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

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

{-# LANGUAGE CPP #-}
{-# LANGUAGE TypeFamilies #-}

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

#include "HsVersions.h"

import GHC.Prelude

import GHC.Platform
import GHC.Driver.Session
import GHC.Driver.Ppr
import GHC.Driver.Config
import GHC.Core.Opt.Simplify.Monad
import GHC.Core.Type hiding ( substTy, substTyVar, extendTvSubst, extendCvSubst )
import GHC.Core.Opt.Simplify.Env
import GHC.Core.Opt.Simplify.Utils
import GHC.Core.Opt.OccurAnal ( occurAnalyseExpr )
import GHC.Types.Literal   ( litIsLifted ) --, mkLitInt ) -- temporalily commented out. See #8326
import GHC.Types.SourceText
import GHC.Types.Id
import GHC.Types.Id.Make   ( seqId )
import GHC.Core.Make       ( FloatBind, mkImpossibleExpr, castBottomExpr )
import qualified GHC.Core.Make
import GHC.Types.Id.Info
import GHC.Types.Name           ( mkSystemVarName, isExternalName, getOccFS )
import GHC.Core.Coercion hiding ( substCo, substCoVar )
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.Monad ( Tick(..), SimplMode(..) )
import GHC.Core
import GHC.Builtin.Types.Prim( realWorldStatePrimTy )
import GHC.Builtin.Names( runRWKey )
import GHC.Types.Demand ( StrictSig(..), Demand, dmdTypeDepth, isStrUsedDmd
                        , mkClosedStrictSig, topDmd, seqDmd, isDeadEndDiv )
import GHC.Types.Cpr    ( mkCprSig, botCpr )
import GHC.Core.Ppr     ( pprCoreExpr )
import GHC.Types.Unique ( hasKey )
import GHC.Core.Unfold
import GHC.Core.Unfold.Make
import GHC.Core.Utils
import GHC.Core.Opt.Arity ( ArityType(..)
                          , pushCoTyArg, pushCoValArg
                          , idArityType, etaExpandAT )
import GHC.Core.SimpleOpt ( exprIsConApp_maybe, joinPointBinding_maybe, joinPointBindings_maybe )
import GHC.Core.FVs     ( mkRuleInfo )
import GHC.Core.Rules   ( lookupRule, getRules, initRuleOpts )
import GHC.Types.Basic
import GHC.Utils.Monad  ( mapAccumLM, liftIO )
import GHC.Utils.Logger
import GHC.Types.Tickish
import GHC.Types.Var    ( isTyCoVar )
import GHC.Data.Maybe   ( isNothing, orElse )
import Control.Monad
import GHC.Utils.Outputable
import GHC.Utils.Panic
import GHC.Data.FastString
import GHC.Utils.Misc
import GHC.Unit.Module ( moduleName, pprModuleName )
import GHC.Core.Multiplicity
import GHC.Builtin.PrimOps ( PrimOp (SeqOp) )


{-
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 (which includes DynFlags for convenience)
     - 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 -> [OutId] -> SimplM SimplEnv
simplRecBndrs SimplEnv
env0 (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
        ; 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 []           = 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
                                      ; 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 [(OutId, CoreExpr)]
pairs)
      = SimplEnv
-> TopLevelFlag
-> MaybeJoinCont
-> [(OutId, CoreExpr)]
-> SimplM (SimplFloats, SimplEnv)
simplRecBind SimplEnv
env TopLevelFlag
TopLevel forall a. Maybe a
Nothing [(OutId, CoreExpr)]
pairs
    simpl_bind SimplEnv
env (NonRec OutId
b CoreExpr
r)
      = do { (SimplEnv
env', OutId
b') <- SimplEnv
-> OutId -> OutId -> MaybeJoinCont -> SimplM (SimplEnv, OutId)
addBndrRules SimplEnv
env OutId
b (SimplEnv -> OutId -> OutId
lookupRecBndr SimplEnv
env OutId
b) forall a. Maybe a
Nothing
           ; SimplEnv
-> TopLevelFlag
-> RecFlag
-> MaybeJoinCont
-> OutId
-> OutId
-> CoreExpr
-> SimplM (SimplFloats, SimplEnv)
simplRecOrTopPair SimplEnv
env' TopLevelFlag
TopLevel RecFlag
NonRecursive forall a. Maybe a
Nothing OutId
b OutId
b' CoreExpr
r }

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

simplRecBind is used for
        * recursive bindings only
-}

simplRecBind :: SimplEnv -> TopLevelFlag -> MaybeJoinCont
             -> [(InId, InExpr)]
             -> SimplM (SimplFloats, SimplEnv)
simplRecBind :: SimplEnv
-> TopLevelFlag
-> MaybeJoinCont
-> [(OutId, CoreExpr)]
-> SimplM (SimplFloats, SimplEnv)
simplRecBind SimplEnv
env0 TopLevelFlag
top_lvl MaybeJoinCont
mb_cont [(OutId, CoreExpr)]
pairs0
  = do  { (SimplEnv
env_with_info, [(OutId, OutId, CoreExpr)]
triples) <- forall (m :: * -> *) acc x y.
Monad m =>
(acc -> x -> m (acc, y)) -> acc -> [x] -> m (acc, [y])
mapAccumLM SimplEnv
-> (OutId, CoreExpr) -> SimplM (SimplEnv, (OutId, OutId, CoreExpr))
add_rules SimplEnv
env0 [(OutId, CoreExpr)]
pairs0
        ; (SimplFloats
rec_floats, SimplEnv
env1) <- SimplEnv
-> [(OutId, OutId, CoreExpr)] -> SimplM (SimplFloats, SimplEnv)
go SimplEnv
env_with_info [(OutId, OutId, CoreExpr)]
triples
        ; forall (m :: * -> *) a. Monad m => a -> m a
return (SimplFloats -> SimplFloats
mkRecFloats SimplFloats
rec_floats, SimplEnv
env1) }
  where
    add_rules :: SimplEnv -> (InBndr,InExpr) -> SimplM (SimplEnv, (InBndr, OutBndr, InExpr))
        -- Add the (substituted) rules to the binder
    add_rules :: SimplEnv
-> (OutId, CoreExpr) -> SimplM (SimplEnv, (OutId, OutId, CoreExpr))
add_rules SimplEnv
env (OutId
bndr, CoreExpr
rhs)
        = do { (SimplEnv
env', OutId
bndr') <- SimplEnv
-> OutId -> OutId -> MaybeJoinCont -> SimplM (SimplEnv, OutId)
addBndrRules SimplEnv
env OutId
bndr (SimplEnv -> OutId -> OutId
lookupRecBndr SimplEnv
env OutId
bndr) MaybeJoinCont
mb_cont
             ; forall (m :: * -> *) a. Monad m => a -> m a
return (SimplEnv
env', (OutId
bndr, OutId
bndr', CoreExpr
rhs)) }

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

    go SimplEnv
env ((OutId
old_bndr, OutId
new_bndr, CoreExpr
rhs) : [(OutId, OutId, CoreExpr)]
pairs)
        = do { (SimplFloats
float, SimplEnv
env1) <- SimplEnv
-> TopLevelFlag
-> RecFlag
-> MaybeJoinCont
-> OutId
-> OutId
-> CoreExpr
-> SimplM (SimplFloats, SimplEnv)
simplRecOrTopPair SimplEnv
env TopLevelFlag
top_lvl RecFlag
Recursive MaybeJoinCont
mb_cont
                                                  OutId
old_bndr OutId
new_bndr CoreExpr
rhs
             ; (SimplFloats
floats, SimplEnv
env2) <- SimplEnv
-> [(OutId, OutId, CoreExpr)] -> SimplM (SimplFloats, SimplEnv)
go SimplEnv
env1 [(OutId, OutId, CoreExpr)]
pairs
             ; 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
                  -> TopLevelFlag -> RecFlag -> MaybeJoinCont
                  -> InId -> OutBndr -> InExpr  -- Binder and rhs
                  -> SimplM (SimplFloats, SimplEnv)

simplRecOrTopPair :: SimplEnv
-> TopLevelFlag
-> RecFlag
-> MaybeJoinCont
-> OutId
-> OutId
-> CoreExpr
-> SimplM (SimplFloats, SimplEnv)
simplRecOrTopPair SimplEnv
env TopLevelFlag
top_lvl RecFlag
is_rec MaybeJoinCont
mb_cont OutId
old_bndr OutId
new_bndr CoreExpr
rhs
  | Just SimplEnv
env' <- SimplEnv
-> TopLevelFlag -> OutId -> CoreExpr -> SimplEnv -> Maybe SimplEnv
preInlineUnconditionally SimplEnv
env TopLevelFlag
top_lvl OutId
old_bndr CoreExpr
rhs SimplEnv
env
  = {-#SCC "simplRecOrTopPair-pre-inline-uncond" #-}
    [Char]
-> SimplM (SimplFloats, SimplEnv) -> SimplM (SimplFloats, SimplEnv)
trace_bind [Char]
"pre-inline-uncond" forall a b. (a -> b) -> a -> b
$
    do { Tick -> SimplM ()
tick (OutId -> Tick
PreInlineUnconditionally OutId
old_bndr)
       ; forall (m :: * -> *) a. Monad m => a -> m a
return ( SimplEnv -> SimplFloats
emptyFloats SimplEnv
env, SimplEnv
env' ) }

  | Just SimplCont
cont <- MaybeJoinCont
mb_cont
  = {-#SCC "simplRecOrTopPair-join" #-}
    ASSERT( isNotTopLevel top_lvl && isJoinId new_bndr )
    [Char]
-> SimplM (SimplFloats, SimplEnv) -> SimplM (SimplFloats, SimplEnv)
trace_bind [Char]
"join" forall a b. (a -> b) -> a -> b
$
    SimplEnv
-> SimplCont
-> OutId
-> OutId
-> CoreExpr
-> SimplEnv
-> SimplM (SimplFloats, SimplEnv)
simplJoinBind SimplEnv
env SimplCont
cont OutId
old_bndr OutId
new_bndr CoreExpr
rhs SimplEnv
env

  | Bool
otherwise
  = {-#SCC "simplRecOrTopPair-normal" #-}
    [Char]
-> SimplM (SimplFloats, SimplEnv) -> SimplM (SimplFloats, SimplEnv)
trace_bind [Char]
"normal" forall a b. (a -> b) -> a -> b
$
    SimplEnv
-> TopLevelFlag
-> RecFlag
-> OutId
-> OutId
-> CoreExpr
-> SimplEnv
-> SimplM (SimplFloats, SimplEnv)
simplLazyBind SimplEnv
env TopLevelFlag
top_lvl RecFlag
is_rec OutId
old_bndr OutId
new_bndr CoreExpr
rhs SimplEnv
env

  where
    dflags :: DynFlags
dflags = SimplEnv -> DynFlags
seDynFlags SimplEnv
env
    logger :: Logger
logger = SimplEnv -> Logger
seLogger SimplEnv
env

