScopeSet, [FloatBind], DataCon, [Kind], [CoreExpr])
InScopeEnv
-> CoreExpr
-> Maybe (InScopeSet, [FloatBind], DataCon, [Kind], [CoreExpr])
exprIsConApp_maybe (SimplEnv -> InScopeEnv
getUnfoldingInRuleMatch SimplEnv
env) CoreExpr
scrut
        -- Works when the scrutinee is a variable with a known unfolding
        -- as well as when it's an explicit constructor application
  , let env0 :: SimplEnv
env0 = SimplEnv -> InScopeSet -> SimplEnv
setInScopeSet SimplEnv
env InScopeSet
in_scope'
  = do  { Tick -> SimplM ()
tick (CoreBndr -> Tick
KnownBranch CoreBndr
case_bndr)
        ; let scaled_wfloats :: [FloatBind]
scaled_wfloats = (FloatBind -> FloatBind) -> [FloatBind] -> [FloatBind]
forall a b. (a -> b) -> [a] -> [b]
map FloatBind -> FloatBind
scale_float [FloatBind]
wfloats
              -- case_bndr_unf: see Note [Do not duplicate constructor applications]
              case_bndr_rhs :: CoreExpr
case_bndr_rhs | CoreExpr -> Bool
exprIsTrivial CoreExpr
scrut = CoreExpr
scrut
                            | Bool
otherwise           = CoreExpr
con_app
              con_app :: CoreExpr
con_app = CoreBndr -> CoreExpr
forall b. CoreBndr -> Expr b
Var (DataCon -> CoreBndr
dataConWorkId DataCon
con) CoreExpr -> [Kind] -> CoreExpr
forall b. Expr b -> [Kind] -> Expr b
`mkTyApps` [Kind]
ty_args
                                                CoreExpr -> [CoreExpr] -> CoreExpr
forall b. Expr b -> [Expr b] -> Expr b
`mkApps`   [CoreExpr]
other_args
        ; case AltCon -> [Alt CoreBndr] -> Maybe (Alt CoreBndr)
forall b. AltCon -> [Alt b] -> Maybe (Alt b)
findAlt (DataCon -> AltCon
DataAlt DataCon
con) [Alt CoreBndr]
alts of
            Maybe (Alt CoreBndr)
Nothing                   -> SimplEnv
-> CoreBndr
-> [Alt CoreBndr]
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
missingAlt SimplEnv
env0 CoreBndr
case_bndr [Alt CoreBndr]
alts SimplCont
cont
            Just (Alt AltCon
DEFAULT [CoreBndr]
bs CoreExpr
rhs) -> SimplEnv
-> [FloatBind]
-> CoreExpr
-> [CoreBndr]
-> CoreExpr
-> SimplM (SimplFloats, CoreExpr)
simple_rhs SimplEnv
env0 [FloatBind]
scaled_wfloats CoreExpr
case_bndr_rhs [CoreBndr]
bs CoreExpr
rhs
            Just (Alt AltCon
_       [CoreBndr]
bs CoreExpr
rhs) -> SimplEnv
-> CoreExpr
-> [FloatBind]
-> DataCon
-> [Kind]
-> [CoreExpr]
-> CoreBndr
-> [CoreBndr]
-> CoreExpr
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
knownCon SimplEnv
env0 CoreExpr
scrut [FloatBind]
scaled_wfloats DataCon
con [Kind]
ty_args
                                                  [CoreExpr]
other_args CoreBndr
case_bndr [CoreBndr]
bs CoreExpr
rhs SimplCont
cont
        }
  where
    simple_rhs :: SimplEnv
-> [FloatBind]
-> CoreExpr
-> [CoreBndr]
-> CoreExpr
-> SimplM (SimplFloats, CoreExpr)
simple_rhs SimplEnv
env [FloatBind]
wfloats CoreExpr
case_bndr_rhs [CoreBndr]
bs CoreExpr
rhs =
      Bool
-> SimplM (SimplFloats, CoreExpr) -> SimplM (SimplFloats, CoreExpr)
forall a. HasCallStack => Bool -> a -> a
assert ([CoreBndr] -> Bool
forall a. [a] -> Bool
forall (t :: * -> *) a. Foldable t => t a -> Bool
null [CoreBndr]
bs) (SimplM (SimplFloats, CoreExpr) -> SimplM (SimplFloats, CoreExpr))
-> SimplM (SimplFloats, CoreExpr) -> SimplM (SimplFloats, CoreExpr)
forall a b. (a -> b) -> a -> b
$
      do { (SimplFloats
floats1, SimplEnv
env') <- SimplEnv -> CoreBndr -> CoreExpr -> SimplM (SimplFloats, SimplEnv)
simplAuxBind SimplEnv
env CoreBndr
case_bndr CoreExpr
case_bndr_rhs
             -- scrut is a constructor application,
             -- hence satisfies let-can-float invariant
         ; (SimplFloats
floats2, CoreExpr
expr') <- SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF SimplEnv
env' CoreExpr
rhs SimplCont
cont
         ; case [FloatBind]
wfloats of
             [] -> (SimplFloats, CoreExpr) -> SimplM (SimplFloats, CoreExpr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplFloats
floats1 SimplFloats -> SimplFloats -> SimplFloats
`addFloats` SimplFloats
floats2, CoreExpr
expr')
             [FloatBind]
_ -> (SimplFloats, CoreExpr) -> SimplM (SimplFloats, CoreExpr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return
               -- See Note [FloatBinds from constructor wrappers]
                   ( SimplEnv -> SimplFloats
emptyFloats SimplEnv
env,
                     [FloatBind] -> CoreExpr -> CoreExpr
GHC.Core.Make.wrapFloats [FloatBind]
wfloats (CoreExpr -> CoreExpr) -> CoreExpr -> CoreExpr
forall a b. (a -> b) -> a -> b
$
                     SimplFloats -> CoreExpr -> CoreExpr
wrapFloats (SimplFloats
floats1 SimplFloats -> SimplFloats -> SimplFloats
`addFloats` SimplFloats
floats2) CoreExpr
expr' )}

    -- This scales case floats by the multiplicity of the continuation hole (see
    -- Note [Scaling in case-of-case]).  Let floats are _not_ scaled, because
    -- they are aliases anyway.
    scale_float :: FloatBind -> FloatBind
scale_float (GHC.Core.Make.FloatCase CoreExpr
scrut CoreBndr
case_bndr AltCon
con [CoreBndr]
vars) =
      let
        scale_id :: CoreBndr -> CoreBndr
scale_id CoreBndr
id = Kind -> CoreBndr -> CoreBndr
scaleVarBy Kind
holeScaling CoreBndr
id
      in
      CoreExpr -> CoreBndr -> AltCon -> [CoreBndr] -> FloatBind
GHC.Core.Make.FloatCase CoreExpr
scrut (CoreBndr -> CoreBndr
scale_id CoreBndr
case_bndr) AltCon
con ((CoreBndr -> CoreBndr) -> [CoreBndr] -> [CoreBndr]
forall a b. (a -> b) -> [a] -> [b]
map CoreBndr -> CoreBndr
scale_id [CoreBndr]
vars)
    scale_float FloatBind
f = FloatBind
f

    holeScaling :: Kind
holeScaling = SimplCont -> Kind
contHoleScaling SimplCont
cont Kind -> Kind -> Kind
`mkMultMul` CoreBndr -> Kind
idMult CoreBndr
case_bndr
     -- We are in the following situation
     --   case[p] case[q] u of { D x -> C v } of { C x -> w }
     -- And we are producing case[??] u of { D x -> w[x\v]}
     --
     -- What should the multiplicity `??` be? In order to preserve the usage of
     -- variables in `u`, it needs to be `pq`.
     --
     -- As an illustration, consider the following
     --   case[Many] case[1] of { C x -> C x } of { C x -> (x, x) }
     -- Where C :: A %1 -> T is linear
     -- If we were to produce a case[1], like the inner case, we would get
     --   case[1] of { C x -> (x, x) }
     -- Which is ill-typed with respect to linearity. So it needs to be a
     -- case[Many].

--------------------------------------------------
--      2. Eliminate the case if scrutinee is evaluated
--------------------------------------------------

rebuildCase SimplEnv
env CoreExpr
scrut CoreBndr
case_bndr alts :: [Alt CoreBndr]
alts@[Alt AltCon
_ [CoreBndr]
bndrs CoreExpr
rhs] SimplCont
cont
  -- See if we can get rid of the case altogether
  -- See Note [Case elimination]
  -- mkCase made sure that if all the alternatives are equal,
  -- then there is now only one (DEFAULT) rhs

  -- 2a.  Dropping the case altogether, if
  --      a) it binds nothing (so it's really just a 'seq')
  --      b) evaluating the scrutinee has no side effects
  | Bool
is_plain_seq
  , CoreExpr -> Bool
exprOkForSideEffects CoreExpr
scrut
          -- The entire case is dead, so we can drop it
          -- if the scrutinee converges without having imperative
          -- side effects or raising a Haskell exception
          -- See Note [PrimOp can_fail and has_side_effects] in GHC.Builtin.PrimOps
   = SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF SimplEnv
env CoreExpr
rhs SimplCont
cont

  -- 2b.  Turn the case into a let, if
  --      a) it binds only the case-binder
  --      b) unlifted case: the scrutinee is ok-for-speculation
  --           lifted case: the scrutinee is in HNF (or will later be demanded)
  -- See Note [Case to let transformation]
  | Bool
all_dead_bndrs
  , CoreExpr -> CoreBndr -> Bool
doCaseToLet CoreExpr
scrut CoreBndr
case_bndr
  = do { Tick -> SimplM ()
tick (CoreBndr -> Tick
CaseElim CoreBndr
case_bndr)
       ; (SimplFloats
floats1, SimplEnv
env')  <- SimplEnv -> CoreBndr -> CoreExpr -> SimplM (SimplFloats, SimplEnv)
simplAuxBind SimplEnv
env CoreBndr
case_bndr CoreExpr
scrut
       ; (SimplFloats
floats2, CoreExpr
expr') <- SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF SimplEnv
env' CoreExpr
rhs SimplCont
cont
       ; (SimplFloats, CoreExpr) -> SimplM (SimplFloats, CoreExpr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplFloats
floats1 SimplFloats -> SimplFloats -> SimplFloats
`addFloats` SimplFloats
floats2, CoreExpr
expr') }

  -- 2c. Try the seq rules if
  --     a) it binds only the case binder
  --     b) a rule for seq applies
  -- See Note [User-defined RULES for seq] in GHC.Types.Id.Make
  | Bool
is_plain_seq
  = do { Maybe (SimplEnv, CoreExpr, SimplCont)
mb_rule <- SimplEnv
-> CoreExpr
-> CoreExpr
-> SimplCont
-> SimplM (Maybe (SimplEnv, CoreExpr, SimplCont))
trySeqRules SimplEnv
env CoreExpr
scrut CoreExpr
rhs SimplCont
cont
       ; case Maybe (SimplEnv, CoreExpr, SimplCont)
mb_rule of
           Just (SimplEnv
env', CoreExpr
rule_rhs, SimplCont
cont') -> SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF SimplEnv
env' CoreExpr
rule_rhs SimplCont
cont'
           Maybe (SimplEnv, CoreExpr, SimplCont)
Nothing                      -> SimplEnv
-> CoreExpr
-> CoreBndr
-> [Alt CoreBndr]
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
reallyRebuildCase SimplEnv
env CoreExpr
scrut CoreBndr
case_bndr [Alt CoreBndr]
alts SimplCont
cont }
  where
    all_dead_bndrs :: Bool
all_dead_bndrs = (CoreBndr -> Bool) -> [CoreBndr] -> Bool
forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
all CoreBndr -> Bool
isDeadBinder [CoreBndr]
bndrs       -- bndrs are [InId]
    is_plain_seq :: Bool
is_plain_seq   = Bool
all_dead_bndrs Bool -> Bool -> Bool
&& CoreBndr -> Bool
isDeadBinder CoreBndr
case_bndr -- Evaluation *only* for effect

rebuildCase SimplEnv
env CoreExpr
scrut CoreBndr
case_bndr [Alt CoreBndr]
alts SimplCont
cont
  = SimplEnv
-> CoreExpr
-> CoreBndr
-> [Alt CoreBndr]
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
reallyRebuildCase SimplEnv
env CoreExpr
scrut CoreBndr
case_bndr [Alt CoreBndr]
alts SimplCont
cont


doCaseToLet :: OutExpr          -- Scrutinee
            -> InId             -- Case binder
            -> Bool
-- The situation is         case scrut of b { DEFAULT -> body }
-- Can we transform thus?   let { b = scrut } in body
doCaseToLet :: CoreExpr -> CoreBndr -> Bool
doCaseToLet CoreExpr
scrut CoreBndr
case_bndr
  | CoreBndr -> Bool
isTyCoVar CoreBndr
case_bndr    -- Respect GHC.Core
  = CoreExpr -> Bool
forall {b}. Expr b -> Bool
isTyCoArg CoreExpr
scrut        -- Note [Core type and coercion invariant]

  | (() :: Constraint) => Kind -> Bool
Kind -> Bool
isUnliftedType ((() :: Constraint) => CoreExpr -> Kind
CoreExpr -> Kind
exprType CoreExpr
scrut)
    -- We can call isUnliftedType here: scrutinees always have a fixed RuntimeRep (see FRRCase).
    -- Note however that we must check 'scrut' (which is an 'OutExpr') and not 'case_bndr'
    -- (which is an 'InId'): see Note [Dark corner with representation polymorphism].
    -- Using `exprType` is typically cheap because `scrut` is typically a variable.
    -- We could instead use mightBeUnliftedType (idType case_bndr), but that hurts
    -- the brain more.  Consider that if this test ever turns out to be a perf
    -- problem (which seems unlikely).
  = CoreExpr -> Bool
exprOkForSpeculation CoreExpr
scrut

  | Bool
otherwise  -- Scrut has a lifted type
  = CoreExpr -> Bool
exprIsHNF CoreExpr
scrut
    Bool -> Bool -> Bool
|| Demand -> Bool
isStrUsedDmd (CoreBndr -> Demand
idDemandInfo CoreBndr
case_bndr)
    -- See Note [Case-to-let for strictly-used binders]

--------------------------------------------------
--      3. Catch-all case
--------------------------------------------------

reallyRebuildCase :: SimplEnv
-> CoreExpr
-> CoreBndr
-> [Alt CoreBndr]
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
reallyRebuildCase SimplEnv
env CoreExpr
scrut CoreBndr
case_bndr [Alt CoreBndr]
alts SimplCont
cont
  | Bool -> Bool
not (SimplEnv -> Bool
seCaseCase SimplEnv
env)
  = do { CoreExpr
case_expr <- SimplEnv
-> CoreExpr
-> CoreBndr
-> [Alt CoreBndr]
-> SimplCont
-> SimplM CoreExpr
simplAlts SimplEnv
env CoreExpr
scrut CoreBndr
case_bndr [Alt CoreBndr]
alts
                                (Kind -> SimplCont
mkBoringStop (SimplCont -> Kind
contHoleType SimplCont
cont))
       ; SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
rebuild SimplEnv
env CoreExpr
case_expr SimplCont
cont }

  | Bool
otherwise
  = do { (SimplFloats
floats, SimplEnv
env', SimplCont
cont') <- SimplEnv
-> [Alt CoreBndr]
-> SimplCont
-> SimplM (SimplFloats, SimplEnv, SimplCont)
mkDupableCaseCont SimplEnv
env [Alt CoreBndr]
alts SimplCont
cont
       ; CoreExpr
case_expr <- SimplEnv
-> CoreExpr
-> CoreBndr
-> [Alt CoreBndr]
-> SimplCont
-> SimplM CoreExpr
simplAlts SimplEnv
env' CoreExpr
scrut
                                (Kind -> CoreBndr -> CoreBndr
scaleIdBy Kind
holeScaling CoreBndr
case_bndr)
                                (Kind -> [Alt CoreBndr] -> [Alt CoreBndr]
scaleAltsBy Kind
holeScaling [Alt CoreBndr]
alts)
                                SimplCont
cont'
       ; (SimplFloats, CoreExpr) -> SimplM (SimplFloats, CoreExpr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplFloats
floats, CoreExpr
case_expr) }
  where
    holeScaling :: Kind
holeScaling = SimplCont -> Kind
contHoleScaling SimplCont
cont
    -- Note [Scaling in case-of-case]

{-
simplCaseBinder checks whether the scrutinee is a variable, v.  If so,
try to eliminate uses of v in the RHSs in favour of case_bndr; that
way, there's a chance that v will now only be used once, and hence
inlined.

Historical note: we use to do the "case binder swap" in the Simplifier
so there were additional complications if the scrutinee was a variable.
Now the binder-swap stuff is done in the occurrence analyser; see
"GHC.Core.Opt.OccurAnal" Note [Binder swap].

Note [knownCon occ info]
~~~~~~~~~~~~~~~~~~~~~~~~
If the case binder is not dead, then neither are the pattern bound
variables:
        case <any> of x { (a,b) ->
        case x of { (p,q) -> p } }
Here (a,b) both look dead, but come alive after the inner case is eliminated.
The point is that we bring into the envt a binding
        let x = (a,b)
after the outer case, and that makes (a,b) alive.  At least we do unless
the case binder is guaranteed dead.

Note [Case alternative occ info]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
When we are simply reconstructing a case (the common case), we always
zap the occurrence info on the binders in the alternatives.  Even
if the case binder is dead, the scrutinee is usually a variable, and *that*
can bring the case-alternative binders back to life.
See Note [Add unfolding for scrutinee]

Note [Improving seq]
~~~~~~~~~~~~~~~~~~~
Consider
        type family F :: * -> *
        type instance F Int = Int

We'd like to transform
        case e of (x :: F Int) { DEFAULT -> rhs }
===>
        case e `cast` co of (x'::Int)
           I# x# -> let x = x' `cast` sym co
                    in rhs

so that 'rhs' can take advantage of the form of x'.  Notice that Note
[Case of cast] (in OccurAnal) may then apply to the result.

We'd also like to eliminate empty types (#13468). So if

    data Void
    type instance F Bool = Void

then we'd like to transform
        case (x :: F Bool) of { _ -> error "urk" }
===>
        case (x |> co) of (x' :: Void) of {}

Nota Bene: we used to have a built-in rule for 'seq' that dropped
casts, so that
    case (x |> co) of { _ -> blah }
dropped the cast; in order to improve the chances of trySeqRules
firing.  But that works in the /opposite/ direction to Note [Improving
seq] so there's a danger of flip/flopping.  Better to make trySeqRules
insensitive to the cast, which is now is.

The need for [Improving seq] showed up in Roman's experiments.  Example:
  foo :: F Int -> Int -> Int
  foo t n = t `seq` bar n
     where
       bar 0 = 0
       bar n = bar (n - case t of TI i -> i)
Here we'd like to avoid repeated evaluating t inside the loop, by
taking advantage of the `seq`.

At one point I did transformation in LiberateCase, but it's more
robust here.  (Otherwise, there's a danger that we'll simply drop the
'seq' altogether, before LiberateCase gets to see it.)

Note [Scaling in case-of-case]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

When two cases commute, if done naively, the multiplicities will be wrong:

  case (case u of w[1] { (x[1], y[1]) } -> f x y) of w'[Many]
  { (z[Many], t[Many]) -> z
  }

The multiplicities here, are correct, but if I perform a case of case:

  case u of w[1]
  { (x[1], y[1]) -> case f x y of w'[Many] of { (z[Many], t[Many]) -> z }
  }

This is wrong! Using `f x y` inside a `case … of w'[Many]` means that `x` and
`y` must have multiplicities `Many` not `1`! The correct solution is to make
all the `1`-s be `Many`-s instead:

  case u of w[Many]
  { (x[Many], y[Many]) -> case f x y of w'[Many] of { (z[Many], t[Many]) -> z }
  }

In general, when commuting two cases, the rule has to be:

  case (case … of x[p] {…}) of y[q] { … }
  ===> case … of x[p*q] { … case … of y[q] { … } }

This is materialised, in the simplifier, by the fact that every time we simplify
case alternatives with a continuation (the surrounded case (or more!)), we must
scale the entire case we are simplifying, by a scaling factor which can be
computed in the continuation (with function `contHoleScaling`).
-}

simplAlts :: SimplEnv
          -> OutExpr         -- Scrutinee
          -> InId            -- Case binder
          -> [InAlt]         -- Non-empty
          -> SimplCont
          -> SimplM OutExpr  -- Returns the complete simplified case expression

simplAlts :: SimplEnv
-> CoreExpr
-> CoreBndr
-> [Alt CoreBndr]
-> SimplCont
-> SimplM CoreExpr
simplAlts SimplEnv
env0 CoreExpr
scrut CoreBndr
case_bndr [Alt CoreBndr]
alts SimplCont
cont'
  = do  { String -> SDoc -> SimplM ()
traceSmpl String
"simplAlts" ([SDoc] -> SDoc
forall doc. IsDoc doc => [doc] -> doc
vcat [ CoreBndr -> SDoc
forall a. Outputable a => a -> SDoc
ppr CoreBndr
case_bndr
                                      , String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"cont':" SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> SimplCont -> SDoc
forall a. Outputable a => a -> SDoc
ppr SimplCont
cont'
                                      , String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"in_scope" SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> InScopeSet -> SDoc
forall a. Outputable a => a -> SDoc
ppr (SimplEnv -> InScopeSet
seInScope SimplEnv
env0) ])
        ; (SimplEnv
env1, CoreBndr
case_bndr1) <- SimplEnv -> CoreBndr -> SimplM (SimplEnv, CoreBndr)
simplBinder SimplEnv
env0 CoreBndr
case_bndr
        ; let case_bndr2 :: CoreBndr
case_bndr2 = CoreBndr
case_bndr1 CoreBndr -> Unfolding -> CoreBndr
`setIdUnfolding` Unfolding
evaldUnfolding
              env2 :: SimplEnv
env2       = SimplEnv -> CoreBndr -> SimplEnv
modifyInScope SimplEnv
env1 CoreBndr
case_bndr2
              -- See Note [Case binder evaluated-ness]
              fam_envs :: (FamInstEnv, FamInstEnv)
fam_envs   = SimplEnv -> (FamInstEnv, FamInstEnv)
seFamEnvs SimplEnv
env0

        ; (SimplEnv
alt_env', CoreExpr
scrut', CoreBndr
case_bndr') <- (FamInstEnv, FamInstEnv)
-> SimplEnv
-> CoreExpr
-> CoreBndr
-> CoreBndr
-> [Alt CoreBndr]
-> SimplM (SimplEnv, CoreExpr, CoreBndr)
improveSeq (FamInstEnv, FamInstEnv)
fam_envs SimplEnv
env2 CoreExpr
scrut
                                                       CoreBndr
case_bndr CoreBndr
case_bndr2 [Alt CoreBndr]
alts

        ; ([AltCon]
imposs_deflt_cons, [Alt CoreBndr]
in_alts) <- CoreExpr
-> CoreBndr -> [Alt CoreBndr] -> SimplM ([AltCon], [Alt CoreBndr])
prepareAlts CoreExpr
scrut' CoreBndr
case_bndr [Alt CoreBndr]
alts
          -- NB: it's possible that the returned in_alts is empty: this is handled
          --     by the caller (rebuildCase) in the missingAlt function
          -- NB: pass case_bndr::InId, not case_bndr' :: OutId, to prepareAlts
          --     See Note [Shadowing in prepareAlts] in GHC.Core.Opt.Simplify.Utils

        ; [Alt CoreBndr]
alts' <- (Alt CoreBndr -> SimplM (Alt CoreBndr))
-> [Alt CoreBndr] -> SimplM [Alt CoreBndr]
forall (t :: * -> *) (m :: * -> *) a b.
(Traversable t, Monad m) =>
(a -> m b) -> t a -> m (t b)
forall (m :: * -> *) a b. Monad m => (a -> m b) -> [a] -> m [b]
mapM (SimplEnv
-> Maybe CoreExpr
-> [AltCon]
-> CoreBndr
-> SimplCont
-> Alt CoreBndr
-> SimplM (Alt CoreBndr)
simplAlt SimplEnv
alt_env' (CoreExpr -> Maybe CoreExpr
forall a. a -> Maybe a
Just CoreExpr
scrut') [AltCon]
imposs_deflt_cons CoreBndr
case_bndr' SimplCont
cont') [Alt CoreBndr]
in_alts
--      ; pprTrace "simplAlts" (ppr case_bndr $$ ppr alts $$ ppr cont') $ return ()

        ; let alts_ty' :: Kind
alts_ty' = SimplCont -> Kind
contResultType SimplCont
cont'
        -- See Note [Avoiding space leaks in OutType]
        ; Kind -> ()
seqType Kind
alts_ty' () -> SimplM CoreExpr -> SimplM CoreExpr
forall a b. a -> b -> b
`seq`
          SimplMode
-> CoreExpr
-> CoreBndr
-> Kind
-> [Alt CoreBndr]
-> SimplM CoreExpr
mkCase (SimplEnv -> SimplMode
seMode SimplEnv
env0) CoreExpr
scrut' CoreBndr
case_bndr' Kind
alts_ty' [Alt CoreBndr]
alts' }


------------------------------------
improveSeq :: (FamInstEnv, FamInstEnv) -> SimplEnv
           -> OutExpr -> InId -> OutId -> [InAlt]
           -> SimplM (SimplEnv, OutExpr, OutId)
-- Note [Improving seq]
improveSeq :: (FamInstEnv, FamInstEnv)
-> SimplEnv
-> CoreExpr
-> CoreBndr
-> CoreBndr
-> [Alt CoreBndr]
-> SimplM (SimplEnv, CoreExpr, CoreBndr)
improveSeq (FamInstEnv, FamInstEnv)
fam_envs SimplEnv
env CoreExpr
scrut CoreBndr
case_bndr CoreBndr
case_bndr1 [Alt AltCon
DEFAULT [CoreBndr]
_ CoreExpr
_]
  | Just (Reduction Coercion
co Kind
ty2) <- (FamInstEnv, FamInstEnv) -> Kind -> Maybe Reduction
topNormaliseType_maybe (FamInstEnv, FamInstEnv)
fam_envs (CoreBndr -> Kind
idType CoreBndr
case_bndr1)
  = do { CoreBndr
case_bndr2 <- FastString -> Kind -> Kind -> SimplM CoreBndr
newId (String -> FastString
fsLit String
"nt") Kind
ManyTy Kind
ty2
        ; let rhs :: SimplSR
rhs  = CoreExpr -> Maybe Int -> SimplSR
DoneEx (CoreBndr -> CoreExpr
forall b. CoreBndr -> Expr b
Var CoreBndr
case_bndr2 CoreExpr -> Coercion -> CoreExpr
forall b. Expr b -> Coercion -> Expr b
`Cast` Coercion -> Coercion
mkSymCo Coercion
co) Maybe Int
forall a. Maybe a
Nothing
              env2 :: SimplEnv
env2 = SimplEnv -> CoreBndr -> SimplSR -> SimplEnv
extendIdSubst SimplEnv
env CoreBndr
case_bndr SimplSR
rhs
        ; (SimplEnv, CoreExpr, CoreBndr)
-> SimplM (SimplEnv, CoreExpr, CoreBndr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplEnv
env2, CoreExpr
scrut CoreExpr -> Coercion -> CoreExpr
forall b. Expr b -> Coercion -> Expr b
`Cast` Coercion
co, CoreBndr
case_bndr2) }

improveSeq (FamInstEnv, FamInstEnv)
_ SimplEnv
env CoreExpr
scrut CoreBndr
_ CoreBndr
case_bndr1 [Alt CoreBndr]
_
  = (SimplEnv, CoreExpr, CoreBndr)
-> SimplM (SimplEnv, CoreExpr, CoreBndr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplEnv
env, CoreExpr
scrut, CoreBndr
case_bndr1)


------------------------------------
simplAlt :: SimplEnv
         -> Maybe OutExpr  -- The scrutinee
         -> [AltCon]       -- These constructors can't be present when
                           -- matching the DEFAULT alternative
         -> OutId          -- The case binder
         -> SimplCont
         -> InAlt
         -> SimplM OutAlt

simplAlt :: SimplEnv
-> Maybe CoreExpr
-> [AltCon]
-> CoreBndr
-> SimplCont
-> Alt CoreBndr
-> SimplM (Alt CoreBndr)
simplAlt SimplEnv
env Maybe CoreExpr
_ [AltCon]
imposs_deflt_cons CoreBndr
case_bndr' SimplCont
cont' (Alt AltCon
DEFAULT [CoreBndr]
bndrs CoreExpr
rhs)
  = Bool -> SimplM (Alt CoreBndr) -> SimplM (Alt CoreBndr)
forall a. HasCallStack => Bool -> a -> a
assert ([CoreBndr] -> Bool
forall a. [a] -> Bool
forall (t :: * -> *) a. Foldable t => t a -> Bool
null [CoreBndr]
bndrs) (SimplM (Alt CoreBndr) -> SimplM (Alt CoreBndr))
-> SimplM (Alt CoreBndr) -> SimplM (Alt CoreBndr)
forall a b. (a -> b) -> a -> b
$
    do  { let env' :: SimplEnv
env' = SimplEnv -> CoreBndr -> Unfolding -> SimplEnv
addBinderUnfolding SimplEnv
env CoreBndr
case_bndr'
                                        ([AltCon] -> Unfolding
mkOtherCon [AltCon]
imposs_deflt_cons)
                -- Record the constructors that the case-binder *can't* be.
        ; CoreExpr
rhs' <- SimplEnv -> CoreExpr -> SimplCont -> SimplM CoreExpr
simplExprC SimplEnv
env' CoreExpr
rhs SimplCont
cont'
        ; Alt CoreBndr -> SimplM (Alt CoreBndr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (AltCon -> [CoreBndr] -> CoreExpr -> Alt CoreBndr
forall b. AltCon -> [b] -> Expr b -> Alt b
Alt AltCon
DEFAULT [] CoreExpr
rhs') }

simplAlt SimplEnv
env Maybe CoreExpr
scrut' [AltCon]
_ CoreBndr
case_bndr' SimplCont
cont' (Alt (LitAlt Literal
lit) [CoreBndr]
bndrs CoreExpr
rhs)
  = Bool -> SimplM (Alt CoreBndr) -> SimplM (Alt CoreBndr)
forall a. HasCallStack => Bool -> a -> a
assert ([CoreBndr] -> Bool
forall a. [a] -> Bool
forall (t :: * -> *) a. Foldable t => t a -> Bool
null [CoreBndr]
bndrs) (SimplM (Alt CoreBndr) -> SimplM (Alt CoreBndr))
-> SimplM (Alt CoreBndr) -> SimplM (Alt CoreBndr)
forall a b. (a -> b) -> a -> b
$
    do  { SimplEnv
env' <- SimplEnv
-> Maybe CoreExpr -> CoreBndr -> CoreExpr -> SimplM SimplEnv
addAltUnfoldings SimplEnv
env Maybe CoreExpr
scrut' CoreBndr
case_bndr' (Literal -> CoreExpr
forall b. Literal -> Expr b
Lit Literal
lit)
        ; CoreExpr
rhs' <- SimplEnv -> CoreExpr -> SimplCont -> SimplM CoreExpr
simplExprC SimplEnv
env' CoreExpr
rhs SimplCont
cont'
        ; Alt CoreBndr -> SimplM (Alt CoreBndr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (AltCon -> [CoreBndr] -> CoreExpr -> Alt CoreBndr
forall b. AltCon -> [b] -> Expr b -> Alt b
Alt (Literal -> AltCon
LitAlt Literal
lit) [] CoreExpr
rhs') }

simplAlt SimplEnv
env Maybe CoreExpr
scrut' [AltCon]
_ CoreBndr
case_bndr' SimplCont
cont' (Alt (DataAlt DataCon
con) [CoreBndr]
vs CoreExpr
rhs)
  = do  { -- See Note [Adding evaluatedness info to pattern-bound variables]
          let vs_with_evals :: [CoreBndr]
vs_with_evals = Maybe CoreExpr -> DataCon -> [CoreBndr] -> [CoreBndr]
addEvals Maybe CoreExpr
scrut' DataCon
con [CoreBndr]
vs
        ; (SimplEnv
env', [CoreBndr]
vs') <- SimplEnv -> [CoreBndr] -> SimplM (SimplEnv, [CoreBndr])
simplBinders SimplEnv
env [CoreBndr]
vs_with_evals

                -- Bind the case-binder to (con args)
        ; let inst_tys' :: [Kind]
inst_tys' = HasCallStack => Kind -> [Kind]
Kind -> [Kind]
tyConAppArgs (CoreBndr -> Kind
idType CoreBndr
case_bndr')
              con_app :: OutExpr
              con_app :: CoreExpr
con_app   = DataCon -> [Kind] -> [CoreBndr] -> CoreExpr
forall b. DataCon -> [Kind] -> [CoreBndr] -> Expr b
mkConApp2 DataCon
con [Kind]
inst_tys' [CoreBndr]
vs'

        ; SimplEnv
env'' <- SimplEnv
-> Maybe CoreExpr -> CoreBndr -> CoreExpr -> SimplM SimplEnv
addAltUnfoldings SimplEnv
env' Maybe CoreExpr
scrut' CoreBndr
case_bndr' CoreExpr
con_app
        ; CoreExpr
rhs' <- SimplEnv -> CoreExpr -> SimplCont -> SimplM CoreExpr
simplExprC SimplEnv
env'' CoreExpr
rhs SimplCont
cont'
        ; Alt CoreBndr -> SimplM (Alt CoreBndr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (AltCon -> [CoreBndr] -> CoreExpr -> Alt CoreBndr
forall b. AltCon -> [b] -> Expr b -> Alt b
Alt (DataCon -> AltCon
DataAlt DataCon
con) [CoreBndr]
vs' CoreExpr
rhs') }

{- Note [Adding evaluatedness info to pattern-bound variables]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
addEvals records the evaluated-ness of the bound variables of
a case pattern.  This is *important*.  Consider

     data T = T !Int !Int

     case x of { T a b -> T (a+1) b }

We really must record that b is already evaluated so that we don't
go and re-evaluate it when constructing the result.
See Note [Data-con worker strictness] in GHC.Core.DataCon

NB: simplLamBndrs preserves this eval info

In addition to handling data constructor fields with !s, addEvals
also records the fact that the result of seq# is always in WHNF.
See Note [seq# magic] in GHC.Core.Opt.ConstantFold.  Example (#15226):

  case seq# v s of
    (# s', v' #) -> E

we want the compiler to be aware that v' is in WHNF in E.