    -- trace_bind emits a trace for each top-level binding, which
    -- helps to locate the tracing for inlining and rule firing
    trace_bind :: [Char]
-> SimplM (SimplFloats, SimplEnv) -> SimplM (SimplFloats, SimplEnv)
trace_bind [Char]
what SimplM (SimplFloats, SimplEnv)
thing_inside
      | Bool -> Bool
not (DumpFlag -> DynFlags -> Bool
dopt DumpFlag
Opt_D_verbose_core2core DynFlags
dflags)
      = SimplM (SimplFloats, SimplEnv)
thing_inside
      | Bool
otherwise
      = forall a. Logger -> TraceAction a
putTraceMsg Logger
logger DynFlags
dflags ([Char]
"SimplBind " forall a. [a] -> [a] -> [a]
++ [Char]
what)
         (forall a. Outputable a => a -> SDoc
ppr OutId
old_bndr) SimplM (SimplFloats, SimplEnv)
thing_inside

--------------------------
simplLazyBind :: SimplEnv
              -> TopLevelFlag -> RecFlag
              -> InId -> OutId          -- Binder, both pre-and post simpl
                                        -- Not a JoinId
                                        -- The OutId has IdInfo, except arity, unfolding
                                        -- Ids only, no TyVars
              -> InExpr -> SimplEnv     -- The RHS and its environment
              -> SimplM (SimplFloats, SimplEnv)
-- Precondition: not a JoinId
-- Precondition: rhs obeys the let/app invariant
-- NOT used for JoinIds
simplLazyBind :: SimplEnv
-> TopLevelFlag
-> RecFlag
-> OutId
-> OutId
-> CoreExpr
-> SimplEnv
-> SimplM (SimplFloats, SimplEnv)
simplLazyBind SimplEnv
env TopLevelFlag
top_lvl RecFlag
is_rec OutId
bndr OutId
bndr1 CoreExpr
rhs SimplEnv
rhs_se
  = ASSERT( isId bndr )
    ASSERT2( not (isJoinId bndr), ppr bndr )
    -- 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]
                ([OutId]
tvs, CoreExpr
body) = case CoreExpr -> ([OutId], [OutId], CoreExpr)
collectTyAndValBinders CoreExpr
rhs of
                                ([OutId]
tvs, [], CoreExpr
body)
                                  | forall {b}. Expr b -> Bool
surely_not_lam CoreExpr
body -> ([OutId]
tvs, CoreExpr
body)
                                ([OutId], [OutId], 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 (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, [OutId]
tvs') <- {-#SCC "simplBinders" #-} SimplEnv -> [OutId] -> SimplM (SimplEnv, [OutId])
simplBinders SimplEnv
rhs_env [OutId]
tvs
                -- See Note [Floating and type abstraction] in GHC.Core.Opt.Simplify.Utils

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

              -- 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: body_floats1 consists only of let-floats
        ; let (SimplFloats
body_floats1, CoreExpr
body1) = SimplFloats -> CoreExpr -> (SimplFloats, CoreExpr)
wrapJoinFloatsX SimplFloats
body_floats0 CoreExpr
body0

        -- ANF-ise a constructor or PAP rhs
        -- We get at most one float per argument here
        ; let body_env1 :: SimplEnv
body_env1 = SimplEnv
body_env SimplEnv -> SimplFloats -> SimplEnv
`setInScopeFromF` SimplFloats
body_floats1
              -- body_env1: add to in-scope set the binders from body_floats1
              -- so that prepareBinding knows what is in scope in body1
        ; (LetFloats
let_floats, OutId
bndr2, CoreExpr
body2) <- {-#SCC "prepareBinding" #-}
                                        SimplEnv
-> TopLevelFlag
-> OutId
-> OutId
-> CoreExpr
-> SimplM (LetFloats, OutId, CoreExpr)
prepareBinding SimplEnv
body_env1 TopLevelFlag
top_lvl OutId
bndr OutId
bndr1 CoreExpr
body1
        ; let body_floats2 :: SimplFloats
body_floats2 = SimplFloats
body_floats1 SimplFloats -> LetFloats -> SimplFloats
`addLetFloats` LetFloats
let_floats

        ; (SimplFloats
rhs_floats, CoreExpr
body3)
            <-  if Bool -> Bool
not (TopLevelFlag -> RecFlag -> Bool -> SimplFloats -> CoreExpr -> Bool
doFloatFromRhs TopLevelFlag
top_lvl RecFlag
is_rec Bool
False SimplFloats
body_floats2 CoreExpr
body2)
                then                    -- No floating, revert to body1
                     forall (m :: * -> *) a. Monad m => a -> m a
return (SimplEnv -> SimplFloats
emptyFloats SimplEnv
env, SimplFloats -> CoreExpr -> CoreExpr
wrapFloats SimplFloats
body_floats2 CoreExpr
body1)

                else if forall (t :: * -> *) a. Foldable t => t a -> Bool
null [OutId]
tvs then   -- Simple floating
                     {-#SCC "simplLazyBind-simple-floating" #-}
                     do { Tick -> SimplM ()
tick Tick
LetFloatFromLet
                        ; forall (m :: * -> *) a. Monad m => a -> m a
return (SimplFloats
body_floats2, CoreExpr
body2) }

                else                    -- Do type-abstraction first
                     {-#SCC "simplLazyBind-type-abstraction-first" #-}
                     do { Tick -> SimplM ()
tick Tick
LetFloatFromLet
                        ; ([InBind]
poly_binds, CoreExpr
body3) <- UnfoldingOpts
-> TopLevelFlag
-> [OutId]
-> SimplFloats
-> CoreExpr
-> SimplM ([InBind], CoreExpr)
abstractFloats (SimplEnv -> UnfoldingOpts
seUnfoldingOpts SimplEnv
env) TopLevelFlag
top_lvl
                                                                [OutId]
tvs' SimplFloats
body_floats2 CoreExpr
body2
                        ; let floats :: SimplFloats
floats = 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
                        ; forall (m :: * -> *) a. Monad m => a -> m a
return (SimplFloats
floats, CoreExpr
body3) }

        ; let env' :: SimplEnv
env' = SimplEnv
env SimplEnv -> SimplFloats -> SimplEnv
`setInScopeFromF` SimplFloats
rhs_floats
        ; CoreExpr
rhs' <- SimplEnv -> [OutId] -> CoreExpr -> SimplCont -> SimplM CoreExpr
mkLam SimplEnv
env' [OutId]
tvs' CoreExpr
body3 SimplCont
rhs_cont
        ; (SimplFloats
bind_float, SimplEnv
env2) <- SimplEnv
-> TopLevelFlag
-> MaybeJoinCont
-> OutId
-> OutId
-> CoreExpr
-> SimplM (SimplFloats, SimplEnv)
completeBind SimplEnv
env' TopLevelFlag
top_lvl forall a. Maybe a
Nothing OutId
bndr OutId
bndr2 CoreExpr
rhs'
        ; forall (m :: * -> *) a. Monad m => a -> m a
return (SimplFloats
rhs_floats SimplFloats -> SimplFloats -> SimplFloats
`addFloats` SimplFloats
bind_float, SimplEnv
env2) }

--------------------------
simplJoinBind :: SimplEnv
              -> 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
-> SimplCont
-> OutId
-> OutId
-> CoreExpr
-> SimplEnv
-> SimplM (SimplFloats, SimplEnv)
simplJoinBind SimplEnv
env SimplCont
cont OutId
old_bndr OutId
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 -> OutId -> CoreExpr -> SimplCont -> SimplM CoreExpr
simplJoinRhs SimplEnv
rhs_env OutId
old_bndr CoreExpr
rhs SimplCont
cont
        ; SimplEnv
-> TopLevelFlag
-> MaybeJoinCont
-> OutId
-> OutId
-> CoreExpr
-> SimplM (SimplFloats, SimplEnv)
completeBind SimplEnv
env TopLevelFlag
NotTopLevel (forall a. a -> Maybe a
Just SimplCont
cont) OutId
old_bndr OutId
new_bndr CoreExpr
rhs' }

--------------------------
simplNonRecX :: SimplEnv
             -> InId            -- Old binder; not a JoinId
             -> OutExpr         -- Simplified RHS
             -> SimplM (SimplFloats, SimplEnv)
-- A specialised variant of simplNonRec used when the RHS is already
-- simplified, notably in knownCon.  It uses case-binding where necessary.
--
-- Precondition: rhs satisfies the let/app invariant

simplNonRecX :: SimplEnv -> OutId -> CoreExpr -> SimplM (SimplFloats, SimplEnv)
simplNonRecX SimplEnv
env OutId
bndr CoreExpr
new_rhs
  | ASSERT2( not (isJoinId bndr), ppr bndr )
    OutId -> Bool
isDeadBinder OutId
bndr   -- Not uncommon; e.g. case (a,b) of c { (p,q) -> p }
  = 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)

  | Coercion Coercion
co <- CoreExpr
new_rhs
  = forall (m :: * -> *) a. Monad m => a -> m a
return (SimplEnv -> SimplFloats
emptyFloats SimplEnv
env, SimplEnv -> OutId -> Coercion -> SimplEnv
extendCvSubst SimplEnv
env OutId
bndr Coercion
co)

  | Bool
otherwise
  = do  { (SimplEnv
env', OutId
bndr') <- SimplEnv -> OutId -> SimplM (SimplEnv, OutId)
simplBinder SimplEnv
env OutId
bndr
        ; TopLevelFlag
-> SimplEnv
-> Bool
-> OutId
-> OutId
-> CoreExpr
-> SimplM (SimplFloats, SimplEnv)
completeNonRecX TopLevelFlag
NotTopLevel SimplEnv
env' (OutId -> Bool
isStrictId OutId
bndr') OutId
bndr OutId
bndr' CoreExpr
new_rhs }
          -- NotTopLevel: simplNonRecX is only used for NotTopLevel things
          --
          -- isStrictId: use bndr' because in a levity-polymorphic setting
          -- the InId bndr might have a levity-polymorphic type, which
          -- which isStrictId doesn't expect
          -- c.f. Note [Dark corner with levity polymorphism]

--------------------------
completeNonRecX :: TopLevelFlag -> SimplEnv
                -> Bool
                -> InId                 -- Old binder; not a JoinId
                -> OutId                -- New binder
                -> OutExpr              -- Simplified RHS
                -> SimplM (SimplFloats, SimplEnv)    -- The new binding is in the floats
-- Precondition: rhs satisfies the let/app invariant
--               See Note [Core let/app invariant] in GHC.Core

completeNonRecX :: TopLevelFlag
-> SimplEnv
-> Bool
-> OutId
-> OutId
-> CoreExpr
-> SimplM (SimplFloats, SimplEnv)
completeNonRecX TopLevelFlag
top_lvl SimplEnv
env Bool
is_strict OutId
old_bndr OutId
new_bndr CoreExpr
new_rhs
  = ASSERT2( not (isJoinId new_bndr), ppr new_bndr )
    do  { (LetFloats
prepd_floats, OutId
new_bndr, CoreExpr
new_rhs)
              <- SimplEnv
-> TopLevelFlag
-> OutId
-> OutId
-> CoreExpr
-> SimplM (LetFloats, OutId, CoreExpr)
prepareBinding SimplEnv
env TopLevelFlag
top_lvl OutId
old_bndr OutId
new_bndr CoreExpr
new_rhs
        ; let floats :: SimplFloats
floats = SimplEnv -> SimplFloats
emptyFloats SimplEnv
env SimplFloats -> LetFloats -> SimplFloats
`addLetFloats` LetFloats
prepd_floats
        ; (SimplFloats
rhs_floats, CoreExpr
rhs2) <-
                if TopLevelFlag -> RecFlag -> Bool -> SimplFloats -> CoreExpr -> Bool
doFloatFromRhs TopLevelFlag
NotTopLevel RecFlag
NonRecursive Bool
is_strict SimplFloats
floats CoreExpr
new_rhs
                then    -- Add the floats to the main env
                     do { Tick -> SimplM ()
tick Tick
LetFloatFromLet
                        ; forall (m :: * -> *) a. Monad m => a -> m a
return (SimplFloats
floats, CoreExpr
new_rhs) }
                else    -- Do not float; wrap the floats around the RHS
                     forall (m :: * -> *) a. Monad m => a -> m a
return (SimplEnv -> SimplFloats
emptyFloats SimplEnv
env, SimplFloats -> CoreExpr -> CoreExpr
wrapFloats SimplFloats
floats CoreExpr
new_rhs)

        ; (SimplFloats
bind_float, SimplEnv
env2) <- SimplEnv
-> TopLevelFlag
-> MaybeJoinCont
-> OutId
-> OutId
-> CoreExpr
-> SimplM (SimplFloats, SimplEnv)
completeBind (SimplEnv
env SimplEnv -> SimplFloats -> SimplEnv
`setInScopeFromF` SimplFloats
rhs_floats)
                                             TopLevelFlag
NotTopLevel forall a. Maybe a
Nothing
                                             OutId
old_bndr OutId
new_bndr CoreExpr
rhs2
        ; forall (m :: * -> *) a. Monad m => a -> m a
return (SimplFloats
rhs_floats SimplFloats -> SimplFloats -> SimplFloats
`addFloats` SimplFloats
bind_float, SimplEnv
env2) }


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

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

So now 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

We call this making a cast worker/wrapper, and it's done by prepareBinding.

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... }
It's 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 NOINLINE functions] in
GHC.Core.Opt.WorkWrap.

See #17673, #18093, #18078.