Open problem: we don't record that v itself is in WHNF (and we can't
do it here).  The right thing is to do some kind of binder-swap;
see #15226 for discussion.
-}

addEvals :: Maybe OutExpr -> DataCon -> [Id] -> [Id]
-- See Note [Adding evaluatedness info to pattern-bound variables]
addEvals :: Maybe CoreExpr -> DataCon -> [CoreBndr] -> [CoreBndr]
addEvals Maybe CoreExpr
scrut DataCon
con [CoreBndr]
vs
  -- Deal with seq# applications
  | Just CoreExpr
scr <- Maybe CoreExpr
scrut
  , DataCon -> Bool
isUnboxedTupleDataCon DataCon
con
  , [CoreBndr
s,CoreBndr
x] <- [CoreBndr]
vs
    -- Use stripNArgs rather than collectArgsTicks to avoid building
    -- a list of arguments only to throw it away immediately.
  , Just (Var CoreBndr
f) <- Word -> CoreExpr -> Maybe CoreExpr
forall a. Word -> Expr a -> Maybe (Expr a)
stripNArgs Word
4 CoreExpr
scr
  , Just PrimOp
SeqOp <- CoreBndr -> Maybe PrimOp
isPrimOpId_maybe CoreBndr
f
  , let x' :: CoreBndr
x' = StrictnessMark -> CoreBndr -> CoreBndr
zapIdOccInfoAndSetEvald StrictnessMark
MarkedStrict CoreBndr
x
  = [CoreBndr
s, CoreBndr
x']

  -- Deal with banged datacon fields
addEvals Maybe CoreExpr
_scrut DataCon
con [CoreBndr]
vs = [CoreBndr] -> [StrictnessMark] -> [CoreBndr]
go [CoreBndr]
vs [StrictnessMark]
the_strs
    where
      the_strs :: [StrictnessMark]
the_strs = DataCon -> [StrictnessMark]
dataConRepStrictness DataCon
con

      go :: [CoreBndr] -> [StrictnessMark] -> [CoreBndr]
go [] [] = []
      go (CoreBndr
v:[CoreBndr]
vs') [StrictnessMark]
strs | CoreBndr -> Bool
isTyVar CoreBndr
v = CoreBndr
v CoreBndr -> [CoreBndr] -> [CoreBndr]
forall a. a -> [a] -> [a]
: [CoreBndr] -> [StrictnessMark] -> [CoreBndr]
go [CoreBndr]
vs' [StrictnessMark]
strs
      go (CoreBndr
v:[CoreBndr]
vs') (StrictnessMark
str:[StrictnessMark]
strs) = StrictnessMark -> CoreBndr -> CoreBndr
zapIdOccInfoAndSetEvald StrictnessMark
str CoreBndr
v CoreBndr -> [CoreBndr] -> [CoreBndr]
forall a. a -> [a] -> [a]
: [CoreBndr] -> [StrictnessMark] -> [CoreBndr]
go [CoreBndr]
vs' [StrictnessMark]
strs
      go [CoreBndr]
_ [StrictnessMark]
_ = String -> SDoc -> [CoreBndr]
forall a. HasCallStack => String -> SDoc -> a
pprPanic String
"Simplify.addEvals"
                (DataCon -> SDoc
forall a. Outputable a => a -> SDoc
ppr DataCon
con SDoc -> SDoc -> SDoc
forall doc. IsDoc doc => doc -> doc -> doc
$$
                 [CoreBndr] -> SDoc
forall a. Outputable a => a -> SDoc
ppr [CoreBndr]
vs  SDoc -> SDoc -> SDoc
forall doc. IsDoc doc => doc -> doc -> doc
$$
                 [SDoc] -> SDoc
forall {t :: * -> *} {a}.
(Outputable (t a), Foldable t) =>
t a -> SDoc
ppr_with_length ((StrictnessMark -> SDoc) -> [StrictnessMark] -> [SDoc]
forall a b. (a -> b) -> [a] -> [b]
map StrictnessMark -> SDoc
strdisp [StrictnessMark]
the_strs) SDoc -> SDoc -> SDoc
forall doc. IsDoc doc => doc -> doc -> doc
$$
                 [Scaled Kind] -> SDoc
forall {t :: * -> *} {a}.
(Outputable (t a), Foldable t) =>
t a -> SDoc
ppr_with_length (DataCon -> [Scaled Kind]
dataConRepArgTys DataCon
con) SDoc -> SDoc -> SDoc
forall doc. IsDoc doc => doc -> doc -> doc
$$
                 [StrictnessMark] -> SDoc
forall {t :: * -> *} {a}.
(Outputable (t a), Foldable t) =>
t a -> SDoc
ppr_with_length (DataCon -> [StrictnessMark]
dataConRepStrictness DataCon
con))
        where
          ppr_with_length :: t a -> SDoc
ppr_with_length t a
list
            = t a -> SDoc
forall a. Outputable a => a -> SDoc
ppr t a
list SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc
parens (String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"length =" SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> Int -> SDoc
forall a. Outputable a => a -> SDoc
ppr (t a -> Int
forall a. t a -> Int
forall (t :: * -> *) a. Foldable t => t a -> Int
length t a
list))
          strdisp :: StrictnessMark -> SDoc
          strdisp :: StrictnessMark -> SDoc
strdisp StrictnessMark
MarkedStrict = String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"MarkedStrict"
          strdisp StrictnessMark
NotMarkedStrict = String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"NotMarkedStrict"

zapIdOccInfoAndSetEvald :: StrictnessMark -> Id -> Id
zapIdOccInfoAndSetEvald :: StrictnessMark -> CoreBndr -> CoreBndr
zapIdOccInfoAndSetEvald StrictnessMark
str CoreBndr
v =
  StrictnessMark -> CoreBndr -> CoreBndr
setCaseBndrEvald StrictnessMark
str (CoreBndr -> CoreBndr) -> CoreBndr -> CoreBndr
forall a b. (a -> b) -> a -> b
$ -- Add eval'dness info
  CoreBndr -> CoreBndr
zapIdOccInfo CoreBndr
v         -- And kill occ info;
                         -- see Note [Case alternative occ info]

addAltUnfoldings :: SimplEnv -> Maybe OutExpr -> OutId -> OutExpr -> SimplM SimplEnv
addAltUnfoldings :: SimplEnv
-> Maybe CoreExpr -> CoreBndr -> CoreExpr -> SimplM SimplEnv
addAltUnfoldings SimplEnv
env Maybe CoreExpr
mb_scrut CoreBndr
case_bndr CoreExpr
con_app
  = do { let con_app_unf :: Unfolding
con_app_unf = CoreExpr -> Unfolding
mk_simple_unf CoreExpr
con_app
             env1 :: SimplEnv
env1 = SimplEnv -> CoreBndr -> Unfolding -> SimplEnv
addBinderUnfolding SimplEnv
env CoreBndr
case_bndr Unfolding
con_app_unf

             -- See Note [Add unfolding for scrutinee]
             env2 :: SimplEnv
env2 | Just CoreExpr
scrut <- Maybe CoreExpr
mb_scrut
                  , Just (CoreBndr
v,MOutCoercion
mco) <- CoreExpr -> Maybe (CoreBndr, MOutCoercion)
scrutBinderSwap_maybe CoreExpr
scrut
                  = SimplEnv -> CoreBndr -> Unfolding -> SimplEnv
addBinderUnfolding SimplEnv
env1 CoreBndr
v (Unfolding -> SimplEnv) -> Unfolding -> SimplEnv
forall a b. (a -> b) -> a -> b
$
                       if MOutCoercion -> Bool
isReflMCo MOutCoercion
mco  -- isReflMCo: avoid calling mk_simple_unf
                       then Unfolding
con_app_unf  --            twice in the common case
                       else CoreExpr -> Unfolding
mk_simple_unf (CoreExpr -> MOutCoercion -> CoreExpr
mkCastMCo CoreExpr
con_app MOutCoercion
mco)

                  | Bool
otherwise = SimplEnv
env1

       ; String -> SDoc -> SimplM ()
traceSmpl String
"addAltUnf" ([SDoc] -> SDoc
forall doc. IsDoc doc => [doc] -> doc
vcat [CoreBndr -> SDoc
forall a. Outputable a => a -> SDoc
ppr CoreBndr
case_bndr SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> Maybe CoreExpr -> SDoc
forall a. Outputable a => a -> SDoc
ppr Maybe CoreExpr
mb_scrut, CoreExpr -> SDoc
forall a. Outputable a => a -> SDoc
ppr CoreExpr
con_app])
       ; SimplEnv -> SimplM SimplEnv
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return SimplEnv
env2 }
  where
    -- Force the opts, so that the whole SimplEnv isn't retained
    !opts :: UnfoldingOpts
opts = SimplEnv -> UnfoldingOpts
seUnfoldingOpts SimplEnv
env
    mk_simple_unf :: CoreExpr -> Unfolding
mk_simple_unf = UnfoldingOpts -> CoreExpr -> Unfolding
mkSimpleUnfolding UnfoldingOpts
opts

addBinderUnfolding :: SimplEnv -> Id -> Unfolding -> SimplEnv
addBinderUnfolding :: SimplEnv -> CoreBndr -> Unfolding -> SimplEnv
addBinderUnfolding SimplEnv
env CoreBndr
bndr Unfolding
unf
  | Bool
debugIsOn, Just CoreExpr
tmpl <- Unfolding -> Maybe CoreExpr
maybeUnfoldingTemplate Unfolding
unf
  = Bool -> String -> SDoc -> SimplEnv -> SimplEnv
forall a. HasCallStack => Bool -> String -> SDoc -> a -> a
warnPprTrace (Bool -> Bool
not (Kind -> Kind -> Bool
eqType (CoreBndr -> Kind
idType CoreBndr
bndr) ((() :: Constraint) => CoreExpr -> Kind
CoreExpr -> Kind
exprType CoreExpr
tmpl)))
          String
"unfolding type mismatch"
          (CoreBndr -> SDoc
forall a. Outputable a => a -> SDoc
ppr CoreBndr
bndr SDoc -> SDoc -> SDoc
forall doc. IsDoc doc => doc -> doc -> doc
$$ Kind -> SDoc
forall a. Outputable a => a -> SDoc
ppr (CoreBndr -> Kind
idType CoreBndr
bndr) SDoc -> SDoc -> SDoc
forall doc. IsDoc doc => doc -> doc -> doc
$$ CoreExpr -> SDoc
forall a. Outputable a => a -> SDoc
ppr CoreExpr
tmpl SDoc -> SDoc -> SDoc
forall doc. IsDoc doc => doc -> doc -> doc
$$ Kind -> SDoc
forall a. Outputable a => a -> SDoc
ppr ((() :: Constraint) => CoreExpr -> Kind
CoreExpr -> Kind
exprType CoreExpr
tmpl)) (SimplEnv -> SimplEnv) -> SimplEnv -> SimplEnv
forall a b. (a -> b) -> a -> b
$
          SimplEnv -> CoreBndr -> SimplEnv
modifyInScope SimplEnv
env (CoreBndr
bndr CoreBndr -> Unfolding -> CoreBndr
`setIdUnfolding` Unfolding
unf)

  | Bool
otherwise
  = SimplEnv -> CoreBndr -> SimplEnv
modifyInScope SimplEnv
env (CoreBndr
bndr CoreBndr -> Unfolding -> CoreBndr
`setIdUnfolding` Unfolding
unf)

zapBndrOccInfo :: Bool -> Id -> Id
-- Consider  case e of b { (a,b) -> ... }
-- Then if we bind b to (a,b) in "...", and b is not dead,
-- then we must zap the deadness info on a,b
zapBndrOccInfo :: Bool -> CoreBndr -> CoreBndr
zapBndrOccInfo Bool
keep_occ_info CoreBndr
pat_id
  | Bool
keep_occ_info = CoreBndr
pat_id
  | Bool
otherwise     = CoreBndr -> CoreBndr
zapIdOccInfo CoreBndr
pat_id

{- Note [Case binder evaluated-ness]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We pin on a (OtherCon []) unfolding to the case-binder of a Case,
even though it'll be over-ridden in every case alternative with a more
informative unfolding.  Why?  Because suppose a later, less clever, pass
simply replaces all occurrences of the case binder with the binder itself;
then Lint may complain about the let-can-float invariant.  Example
    case e of b { DEFAULT -> let v = reallyUnsafePtrEquality# b y in ....
                ; K       -> blah }

The let-can-float invariant requires that y is evaluated in the call to
reallyUnsafePtrEquality#, which it is.  But we still want that to be true if we
propagate binders to occurrences.

This showed up in #13027.

Note [Add unfolding for scrutinee]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In general it's unlikely that a variable scrutinee will appear
in the case alternatives   case x of { ...x unlikely to appear... }
because the binder-swap in OccurAnal has got rid of all such occurrences
See Note [Binder swap] in "GHC.Core.Opt.OccurAnal".

BUT it is still VERY IMPORTANT to add a suitable unfolding for a
variable scrutinee, in simplAlt.  Here's why
   case x of y
     (a,b) -> case b of c
                I# v -> ...(f y)...
There is no occurrence of 'b' in the (...(f y)...).  But y gets
the unfolding (a,b), and *that* mentions b.  If f has a RULE
    RULE f (p, I# q) = ...
we want that rule to match, so we must extend the in-scope env with a
suitable unfolding for 'y'.  It's *essential* for rule matching; but
it's also good for case-elimination -- suppose that 'f' was inlined
and did multi-level case analysis, then we'd solve it in one
simplifier sweep instead of two.

HOWEVER, given
  case x of y { Just a -> r1; Nothing -> r2 }
we do not want to add the unfolding x -> y to 'x', which might seem cool,
since 'y' itself has different unfoldings in r1 and r2.  Reason: if we
did that, we'd have to zap y's deadness info and that is a very useful
piece of information.

So instead we add the unfolding x -> Just a, and x -> Nothing in the
respective RHSs.

Since this transformation is tantamount to a binder swap, we use
GHC.Core.Opt.OccurAnal.scrutBinderSwap_maybe to do the check.