Note [Preserve strictness in cast w/w]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In the Note [Cast worker/wrappers] 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 [Cast w/w: unlifted]
~~~~~~~~~~~~~~~~~~~~~~~~~
BUT don't do cast worker/wrapper if 'e' has an unlifted type.
This *can* happen:

     foo :: Int = (error (# Int,Int #) "urk")
                  `cast` CoUnsafe (# Int,Int #) Int

If do the makeTrivial thing to the error call, we'll get
    foo = case error (# Int,Int #) "urk" of v -> v `cast` ...
But 'v' isn't in scope!

These strange casts can happen as a result of case-of-case
        bar = case (case x of { T -> (# 2,3 #); F -> error "urk" }) of
                (# p,q #) -> p+q

NOTE: Nowadays we don't use casts for these error functions;
instead, we use (case erorr ... of {}). So I'm not sure
this Note makes much sense any more.
-}

prepareBinding :: SimplEnv -> TopLevelFlag
               -> InId -> OutId -> OutExpr
               -> SimplM (LetFloats, OutId, OutExpr)

prepareBinding :: SimplEnv
-> TopLevelFlag
-> OutId
-> OutId
-> CoreExpr
-> SimplM (LetFloats, OutId, CoreExpr)
prepareBinding SimplEnv
env TopLevelFlag
top_lvl OutId
old_bndr OutId
bndr CoreExpr
rhs
  | Cast CoreExpr
rhs1 Coercion
co <- CoreExpr
rhs
    -- Try for cast worker/wrapper
    -- See Note [Cast worker/wrappers]
  , Bool -> Bool
not (Unfolding -> Bool
isStableUnfolding (OutId -> Unfolding
realIdUnfolding OutId
old_bndr))
        -- Don't make a cast w/w if the thing is going to be inlined anyway
  , Bool -> Bool
not (CoreExpr -> Bool
exprIsTrivial CoreExpr
rhs1)
        -- Nor if the RHS is trivial; then again it'll be inlined
  , let ty1 :: Kind
ty1 = Coercion -> Kind
coercionLKind Coercion
co
  , Bool -> Bool
not (HasDebugCallStack => Kind -> Bool
isUnliftedType Kind
ty1)
        -- Not if rhs has an unlifted type; see Note [Cast w/w: unlifted]
  = do { (LetFloats
floats, OutId
new_id) <- SimplMode
-> TopLevelFlag
-> FastString
-> IdInfo
-> CoreExpr
-> Kind
-> SimplM (LetFloats, OutId)
makeTrivialBinding (SimplEnv -> SimplMode
getMode SimplEnv
env) TopLevelFlag
top_lvl
                                   (forall a. NamedThing a => a -> FastString
getOccFS OutId
bndr) IdInfo
worker_info CoreExpr
rhs1 Kind
ty1
       ; let bndr' :: OutId
bndr' = OutId
bndr OutId -> InlinePragma -> OutId
`setInlinePragma` InlinePragma -> InlinePragma
mkCastWrapperInlinePrag (OutId -> InlinePragma
idInlinePragma OutId
bndr)
       ; forall (m :: * -> *) a. Monad m => a -> m a
return (LetFloats
floats, OutId
bndr', forall b. Expr b -> Coercion -> Expr b
Cast (forall b. OutId -> Expr b
Var OutId
new_id) Coercion
co) }

  | Bool
otherwise
  = do { (LetFloats
floats, CoreExpr
rhs') <- SimplMode
-> TopLevelFlag
-> FastString
-> CoreExpr
-> SimplM (LetFloats, CoreExpr)
prepareRhs (SimplEnv -> SimplMode
getMode SimplEnv
env) TopLevelFlag
top_lvl (forall a. NamedThing a => a -> FastString
getOccFS OutId
bndr) CoreExpr
rhs
       ; forall (m :: * -> *) a. Monad m => a -> m a
return (LetFloats
floats, OutId
bndr, CoreExpr
rhs') }
 where
   info :: IdInfo
info = HasDebugCallStack => OutId -> IdInfo
idInfo OutId
bndr
   worker_info :: IdInfo
worker_info = IdInfo
vanillaIdInfo IdInfo -> StrictSig -> IdInfo
`setStrictnessInfo` IdInfo -> StrictSig
strictnessInfo IdInfo
info
                               IdInfo -> CprSig -> IdInfo
`setCprInfo`        IdInfo -> CprSig
cprInfo IdInfo
info
                               IdInfo -> Demand -> IdInfo
`setDemandInfo`     IdInfo -> Demand
demandInfo IdInfo
info
                               IdInfo -> InlinePragma -> IdInfo
`setInlinePragInfo` IdInfo -> InlinePragma
inlinePragInfo IdInfo
info
                               IdInfo -> Int -> IdInfo
`setArityInfo`      IdInfo -> Int
arityInfo IdInfo
info
          -- We do /not/ want to transfer OccInfo, Rules, Unfolding
          -- Note [Preserve strictness in cast w/w]

mkCastWrapperInlinePrag :: InlinePragma -> InlinePragma
-- See Note [Cast wrappers]
mkCastWrapperInlinePrag :: InlinePragma -> InlinePragma
mkCastWrapperInlinePrag (InlinePragma { inl_act :: InlinePragma -> Activation
inl_act = Activation
act, inl_rule :: InlinePragma -> RuleMatchInfo
inl_rule = RuleMatchInfo
rule_info })
  = InlinePragma { inl_src :: SourceText
inl_src    = [Char] -> SourceText
SourceText [Char]
"{-# INLINE"
                 , inl_inline :: InlineSpec
inl_inline = InlineSpec
NoUserInlinePrag -- See Note [Wrapper NoUserInline]
                 , inl_sat :: Maybe Int
inl_sat    = 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
act = Activation
activateDuringFinal
             | Bool
otherwise         = Activation
act

{- 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 :: SimplMode -> 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 :: SimplMode
-> TopLevelFlag
-> FastString
-> CoreExpr
-> SimplM (LetFloats, CoreExpr)
prepareRhs SimplMode
mode TopLevelFlag
top_lvl FastString
occ CoreExpr
rhs0
  = do  { (Bool
_is_exp, LetFloats
floats, CoreExpr
rhs1) <- Int -> CoreExpr -> SimplM (Bool, LetFloats, CoreExpr)
go Int
0 CoreExpr
rhs0
        ; forall (m :: * -> *) a. Monad m => a -> m a
return (LetFloats
floats, CoreExpr
rhs1) }
  where
    go :: Int -> OutExpr -> SimplM (Bool, LetFloats, OutExpr)
    go :: Int -> CoreExpr -> SimplM (Bool, LetFloats, CoreExpr)
go Int
n_val_args (Cast CoreExpr
rhs Coercion
co)
        = do { (Bool
is_exp, LetFloats
floats, CoreExpr
rhs') <- Int -> CoreExpr -> SimplM (Bool, LetFloats, CoreExpr)
go Int
n_val_args CoreExpr
rhs
             ; forall (m :: * -> *) a. Monad m => a -> m a
return (Bool
is_exp, LetFloats
floats, forall b. Expr b -> Coercion -> Expr b
Cast CoreExpr
rhs' Coercion
co) }
    go Int
n_val_args (App CoreExpr
fun (Type Kind
ty))
        = do { (Bool
is_exp, LetFloats
floats, CoreExpr
rhs') <- Int -> CoreExpr -> SimplM (Bool, LetFloats, CoreExpr)
go Int
n_val_args CoreExpr
fun
             ; forall (m :: * -> *) a. Monad m => a -> m a
return (Bool
is_exp, LetFloats
floats, forall b. Expr b -> Expr b -> Expr b
App CoreExpr
rhs' (forall b. Kind -> Expr b
Type Kind
ty)) }
    go Int
n_val_args (App CoreExpr
fun CoreExpr
arg)
        = do { (Bool
is_exp, LetFloats
floats1, CoreExpr
fun') <- Int -> CoreExpr -> SimplM (Bool, LetFloats, CoreExpr)
go (Int
n_val_argsforall a. Num a => a -> a -> a
+Int
1) CoreExpr
fun
             ; case Bool
is_exp of
                Bool
False -> forall (m :: * -> *) a. Monad m => a -> m a
return (Bool
False, LetFloats
emptyLetFloats, forall b. Expr b -> Expr b -> Expr b
App CoreExpr
fun CoreExpr
arg)
                Bool
True  -> do { (LetFloats
floats2, CoreExpr
arg') <- SimplMode
-> TopLevelFlag
-> Demand
-> FastString
-> CoreExpr
-> SimplM (LetFloats, CoreExpr)
makeTrivial SimplMode
mode TopLevelFlag
top_lvl Demand
topDmd FastString
occ CoreExpr
arg
                            ; forall (m :: * -> *) a. Monad m => a -> m a
return (Bool
True, LetFloats
floats1 LetFloats -> LetFloats -> LetFloats
`addLetFlts` LetFloats
floats2, forall b. Expr b -> Expr b -> Expr b
App CoreExpr
fun' CoreExpr
arg') } }
    go Int
n_val_args (Var OutId
fun)
        = forall (m :: * -> *) a. Monad m => a -> m a
return (Bool
is_exp, LetFloats
emptyLetFloats, forall b. OutId -> Expr b
Var OutId
fun)
        where
          is_exp :: Bool
is_exp = CheapAppFun
isExpandableApp OutId
fun Int
n_val_args   -- The fun a constructor or PAP
                        -- See Note [CONLIKE pragma] in GHC.Types.Basic
                        -- The definition of is_exp should match that in
                        -- 'GHC.Core.Opt.OccurAnal.occAnalApp'

    go Int
n_val_args (Tick CoreTickish
t CoreExpr
rhs)
        -- We want to be able to float bindings past this
        -- tick. Non-scoping ticks don't care.
        | forall (pass :: TickishPass). GenTickish pass -> TickishScoping
tickishScoped CoreTickish
t forall a. Eq a => a -> a -> Bool
== TickishScoping
NoScope
        = do { (Bool
is_exp, LetFloats
floats, CoreExpr
rhs') <- Int -> CoreExpr -> SimplM (Bool, LetFloats, CoreExpr)
go Int
n_val_args CoreExpr
rhs
             ; forall (m :: * -> *) a. Monad m => a -> m a
return (Bool
is_exp, LetFloats
floats, 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 (forall (pass :: TickishPass). GenTickish pass -> Bool
tickishCounts CoreTickish
t) Bool -> Bool -> Bool
|| forall (pass :: TickishPass). GenTickish pass -> Bool
tickishCanSplit CoreTickish
t)
        = do { (Bool
is_exp, LetFloats
floats, CoreExpr
rhs') <- Int -> CoreExpr -> SimplM (Bool, LetFloats, CoreExpr)
go Int
n_val_args CoreExpr
rhs
             ; let tickIt :: (OutId, CoreExpr) -> (OutId, CoreExpr)
tickIt (OutId
id, CoreExpr
expr) = (OutId
id, CoreTickish -> CoreExpr -> CoreExpr
mkTick (forall (pass :: TickishPass). GenTickish pass -> GenTickish pass
mkNoCount CoreTickish
t) CoreExpr
expr)
                   floats' :: LetFloats
floats' = LetFloats -> ((OutId, CoreExpr) -> (OutId, CoreExpr)) -> LetFloats
mapLetFloats LetFloats
floats (OutId, CoreExpr) -> (OutId, CoreExpr)
tickIt
             ; forall (m :: * -> *) a. Monad m => a -> m a
return (Bool
is_exp, LetFloats
floats', forall b. CoreTickish -> Expr b -> Expr b
Tick CoreTickish
t CoreExpr
rhs') }

    go Int
_ CoreExpr
other
        = forall (m :: * -> *) a. Monad m => a -> m a
return (Bool
False, LetFloats
emptyLetFloats, CoreExpr
other)

makeTrivialArg :: SimplMode -> ArgSpec -> SimplM (LetFloats, ArgSpec)
makeTrivialArg :: SimplMode -> ArgSpec -> SimplM (LetFloats, ArgSpec)
makeTrivialArg SimplMode
mode 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') <- SimplMode
-> TopLevelFlag
-> Demand
-> FastString
-> CoreExpr
-> SimplM (LetFloats, CoreExpr)
makeTrivial SimplMode
mode TopLevelFlag
NotTopLevel Demand
dmd ([Char] -> FastString
fsLit [Char]
"arg") CoreExpr
e
       ; forall (m :: * -> *) a. Monad m => a -> m a
return (LetFloats
floats, ArgSpec
arg { as_arg :: CoreExpr
as_arg = CoreExpr
e' }) }
makeTrivialArg SimplMode
_ ArgSpec
arg
  = forall (m :: * -> *) a. Monad m => a -> m a
return (LetFloats
emptyLetFloats, ArgSpec
arg)  -- CastBy, TyArg

makeTrivial :: SimplMode -> TopLevelFlag -> Demand
            -> FastString  -- ^ A "friendly name" to build the new binder from
            -> OutExpr     -- ^ This expression satisfies the let/app invariant
            -> 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 :: SimplMode
-> TopLevelFlag
-> Demand
-> FastString
-> CoreExpr
-> SimplM (LetFloats, CoreExpr)
makeTrivial SimplMode
mode 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]
  = 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) <- SimplMode
-> TopLevelFlag
-> Demand
-> FastString
-> CoreExpr
-> SimplM (LetFloats, CoreExpr)
makeTrivial SimplMode
mode TopLevelFlag
top_lvl Demand
dmd FastString
occ_fs CoreExpr
expr'
       ; forall (m :: * -> *) a. Monad m => a -> m a
return (LetFloats
floats, forall b. Expr b -> Coercion -> Expr b
Cast CoreExpr
triv_expr Coercion
co) }

  | Bool
otherwise
  = do { (LetFloats
floats, OutId
new_id) <- SimplMode
-> TopLevelFlag
-> FastString
-> IdInfo
-> CoreExpr
-> Kind
-> SimplM (LetFloats, OutId)
makeTrivialBinding SimplMode
mode TopLevelFlag
top_lvl FastString
occ_fs
                                                IdInfo
id_info CoreExpr
expr Kind
expr_ty
       ; forall (m :: * -> *) a. Monad m => a -> m a
return (LetFloats
floats, forall b. OutId -> Expr b
Var OutId
new_id) }
  where
    id_info :: IdInfo
id_info = IdInfo
vanillaIdInfo IdInfo -> Demand -> IdInfo
`setDemandInfo` Demand
dmd
    expr_ty :: Kind
expr_ty = CoreExpr -> Kind
exprType CoreExpr
expr

makeTrivialBinding :: SimplMode -> TopLevelFlag
                   -> FastString  -- ^ a "friendly name" to build the new binder from
                   -> IdInfo
                   -> OutExpr     -- ^ This expression satisfies the let/app invariant
                   -> OutType     -- Type of the expression
                   -> SimplM (LetFloats, OutId)
makeTrivialBinding :: SimplMode
-> TopLevelFlag
-> FastString
-> IdInfo
-> CoreExpr
-> Kind
-> SimplM (LetFloats, OutId)
makeTrivialBinding SimplMode
mode TopLevelFlag
top_lvl FastString
occ_fs IdInfo
info CoreExpr
expr Kind
expr_ty
  = do  { (LetFloats
floats, CoreExpr
expr1) <- SimplMode
-> TopLevelFlag
-> FastString
-> CoreExpr
-> SimplM (LetFloats, CoreExpr)
prepareRhs SimplMode
mode TopLevelFlag
top_lvl FastString
occ_fs CoreExpr
expr
        ; Unique
uniq <- forall (m :: * -> *). MonadUnique m => m Unique
getUniqueM
        ; let name :: Name
name = Unique -> FastString -> Name
mkSystemVarName Unique
uniq FastString
occ_fs
              var :: OutId
var  = HasDebugCallStack => Name -> Kind -> Kind -> IdInfo -> OutId
mkLocalIdWithInfo Name
name Kind
Many Kind
expr_ty IdInfo
info

        -- Now something very like completeBind,
        -- but without the postInlineUnconditionally part
        ; (ArityType
arity_type, CoreExpr
expr2) <- SimplMode -> OutId -> CoreExpr -> SimplM (ArityType, CoreExpr)
tryEtaExpandRhs SimplMode
mode OutId
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
-> OutId
-> CoreExpr
-> SimplM Unfolding
mkLetUnfolding (SimplMode -> UnfoldingOpts
sm_uf_opts SimplMode
mode) TopLevelFlag
top_lvl UnfoldingSource
InlineRhs OutId
var CoreExpr
expr2

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

        ; forall (m :: * -> *) a. Monad m => a -> m a
return ( LetFloats
floats LetFloats -> LetFloats -> LetFloats
`addLetFlts` InBind -> LetFloats
unitLetFloat InBind
bind, OutId
final_id ) }

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

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
             -> TopLevelFlag            -- Flag stuck into unfolding
             -> MaybeJoinCont           -- Required only for join point
             -> InId                    -- Old binder
             -> OutId -> OutExpr        -- New binder and 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/app invariant
completeBind :: SimplEnv
-> TopLevelFlag
-> MaybeJoinCont
-> OutId
-> OutId
-> CoreExpr
-> SimplM (SimplFloats, SimplEnv)
completeBind SimplEnv
env TopLevelFlag
top_lvl MaybeJoinCont
mb_cont OutId
old_bndr OutId
new_bndr CoreExpr
new_rhs
 | OutId -> Bool
isCoVar OutId
old_bndr
 = case CoreExpr
new_rhs of
     Coercion Coercion
co -> forall (m :: * -> *) a. Monad m => a -> m a
return (SimplEnv -> SimplFloats
emptyFloats SimplEnv
env, SimplEnv -> OutId -> Coercion -> SimplEnv
extendCvSubst SimplEnv
env OutId
old_bndr Coercion
co)
     CoreExpr
_           -> forall (m :: * -> *) a. Monad m => a -> m a
return (SimplEnv -> InBind -> (SimplFloats, SimplEnv)
mkFloatBind SimplEnv
env (forall b. b -> Expr b -> Bind b
NonRec OutId
new_bndr CoreExpr
new_rhs))

 | Bool
otherwise
 = ASSERT( isId new_bndr )
   do { let old_info :: IdInfo
old_info = HasDebugCallStack => OutId -> IdInfo
idInfo OutId
old_bndr
            old_unf :: Unfolding
old_unf  = IdInfo -> Unfolding
unfoldingInfo 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
final_rhs) <- SimplMode -> OutId -> CoreExpr -> SimplM (ArityType, CoreExpr)
tryEtaExpandRhs (SimplEnv -> SimplMode
getMode SimplEnv
env) OutId
new_bndr CoreExpr
new_rhs

        -- Simplify the unfolding
      ; Unfolding
new_unfolding <- SimplEnv
-> TopLevelFlag
-> MaybeJoinCont
-> OutId
-> CoreExpr
-> Kind
-> ArityType
-> Unfolding
-> SimplM Unfolding
simplLetUnfolding SimplEnv
env TopLevelFlag
top_lvl MaybeJoinCont
mb_cont OutId
old_bndr
                          CoreExpr
final_rhs (OutId -> Kind
idType OutId
new_bndr) ArityType
new_arity Unfolding
old_unf

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

      ; if SimplEnv -> TopLevelFlag -> OutId -> OccInfo -> CoreExpr -> Bool
postInlineUnconditionally SimplEnv
env TopLevelFlag
top_lvl OutId
final_bndr OccInfo
occ_info CoreExpr
final_rhs

        then -- Inline and discard the binding
             do  { Tick -> SimplM ()
tick (OutId -> Tick
PostInlineUnconditionally OutId
old_bndr)
                 ; forall (m :: * -> *) a. Monad m => a -> m a
return ( SimplEnv -> SimplFloats
emptyFloats SimplEnv
env
                          , SimplEnv -> OutId -> SimplSR -> SimplEnv
extendIdSubst SimplEnv
env OutId
old_bndr forall a b. (a -> b) -> a -> b
$
                            CoreExpr -> Maybe Int -> SimplSR
DoneEx CoreExpr
final_rhs (OutId -> Maybe Int
isJoinId_maybe OutId
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
             -- pprTrace "Binding" (ppr final_bndr <+> ppr new_unfolding) $
             forall (m :: * -> *) a. Monad m => a -> m a
return (SimplEnv -> InBind -> (SimplFloats, SimplEnv)
mkFloatBind SimplEnv
env (forall b. b -> Expr b -> Bind b
NonRec OutId
final_bndr CoreExpr
final_rhs)) }

addLetBndrInfo :: OutId -> ArityType -> Unfolding -> OutId
addLetBndrInfo :: OutId -> ArityType -> Unfolding -> OutId
addLetBndrInfo OutId
new_bndr ArityType
new_arity_type Unfolding
new_unf
  = OutId
new_bndr OutId -> IdInfo -> OutId
`setIdInfo` IdInfo
info5
  where
    AT [OneShotInfo]
oss Divergence
div = ArityType
new_arity_type
    new_arity :: Int
new_arity  = forall (t :: * -> *) a. Foldable t => t a -> Int
length [OneShotInfo]
oss

    info1 :: IdInfo
info1 = HasDebugCallStack => OutId -> IdInfo
idInfo OutId
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]
    -- We also have to nuke demand info if for some reason
    -- eta-expansion *reduces* the arity of the binding to less
    -- than that of the strictness sig. This can happen: see Note [Arity decrease].
    info3 :: IdInfo
info3 | Unfolding -> Bool
isEvaldUnfolding Unfolding
new_unf
            Bool -> Bool -> Bool
|| (case IdInfo -> StrictSig
strictnessInfo IdInfo
info2 of
                  StrictSig DmdType
dmd_ty -> Int
new_arity forall a. Ord a => a -> a -> Bool
< DmdType -> Int
dmdTypeDepth DmdType
dmd_ty)
          = IdInfo -> Maybe IdInfo
zapDemandInfo IdInfo
info2 forall a. Maybe a -> a -> a
`orElse` IdInfo
info2
          | Bool
otherwise
          = IdInfo
info2

    -- Bottoming bindings: see Note [Bottoming bindings]
    info4 :: IdInfo
info4 | Divergence -> Bool
isDeadEndDiv Divergence
div = IdInfo
info3 IdInfo -> StrictSig -> IdInfo
`setStrictnessInfo` StrictSig
bot_sig
                                     IdInfo -> CprSig -> IdInfo
`setCprInfo`        CprSig
bot_cpr
          | Bool
otherwise        = IdInfo
info3

    bot_sig :: StrictSig
bot_sig = [Demand] -> Divergence -> StrictSig
mkClosedStrictSig (forall a. Int -> a -> [a]
replicate Int
new_arity Demand
topDmd) Divergence
div
    bot_cpr :: CprSig
bot_cpr = Int -> Cpr -> CprSig
mkCprSig Int
new_arity Cpr
botCpr

     -- 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 [Arity decrease]
~~~~~~~~~~~~~~~~~~~~~~~~
Generally speaking the arity of a binding should not decrease.  But it *can*
legitimately happen because of RULES.  Eg
        f = g @Int
where g has arity 2, will have arity 2.  But if there's a rewrite rule
        g @Int --> h
where h has arity 1, then f's arity will decrease.  Here's a real-life example,
which is in the output of Specialise:

     Rec {
        $dm {Arity 2} = \d.\x. op d
        {-# RULES forall d. $dm Int d = $s$dm #-}

        dInt = MkD .... opInt ...
        opInt {Arity 1} = $dm dInt

        $s$dm {Arity 0} = \x. op dInt }

Here opInt has arity 1; but when we apply the rule its arity drops to 0.
That's why Specialise goes to a little trouble to pin the right arity
on specialised functions too.

Note [Bottoming bindings]
~~~~~~~~~~~~~~~~~~~~~~~~~
Suppose we have
   let x = error "urk"
   in ...(case x of <alts>)...
or
   let f = \x. error (x ++ "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 RHS is bottom to x'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.

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...


************************************************************************
*                                                                      *
\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]
       ; forall (m :: * -> *) a. Monad m => a -> m a
return (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 = SimplEnv -> Kind -> Kind
substTy SimplEnv
env (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 $$ ppr cont {- $$ ppr (seIdSubst env) -} $$ ppr (seLetFloats env) ) $
    do  { (SimplFloats
floats, CoreExpr
expr') <- SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF SimplEnv
env CoreExpr
expr SimplCont
cont
        ; -- pprTrace "simplExprC ret" (ppr expr $$ ppr expr') $
          -- pprTrace "simplExprC ret3" (ppr (seInScope env')) $
          -- pprTrace "simplExprC ret4" (ppr (seLetFloats env')) $
          forall (m :: * -> *) a. Monad m => a -> m a
return forall a b. (a -> b) -> a -> b
$! 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
  = forall a. HasCallStack => [Char] -> SDoc -> a
pprPanic [Char]
"simplExprF: type" (forall a. Outputable a => a -> SDoc
ppr Kind
ty SDoc -> SDoc -> SDoc
<+> [Char] -> SDoc
text[Char]
"cont: " SDoc -> SDoc -> 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 OutId
v)        SimplCont
cont = {-#SCC "simplIdF" #-} SimplEnv -> OutId -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplIdF SimplEnv
env OutId
v SimplCont
cont
simplExprF1 SimplEnv
env (Lit Literal
lit)      SimplCont
cont = {-#SCC "rebuild" #-} SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
rebuild SimplEnv
env (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' = SimplEnv -> Kind -> Kind
substTy SimplEnv
env (CoreExpr -> Kind
exprType CoreExpr
fun)

                    ; SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF SimplEnv
env CoreExpr
fun 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 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 = SimplEnv -> Kind -> Kind
substTy SimplEnv
env (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
-> [OutId]
-> CoreExpr
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
simplLam SimplEnv
env [OutId]
zapped_bndrs CoreExpr
body SimplCont
cont
        -- The main 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
    ([OutId]
bndrs, CoreExpr
body) = forall b. Expr b -> ([b], Expr b)
collectBinders CoreExpr
expr
    zapped_bndrs :: [OutId]
zapped_bndrs = Int -> [OutId] -> [OutId]
zapLamBndrs Int
n_args [OutId]
bndrs
    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 OutId
bndr Kind
_ [Alt OutId]
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 :: OutId
sc_bndr = OutId
bndr
                                 , sc_alts :: [Alt OutId]
sc_alts = [Alt OutId]
alts
                                 , sc_env :: SimplEnv
sc_env = SimplEnv
env, sc_cont :: SimplCont
sc_cont = SimplCont
cont })

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

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

simplExprF1 SimplEnv
env (Let (NonRec OutId
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" #-}
    ASSERT( isTyVar bndr )
    do { Kind
ty' <- SimplEnv -> Kind -> SimplM Kind
simplType SimplEnv
env Kind
ty
       ; SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF (SimplEnv -> OutId -> Kind -> SimplEnv
extendTvSubst SimplEnv
env OutId
bndr Kind
ty') CoreExpr
body SimplCont
cont }

  | Just (OutId
bndr', CoreExpr
rhs') <- OutId -> CoreExpr -> Maybe (OutId, CoreExpr)
joinPointBinding_maybe OutId
bndr CoreExpr
rhs
  = {-#SCC "simplNonRecJoinPoint" #-} SimplEnv
-> OutId
-> CoreExpr
-> CoreExpr
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
simplNonRecJoinPoint SimplEnv
env OutId
bndr' CoreExpr
rhs' CoreExpr
body SimplCont
cont

  | Bool
otherwise
  = {-#SCC "simplNonRecE" #-} SimplEnv
-> OutId
-> (CoreExpr, SimplEnv)
-> ([OutId], CoreExpr)
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
simplNonRecE SimplEnv
env OutId
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 -> OutId -> CoreExpr -> SimplCont -> SimplM CoreExpr
simplJoinRhs SimplEnv
env OutId
bndr CoreExpr
expr SimplCont
cont
  | Just Int
arity <- OutId -> Maybe Int
isJoinId_maybe OutId
bndr
  =  do { let ([OutId]
join_bndrs, CoreExpr
join_body) = forall b. Int -> Expr b -> ([b], Expr b)
collectNBinders Int
arity CoreExpr
expr
              mult :: Kind
mult = SimplCont -> Kind
contHoleScaling SimplCont
cont
        ; (SimplEnv
env', [OutId]
join_bndrs') <- SimplEnv -> [OutId] -> SimplM (SimplEnv, [OutId])
simplLamBndrs SimplEnv
env (forall a b. (a -> b) -> [a] -> [b]
map (Kind -> OutId -> OutId
scaleVarBy Kind
mult) [OutId]
join_bndrs)
        ; CoreExpr
join_body' <- SimplEnv -> CoreExpr -> SimplCont -> SimplM CoreExpr
simplExprC SimplEnv
env' CoreExpr
join_body SimplCont
cont
        ; forall (m :: * -> *) a. Monad m => a -> m a
return forall a b. (a -> b) -> a -> b
$ forall b. [b] -> Expr b -> Expr b
mkLams [OutId]
join_bndrs' CoreExpr
join_body' }

  | Bool
otherwise
  = forall a. HasCallStack => [Char] -> SDoc -> a
pprPanic [Char]
"simplJoinRhs" (forall a. Outputable a => a -> SDoc
ppr OutId
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 seq :: forall a b. a -> b -> b
`seq` forall (m :: * -> *) a. Monad m => a -> m a
return Kind
new_ty
  where
    new_ty :: Kind
new_ty = 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 (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 { OptCoercionOpts
opts <- SimplM OptCoercionOpts
getOptCoercionOpts
       ; let opt_co :: Coercion
opt_co = OptCoercionOpts -> TCvSubst -> Coercion -> Coercion
optCoercion OptCoercionOpts
opts (SimplEnv -> TCvSubst
getTCvSubst SimplEnv
env) Coercion
co
       ; Coercion -> ()
seqCo Coercion
opt_co seq :: forall a b. a -> b -> b
`seq` forall (m :: * -> *) a. Monad m => a -> m a
return Coercion
opt_co }

-----------------------------------
-- | 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 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
       ; 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 OutId
bndr Kind
ty [Alt OutId]
alts
             -> forall a. a -> Maybe a
Just forall a b. (a -> b) -> a -> b
$ forall b. Expr b -> b -> Kind -> [Alt b] -> Expr b
Case (CoreExpr -> CoreExpr
tickScrut CoreExpr
scrut) OutId
bndr Kind
ty (forall a b. (a -> b) -> [a] -> [b]
map Alt OutId -> Alt OutId
tickAlt [Alt OutId]
alts)
      CoreExpr
_other -> forall a. Maybe a
Nothing
   where ([CoreTickish]
ticks, CoreExpr
expr0) = forall b.
(CoreTickish -> Bool) -> Expr b -> ([CoreTickish], Expr b)
stripTicksTop forall (pass :: TickishPass). GenTickish pass -> Bool
movable (forall b. CoreTickish -> Expr b -> Expr b
Tick CoreTickish
tickish CoreExpr
expr)
         movable :: GenTickish pass -> Bool
movable GenTickish pass
t      = Bool -> Bool
not (forall (pass :: TickishPass). GenTickish pass -> Bool
tickishCounts GenTickish pass
t) Bool -> Bool -> Bool
||
                          GenTickish pass
t forall (pass :: TickishPass).
GenTickish pass -> TickishScoping -> Bool
`tickishScopesLike` TickishScoping
NoScope Bool -> Bool -> Bool
||
                          forall (pass :: TickishPass). GenTickish pass -> Bool
tickishCanSplit GenTickish pass
t
         tickScrut :: CoreExpr -> CoreExpr
tickScrut CoreExpr
e    = 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 OutId -> Alt OutId
tickAlt (Alt AltCon
c [OutId]
bs CoreExpr
e) = forall b. AltCon -> [b] -> Expr b -> Alt b
Alt AltCon
c [OutId]
bs (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         = forall a b. (a -> b) -> [a] -> [b]
map forall (pass :: TickishPass). GenTickish pass -> GenTickish pass
mkNoCount forall a b. (a -> b) -> a -> b
$
                            forall a. (a -> Bool) -> [a] -> [a]
filter (Bool -> Bool
not forall b c a. (b -> c) -> (a -> b) -> a -> c
. (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' = forall {pass :: TickishPass}.
(XTickishId pass ~ OutId) =>
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) = (zapIdStrictness (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
          = forall (pass :: TickishPass).
XBreakpoint pass -> Int -> [XTickishId pass] -> GenTickish pass
Breakpoint XBreakpoint pass
ext Int
n (forall a b. (a -> b) -> [a] -> [b]
map (SimplSR -> OutId
getDoneId forall b c a. (b -> c) -> (a -> b) -> a -> c
. SimplEnv -> OutId -> SimplSR
substId SimplEnv
env) [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 :: SimplCont
sc_cont = SimplCont
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 -> OutId
getDoneId (DoneId OutId
id)  = OutId
id
  getDoneId (DoneEx CoreExpr
e Maybe Int
_) = HasDebugCallStack => CoreExpr -> OutId
getIdFromTrivialExpr CoreExpr
e -- Note [substTickish] in GHC.Core.Subst
  getDoneId SimplSR
other = forall a. HasCallStack => [Char] -> SDoc -> a
pprPanic [Char]
"getDoneId" (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 {}          -> 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 (CoreExpr -> Coercion -> CoreExpr
mkCast CoreExpr
expr Coercion
co) SimplCont
cont
                       -- NB: mkCast implements the (Coercion co |> g) optimisation

      Select { sc_bndr :: SimplCont -> OutId
sc_bndr = OutId
bndr, sc_alts :: SimplCont -> [Alt OutId]
sc_alts = [Alt OutId]
alts, sc_env :: SimplCont -> SimplEnv
sc_env = SimplEnv
se, sc_cont :: SimplCont -> SimplCont
sc_cont = SimplCont
cont }
        -> SimplEnv
-> CoreExpr
-> OutId
-> [Alt OutId]
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
rebuildCase (SimplEnv
se SimplEnv -> SimplEnv -> SimplEnv
`setInScopeFromE` SimplEnv
env) CoreExpr
expr OutId
bndr [Alt OutId]
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 -> OutId
sc_bndr = OutId
b, sc_bndrs :: SimplCont -> [OutId]
sc_bndrs = [OutId]
bs, sc_body :: SimplCont -> CoreExpr
sc_body = CoreExpr
body
                 , sc_env :: SimplCont -> SimplEnv
sc_env = SimplEnv
se, sc_cont :: SimplCont -> SimplCont
sc_cont = SimplCont
cont }
        -> do { (SimplFloats
floats1, SimplEnv
env') <- SimplEnv -> OutId -> CoreExpr -> SimplM (SimplFloats, SimplEnv)
simplNonRecX (SimplEnv
se SimplEnv -> SimplEnv -> SimplEnv
`setInScopeFromE` SimplEnv
env) OutId
b CoreExpr
expr
                                  -- expr satisfies let/app since it started life
                                  -- in a call to simplNonRecE
              ; (SimplFloats
floats2, CoreExpr
expr') <- SimplEnv
-> [OutId]
-> CoreExpr
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
simplLam SimplEnv
env' [OutId]
bs CoreExpr
body SimplCont
cont
              ; forall (m :: * -> *) a. Monad m => a -> m a
return (SimplFloats
floats1 SimplFloats -> SimplFloats -> SimplFloats
`addFloats` SimplFloats
floats2, CoreExpr
expr') }

      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 (forall b. Expr b -> Expr b -> Expr b
App CoreExpr