Exactly the same issue arises in GHC.Core.Opt.SpecConstr;
see Note [Add scrutinee to ValueEnv too] in GHC.Core.Opt.SpecConstr


************************************************************************
*                                                                      *
\subsection{Known constructor}
*                                                                      *
************************************************************************

We are a bit careful with occurrence info.  Here's an example

        (\x* -> case x of (a*, b) -> f a) (h v, e)

where the * means "occurs once".  This effectively becomes
        case (h v, e) of (a*, b) -> f a)
and then
        let a* = h v; b = e in f a
and then
        f (h v)

All this should happen in one sweep.
-}

knownCon :: SimplEnv
         -> OutExpr                                           -- The scrutinee
         -> [FloatBind] -> DataCon -> [OutType] -> [OutExpr]  -- The scrutinee (in pieces)
         -> InId -> [InBndr] -> InExpr                        -- The alternative
         -> SimplCont
         -> SimplM (SimplFloats, OutExpr)

knownCon :: SimplEnv
-> CoreExpr
-> [FloatBind]
-> DataCon
-> [Kind]
-> [CoreExpr]
-> CoreBndr
-> [CoreBndr]
-> CoreExpr
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
knownCon SimplEnv
env CoreExpr
scrut [FloatBind]
dc_floats DataCon
dc [Kind]
dc_ty_args [CoreExpr]
dc_args CoreBndr
bndr [CoreBndr]
bs CoreExpr
rhs SimplCont
cont
  = do  { (SimplFloats
floats1, SimplEnv
env1)  <- SimplEnv
-> [CoreBndr] -> [CoreExpr] -> SimplM (SimplFloats, SimplEnv)
bind_args SimplEnv
env [CoreBndr]
bs [CoreExpr]
dc_args
        ; (SimplFloats
floats2, SimplEnv
env2)  <- SimplEnv -> SimplM (SimplFloats, SimplEnv)
bind_case_bndr SimplEnv
env1
        ; (SimplFloats
floats3, CoreExpr
expr') <- SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF SimplEnv
env2 CoreExpr
rhs SimplCont
cont
        ; case [FloatBind]
dc_floats of
            [] ->
              (SimplFloats, CoreExpr) -> SimplM (SimplFloats, CoreExpr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplFloats
floats1 SimplFloats -> SimplFloats -> SimplFloats
`addFloats` SimplFloats
floats2 SimplFloats -> SimplFloats -> SimplFloats
`addFloats` SimplFloats
floats3, CoreExpr
expr')
            [FloatBind]
_ ->
              (SimplFloats, CoreExpr) -> SimplM (SimplFloats, CoreExpr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return ( SimplEnv -> SimplFloats
emptyFloats SimplEnv
env
               -- See Note [FloatBinds from constructor wrappers]
                     , [FloatBind] -> CoreExpr -> CoreExpr
GHC.Core.Make.wrapFloats [FloatBind]
dc_floats (CoreExpr -> CoreExpr) -> CoreExpr -> CoreExpr
forall a b. (a -> b) -> a -> b
$
                       SimplFloats -> CoreExpr -> CoreExpr
wrapFloats (SimplFloats
floats1 SimplFloats -> SimplFloats -> SimplFloats
`addFloats` SimplFloats
floats2 SimplFloats -> SimplFloats -> SimplFloats
`addFloats` SimplFloats
floats3) CoreExpr
expr') }
  where
    zap_occ :: CoreBndr -> CoreBndr
zap_occ = Bool -> CoreBndr -> CoreBndr
zapBndrOccInfo (CoreBndr -> Bool
isDeadBinder CoreBndr
bndr)    -- bndr is an InId

                  -- Ugh!
    bind_args :: SimplEnv
-> [CoreBndr] -> [CoreExpr] -> SimplM (SimplFloats, SimplEnv)
bind_args SimplEnv
env' [] [CoreExpr]
_  = (SimplFloats, SimplEnv) -> SimplM (SimplFloats, SimplEnv)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplEnv -> SimplFloats
emptyFloats SimplEnv
env', SimplEnv
env')

    bind_args SimplEnv
env' (CoreBndr
b:[CoreBndr]
bs') (Type Kind
ty : [CoreExpr]
args)
      = Bool
-> (SimplEnv
    -> [CoreBndr] -> [CoreExpr] -> SimplM (SimplFloats, SimplEnv))
-> SimplEnv
-> [CoreBndr]
-> [CoreExpr]
-> SimplM (SimplFloats, SimplEnv)
forall a. HasCallStack => Bool -> a -> a
assert (CoreBndr -> Bool
isTyVar CoreBndr
b )
        SimplEnv
-> [CoreBndr] -> [CoreExpr] -> SimplM (SimplFloats, SimplEnv)
bind_args (SimplEnv -> CoreBndr -> Kind -> SimplEnv
extendTvSubst SimplEnv
env' CoreBndr
b Kind
ty) [CoreBndr]
bs' [CoreExpr]
args

    bind_args SimplEnv
env' (CoreBndr
b:[CoreBndr]
bs') (Coercion Coercion
co : [CoreExpr]
args)
      = Bool
-> (SimplEnv
    -> [CoreBndr] -> [CoreExpr] -> SimplM (SimplFloats, SimplEnv))
-> SimplEnv
-> [CoreBndr]
-> [CoreExpr]
-> SimplM (SimplFloats, SimplEnv)
forall a. HasCallStack => Bool -> a -> a
assert (CoreBndr -> Bool
isCoVar CoreBndr
b )
        SimplEnv
-> [CoreBndr] -> [CoreExpr] -> SimplM (SimplFloats, SimplEnv)
bind_args (SimplEnv -> CoreBndr -> Coercion -> SimplEnv
extendCvSubst SimplEnv
env' CoreBndr
b Coercion
co) [CoreBndr]
bs' [CoreExpr]
args

    bind_args SimplEnv
env' (CoreBndr
b:[CoreBndr]
bs') (CoreExpr
arg : [CoreExpr]
args)
      = Bool
-> SimplM (SimplFloats, SimplEnv) -> SimplM (SimplFloats, SimplEnv)
forall a. HasCallStack => Bool -> a -> a
assert (CoreBndr -> Bool
isId CoreBndr
b) (SimplM (SimplFloats, SimplEnv) -> SimplM (SimplFloats, SimplEnv))
-> SimplM (SimplFloats, SimplEnv) -> SimplM (SimplFloats, SimplEnv)
forall a b. (a -> b) -> a -> b
$
        do { let b' :: CoreBndr
b' = CoreBndr -> CoreBndr
zap_occ CoreBndr
b
             -- zap_occ: the binder might be "dead", because it doesn't
             -- occur in the RHS; and simplAuxBind may therefore discard it.
             -- Nevertheless we must keep it if the case-binder is alive,
             -- because it may be used in the con_app.  See Note [knownCon occ info]
           ; (SimplFloats
floats1, SimplEnv
env2) <- SimplEnv -> CoreBndr -> CoreExpr -> SimplM (SimplFloats, SimplEnv)
simplAuxBind SimplEnv
env' CoreBndr
b' CoreExpr
arg  -- arg satisfies let-can-float invariant
           ; (SimplFloats
floats2, SimplEnv
env3)  <- SimplEnv
-> [CoreBndr] -> [CoreExpr] -> SimplM (SimplFloats, SimplEnv)
bind_args SimplEnv
env2 [CoreBndr]
bs' [CoreExpr]
args
           ; (SimplFloats, SimplEnv) -> SimplM (SimplFloats, SimplEnv)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplFloats
floats1 SimplFloats -> SimplFloats -> SimplFloats
`addFloats` SimplFloats
floats2, SimplEnv
env3) }

    bind_args SimplEnv
_ [CoreBndr]
_ [CoreExpr]
_ =
      String -> SDoc -> SimplM (SimplFloats, SimplEnv)
forall a. HasCallStack => String -> SDoc -> a
pprPanic String
"bind_args" (SDoc -> SimplM (SimplFloats, SimplEnv))
-> SDoc -> SimplM (SimplFloats, SimplEnv)
forall a b. (a -> b) -> a -> b
$ DataCon -> SDoc
forall a. Outputable a => a -> SDoc
ppr DataCon
dc SDoc -> SDoc -> SDoc
forall doc. IsDoc doc => doc -> doc -> doc
$$ [CoreBndr] -> SDoc
forall a. Outputable a => a -> SDoc
ppr [CoreBndr]
bs SDoc -> SDoc -> SDoc
forall doc. IsDoc doc => doc -> doc -> doc
$$ [CoreExpr] -> SDoc
forall a. Outputable a => a -> SDoc
ppr [CoreExpr]
dc_args SDoc -> SDoc -> SDoc
forall doc. IsDoc doc => doc -> doc -> doc
$$
                             String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"scrut:" SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> CoreExpr -> SDoc
forall a. Outputable a => a -> SDoc
ppr CoreExpr
scrut

       -- It's useful to bind bndr to scrut, rather than to a fresh
       -- binding      x = Con arg1 .. argn
       -- because very often the scrut is a variable, so we avoid
       -- creating, and then subsequently eliminating, a let-binding
       -- BUT, if scrut is a not a variable, we must be careful
       -- about duplicating the arg redexes; in that case, make
       -- a new con-app from the args
    bind_case_bndr :: SimplEnv -> SimplM (SimplFloats, SimplEnv)
bind_case_bndr SimplEnv
env
      | CoreBndr -> Bool
isDeadBinder CoreBndr
bndr   = (SimplFloats, SimplEnv) -> SimplM (SimplFloats, SimplEnv)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplEnv -> SimplFloats
emptyFloats SimplEnv
env, SimplEnv
env)
      | CoreExpr -> Bool
exprIsTrivial CoreExpr
scrut = (SimplFloats, SimplEnv) -> SimplM (SimplFloats, SimplEnv)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplEnv -> SimplFloats
emptyFloats SimplEnv
env
                                     , SimplEnv -> CoreBndr -> SimplSR -> SimplEnv
extendIdSubst SimplEnv
env CoreBndr
bndr (CoreExpr -> Maybe Int -> SimplSR
DoneEx CoreExpr
scrut Maybe Int
forall a. Maybe a
Nothing))
                              -- See Note [Do not duplicate constructor applications]
      | Bool
otherwise           = do { [CoreExpr]
dc_args <- (CoreBndr -> SimplM CoreExpr) -> [CoreBndr] -> SimplM [CoreExpr]
forall (t :: * -> *) (m :: * -> *) a b.
(Traversable t, Monad m) =>
(a -> m b) -> t a -> m (t b)
forall (m :: * -> *) a b. Monad m => (a -> m b) -> [a] -> m [b]
mapM (SimplEnv -> CoreBndr -> SimplM CoreExpr
simplVar SimplEnv
env) [CoreBndr]
bs
                                         -- dc_ty_args are already OutTypes,
                                         -- but bs are InBndrs
                                 ; let con_app :: CoreExpr
con_app = CoreBndr -> CoreExpr
forall b. CoreBndr -> Expr b
Var (DataCon -> CoreBndr
dataConWorkId DataCon
dc)
                                                 CoreExpr -> [Kind] -> CoreExpr
forall b. Expr b -> [Kind] -> Expr b
`mkTyApps` [Kind]
dc_ty_args
                                                 CoreExpr -> [CoreExpr] -> CoreExpr
forall b. Expr b -> [Expr b] -> Expr b
`mkApps`   [CoreExpr]
dc_args
                                 ; SimplEnv -> CoreBndr -> CoreExpr -> SimplM (SimplFloats, SimplEnv)
simplAuxBind SimplEnv
env CoreBndr
bndr CoreExpr
con_app }

-------------------
missingAlt :: SimplEnv -> Id -> [InAlt] -> SimplCont
           -> SimplM (SimplFloats, OutExpr)
                -- This isn't strictly an error, although it is unusual.
                -- It's possible that the simplifier might "see" that
                -- an inner case has no accessible alternatives before
                -- it "sees" that the entire branch of an outer case is
                -- inaccessible.  So we simply put an error case here instead.
missingAlt :: SimplEnv
-> CoreBndr
-> [Alt CoreBndr]
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
missingAlt SimplEnv
env CoreBndr
case_bndr [Alt CoreBndr]
_ SimplCont
cont
  = Bool
-> String
-> SDoc
-> SimplM (SimplFloats, CoreExpr)
-> SimplM (SimplFloats, CoreExpr)
forall a. HasCallStack => Bool -> String -> SDoc -> a -> a
warnPprTrace Bool
True String
"missingAlt" (CoreBndr -> SDoc
forall a. Outputable a => a -> SDoc
ppr CoreBndr
case_bndr) (SimplM (SimplFloats, CoreExpr) -> SimplM (SimplFloats, CoreExpr))
-> SimplM (SimplFloats, CoreExpr) -> SimplM (SimplFloats, CoreExpr)
forall a b. (a -> b) -> a -> b
$
    -- See Note [Avoiding space leaks in OutType]
    let cont_ty :: Kind
cont_ty = SimplCont -> Kind
contResultType SimplCont
cont
    in Kind -> ()
seqType Kind
cont_ty ()
-> SimplM (SimplFloats, CoreExpr) -> SimplM (SimplFloats, CoreExpr)
forall a b. a -> b -> b
`seq`
       (SimplFloats, CoreExpr) -> SimplM (SimplFloats, CoreExpr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplEnv -> SimplFloats
emptyFloats SimplEnv
env, Kind -> String -> CoreExpr
mkImpossibleExpr Kind
cont_ty String
"Simplify.Iteration.missingAlt")

{-
************************************************************************
*                                                                      *
\subsection{Duplicating continuations}
*                                                                      *
************************************************************************

Consider
  let x* = case e of { True -> e1; False -> e2 }
  in b
where x* is a strict binding.  Then mkDupableCont will be given
the continuation
   case [] of { True -> e1; False -> e2 } ; let x* = [] in b ; stop
and will split it into
   dupable:      case [] of { True -> $j1; False -> $j2 } ; stop
   join floats:  $j1 = e1, $j2 = e2
   non_dupable:  let x* = [] in b; stop

Putting this back together would give
   let x* = let { $j1 = e1; $j2 = e2 } in
            case e of { True -> $j1; False -> $j2 }
   in b
(Of course we only do this if 'e' wants to duplicate that continuation.)
Note how important it is that the new join points wrap around the
inner expression, and not around the whole thing.

In contrast, any let-bindings introduced by mkDupableCont can wrap
around the entire thing.

Note [Bottom alternatives]
~~~~~~~~~~~~~~~~~~~~~~~~~~
When we have
     case (case x of { A -> error .. ; B -> e; C -> error ..)
       of alts
then we can just duplicate those alts because the A and C cases
will disappear immediately.  This is more direct than creating
join points and inlining them away.  See #4930.
-}

--------------------
mkDupableCaseCont :: SimplEnv -> [InAlt] -> SimplCont
                  -> SimplM ( SimplFloats  -- Join points (if any)
                            , SimplEnv     -- Use this for the alts
                            , SimplCont)
mkDupableCaseCont :: SimplEnv
-> [Alt CoreBndr]
-> SimplCont
-> SimplM (SimplFloats, SimplEnv, SimplCont)
mkDupableCaseCont SimplEnv
env [Alt CoreBndr]
alts SimplCont
cont
  | [Alt CoreBndr] -> Bool
altsWouldDup [Alt CoreBndr]
alts = do { (SimplFloats
floats, SimplCont
cont) <- SimplEnv -> SimplCont -> SimplM (SimplFloats, SimplCont)
mkDupableCont SimplEnv
env SimplCont
cont
                           ; let env' :: SimplEnv
env' = SimplEnv -> SimplEnv
bumpCaseDepth (SimplEnv -> SimplEnv) -> SimplEnv -> SimplEnv
forall a b. (a -> b) -> a -> b
$
                                        SimplEnv
env SimplEnv -> SimplFloats -> SimplEnv
`setInScopeFromF` SimplFloats
floats
                           ; (SimplFloats, SimplEnv, SimplCont)
-> SimplM (SimplFloats, SimplEnv, SimplCont)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplFloats
floats, SimplEnv
env', SimplCont
cont) }
  | Bool
otherwise         = (SimplFloats, SimplEnv, SimplCont)
-> SimplM (SimplFloats, SimplEnv, SimplCont)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplEnv -> SimplFloats
emptyFloats SimplEnv
env, SimplEnv
env, SimplCont
cont)

altsWouldDup :: [InAlt] -> Bool -- True iff strictly > 1 non-bottom alternative
altsWouldDup :: [Alt CoreBndr] -> Bool
altsWouldDup []  = Bool
False        -- See Note [Bottom alternatives]
altsWouldDup [Alt CoreBndr
_] = Bool
False
altsWouldDup (Alt CoreBndr
alt:[Alt CoreBndr]
alts)
  | Alt CoreBndr -> Bool
is_bot_alt Alt CoreBndr
alt = [Alt CoreBndr] -> Bool
altsWouldDup [Alt CoreBndr]
alts
  | Bool
otherwise      = Bool -> Bool
not ((Alt CoreBndr -> Bool) -> [Alt CoreBndr] -> Bool
forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
all Alt CoreBndr -> Bool
is_bot_alt [Alt CoreBndr]
alts)
    -- otherwise case: first alt is non-bot, so all the rest must be bot
  where
    is_bot_alt :: Alt CoreBndr -> Bool
is_bot_alt (Alt AltCon
_ [CoreBndr]
_ CoreExpr
rhs) = CoreExpr -> Bool
exprIsDeadEnd CoreExpr
rhs

-------------------------
mkDupableCont :: SimplEnv
              -> SimplCont
              -> SimplM ( SimplFloats  -- Incoming SimplEnv augmented with
                                       --   extra let/join-floats and in-scope variables
                        , SimplCont)   -- dup_cont: duplicable continuation
mkDupableCont :: SimplEnv -> SimplCont -> SimplM (SimplFloats, SimplCont)
mkDupableCont SimplEnv
env SimplCont
cont
  = SimplEnv
-> [Demand] -> SimplCont -> SimplM (SimplFloats, SimplCont)
mkDupableContWithDmds SimplEnv
env (Demand -> [Demand]
forall a. a -> [a]
repeat Demand
topDmd) SimplCont
cont

mkDupableContWithDmds
   :: SimplEnv  -> [Demand]  -- Demands on arguments; always infinite
   -> SimplCont -> SimplM ( SimplFloats, SimplCont)

mkDupableContWithDmds :: SimplEnv
-> [Demand] -> SimplCont -> SimplM (SimplFloats, SimplCont)
mkDupableContWithDmds SimplEnv
env [Demand]
_ SimplCont
cont
  | SimplCont -> Bool
contIsDupable SimplCont
cont
  = (SimplFloats, SimplCont) -> SimplM (SimplFloats, SimplCont)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplEnv -> SimplFloats
emptyFloats SimplEnv
env, SimplCont
cont)

mkDupableContWithDmds SimplEnv
_ [Demand]
_ (Stop {}) = String -> SimplM (SimplFloats, SimplCont)
forall a. HasCallStack => String -> a
panic String
"mkDupableCont"     -- Handled by previous eqn

mkDupableContWithDmds SimplEnv
env [Demand]
dmds (CastIt Coercion
ty SimplCont
cont)
  = do  { (SimplFloats
floats, SimplCont
cont') <- SimplEnv
-> [Demand] -> SimplCont -> SimplM (SimplFloats, SimplCont)
mkDupableContWithDmds SimplEnv
env [Demand]
dmds SimplCont
cont
        ; (SimplFloats, SimplCont) -> SimplM (SimplFloats, SimplCont)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplFloats
floats, Coercion -> SimplCont -> SimplCont
CastIt Coercion
ty SimplCont
cont') }

-- Duplicating ticks for now, not sure if this is good or not
mkDupableContWithDmds SimplEnv
env [Demand]
dmds (TickIt CoreTickish
t SimplCont
cont)
  = do  { (SimplFloats
floats, SimplCont
cont') <- SimplEnv
-> [Demand] -> SimplCont -> SimplM (SimplFloats, SimplCont)
mkDupableContWithDmds SimplEnv
env [Demand]
dmds SimplCont
cont
        ; (SimplFloats, SimplCont) -> SimplM (SimplFloats, SimplCont)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplFloats
floats, CoreTickish -> SimplCont -> SimplCont
TickIt CoreTickish
t SimplCont
cont') }

mkDupableContWithDmds SimplEnv
env [Demand]
_
     (StrictBind { sc_bndr :: SimplCont -> CoreBndr
sc_bndr = CoreBndr
bndr, sc_body :: SimplCont -> CoreExpr
sc_body = CoreExpr
body, sc_from :: SimplCont -> FromWhat
sc_from = FromWhat
from_what
                 , sc_env :: SimplCont -> SimplEnv
sc_env = SimplEnv
se, sc_cont :: SimplCont -> SimplCont
sc_cont = SimplCont
cont})
-- See Note [Duplicating StrictBind]
-- K[ let x = <> in b ]  -->   join j x = K[ b ]
--                             j <>
  = do { let sb_env :: SimplEnv
sb_env = SimplEnv
se SimplEnv -> SimplEnv -> SimplEnv
`setInScopeFromE` SimplEnv
env
       ; (SimplEnv
sb_env1, CoreBndr
bndr')      <- SimplEnv -> CoreBndr -> SimplM (SimplEnv, CoreBndr)
simplBinder SimplEnv
sb_env CoreBndr
bndr
       ; (SimplFloats
floats1, CoreExpr
join_inner) <- SimplEnv
-> FromWhat
-> CoreExpr
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
simplNonRecBody SimplEnv
sb_env1 FromWhat
from_what CoreExpr
body SimplCont
cont
          -- No need to use mkDupableCont before simplNonRecBody; we
          -- use cont once here, and then share the result if necessary

       ; let join_body :: CoreExpr
join_body = SimplFloats -> CoreExpr -> CoreExpr
wrapFloats SimplFloats
floats1 CoreExpr
join_inner
             res_ty :: Kind
res_ty    = SimplCont -> Kind
contResultType SimplCont
cont

       ; SimplEnv
-> CoreBndr -> CoreExpr -> Kind -> SimplM (SimplFloats, SimplCont)
mkDupableStrictBind SimplEnv
env CoreBndr
bndr' CoreExpr
join_body Kind
res_ty }

mkDupableContWithDmds SimplEnv
env [Demand]
_
    (StrictArg { sc_fun :: SimplCont -> ArgInfo
sc_fun = ArgInfo
fun, sc_cont :: SimplCont -> SimplCont
sc_cont = SimplCont
cont
               , sc_fun_ty :: SimplCont -> Kind
sc_fun_ty = Kind
fun_ty })
  -- NB: sc_dup /= OkToDup; that is caught earlier by contIsDupable
  | Maybe DataCon -> Bool
forall a. Maybe a -> Bool
isNothing (CoreBndr -> Maybe DataCon
isDataConId_maybe (ArgInfo -> CoreBndr
ai_fun ArgInfo
fun))
  , SimplCont -> Bool
thumbsUpPlanA SimplCont
cont  -- See point (3) of Note [Duplicating join points]
  = -- Use Plan A of Note [Duplicating StrictArg]
    do { let (Demand
_ : [Demand]
dmds) = ArgInfo -> [Demand]
ai_dmds ArgInfo
fun
       ; (SimplFloats
floats1, SimplCont
cont')  <- SimplEnv
-> [Demand] -> SimplCont -> SimplM (SimplFloats, SimplCont)
mkDupableContWithDmds SimplEnv
env [Demand]
dmds SimplCont
cont
                              -- Use the demands from the function to add the right
                              -- demand info on any bindings we make for further args
       ; ([LetFloats]
floats_s, [ArgSpec]
args') <- (ArgSpec -> SimplM (LetFloats, ArgSpec))
-> [ArgSpec] -> SimplM ([LetFloats], [ArgSpec])
forall (m :: * -> *) a b c.
Applicative m =>
(a -> m (b, c)) -> [a] -> m ([b], [c])
mapAndUnzipM ((() :: Constraint) =>
SimplEnv -> ArgSpec -> SimplM (LetFloats, ArgSpec)
SimplEnv -> ArgSpec -> SimplM (LetFloats, ArgSpec)
makeTrivialArg SimplEnv
env)
                                           (ArgInfo -> [ArgSpec]
ai_args ArgInfo
fun)
       ; (SimplFloats, SimplCont) -> SimplM (SimplFloats, SimplCont)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return ( (SimplFloats -> LetFloats -> SimplFloats)
-> SimplFloats -> [LetFloats] -> SimplFloats
forall b a. (b -> a -> b) -> b -> [a] -> b
forall (t :: * -> *) b a.
Foldable t =>
(b -> a -> b) -> b -> t a -> b
foldl' SimplFloats -> LetFloats -> SimplFloats
addLetFloats SimplFloats
floats1 [LetFloats]
floats_s
                , StrictArg { sc_fun :: ArgInfo
sc_fun = ArgInfo
fun { ai_args = args' }
                            , sc_cont :: SimplCont
sc_cont = SimplCont
cont'
                            , sc_fun_ty :: Kind
sc_fun_ty = Kind
fun_ty
                            , sc_dup :: DupFlag
sc_dup = DupFlag
OkToDup} ) }

  | Bool
otherwise
  = -- Use Plan B of Note [Duplicating StrictArg]
    --   K[ f a b <> ]   -->   join j x = K[ f a b x ]
    --                         j <>
    do { let rhs_ty :: Kind
rhs_ty       = SimplCont -> Kind
contResultType SimplCont
cont
             (Kind
m,Kind
arg_ty,Kind
_) = Kind -> (Kind, Kind, Kind)
splitFunTy Kind
fun_ty
       ; CoreBndr
arg_bndr <- FastString -> Kind -> Kind -> SimplM CoreBndr
newId (String -> FastString
fsLit String
"arg") Kind
m Kind
arg_ty
       ; let env' :: SimplEnv
env' = SimplEnv
env SimplEnv -> [CoreBndr] -> SimplEnv
`addNewInScopeIds` [CoreBndr
arg_bndr]
       ; (SimplFloats
floats, CoreExpr
join_rhs) <- SimplEnv -> ArgInfo -> SimplCont -> SimplM (SimplFloats, CoreExpr)
rebuildCall SimplEnv
env' (ArgInfo -> CoreExpr -> Kind -> ArgInfo
addValArgTo ArgInfo
fun (CoreBndr -> CoreExpr
forall b. CoreBndr -> Expr b
Var CoreBndr
arg_bndr) Kind
fun_ty) SimplCont
cont
       ; SimplEnv
-> CoreBndr -> CoreExpr -> Kind -> SimplM (SimplFloats, SimplCont)
mkDupableStrictBind SimplEnv
env' CoreBndr
arg_bndr (SimplFloats -> CoreExpr -> CoreExpr
wrapFloats SimplFloats
floats CoreExpr
join_rhs) Kind
rhs_ty }
  where
    thumbsUpPlanA :: SimplCont -> Bool
thumbsUpPlanA (StrictArg {})               = Bool
False
    thumbsUpPlanA (CastIt Coercion
_ SimplCont
k)                 = SimplCont -> Bool
thumbsUpPlanA SimplCont
k
    thumbsUpPlanA (TickIt CoreTickish
_ SimplCont
k)                 = SimplCont -> Bool
thumbsUpPlanA SimplCont
k
    thumbsUpPlanA (ApplyToVal { sc_cont :: SimplCont -> SimplCont
sc_cont = SimplCont
k }) = SimplCont -> Bool
thumbsUpPlanA SimplCont
k
    thumbsUpPlanA (ApplyToTy  { sc_cont :: SimplCont -> SimplCont
sc_cont = SimplCont
k }) = SimplCont -> Bool
thumbsUpPlanA SimplCont
k
    thumbsUpPlanA (Select {})                  = Bool
True
    thumbsUpPlanA (StrictBind {})              = Bool
True
    thumbsUpPlanA (Stop {})                    = Bool
True

mkDupableContWithDmds SimplEnv
env [Demand]
dmds
    (ApplyToTy { sc_cont :: SimplCont -> SimplCont
sc_cont = SimplCont
cont, sc_arg_ty :: SimplCont -> Kind
sc_arg_ty = Kind
arg_ty, sc_hole_ty :: SimplCont -> Kind
sc_hole_ty = Kind
hole_ty })
  = do  { (SimplFloats
floats, SimplCont
cont') <- SimplEnv
-> [Demand] -> SimplCont -> SimplM (SimplFloats, SimplCont)
mkDupableContWithDmds SimplEnv
env [Demand]
dmds SimplCont
cont
        ; (SimplFloats, SimplCont) -> SimplM (SimplFloats, SimplCont)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplFloats
floats, ApplyToTy { sc_cont :: SimplCont
sc_cont = SimplCont
cont'
                                    , sc_arg_ty :: Kind
sc_arg_ty = Kind
arg_ty, sc_hole_ty :: Kind
sc_hole_ty = Kind
hole_ty }) }

mkDupableContWithDmds SimplEnv
env [Demand]
dmds
    (ApplyToVal { sc_arg :: SimplCont -> CoreExpr
sc_arg = CoreExpr
arg, sc_dup :: SimplCont -> DupFlag
sc_dup = DupFlag
dup, sc_env :: SimplCont -> SimplEnv
sc_env = SimplEnv
se
                , sc_cont :: SimplCont -> SimplCont
sc_cont = SimplCont
cont, sc_hole_ty :: SimplCont -> Kind
sc_hole_ty = Kind
hole_ty })
  =     -- e.g.         [...hole...] (...arg...)
        --      ==>
        --              let a = ...arg...
        --              in [...hole...] a
        -- NB: sc_dup /= OkToDup; that is caught earlier by contIsDupable
    do  { let (Demand
dmd:[Demand]
cont_dmds) = [Demand]
dmds   -- Never fails
        ; (SimplFloats
floats1, SimplCont
cont') <- SimplEnv
-> [Demand] -> SimplCont -> SimplM (SimplFloats, SimplCont)
mkDupableContWithDmds SimplEnv
env [Demand]
cont_dmds SimplCont
cont
        ; let env' :: SimplEnv
env' = SimplEnv
env SimplEnv -> SimplFloats -> SimplEnv
`setInScopeFromF` SimplFloats
floats1
        ; (DupFlag
_, SimplEnv
se', CoreExpr
arg') <- SimplEnv
-> DupFlag
-> Kind
-> SimplEnv
-> CoreExpr
-> SimplM (DupFlag, SimplEnv, CoreExpr)
simplArg SimplEnv
env' DupFlag
dup Kind
hole_ty SimplEnv
se CoreExpr
arg
        ; (LetFloats
let_floats2, CoreExpr
arg'') <- (() :: Constraint) =>
SimplEnv
-> TopLevelFlag
-> Demand
-> FastString
-> CoreExpr
-> SimplM (LetFloats, CoreExpr)
SimplEnv
-> TopLevelFlag
-> Demand
-> FastString
-> CoreExpr
-> SimplM (LetFloats, CoreExpr)
makeTrivial SimplEnv
env TopLevelFlag
NotTopLevel Demand
dmd (String -> FastString
fsLit String
"karg") CoreExpr
arg'
        ; let all_floats :: SimplFloats
all_floats = SimplFloats
floats1 SimplFloats -> LetFloats -> SimplFloats
`addLetFloats` LetFloats
let_floats2
        ; (SimplFloats, SimplCont) -> SimplM (SimplFloats, SimplCont)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return ( SimplFloats
all_floats
                 , ApplyToVal { sc_arg :: CoreExpr
sc_arg = CoreExpr
arg''
                              , sc_env :: SimplEnv
sc_env = SimplEnv
se' SimplEnv -> SimplFloats -> SimplEnv
`setInScopeFromF` SimplFloats
all_floats
                                         -- Ensure that sc_env includes the free vars of
                                         -- arg'' in its in-scope set, even if makeTrivial
                                         -- has turned arg'' into a fresh variable
                                         -- See Note [StaticEnv invariant] in GHC.Core.Opt.Simplify.Utils
                              , sc_dup :: DupFlag
sc_dup = DupFlag
OkToDup, sc_cont :: SimplCont
sc_cont = SimplCont
cont'
                              , sc_hole_ty :: Kind
sc_hole_ty = Kind
hole_ty }) }

mkDupableContWithDmds SimplEnv
env [Demand]
_
    (Select { sc_bndr :: SimplCont -> CoreBndr
sc_bndr = CoreBndr
case_bndr, sc_alts :: SimplCont -> [Alt CoreBndr]
sc_alts = [Alt CoreBndr]
alts, sc_env :: SimplCont -> SimplEnv
sc_env = SimplEnv
se, sc_cont :: SimplCont -> SimplCont
sc_cont = SimplCont
cont })
  =     -- e.g.         (case [...hole...] of { pi -> ei })
        --      ===>
        --              let ji = \xij -> ei
        --              in case [...hole...] of { pi -> ji xij }
        -- NB: sc_dup /= OkToDup; that is caught earlier by contIsDupable
    do  { Tick -> SimplM ()
tick (CoreBndr -> Tick
CaseOfCase CoreBndr
case_bndr)
        ; (SimplFloats
floats, SimplEnv
alt_env, SimplCont
alt_cont) <- SimplEnv
-> [Alt CoreBndr]
-> SimplCont
-> SimplM (SimplFloats, SimplEnv, SimplCont)
mkDupableCaseCont (SimplEnv
se SimplEnv -> SimplEnv -> SimplEnv
`setInScopeFromE` SimplEnv
env) [Alt CoreBndr]
alts SimplCont
cont
                -- NB: We call mkDupableCaseCont here to make cont duplicable
                --     (if necessary, depending on the number of alts)
                -- And this is important: see Note [Fusing case continuations]

        ; let cont_scaling :: Kind
cont_scaling = SimplCont -> Kind
contHoleScaling SimplCont
cont
          -- See Note [Scaling in case-of-case]
        ; (SimplEnv
alt_env', CoreBndr
case_bndr') <- SimplEnv -> CoreBndr -> SimplM (SimplEnv, CoreBndr)
simplBinder SimplEnv
alt_env (Kind -> CoreBndr -> CoreBndr
scaleIdBy Kind
cont_scaling CoreBndr
case_bndr)
        ; [Alt CoreBndr]
alts' <- (Alt CoreBndr -> SimplM (Alt CoreBndr))
-> [Alt CoreBndr] -> SimplM [Alt CoreBndr]
forall (t :: * -> *) (m :: * -> *) a b.
(Traversable t, Monad m) =>
(a -> m b) -> t a -> m (t b)
forall (m :: * -> *) a b. Monad m => (a -> m b) -> [a] -> m [b]
mapM (SimplEnv
-> Maybe CoreExpr
-> [AltCon]
-> CoreBndr
-> SimplCont
-> Alt CoreBndr
-> SimplM (Alt CoreBndr)
simplAlt SimplEnv
alt_env' Maybe CoreExpr
forall a. Maybe a
Nothing [] CoreBndr
case_bndr' SimplCont
alt_cont) (Kind -> [Alt CoreBndr] -> [Alt CoreBndr]
scaleAltsBy Kind
cont_scaling [Alt CoreBndr]
alts)
        -- Safe to say that there are no handled-cons for the DEFAULT case
                -- NB: simplBinder does not zap deadness occ-info, so
                -- a dead case_bndr' will still advertise its deadness
                -- This is really important because in
                --      case e of b { (# p,q #) -> ... }
                -- b is always dead, and indeed we are not allowed to bind b to (# p,q #),
                -- which might happen if e was an explicit unboxed pair and b wasn't marked dead.
                -- In the new alts we build, we have the new case binder, so it must retain
                -- its deadness.
        -- NB: we don't use alt_env further; it has the substEnv for
        --     the alternatives, and we don't want that