expr (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}
        -- See Note [Avoid redundant simplification]
        -> do { (DupFlag
_, SimplEnv
_, CoreExpr
arg') <- SimplEnv
-> DupFlag
-> SimplEnv
-> CoreExpr
-> SimplM (DupFlag, SimplEnv, CoreExpr)
simplArg SimplEnv
env DupFlag
dup_flag SimplEnv
se CoreExpr
arg
              ; SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
rebuild SimplEnv
env (forall b. Expr b -> Expr b -> Expr b
App CoreExpr
expr CoreExpr
arg') SimplCont
cont }

{-
************************************************************************
*                                                                      *
\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 NthCo 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 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 = 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' = 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
               ; 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 })
          | Just (MOutCoercion
m_co1, MOutCoercion
m_co2) <- Coercion -> Maybe (MOutCoercion, MOutCoercion)
pushCoValArg Coercion
co
          , MOutCoercion -> Bool
levity_ok 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 -> forall (m :: * -> *) a. Monad m => a -> m a
return (SimplCont
cont { sc_cont :: SimplCont
sc_cont = SimplCont
tail'
                                         , sc_hole_ty :: Kind
sc_hole_ty = Coercion -> Kind
coercionLKind Coercion
co }) ;
                      -- Avoid simplifying if possible;
                      -- See Note [Avoiding exponential behaviour]

                   MCo Coercion
co1 ->
            do { (DupFlag
dup', SimplEnv
arg_se', CoreExpr
arg') <- SimplEnv
-> DupFlag
-> SimplEnv
-> CoreExpr
-> SimplM (DupFlag, SimplEnv, CoreExpr)
simplArg SimplEnv
env DupFlag
dup 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
               ; forall (m :: * -> *) a. Monad m => a -> m a
return (ApplyToVal { sc_arg :: CoreExpr
sc_arg  = 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 = 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        = forall (m :: * -> *) a. Monad m => a -> m a
return (Coercion -> SimplCont -> SimplCont
CastIt Coercion
co SimplCont
cont)

        levity_ok :: MCoercionR -> Bool
        levity_ok :: MOutCoercion -> Bool
levity_ok MOutCoercion
MRefl = Bool
True
        levity_ok (MCo Coercion
co) = Bool -> Bool
not forall a b. (a -> b) -> a -> b
$ Kind -> Bool
isTypeLevPoly forall a b. (a -> b) -> a -> b
$ Coercion -> Kind
coercionRKind Coercion
co
          -- Without this check, we get a lev-poly arg
          -- See Note [Levity polymorphism invariants] in GHC.Core
          -- test: typecheck/should_run/EtaExpandLevPoly

simplArg :: SimplEnv -> DupFlag -> StaticEnv -> CoreExpr
         -> SimplM (DupFlag, StaticEnv, OutExpr)
simplArg :: SimplEnv
-> DupFlag
-> SimplEnv
-> CoreExpr
-> SimplM (DupFlag, SimplEnv, CoreExpr)
simplArg SimplEnv
env DupFlag
dup_flag SimplEnv
arg_env CoreExpr
arg
  | DupFlag -> Bool
isSimplified DupFlag
dup_flag
  = 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 -> SimplM CoreExpr
simplExpr SimplEnv
arg_env'  CoreExpr
arg
       ; 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}
*                                                                      *
************************************************************************
-}

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

simplLam :: SimplEnv
-> [OutId]
-> CoreExpr
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
simplLam SimplEnv
env [] CoreExpr
body SimplCont
cont
  = SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF SimplEnv
env CoreExpr
body SimplCont
cont

simplLam SimplEnv
env (OutId
bndr:[OutId]
bndrs) 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 (OutId -> Tick
BetaReduction OutId
bndr)
       ; SimplEnv
-> [OutId]
-> CoreExpr
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
simplLam (SimplEnv -> OutId -> Kind -> SimplEnv
extendTvSubst SimplEnv
env OutId
bndr Kind
arg_ty) [OutId]
bndrs CoreExpr
body SimplCont
cont }

simplLam SimplEnv
env (OutId
bndr:[OutId]
bndrs) 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 })
  | DupFlag -> Bool
isSimplified DupFlag
dup  -- Don't re-simplify if we've simplified it once
                      -- See Note [Avoiding exponential behaviour]
  = do  { Tick -> SimplM ()
tick (OutId -> Tick
BetaReduction OutId
bndr)
        ; (SimplFloats
floats1, SimplEnv
env') <- SimplEnv -> OutId -> CoreExpr -> SimplM (SimplFloats, SimplEnv)
simplNonRecX SimplEnv
env OutId
zapped_bndr CoreExpr
arg
        ; (SimplFloats
floats2, CoreExpr
expr') <- SimplEnv
-> [OutId]
-> CoreExpr
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
simplLam SimplEnv
env' [OutId]
bndrs CoreExpr
body SimplCont
cont
        ; forall (m :: * -> *) a. Monad m => a -> m a
return (SimplFloats
floats1 SimplFloats -> SimplFloats -> SimplFloats
`addFloats` SimplFloats
floats2, CoreExpr
expr') }

  | Bool
otherwise
  = do  { Tick -> SimplM ()
tick (OutId -> Tick
BetaReduction OutId
bndr)
        ; SimplEnv
-> OutId
-> (CoreExpr, SimplEnv)
-> ([OutId], CoreExpr)
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
simplNonRecE SimplEnv
env OutId
zapped_bndr (CoreExpr
arg, SimplEnv
arg_se) ([OutId]
bndrs, CoreExpr
body) SimplCont
cont }
  where
    zapped_bndr :: OutId
zapped_bndr  -- See Note [Zap unfolding when beta-reducing]
      | OutId -> Bool
isId OutId
bndr = OutId -> OutId
zapStableUnfolding OutId
bndr
      | Bool
otherwise = OutId
bndr

      -- 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.
simplLam SimplEnv
env [OutId]
bndrs CoreExpr
body (TickIt CoreTickish
tickish SimplCont
cont)
  | Bool -> Bool
not (forall (pass :: TickishPass). GenTickish pass -> Bool
tickishCounts CoreTickish
tickish)
  = SimplEnv
-> [OutId]
-> CoreExpr
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
simplLam SimplEnv
env [OutId]
bndrs CoreExpr
body SimplCont
cont

        -- Not enough args, so there are real lambdas left to put in the result
simplLam SimplEnv
env [OutId]
bndrs CoreExpr
body SimplCont
cont
  = do  { (SimplEnv
env', [OutId]
bndrs') <- SimplEnv -> [OutId] -> SimplM (SimplEnv, [OutId])
simplLamBndrs SimplEnv
env [OutId]
bndrs
        ; CoreExpr
body' <- SimplEnv -> CoreExpr -> SimplM CoreExpr
simplExpr SimplEnv
env' CoreExpr
body
        ; CoreExpr
new_lam <- SimplEnv -> [OutId] -> CoreExpr -> SimplCont -> SimplM CoreExpr
mkLam SimplEnv
env [OutId]
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)
-- Used for lambda binders.  These sometimes have unfoldings added by
-- the worker/wrapper pass that must be preserved, because they can't
-- be reconstructed from context.  For example:
--      f x = case x of (a,b) -> fw a b x
--      fw a b x{=(a,b)} = ...
-- The "{=(a,b)}" is an unfolding we can't reconstruct otherwise.
simplLamBndr :: SimplEnv -> OutId -> SimplM (SimplEnv, OutId)
simplLamBndr SimplEnv
env OutId
bndr
  | OutId -> Bool
isId OutId
bndr Bool -> Bool -> Bool
&& Unfolding -> Bool
hasCoreUnfolding Unfolding
old_unf   -- Special case
  = do { (SimplEnv
env1, OutId
bndr1) <- SimplEnv -> OutId -> SimplM (SimplEnv, OutId)
simplBinder SimplEnv
env OutId
bndr
       ; Unfolding
unf'          <- SimplEnv
-> TopLevelFlag
-> MaybeJoinCont
-> OutId
-> Kind
-> ArityType
-> Unfolding
-> SimplM Unfolding
simplStableUnfolding SimplEnv
env1 TopLevelFlag
NotTopLevel forall a. Maybe a
Nothing OutId
bndr
                                      (OutId -> Kind
idType OutId
bndr1) (OutId -> ArityType
idArityType OutId
bndr1) Unfolding
old_unf
       ; let bndr2 :: OutId
bndr2 = OutId
bndr1 OutId -> Unfolding -> OutId
`setIdUnfolding` Unfolding
unf'
       ; forall (m :: * -> *) a. Monad m => a -> m a
return (SimplEnv -> OutId -> SimplEnv
modifyInScope SimplEnv
env1 OutId
bndr2, OutId
bndr2) }

  | Bool
otherwise
  = SimplEnv -> OutId -> SimplM (SimplEnv, OutId)
simplBinder SimplEnv
env OutId
bndr                -- Normal case
  where
    old_unf :: Unfolding
old_unf = OutId -> Unfolding
idUnfolding OutId
bndr

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

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

-- simplNonRecE is used for
--  * non-top-level non-recursive non-join-point lets in expressions
--  * beta reduction
--
-- simplNonRec env b (rhs, rhs_se) (bs, body) k
--   = let env in
--     cont< let b = rhs_se(rhs) in \bs.body >
--
-- It deals with strict bindings, via the StrictBind continuation,
-- which may abort the whole process
--
-- Precondition: rhs satisfies the let/app invariant
--               Note [Core let/app invariant] in GHC.Core
--
-- The "body" of the binding comes as a pair of ([InId],InExpr)
-- representing a lambda; so we recurse back to simplLam
-- Why?  Because of the binder-occ-info-zapping done before
--       the call to simplLam in simplExprF (Lam ...)

simplNonRecE :: SimplEnv
-> OutId
-> (CoreExpr, SimplEnv)
-> ([OutId], CoreExpr)
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
simplNonRecE SimplEnv
env OutId
bndr (CoreExpr
rhs, SimplEnv
rhs_se) ([OutId]
bndrs, CoreExpr
body) SimplCont
cont
  | ASSERT( isId bndr && not (isJoinId bndr) ) True
  , Just SimplEnv
env' <- SimplEnv
-> TopLevelFlag -> OutId -> CoreExpr -> SimplEnv -> Maybe SimplEnv
preInlineUnconditionally SimplEnv
env TopLevelFlag
NotTopLevel OutId
bndr CoreExpr
rhs SimplEnv
rhs_se
  = do { Tick -> SimplM ()
tick (OutId -> Tick
PreInlineUnconditionally OutId
bndr)
       ; -- pprTrace "preInlineUncond" (ppr bndr <+> ppr rhs) $
         SimplEnv
-> [OutId]
-> CoreExpr
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
simplLam SimplEnv
env' [OutId]
bndrs CoreExpr
body SimplCont
cont }

  | Bool
otherwise
  = do { (SimplEnv
env1, OutId
bndr1) <- SimplEnv -> OutId -> SimplM (SimplEnv, OutId)
simplNonRecBndr SimplEnv
env OutId
bndr

       -- Deal with strict bindings
       -- See Note [Dark corner with levity polymorphism]
       ; if OutId -> Bool
isStrictId OutId
bndr1 Bool -> Bool -> Bool
&& SimplMode -> Bool
sm_case_case (SimplEnv -> SimplMode
getMode SimplEnv
env)
         then SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF (SimplEnv
rhs_se SimplEnv -> SimplEnv -> SimplEnv
`setInScopeFromE` SimplEnv
env) CoreExpr
rhs
                   (StrictBind { sc_bndr :: OutId
sc_bndr = OutId
bndr, sc_bndrs :: [OutId]
sc_bndrs = [OutId]
bndrs, sc_body :: CoreExpr
sc_body = CoreExpr
body
                               , sc_env :: SimplEnv
sc_env = SimplEnv
env, sc_cont :: SimplCont
sc_cont = SimplCont
cont, sc_dup :: DupFlag
sc_dup = DupFlag
NoDup })

       -- Deal with lazy bindings
         else do
       { (SimplEnv
env2, OutId
bndr2) <- SimplEnv
-> OutId -> OutId -> MaybeJoinCont -> SimplM (SimplEnv, OutId)
addBndrRules SimplEnv
env1 OutId
bndr OutId
bndr1 forall a. Maybe a
Nothing
       ; (SimplFloats
floats1, SimplEnv
env3) <- SimplEnv
-> TopLevelFlag
-> RecFlag
-> OutId
-> OutId
-> CoreExpr
-> SimplEnv
-> SimplM (SimplFloats, SimplEnv)
simplLazyBind SimplEnv
env2 TopLevelFlag
NotTopLevel RecFlag
NonRecursive OutId
bndr OutId
bndr2 CoreExpr
rhs SimplEnv
rhs_se
       ; (SimplFloats
floats2, CoreExpr
expr') <- SimplEnv
-> [OutId]
-> CoreExpr
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
simplLam SimplEnv
env3 [OutId]
bndrs CoreExpr
body SimplCont
cont
       ; forall (m :: * -> *) a. Monad m => a -> m a
return (SimplFloats
floats1 SimplFloats -> SimplFloats -> SimplFloats
`addFloats` SimplFloats
floats2, CoreExpr
expr') } }

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