        ; let platform :: Platform
platform = SimplEnv -> Platform
sePlatform SimplEnv
env
        ; (JoinFloats
join_floats, [Alt CoreBndr]
alts'') <- (JoinFloats -> Alt CoreBndr -> SimplM (JoinFloats, Alt CoreBndr))
-> JoinFloats
-> [Alt CoreBndr]
-> SimplM (JoinFloats, [Alt CoreBndr])
forall (m :: * -> *) (t :: * -> *) acc x y.
(Monad m, Traversable t) =>
(acc -> x -> m (acc, y)) -> acc -> t x -> m (acc, t y)
mapAccumLM (Platform
-> CoreBndr
-> JoinFloats
-> Alt CoreBndr
-> SimplM (JoinFloats, Alt CoreBndr)
mkDupableAlt Platform
platform CoreBndr
case_bndr')
                                              JoinFloats
emptyJoinFloats [Alt CoreBndr]
alts'

        ; let all_floats :: SimplFloats
all_floats = SimplFloats
floats SimplFloats -> JoinFloats -> SimplFloats
`addJoinFloats` JoinFloats
join_floats
                           -- Note [Duplicated env]
        ; (SimplFloats, SimplCont) -> SimplM (SimplFloats, SimplCont)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplFloats
all_floats
                 , Select { sc_dup :: DupFlag
sc_dup  = DupFlag
OkToDup
                          , sc_bndr :: CoreBndr
sc_bndr = CoreBndr
case_bndr'
                          , sc_alts :: [Alt CoreBndr]
sc_alts = [Alt CoreBndr]
alts''
                          , sc_env :: SimplEnv
sc_env  = SimplEnv -> SimplEnv
zapSubstEnv SimplEnv
se SimplEnv -> SimplFloats -> SimplEnv
`setInScopeFromF` SimplFloats
all_floats
                                      -- See Note [StaticEnv invariant] in GHC.Core.Opt.Simplify.Utils
                          , sc_cont :: SimplCont
sc_cont = Kind -> SimplCont
mkBoringStop (SimplCont -> Kind
contResultType SimplCont
cont) } ) }

mkDupableStrictBind :: SimplEnv -> OutId -> OutExpr -> OutType
                    -> SimplM (SimplFloats, SimplCont)
mkDupableStrictBind :: SimplEnv
-> CoreBndr -> CoreExpr -> Kind -> SimplM (SimplFloats, SimplCont)
mkDupableStrictBind SimplEnv
env CoreBndr
arg_bndr CoreExpr
join_rhs Kind
res_ty
  | CoreExpr -> Bool
exprIsTrivial CoreExpr
join_rhs   -- See point (2) of Note [Duplicating join points]
  = (SimplFloats, SimplCont) -> SimplM (SimplFloats, SimplCont)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplEnv -> SimplFloats
emptyFloats SimplEnv
env
           , StrictBind { sc_bndr :: CoreBndr
sc_bndr = CoreBndr
arg_bndr
                        , sc_body :: CoreExpr
sc_body = CoreExpr
join_rhs
                        , sc_env :: SimplEnv
sc_env  = SimplEnv -> SimplEnv
zapSubstEnv SimplEnv
env
                        , sc_from :: FromWhat
sc_from = FromWhat
FromLet
                          -- See Note [StaticEnv invariant] in GHC.Core.Opt.Simplify.Utils
                        , sc_dup :: DupFlag
sc_dup  = DupFlag
OkToDup
                        , sc_cont :: SimplCont
sc_cont = Kind -> SimplCont
mkBoringStop Kind
res_ty } )
  | Bool
otherwise
  = do { CoreBndr
join_bndr <- [CoreBndr] -> Kind -> SimplM CoreBndr
newJoinId [CoreBndr
arg_bndr] Kind
res_ty
       ; let arg_info :: ArgInfo
arg_info = ArgInfo { ai_fun :: CoreBndr
ai_fun   = CoreBndr
join_bndr
                                , ai_rewrite :: RewriteCall
ai_rewrite = RewriteCall
TryNothing, ai_args :: [ArgSpec]
ai_args  = []
                                , ai_encl :: Bool
ai_encl  = Bool
False, ai_dmds :: [Demand]
ai_dmds  = Demand -> [Demand]
forall a. a -> [a]
repeat Demand
topDmd
                                , ai_discs :: [Int]
ai_discs = Int -> [Int]
forall a. a -> [a]
repeat Int
0 }
       ; (SimplFloats, SimplCont) -> SimplM (SimplFloats, SimplCont)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return ( SimplFloats -> JoinFloats -> SimplFloats
addJoinFloats (SimplEnv -> SimplFloats
emptyFloats SimplEnv
env) (JoinFloats -> SimplFloats) -> JoinFloats -> SimplFloats
forall a b. (a -> b) -> a -> b
$
                  InBind -> JoinFloats
unitJoinFloat                   (InBind -> JoinFloats) -> InBind -> JoinFloats
forall a b. (a -> b) -> a -> b
$
                  CoreBndr -> CoreExpr -> InBind
forall b. b -> Expr b -> Bind b
NonRec CoreBndr
join_bndr                (CoreExpr -> InBind) -> CoreExpr -> InBind
forall a b. (a -> b) -> a -> b
$
                  CoreBndr -> CoreExpr -> CoreExpr
forall b. b -> Expr b -> Expr b
Lam (CoreBndr -> CoreBndr
setOneShotLambda CoreBndr
arg_bndr) CoreExpr
join_rhs
                , StrictArg { sc_dup :: DupFlag
sc_dup    = DupFlag
OkToDup
                            , sc_fun :: ArgInfo
sc_fun    = ArgInfo
arg_info
                            , sc_fun_ty :: Kind
sc_fun_ty = CoreBndr -> Kind
idType CoreBndr
join_bndr
                            , sc_cont :: SimplCont
sc_cont   = Kind -> SimplCont
mkBoringStop Kind
res_ty
                            } ) }

mkDupableAlt :: Platform -> OutId
             -> JoinFloats -> OutAlt
             -> SimplM (JoinFloats, OutAlt)
mkDupableAlt :: Platform
-> CoreBndr
-> JoinFloats
-> Alt CoreBndr
-> SimplM (JoinFloats, Alt CoreBndr)
mkDupableAlt Platform
_platform CoreBndr
case_bndr JoinFloats
jfloats (Alt AltCon
con [CoreBndr]
alt_bndrs CoreExpr
alt_rhs_in)
  | CoreExpr -> Bool
exprIsTrivial CoreExpr
alt_rhs_in   -- See point (2) of Note [Duplicating join points]
  = (JoinFloats, Alt CoreBndr) -> SimplM (JoinFloats, Alt CoreBndr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (JoinFloats
jfloats, AltCon -> [CoreBndr] -> CoreExpr -> Alt CoreBndr
forall b. AltCon -> [b] -> Expr b -> Alt b
Alt AltCon
con [CoreBndr]
alt_bndrs CoreExpr
alt_rhs_in)

  | Bool
otherwise
  = do  { let rhs_ty' :: Kind
rhs_ty'  = (() :: Constraint) => CoreExpr -> Kind
CoreExpr -> Kind
exprType CoreExpr
alt_rhs_in

              bangs :: [StrictnessMark]
bangs
                | DataAlt DataCon
c <- AltCon
con
                = DataCon -> [StrictnessMark]
dataConRepStrictness DataCon
c
                | Bool
otherwise = []

              abstracted_binders :: [(CoreBndr, StrictnessMark)]
abstracted_binders = [CoreBndr] -> [StrictnessMark] -> [(CoreBndr, StrictnessMark)]
abstract_binders [CoreBndr]
alt_bndrs [StrictnessMark]
bangs

              abstract_binders :: [Var] -> [StrictnessMark] -> [(Id,StrictnessMark)]
              abstract_binders :: [CoreBndr] -> [StrictnessMark] -> [(CoreBndr, StrictnessMark)]
abstract_binders [] []
                -- Abstract over the case binder too if it's used.
                | CoreBndr -> Bool
isDeadBinder CoreBndr
case_bndr  = []
                | Bool
otherwise               = [(CoreBndr
case_bndr,StrictnessMark
MarkedStrict)]
              abstract_binders (CoreBndr
alt_bndr:[CoreBndr]
alt_bndrs) [StrictnessMark]
marks
                -- Abstract over all type variables just in case
                | CoreBndr -> Bool
isTyVar CoreBndr
alt_bndr        = (CoreBndr
alt_bndr,StrictnessMark
NotMarkedStrict) (CoreBndr, StrictnessMark)
-> [(CoreBndr, StrictnessMark)] -> [(CoreBndr, StrictnessMark)]
forall a. a -> [a] -> [a]
: [CoreBndr] -> [StrictnessMark] -> [(CoreBndr, StrictnessMark)]
abstract_binders [CoreBndr]
alt_bndrs [StrictnessMark]
marks
              abstract_binders (CoreBndr
alt_bndr:[CoreBndr]
alt_bndrs) (StrictnessMark
mark:[StrictnessMark]
marks)
                -- The deadness info on the new Ids is preserved by simplBinders
                -- We don't abstract over dead ids here.
                | CoreBndr -> Bool
isDeadBinder CoreBndr
alt_bndr   = [CoreBndr] -> [StrictnessMark] -> [(CoreBndr, StrictnessMark)]
abstract_binders [CoreBndr]
alt_bndrs [StrictnessMark]
marks
                | Bool
otherwise               = (CoreBndr
alt_bndr,StrictnessMark
mark) (CoreBndr, StrictnessMark)
-> [(CoreBndr, StrictnessMark)] -> [(CoreBndr, StrictnessMark)]
forall a. a -> [a] -> [a]
: [CoreBndr] -> [StrictnessMark] -> [(CoreBndr, StrictnessMark)]
abstract_binders [CoreBndr]
alt_bndrs [StrictnessMark]
marks
              abstract_binders [CoreBndr]
_ [StrictnessMark]
_ = String -> SDoc -> [(CoreBndr, StrictnessMark)]
forall a. HasCallStack => String -> SDoc -> a
pprPanic String
"abstrict_binders - failed to abstract" (Alt CoreBndr -> SDoc
forall a. Outputable a => a -> SDoc
ppr (Alt CoreBndr -> SDoc) -> Alt CoreBndr -> SDoc
forall a b. (a -> b) -> a -> b
$ AltCon -> [CoreBndr] -> CoreExpr -> Alt CoreBndr
forall b. AltCon -> [b] -> Expr b -> Alt b
Alt AltCon
con [CoreBndr]
alt_bndrs CoreExpr
alt_rhs_in)

              filtered_binders :: [CoreBndr]
filtered_binders = ((CoreBndr, StrictnessMark) -> CoreBndr)
-> [(CoreBndr, StrictnessMark)] -> [CoreBndr]
forall a b. (a -> b) -> [a] -> [b]
map (CoreBndr, StrictnessMark) -> CoreBndr
forall a b. (a, b) -> a
fst [(CoreBndr, StrictnessMark)]
abstracted_binders
              -- We want to make any binder with an evaldUnfolding strict in the rhs.
              -- See Note [Call-by-value for worker args] (which also applies to join points)
              (CoreExpr
rhs_with_seqs) = [(CoreBndr, StrictnessMark)] -> CoreExpr -> CoreExpr
mkStrictFieldSeqs [(CoreBndr, StrictnessMark)]
abstracted_binders CoreExpr
alt_rhs_in

              final_args :: [CoreExpr]
final_args = [CoreBndr] -> [CoreExpr]
forall b. [CoreBndr] -> [Expr b]
varsToCoreExprs [CoreBndr]
filtered_binders
                           -- Note [Join point abstraction]

                -- We make the lambdas into one-shot-lambdas.  The
                -- join point is sure to be applied at most once, and doing so
                -- prevents the body of the join point being floated out by
                -- the full laziness pass
              final_bndrs :: [CoreBndr]
final_bndrs     = (CoreBndr -> CoreBndr) -> [CoreBndr] -> [CoreBndr]
forall a b. (a -> b) -> [a] -> [b]
map CoreBndr -> CoreBndr
one_shot [CoreBndr]
filtered_binders
              one_shot :: CoreBndr -> CoreBndr
one_shot CoreBndr
v | CoreBndr -> Bool
isId CoreBndr
v    = CoreBndr -> CoreBndr
setOneShotLambda CoreBndr
v
                         | Bool
otherwise = CoreBndr
v

              -- No lambda binder has an unfolding, but (currently) case binders can,
              -- so we must zap them here.
              join_rhs :: CoreExpr
join_rhs   = [CoreBndr] -> CoreExpr -> CoreExpr
forall b. [b] -> Expr b -> Expr b
mkLams ((CoreBndr -> CoreBndr) -> [CoreBndr] -> [CoreBndr]
forall a b. (a -> b) -> [a] -> [b]
map CoreBndr -> CoreBndr
zapIdUnfolding [CoreBndr]
final_bndrs) CoreExpr
rhs_with_seqs

        ; CoreBndr
join_bndr <- [CoreBndr] -> Kind -> SimplM CoreBndr
newJoinId [CoreBndr]
filtered_binders Kind
rhs_ty'

        ; let join_call :: CoreExpr
join_call = CoreExpr -> [CoreExpr] -> CoreExpr
forall b. Expr b -> [Expr b] -> Expr b
mkApps (CoreBndr -> CoreExpr
forall b. CoreBndr -> Expr b
Var CoreBndr
join_bndr) [CoreExpr]
final_args
              alt' :: Alt CoreBndr
alt'      = AltCon -> [CoreBndr] -> CoreExpr -> Alt CoreBndr
forall b. AltCon -> [b] -> Expr b -> Alt b
Alt AltCon
con [CoreBndr]
alt_bndrs CoreExpr
join_call

        ; (JoinFloats, Alt CoreBndr) -> SimplM (JoinFloats, Alt CoreBndr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return ( JoinFloats
jfloats JoinFloats -> JoinFloats -> JoinFloats
`addJoinFlts` InBind -> JoinFloats
unitJoinFloat (CoreBndr -> CoreExpr -> InBind
forall b. b -> Expr b -> Bind b
NonRec CoreBndr
join_bndr CoreExpr
join_rhs)
                 , Alt CoreBndr
alt') }
                -- See Note [Duplicated env]

{-
Note [Fusing case continuations]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
It's important to fuse two successive case continuations when the
first has one alternative.  That's why we call prepareCaseCont here.
Consider this, which arises from thunk splitting (see Note [Thunk
splitting] in GHC.Core.Opt.WorkWrap):

      let
        x* = case (case v of {pn -> rn}) of
               I# a -> I# a
      in body

The simplifier will find
    (Var v) with continuation
            Select (pn -> rn) (
            Select [I# a -> I# a] (
            StrictBind body Stop

So we'll call mkDupableCont on
   Select [I# a -> I# a] (StrictBind body Stop)
There is just one alternative in the first Select, so we want to
simplify the rhs (I# a) with continuation (StrictBind body Stop)
Supposing that body is big, we end up with
          let $j a = <let x = I# a in body>
          in case v of { pn -> case rn of
                                 I# a -> $j a }
This is just what we want because the rn produces a box that
the case rn cancels with.

See #4957 a fuller example.

Note [Duplicating join points]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
IN #19996 we discovered that we want to be really careful about
inlining join points.   Consider
    case (join $j x = K f x )
         (in case v of      )
         (     p1 -> $j x1  ) of
         (     p2 -> $j x2  )
         (     p3 -> $j x3  )
      K g y -> blah[g,y]

Here the join-point RHS is very small, just a constructor
application (K x y).  So we might inline it to get
    case (case v of        )
         (     p1 -> K f x1  ) of
         (     p2 -> K f x2  )
         (     p3 -> K f x3  )
      K g y -> blah[g,y]

But now we have to make `blah` into a join point, /abstracted/
over `g` and `y`.   In contrast, if we /don't/ inline $j we
don't need a join point for `blah` and we'll get
    join $j x = let g=f, y=x in blah[g,y]
    in case v of
       p1 -> $j x1
       p2 -> $j x2
       p3 -> $j x3

This can make a /massive/ difference, because `blah` can see
what `f` is, instead of lambda-abstracting over it.

To achieve this:

1. Do not postInlineUnconditionally a join point, until the Final
   phase.  (The Final phase is still quite early, so we might consider
   delaying still more.)

2. In mkDupableAlt and mkDupableStrictBind, generate an alterative for
   all alternatives, except for exprIsTrival RHSs. Previously we used
   exprIsDupable.  This generates a lot more join points, but makes
   them much more case-of-case friendly.

   It is definitely worth checking for exprIsTrivial, otherwise we get
   an extra Simplifier iteration, because it is inlined in the next
   round.

3. By the same token we want to use Plan B in
   Note [Duplicating StrictArg] when the RHS of the new join point
   is a data constructor application.  That same Note explains why we
   want Plan A when the RHS of the new join point would be a
   non-data-constructor application

4. You might worry that $j will be inlined by the call-site inliner,
   but it won't because the call-site context for a join is usually
   extremely boring (the arguments come from the pattern match).
   And if not, then perhaps inlining it would be a good idea.

   You might also wonder if we get UnfWhen, because the RHS of the
   join point is no bigger than the call. But in the cases we care
   about it will be a little bigger, because of that free `f` in
       $j x = K f x
   So for now we don't do anything special in callSiteInline

There is a bit of tension between (2) and (3).  Do we want to retain
the join point only when the RHS is
* a constructor application? or
* just non-trivial?
Currently, a bit ad-hoc, but we definitely want to retain the join
point for data constructors in mkDupalbleALt (point 2); that is the
whole point of #19996 described above.

Historical Note [Case binders and join points]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
NB: this entire Note is now irrelevant.  In Jun 21 we stopped
adding unfoldings to lambda binders (#17530).  It was always a
hack and bit us in multiple small and not-so-small ways

Consider this
   case (case .. ) of c {
     I# c# -> ....c....

If we make a join point with c but not c# we get
  $j = \c -> ....c....

But if later inlining scrutinises the c, thus

  $j = \c -> ... case c of { I# y -> ... } ...

we won't see that 'c' has already been scrutinised.  This actually
happens in the 'tabulate' function in wave4main, and makes a significant
difference to allocation.

An alternative plan is this:

   $j = \c# -> let c = I# c# in ...c....

but that is bad if 'c' is *not* later scrutinised.

So instead we do both: we pass 'c' and 'c#' , and record in c's inlining
(a stable unfolding) that it's really I# c#, thus

   $j = \c# -> \c[=I# c#] -> ...c....

Absence analysis may later discard 'c'.

NB: take great care when doing strictness analysis;
    see Note [Lambda-bound unfoldings] in GHC.Core.Opt.DmdAnal.

Also note that we can still end up passing stuff that isn't used.  Before
strictness analysis we have
   let $j x y c{=(x,y)} = (h c, ...)
   in ...
After strictness analysis we see that h is strict, we end up with
   let $j x y c{=(x,y)} = ($wh x y, ...)
and c is unused.

Note [Duplicated env]
~~~~~~~~~~~~~~~~~~~~~
Some of the alternatives are simplified, but have not been turned into a join point
So they *must* have a zapped subst-env.  So we can't use completeNonRecX to
bind the join point, because it might to do PostInlineUnconditionally, and
we'd lose that when zapping the subst-env.  We could have a per-alt subst-env,
but zapping it (as we do in mkDupableCont, the Select case) is safe, and
at worst delays the join-point inlining.

Note [Funky mkLamTypes]
~~~~~~~~~~~~~~~~~~~~~~
Notice the funky mkLamTypes.  If the constructor has existentials
it's possible that the join point will be abstracted over
type variables as well as term variables.
 Example:  Suppose we have
        data T = forall t.  C [t]
 Then faced with
        case (case e of ...) of
            C t xs::[t] -> rhs
 We get the join point
        let j :: forall t. [t] -> ...
            j = /\t \xs::[t] -> rhs
        in
        case (case e of ...) of
            C t xs::[t] -> j t xs

Note [Duplicating StrictArg]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Dealing with making a StrictArg continuation duplicable has turned out
to be one of the trickiest corners of the simplifier, giving rise
to several cases in which the simplier expanded the program's size
*exponentially*.  They include
  #13253 exponential inlining
  #10421 ditto
  #18140 strict constructors
  #18282 another nested-function call case

Suppose we have a call
  f e1 (case x of { True -> r1; False -> r2 }) e3
and f is strict in its second argument.  Then we end up in
mkDupableCont with a StrictArg continuation for (f e1 <> e3).
There are two ways to make it duplicable.

* Plan A: move the entire call inwards, being careful not
  to duplicate e1 or e3, thus:
     let a1 = e1
         a3 = e3
     in case x of { True  -> f a1 r1 a3
                  ; False -> f a1 r2 a3 }

* Plan B: make a join point:
     join $j x = f e1 x e3
     in case x of { True  -> jump $j r1
                  ; False -> jump $j r2 }

  Notice that Plan B is very like the way we handle strict bindings;
  see Note [Duplicating StrictBind].  And Plan B is exactly what we'd
  get if we turned use a case expression to evaluate the strict arg:

       case (case x of { True -> r1; False -> r2 }) of
         r -> f e1 r e3

  So, looking at Note [Duplicating join points], we also want Plan B
  when `f` is a data constructor.

Plan A is often good. Here's an example from #3116
     go (n+1) (case l of
                 1  -> bs'
                 _  -> Chunk p fpc (o+1) (l-1) bs')

If we pushed the entire call for 'go' inside the case, we get
call-pattern specialisation for 'go', which is *crucial* for
this particular program.

Here is another example.
        && E (case x of { T -> F; F -> T })

Pushing the call inward (being careful not to duplicate E)
        let a = E
        in case x of { T -> && a F; F -> && a T }

and now the (&& a F) etc can optimise.  Moreover there might
be a RULE for the function that can fire when it "sees" the
particular case alternative.

But Plan A can have terrible, terrible behaviour. Here is a classic
case:
  f (f (f (f (f True))))

Suppose f is strict, and has a body that is small enough to inline.
The innermost call inlines (seeing the True) to give
  f (f (f (f (case v of { True -> e1; False -> e2 }))))

Now, suppose we naively push the entire continuation into both
case branches (it doesn't look large, just f.f.f.f). We get
  case v of
    True  -> f (f (f (f e1)))
    False -> f (f (f (f e2)))

And now the process repeats, so we end up with an exponentially large
number of copies of f. No good!

CONCLUSION: we want Plan A in general, but do Plan B is there a
danger of this nested call behaviour. The function that decides
this is called thumbsUpPlanA.

Note [Keeping demand info in StrictArg Plan A]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Following on from Note [Duplicating StrictArg], another common code
pattern that can go bad is this:
   f (case x1 of { T -> F; F -> T })
     (case x2 of { T -> F; F -> T })
     ...etc...
when f is strict in all its arguments.  (It might, for example, be a
strict data constructor whose wrapper has not yet been inlined.)

We use Plan A (because there is no nesting) giving
  let a2 = case x2 of ...
      a3 = case x3 of ...
  in case x1 of { T -> f F a2 a3 ... ; F -> f T a2 a3 ... }

Now we must be careful!  a2 and a3 are small, and the OneOcc code in
postInlineUnconditionally may inline them both at both sites; see Note
Note [Inline small things to avoid creating a thunk] in
Simplify.Utils. But if we do inline them, the entire process will
repeat -- back to exponential behaviour.

So we are careful to keep the demand-info on a2 and a3.  Then they'll
be /strict/ let-bindings, which will be dealt with by StrictBind.
That's why contIsDupableWithDmds is careful to propagage demand
info to the auxiliary bindings it creates.  See the Demand argument
to makeTrivial.

Note [Duplicating StrictBind]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We make a StrictBind duplicable in a very similar way to
that for case expressions.  After all,
   let x* = e in b   is similar to    case e of x -> b

So we potentially make a join-point for the body, thus:
   let x = <> in b   ==>   join j x = b
                           in j <>

Just like StrictArg in fact -- and indeed they share code.

Note [Join point abstraction]  Historical note
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
NB: This note is now historical, describing how (in the past) we used
to add a void argument to nullary join points.  But now that "join
point" is not a fuzzy concept but a formal syntactic construct (as
distinguished by the JoinId constructor of IdDetails), each of these
concerns is handled separately, with no need for a vestigial extra
argument.

Join points always have at least one value argument,
for several reasons

* If we try to lift a primitive-typed something out
  for let-binding-purposes, we will *caseify* it (!),
  with potentially-disastrous strictness results.  So
  instead we turn it into a function: \v -> e
  where v::Void#.  The value passed to this function is void,
  which generates (almost) no code.

* CPR.  We used to say "&& isUnliftedType rhs_ty'" here, but now
  we make the join point into a function whenever used_bndrs'
  is empty.  This makes the join-point more CPR friendly.
  Consider:       let j = if .. then I# 3 else I# 4
                  in case .. of { A -> j; B -> j; C -> ... }

  Now CPR doesn't w/w j because it's a thunk, so
  that means that the enclosing function can't w/w either,
  which is a lose.  Here's the example that happened in practice:
          kgmod :: Int -> Int -> Int
          kgmod x y = if x > 0 && y < 0 || x < 0 && y > 0
                      then 78
                      else 5

* Let-no-escape.  We want a join point to turn into a let-no-escape
  so that it is implemented as a jump, and one of the conditions
  for LNE is that it's not updatable.  In CoreToStg, see
  Note [What is a non-escaping let]

* Floating.  Since a join point will be entered once, no sharing is
  gained by floating out, but something might be lost by doing
  so because it might be allocated.

I have seen a case alternative like this:
        True -> \v -> ...
It's a bit silly to add the realWorld dummy arg in this case, making
        $j = \s v -> ...
           True -> $j s
(the \v alone is enough to make CPR happy) but I think it's rare

There's a slight infelicity here: we pass the overall
case_bndr to all the join points if it's used in *any* RHS,
because we don't know its usage in each RHS separately



************************************************************************
*                                                                      *
                    Unfoldings
*                                                                      *
************************************************************************
-}

simplLetUnfolding :: SimplEnv
                  -> BindContext
                  -> InId
                  -> OutExpr -> OutType -> ArityType
                  -> Unfolding -> SimplM Unfolding
simplLetUnfolding :: SimplEnv
-> BindContext
-> CoreBndr
-> CoreExpr
-> Kind
-> ArityType
-> Unfolding
-> SimplM Unfolding
simplLetUnfolding SimplEnv
env BindContext
bind_cxt CoreBndr
id CoreExpr
new_rhs Kind
rhs_ty ArityType
arity Unfolding
unf
  | Unfolding -> Bool
isStableUnfolding Unfolding
unf
  = SimplEnv
-> BindContext
-> CoreBndr
-> Kind
-> ArityType
-> Unfolding
-> SimplM Unfolding
simplStableUnfolding SimplEnv
env BindContext
bind_cxt CoreBndr
id Kind
rhs_ty ArityType
arity Unfolding
unf
  | CoreBndr -> Bool
isExitJoinId CoreBndr
id
  = Unfolding -> SimplM Unfolding
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return Unfolding
noUnfolding -- See Note [Do not inline exit join points] in GHC.Core.Opt.Exitify
  | Bool
otherwise
  = -- Otherwise, we end up retaining all the SimpleEnv
    let !opts :: UnfoldingOpts
opts = SimplEnv -> UnfoldingOpts
seUnfoldingOpts SimplEnv
env
    in UnfoldingOpts
-> TopLevelFlag
-> UnfoldingSource
-> CoreBndr
-> CoreExpr
-> SimplM Unfolding
mkLetUnfolding UnfoldingOpts
opts (BindContext -> TopLevelFlag
bindContextLevel BindContext
bind_cxt) UnfoldingSource
VanillaSrc CoreBndr
id CoreExpr
new_rhs

-------------------
mkLetUnfolding :: UnfoldingOpts -> TopLevelFlag -> UnfoldingSource
               -> InId -> OutExpr -> SimplM Unfolding
mkLetUnfolding :: UnfoldingOpts
-> TopLevelFlag
-> UnfoldingSource
-> CoreBndr
-> CoreExpr
-> SimplM Unfolding
mkLetUnfolding !UnfoldingOpts
uf_opts TopLevelFlag
top_lvl UnfoldingSource
src CoreBndr
id CoreExpr
new_rhs
  = Unfolding -> SimplM Unfolding
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (UnfoldingOpts
-> UnfoldingSource
-> Bool
-> Bool
-> CoreExpr
-> Maybe UnfoldingCache
-> Unfolding
mkUnfolding UnfoldingOpts
uf_opts UnfoldingSource
src Bool
is_top_lvl Bool
is_bottoming CoreExpr
new_rhs Maybe UnfoldingCache
forall a. Maybe a
Nothing)
            -- We make an  unfolding *even for loop-breakers*.
            -- Reason: (a) It might be useful to know that they are WHNF
            --         (b) In GHC.Iface.Tidy we currently assume that, if we want to
            --             expose the unfolding then indeed we *have* an unfolding
            --             to expose.  (We could instead use the RHS, but currently
            --             we don't.)  The simple thing is always to have one.
  where
    -- Might as well force this, profiles indicate up to 0.5MB of thunks
    -- just from this site.
    !is_top_lvl :: Bool
is_top_lvl   = TopLevelFlag -> Bool
isTopLevel TopLevelFlag
top_lvl
    -- See Note [Force bottoming field]
    !is_bottoming :: Bool
is_bottoming = CoreBndr -> Bool
isDeadEndId CoreBndr
id

-------------------
simplStableUnfolding :: SimplEnv -> BindContext
                     -> InId
                     -> OutType
                     -> ArityType      -- Used to eta expand, but only for non-join-points
                     -> Unfolding
                     ->SimplM Unfolding
-- Note [Setting the new unfolding]
simplStableUnfolding :: SimplEnv
-> BindContext
-> CoreBndr
-> Kind
-> ArityType
-> Unfolding
-> SimplM Unfolding
simplStableUnfolding SimplEnv
env BindContext
bind_cxt CoreBndr
id Kind
rhs_ty ArityType
id_arity Unfolding
unf
  = case Unfolding
unf of
      Unfolding
NoUnfolding   -> Unfolding -> SimplM Unfolding
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return Unfolding
unf
      Unfolding
BootUnfolding -> Unfolding -> SimplM Unfolding
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return Unfolding
unf
      OtherCon {}   -> Unfolding -> SimplM Unfolding
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return Unfolding
unf

      DFunUnfolding { df_bndrs :: Unfolding -> [CoreBndr]
df_bndrs = [CoreBndr]
bndrs, df_con :: Unfolding -> DataCon
df_con = DataCon
con, df_args :: Unfolding -> [CoreExpr]
df_args = [CoreExpr]
args }
        -> do { (SimplEnv
env', [CoreBndr]
bndrs') <- SimplEnv -> [CoreBndr] -> SimplM (SimplEnv, [CoreBndr])
simplBinders SimplEnv
unf_env [CoreBndr]
bndrs
              ; [CoreExpr]
args' <- (CoreExpr -> SimplM CoreExpr) -> [CoreExpr] -> SimplM [CoreExpr]
forall (t :: * -> *) (m :: * -> *) a b.
(Traversable t, Monad m) =>
(a -> m b) -> t a -> m (t b)
forall (m :: * -> *) a b. Monad m => (a -> m b) -> [a] -> m [b]
mapM (SimplEnv -> CoreExpr -> SimplM CoreExpr
simplExpr SimplEnv
env') [CoreExpr]
args
              ; Unfolding -> SimplM Unfolding
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return ([CoreBndr] -> DataCon -> [CoreExpr] -> Unfolding
mkDFunUnfolding [CoreBndr]
bndrs' DataCon
con [CoreExpr]
args') }

      CoreUnfolding { uf_tmpl :: Unfolding -> CoreExpr
uf_tmpl = CoreExpr
expr, uf_src :: Unfolding -> UnfoldingSource
uf_src = UnfoldingSource
src, uf_guidance :: Unfolding -> UnfoldingGuidance
uf_guidance = UnfoldingGuidance
guide }
        | UnfoldingSource -> Bool
isStableSource UnfoldingSource
src
        -> do { CoreExpr
expr' <- case BindContext
bind_cxt of
                  BC_Join RecFlag
_ SimplCont
cont    -> -- Binder is a join point
                                       -- See Note [Rules and unfolding for join points]
                                       SimplEnv -> CoreBndr -> CoreExpr -> SimplCont -> SimplM CoreExpr
simplJoinRhs SimplEnv
unf_env CoreBndr
id CoreExpr
expr SimplCont
cont
                  BC_Let TopLevelFlag
_ RecFlag
is_rec -> -- Binder is not a join point
                                     do { let cont :: SimplCont
cont = Kind -> RecFlag -> Demand -> SimplCont
mkRhsStop Kind
rhs_ty RecFlag
is_rec Demand
topDmd
                                           -- mkRhsStop: switch off eta-expansion at the top level
                                        ; CoreExpr
expr' <- SimplEnv -> CoreExpr -> SimplCont -> SimplM CoreExpr
simplExprC SimplEnv
unf_env CoreExpr
expr SimplCont
cont
                                        ; CoreExpr -> SimplM CoreExpr
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (CoreExpr -> CoreExpr
eta_expand CoreExpr
expr') }
              ; case UnfoldingGuidance
guide of
                  UnfWhen { ug_boring_ok :: UnfoldingGuidance -> Bool
ug_boring_ok = Bool
boring_ok }
                     -- Happens for INLINE things
                     -- Really important to force new_boring_ok since otherwise
                     --   `ug_boring_ok` is a thunk chain of
                     --   inlineBoringExprOk expr0 || inlineBoringExprOk expr1 || ...
                     -- See #20134
                     -> let !new_boring_ok :: Bool
new_boring_ok = Bool
boring_ok Bool -> Bool -> Bool
|| CoreExpr -> Bool
inlineBoringOk CoreExpr
expr'
                            guide' :: UnfoldingGuidance
guide' = UnfoldingGuidance
guide { ug_boring_ok = new_boring_ok }
                        -- Refresh the boring-ok flag, in case expr'
                        -- has got small. This happens, notably in the inlinings
                        -- for dfuns for single-method classes; see
                        -- Note [Single-method classes] in GHC.Tc.TyCl.Instance.
                        -- A test case is #4138
                        -- But retain a previous boring_ok of True; e.g. see
                        -- the way it is set in calcUnfoldingGuidanceWithArity
                        in Unfolding -> SimplM Unfolding
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (UnfoldingSource
-> Bool
-> CoreExpr
-> Maybe UnfoldingCache
-> UnfoldingGuidance
-> Unfolding
mkCoreUnfolding UnfoldingSource
src Bool
is_top_lvl CoreExpr
expr' Maybe UnfoldingCache
forall a. Maybe a
Nothing UnfoldingGuidance
guide')
                            -- See Note [Top-level flag on inline rules] in GHC.Core.Unfold

                  UnfoldingGuidance
_other              -- Happens for INLINABLE things
                     -> UnfoldingOpts
-> TopLevelFlag
-> UnfoldingSource
-> CoreBndr
-> CoreExpr
-> SimplM Unfolding
mkLetUnfolding UnfoldingOpts
uf_opts TopLevelFlag
top_lvl UnfoldingSource
src CoreBndr
id CoreExpr
expr' }
                -- If the guidance is UnfIfGoodArgs, this is an INLINABLE
                -- unfolding, and we need to make sure the guidance is kept up
                -- to date with respect to any changes in the unfolding.

        | Bool
otherwise -> Unfolding -> SimplM Unfolding
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return Unfolding
noUnfolding   -- Discard unstable unfoldings
  where
    uf_opts :: UnfoldingOpts
uf_opts    = SimplEnv -> UnfoldingOpts
seUnfoldingOpts SimplEnv
env
    -- Forcing this can save about 0.5MB of max residency and the result
    -- is small and easy to compute so might as well force it.
    top_lvl :: TopLevelFlag
top_lvl     = BindContext -> TopLevelFlag
bindContextLevel BindContext
bind_cxt
    !is_top_lvl :: Bool
is_top_lvl = TopLevelFlag -> Bool
isTopLevel TopLevelFlag
top_lvl
    act :: Activation
act        = CoreBndr -> Activation
idInlineActivation CoreBndr
id
    unf_env :: SimplEnv
unf_env    = (SimplMode -> SimplMode) -> SimplEnv -> SimplEnv
updMode (Activation -> SimplMode -> SimplMode
updModeForStableUnfoldings Activation
act) SimplEnv
env
         -- See Note [Simplifying inside stable unfoldings] in GHC.Core.Opt.Simplify.Utils

    -- See Note [Eta-expand stable unfoldings]
    -- Use the arity from the main Id (in id_arity), rather than computing it from rhs
    -- Not used for join points
    eta_expand :: CoreExpr -> CoreExpr
eta_expand CoreExpr
expr | SimplEnv -> Bool
seEtaExpand SimplEnv
env
                    , CoreExpr -> Int
exprArity CoreExpr
expr Int -> Int -> Bool
forall a. Ord a => a -> a -> Bool
< ArityType -> Int
arityTypeArity ArityType
id_arity
                    , CoreExpr -> Bool
wantEtaExpansion CoreExpr
expr
                    = InScopeSet -> ArityType -> CoreExpr -> CoreExpr
etaExpandAT (SimplEnv -> InScopeSet
getInScope SimplEnv
env) ArityType
id_arity CoreExpr
expr
                    | Bool
otherwise
                    = CoreExpr
expr

{- Note [Eta-expand stable unfoldings]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
For INLINE/INLINABLE things (which get stable unfoldings) there's a danger
of getting
   f :: Int -> Int -> Int -> Blah
   [ Arity = 3                 -- Good arity
   , Unf=Stable (\xy. blah)    -- Less good arity, only 2
   f = \pqr. e

This can happen because f's RHS is optimised more vigorously than
its stable unfolding.  Now suppose we have a call
   g = f x
Because f has arity=3, g will have arity=2.  But if we inline f (using
its stable unfolding) g's arity will reduce to 1, because <blah>
hasn't been optimised yet.  This happened in the 'parsec' library,
for Text.Pasec.Char.string.

Generally, if we know that 'f' has arity N, it seems sensible to
eta-expand the stable unfolding to arity N too. Simple and consistent.

Wrinkles

* See Historical-note [Eta-expansion in stable unfoldings] in
  GHC.Core.Opt.Simplify.Utils

* Don't eta-expand a trivial expr, else each pass will eta-reduce it,
  and then eta-expand again. See Note [Which RHSs do we eta-expand?]
  in GHC.Core.Opt.Simplify.Utils.

* Don't eta-expand join points; see Note [Do not eta-expand join points]
  in GHC.Core.Opt.Simplify.Utils.  We uphold this because the join-point
  case (bind_cxt = BC_Join {}) doesn't use eta_expand.

Note [Force bottoming field]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We need to force bottoming, or the new unfolding holds
on to the old unfolding (which is part of the id).

Note [Setting the new unfolding]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
* If there's an INLINE pragma, we simplify the RHS gently.  Maybe we
  should do nothing at all, but simplifying gently might get rid of
  more crap.

* If not, we make an unfolding from the new RHS.  But *only* for
  non-loop-breakers. Making loop breakers not have an unfolding at all
  means that we can avoid tests in exprIsConApp, for example.  This is
  important: if exprIsConApp says 'yes' for a recursive thing, then we
  can get into an infinite loop

If there's a stable unfolding on a loop breaker (which happens for
INLINABLE), we hang on to the inlining.  It's pretty dodgy, but the
user did say 'INLINE'.  May need to revisit this choice.

************************************************************************
*                                                                      *
                    Rules
*                                                                      *
************************************************************************

Note [Rules in a letrec]
~~~~~~~~~~~~~~~~~~~~~~~~
After creating fresh binders for the binders of a letrec, we
substitute the RULES and add them back onto the binders; this is done
*before* processing any of the RHSs.  This is important.  Manuel found
cases where he really, really wanted a RULE for a recursive function
to apply in that function's own right-hand side.

See Note [Forming Rec groups] in "GHC.Core.Opt.OccurAnal"
-}

addBndrRules :: SimplEnv -> InBndr -> OutBndr
             -> BindContext
             -> SimplM (SimplEnv, OutBndr)
-- Rules are added back into the bin
addBndrRules :: SimplEnv
-> CoreBndr
-> CoreBndr
-> BindContext
-> SimplM (SimplEnv, CoreBndr)
addBndrRules SimplEnv
env CoreBndr
in_id CoreBndr
out_id BindContext
bind_cxt
  | [CoreRule] -> Bool
forall a. [a] -> Bool
forall (t :: * -> *) a. Foldable t => t a -> Bool
null [CoreRule]
old_rules
  = (SimplEnv, CoreBndr) -> SimplM (SimplEnv, CoreBndr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplEnv
env, CoreBndr
out_id)
  | Bool
otherwise
  = do { [CoreRule]
new_rules <- SimplEnv
-> Maybe CoreBndr -> [CoreRule] -> BindContext -> SimplM [CoreRule]
simplRules SimplEnv
env (CoreBndr -> Maybe CoreBndr
forall a. a -> Maybe a
Just CoreBndr
out_id) [CoreRule]
old_rules BindContext
bind_cxt
       ; let final_id :: CoreBndr
final_id  = CoreBndr
out_id CoreBndr -> RuleInfo -> CoreBndr
`setIdSpecialisation` [CoreRule] -> RuleInfo
mkRuleInfo [CoreRule]
new_rules
       ; (SimplEnv, CoreBndr) -> SimplM (SimplEnv, CoreBndr)
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (SimplEnv -> CoreBndr -> SimplEnv
modifyInScope SimplEnv
env CoreBndr
final_id, CoreBndr
final_id) }
  where
    old_rules :: [CoreRule]
old_rules = RuleInfo -> [CoreRule]
ruleInfoRules (CoreBndr -> RuleInfo
idSpecialisation CoreBndr
in_id)

simplImpRules :: SimplEnv -> [CoreRule] -> SimplM [CoreRule]
-- Simplify local rules for imported Ids
simplImpRules :: SimplEnv -> [CoreRule] -> SimplM [CoreRule]
simplImpRules SimplEnv
env [CoreRule]
rules
  = SimplEnv
-> Maybe CoreBndr -> [CoreRule] -> BindContext -> SimplM [CoreRule]
simplRules SimplEnv
env Maybe CoreBndr
forall a. Maybe a
Nothing [CoreRule]
rules (TopLevelFlag -> RecFlag -> BindContext
BC_Let TopLevelFlag
TopLevel RecFlag
NonRecursive)

simplRules :: SimplEnv -> Maybe OutId -> [CoreRule]
           -> BindContext -> SimplM [CoreRule]
simplRules :: SimplEnv
-> Maybe CoreBndr -> [CoreRule] -> BindContext -> SimplM [CoreRule]
simplRules SimplEnv
env Maybe CoreBndr
mb_new_id [CoreRule]
rules BindContext
bind_cxt
  = (CoreRule -> SimplM CoreRule) -> [CoreRule] -> SimplM [CoreRule]
forall (t :: * -> *) (m :: * -> *) a b.
(Traversable t, Monad m) =>
(a -> m b) -> t a -> m (t b)
forall (m :: * -> *) a b. Monad m => (a -> m b) -> [a] -> m [b]
mapM CoreRule -> SimplM CoreRule
simpl_rule [CoreRule]
rules
  where
    simpl_rule :: CoreRule -> SimplM CoreRule
simpl_rule rule :: CoreRule
rule@(BuiltinRule {})
      = CoreRule -> SimplM CoreRule
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return CoreRule
rule

    simpl_rule rule :: CoreRule
rule@(Rule { ru_bndrs :: CoreRule -> [CoreBndr]
ru_bndrs = [CoreBndr]
bndrs, ru_args :: CoreRule -> [CoreExpr]
ru_args = [CoreExpr]
args
                          , ru_fn :: CoreRule -> Name
ru_fn = Name
fn_name, ru_rhs :: CoreRule -> CoreExpr
ru_rhs = CoreExpr
rhs
                          , ru_act :: CoreRule -> Activation
ru_act = Activation
act })
      = do { (SimplEnv
env', [CoreBndr]
bndrs') <- SimplEnv -> [CoreBndr] -> SimplM (SimplEnv, [CoreBndr])
simplBinders SimplEnv
env [CoreBndr]
bndrs
           ; let rhs_ty :: Kind
rhs_ty = (() :: Constraint) => SimplEnv -> Kind -> Kind
SimplEnv -> Kind -> Kind
substTy SimplEnv
env' ((() :: Constraint) => CoreExpr -> Kind
CoreExpr -> Kind
exprType CoreExpr
rhs)
                 rhs_cont :: SimplCont
rhs_cont = case BindContext
bind_cxt of  -- See Note [Rules and unfolding for join points]
                                BC_Let {}      -> Kind -> SimplCont
mkBoringStop Kind
rhs_ty
                                BC_Join RecFlag
_ SimplCont
cont -> Bool -> SDoc -> SimplCont -> SimplCont
forall a. HasCallStack => Bool -> SDoc -> a -> a
assertPpr Bool
join_ok SDoc
bad_join_msg SimplCont
cont
                 lhs_env :: SimplEnv
lhs_env = (SimplMode -> SimplMode) -> SimplEnv -> SimplEnv
updMode SimplMode -> SimplMode
updModeForRules SimplEnv
env'
                 rhs_env :: SimplEnv
rhs_env = (SimplMode -> SimplMode) -> SimplEnv -> SimplEnv
updMode (Activation -> SimplMode -> SimplMode
updModeForStableUnfoldings Activation
act) SimplEnv
env'
                           -- See Note [Simplifying the RHS of a RULE]
                 -- Force this to avoid retaining reference to old Id
                 !fn_name' :: Name
fn_name' = case Maybe CoreBndr
mb_new_id of
                              Just CoreBndr
id -> CoreBndr -> Name
idName CoreBndr
id
                              Maybe CoreBndr
Nothing -> Name
fn_name

                 -- join_ok is an assertion check that the join-arity of the
                 -- binder matches that of the rule, so that pushing the
                 -- continuation into the RHS makes sense
                 join_ok :: Bool
join_ok = case Maybe CoreBndr
mb_new_id of
                             Just CoreBndr
id | Just Int
join_arity <- CoreBndr -> Maybe Int
isJoinId_maybe CoreBndr
id
                                     -> [CoreExpr] -> Int
forall a. [a] -> Int
forall (t :: * -> *) a. Foldable t => t a -> Int
length [CoreExpr]
args Int -> Int -> Bool
forall a. Eq a => a -> a -> Bool
== Int
join_arity
                             Maybe CoreBndr
_ -> Bool
False
                 bad_join_msg :: SDoc
bad_join_msg = [SDoc] -> SDoc
forall doc. IsDoc doc => [doc] -> doc
vcat [ Maybe CoreBndr -> SDoc
forall a. Outputable a => a -> SDoc
ppr Maybe CoreBndr
mb_new_id, CoreRule -> SDoc
forall a. Outputable a => a -> SDoc
ppr CoreRule
rule
                                     , Maybe (Maybe Int) -> SDoc
forall a. Outputable a => a -> SDoc
ppr ((CoreBndr -> Maybe Int) -> Maybe CoreBndr -> Maybe (Maybe Int)
forall a b. (a -> b) -> Maybe a -> Maybe b
forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
fmap CoreBndr -> Maybe Int
isJoinId_maybe Maybe CoreBndr
mb_new_id) ]

           ; [CoreExpr]
args' <- (CoreExpr -> SimplM CoreExpr) -> [CoreExpr] -> SimplM [CoreExpr]
forall (t :: * -> *) (m :: * -> *) a b.
(Traversable t, Monad m) =>
(a -> m b) -> t a -> m (t b)
forall (m :: * -> *) a b. Monad m => (a -> m b) -> [a] -> m [b]
mapM (SimplEnv -> CoreExpr -> SimplM CoreExpr
simplExpr SimplEnv
lhs_env) [CoreExpr]
args
           ; CoreExpr
rhs'  <- SimplEnv -> CoreExpr -> SimplCont -> SimplM CoreExpr
simplExprC SimplEnv
rhs_env CoreExpr
rhs SimplCont
rhs_cont
           ; CoreRule -> SimplM CoreRule
forall a. a -> SimplM a
forall (m :: * -> *) a. Monad m => a -> m a
return (CoreRule
rule { ru_bndrs = bndrs'
                          , ru_fn    = fn_name'
                          , ru_args  = args'
                          , ru_rhs   = occurAnalyseExpr rhs' }) }
                            -- Remember to occ-analyse, to drop dead code.
                            -- See Note [OccInfo in unfoldings and rules] in GHC.Core

{- Note [Simplifying the RHS of a RULE]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We can simplify the RHS of a RULE much as we do the RHS of a stable
unfolding.  We used to use the much more conservative updModeForRules
for the RHS as well as the LHS, but that seems more conservative
than necesary.  Allowing some inlining might, for example, eliminate
a binding.
-}