-- simplRecE is used for
--  * non-top-level recursive lets in expressions
simplRecE :: SimplEnv
-> [(OutId, CoreExpr)]
-> CoreExpr
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
simplRecE SimplEnv
env [(OutId, CoreExpr)]
pairs CoreExpr
body SimplCont
cont
  = do  { let bndrs :: [OutId]
bndrs = forall a b. (a -> b) -> [a] -> [b]
map forall a b. (a, b) -> a
fst [(OutId, CoreExpr)]
pairs
        ; MASSERT(all (not . isJoinId) bndrs)
        ; SimplEnv
env1 <- SimplEnv -> [OutId] -> SimplM SimplEnv
simplRecBndrs SimplEnv
env [OutId]
bndrs
                -- NB: bndrs' don't have unfoldings or rules
                -- We add them as we go down
        ; (SimplFloats
floats1, SimplEnv
env2) <- SimplEnv
-> TopLevelFlag
-> MaybeJoinCont
-> [(OutId, CoreExpr)]
-> SimplM (SimplFloats, SimplEnv)
simplRecBind SimplEnv
env1 TopLevelFlag
NotTopLevel forall a. Maybe a
Nothing [(OutId, CoreExpr)]
pairs
        ; (SimplFloats
floats2, CoreExpr
expr') <- SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF SimplEnv
env2 CoreExpr
body SimplCont
cont
        ; forall (m :: * -> *) a. Monad m => a -> m a
return (SimplFloats
floats1 SimplFloats -> SimplFloats -> SimplFloats
`addFloats` SimplFloats
floats2, CoreExpr
expr') }

{- Note [Dark corner with levity polymorphism]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In `simplNonRecE`, the call to `isStrictId` will fail if the binder
has a levity-polymorphic type, 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,
levity-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 the re-simplify it -- and then this happens in a
deeply-nested way.  So we must be jolly careful about re-simplifying
an expression.  That is why completeNonRecX does not try
preInlineUnconditionally.

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])


Note [Zap unfolding when beta-reducing]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Lambda-bound variables can have stable unfoldings, such as
   $j = \x. \b{Unf=Just x}. e
See Note [Case binders and join points] below; the unfolding for lets
us optimise e better.  However when we beta-reduce it we want to
revert to using the actual value, otherwise we can end up in the
stupid situation of
          let x = blah in
          let b{Unf=Just x} = y
          in ...b...
Here it'd be far better to drop the unfolding and use the actual RHS.

************************************************************************
*                                                                      *
                     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.
-}

type MaybeJoinCont = Maybe SimplCont
  -- Nothing => Not a join point
  -- Just k  => This is a join binding with continuation k
  -- See Note [Rules and unfolding for join points]

simplNonRecJoinPoint :: SimplEnv -> InId -> InExpr
                     -> InExpr -> SimplCont
                     -> SimplM (SimplFloats, OutExpr)
simplNonRecJoinPoint :: SimplEnv
-> OutId
-> CoreExpr
-> CoreExpr
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
simplNonRecJoinPoint SimplEnv
env OutId
bndr CoreExpr
rhs CoreExpr
body SimplCont
cont
  | ASSERT( isJoinId bndr ) True
  , Just SimplEnv
env' <- SimplEnv
-> TopLevelFlag -> OutId -> CoreExpr -> SimplEnv -> Maybe SimplEnv
preInlineUnconditionally SimplEnv
env TopLevelFlag
NotTopLevel OutId
bndr CoreExpr
rhs SimplEnv
env
  = do { Tick -> SimplM ()
tick (OutId -> Tick
PreInlineUnconditionally OutId
bndr)
       ; SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF SimplEnv
env' CoreExpr
body SimplCont
cont }

   | Bool
otherwise
   = SimplEnv
-> SimplCont
-> (SimplEnv -> SimplCont -> SimplM (SimplFloats, CoreExpr))
-> SimplM (SimplFloats, CoreExpr)
wrapJoinCont SimplEnv
env SimplCont
cont 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, OutId
bndr1)    <- SimplEnv -> OutId -> Kind -> Kind -> SimplM (SimplEnv, OutId)
simplNonRecJoinBndr SimplEnv
env OutId
bndr Kind
mult Kind
res_ty
        ; (SimplEnv
env2, OutId
bndr2)    <- SimplEnv
-> OutId -> OutId -> MaybeJoinCont -> SimplM (SimplEnv, OutId)
addBndrRules SimplEnv
env1 OutId
bndr OutId
bndr1 (forall a. a -> Maybe a
Just SimplCont
cont)
        ; (SimplFloats
floats1, SimplEnv
env3)  <- SimplEnv
-> SimplCont
-> OutId
-> OutId
-> CoreExpr
-> SimplEnv
-> SimplM (SimplFloats, SimplEnv)
simplJoinBind SimplEnv
env2 SimplCont
cont OutId
bndr OutId
bndr2 CoreExpr
rhs SimplEnv
env
        ; (SimplFloats
floats2, CoreExpr
body') <- SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF SimplEnv
env3 CoreExpr
body SimplCont
cont
        ; 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
-> [(OutId, CoreExpr)]
-> CoreExpr
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
simplRecJoinPoint SimplEnv
env [(OutId, CoreExpr)]
pairs CoreExpr
body SimplCont
cont
  = SimplEnv
-> SimplCont
-> (SimplEnv -> SimplCont -> SimplM (SimplFloats, CoreExpr))
-> SimplM (SimplFloats, CoreExpr)
wrapJoinCont SimplEnv
env SimplCont
cont forall a b. (a -> b) -> a -> b
$ \ SimplEnv
env SimplCont
cont ->
    do { let bndrs :: [OutId]
bndrs  = forall a b. (a -> b) -> [a] -> [b]
map forall a b. (a, b) -> a
fst [(OutId, CoreExpr)]
pairs
             mult :: Kind
mult   = SimplCont -> Kind
contHoleScaling SimplCont
cont
             res_ty :: Kind
res_ty = SimplCont -> Kind
contResultType SimplCont
cont
       ; SimplEnv
env1 <- SimplEnv -> [OutId] -> Kind -> Kind -> SimplM SimplEnv
simplRecJoinBndrs SimplEnv
env [OutId]
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
-> TopLevelFlag
-> MaybeJoinCont
-> [(OutId, CoreExpr)]
-> SimplM (SimplFloats, SimplEnv)
simplRecBind SimplEnv
env1 TopLevelFlag
NotTopLevel (forall a. a -> Maybe a
Just SimplCont
cont) [(OutId, CoreExpr)]
pairs
       ; (SimplFloats
floats2, CoreExpr
body') <- SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF SimplEnv
env2 CoreExpr
body SimplCont
cont
       ; 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 (SimplMode -> Bool
sm_case_case (SimplEnv -> SimplMode
getMode 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
       ; 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'
       ; forall (m :: * -> *) a. Monad m => a -> m a
return (SimplFloats
floats1 SimplFloats -> SimplFloats -> SimplFloats
`addFloats` SimplFloats
floats2, CoreExpr
result) }


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

trimJoinCont :: OutId -> Maybe Int -> SimplCont -> SimplCont
trimJoinCont OutId
_ Maybe Int
Nothing SimplCont
cont
  = SimplCont
cont -- Not a jump
trimJoinCont OutId
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 :: SimplCont
sc_cont = Int -> SimplCont -> SimplCont
trim (Int
nforall a. Num a => a -> a -> a
-Int
1) SimplCont
k }
    trim Int
n cont :: SimplCont
cont@(ApplyToTy { sc_cont :: SimplCont -> SimplCont
sc_cont = SimplCont
k })
      = SimplCont
cont { sc_cont :: SimplCont
sc_cont = Int -> SimplCont -> SimplCont
trim (Int
nforall a. Num a => a -> a -> a
-Int
1) SimplCont
k } -- join arity counts types!
    trim Int
_ SimplCont
cont
      = forall a. HasCallStack => [Char] -> SDoc -> a
pprPanic [Char]
"completeCall" forall a b. (a -> b) -> a -> b
$ forall a. Outputable a => a -> SDoc
ppr OutId
var SDoc -> SDoc -> 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
*                                                                      *
************************************************************************
-}

simplVar :: SimplEnv -> InVar -> SimplM OutExpr
-- Look up an InVar in the environment
simplVar :: SimplEnv -> OutId -> SimplM CoreExpr
simplVar SimplEnv
env OutId
var
  -- Why $! ? See Note [Bangs in the Simplifier]
  | OutId -> Bool
isTyVar OutId
var = forall (m :: * -> *) a. Monad m => a -> m a
return forall a b. (a -> b) -> a -> b
$! forall b. Kind -> Expr b
Type forall a b. (a -> b) -> a -> b
$! (SimplEnv -> OutId -> Kind
substTyVar SimplEnv
env OutId
var)
  | OutId -> Bool
isCoVar OutId
var = forall (m :: * -> *) a. Monad m => a -> m a
return forall a b. (a -> b) -> a -> b
$! forall b. Coercion -> Expr b
Coercion forall a b. (a -> b) -> a -> b
$! (SimplEnv -> OutId -> Coercion
substCoVar SimplEnv
env OutId
var)
  | Bool
otherwise
  = case SimplEnv -> OutId -> SimplSR
substId SimplEnv
env OutId
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 OutId
var1          -> forall (m :: * -> *) a. Monad m => a -> m a
return (forall b. OutId -> Expr b
Var OutId
var1)
        DoneEx CoreExpr
e Maybe Int
_           -> forall (m :: * -> *) a. Monad m => a -> m a
return CoreExpr
e

simplIdF :: SimplEnv -> InId -> SimplCont -> SimplM (SimplFloats, OutExpr)
simplIdF :: SimplEnv -> OutId -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplIdF SimplEnv
env OutId
var SimplCont
cont
  = case SimplEnv -> OutId -> SimplSR
substId SimplEnv
env OutId
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 -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF SimplEnv
env' CoreExpr
e SimplCont
cont
          -- Don't trim; haven't already simplified e,
          -- so the cont is not embodied in e

      DoneId OutId
var1 ->
          let cont' :: SimplCont
cont' = OutId -> Maybe Int -> SimplCont -> SimplCont
trimJoinCont OutId
var (OutId -> Maybe Int
isJoinId_maybe OutId
var1) SimplCont
cont
          in SimplEnv -> OutId -> SimplCont -> SimplM (SimplFloats, CoreExpr)
completeCall SimplEnv
env OutId
var1 SimplCont
cont'

      DoneEx CoreExpr
e Maybe Int
mb_join ->
          let env' :: SimplEnv
env' = SimplEnv -> SimplEnv
zapSubstEnv SimplEnv
env
              cont' :: SimplCont
cont' = OutId -> Maybe Int -> SimplCont -> SimplCont
trimJoinCont OutId
var Maybe Int
mb_join SimplCont
cont
          in SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF SimplEnv
env' CoreExpr
e SimplCont
cont'
              -- Note [zapSubstEnv]
              -- The template is already simplified, so don't re-substitute.
              -- 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!!

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

completeCall :: SimplEnv -> OutId -> SimplCont -> SimplM (SimplFloats, OutExpr)
completeCall :: SimplEnv -> OutId -> SimplCont -> SimplM (SimplFloats, CoreExpr)
completeCall SimplEnv
env OutId
var SimplCont
cont
  | Just CoreExpr
expr <- Logger
-> DynFlags
-> Int
-> OutId
-> Bool
-> Bool
-> [ArgSummary]
-> CallCtxt
-> Maybe CoreExpr
callSiteInline Logger
logger DynFlags
dflags Int
case_depth OutId
var Bool
active_unf
                                Bool
lone_variable [ArgSummary]
arg_infos CallCtxt
interesting_cont
  -- Inline the variable's RHS
  = do { Tick -> SimplM ()
checkedTick (OutId -> Tick
UnfoldingDone OutId
var)
       ; CoreExpr -> SimplCont -> SimplM ()
dump_inline CoreExpr
expr SimplCont
cont
       ; let env1 :: SimplEnv
env1 = SimplEnv -> SimplEnv
zapSubstEnv SimplEnv
env
       ; SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF SimplEnv
env1 CoreExpr
expr SimplCont
cont }

  | Bool
otherwise
  -- Don't inline; instead rebuild the call
  = do { RuleEnv
rule_base <- SimplM RuleEnv
getSimplRules
       ; let rules :: [CoreRule]
rules = RuleEnv -> OutId -> [CoreRule]
getRules RuleEnv
rule_base OutId
var
             info :: ArgInfo
info = SimplEnv -> OutId -> [CoreRule] -> Int -> SimplCont -> ArgInfo
mkArgInfo SimplEnv
env OutId
var [CoreRule]
rules
                              Int
n_val_args SimplCont
call_cont
       ; SimplEnv -> ArgInfo -> SimplCont -> SimplM (SimplFloats, CoreExpr)
rebuildCall SimplEnv
env ArgInfo
info SimplCont
cont }

  where
    dflags :: DynFlags
dflags     = SimplEnv -> DynFlags
seDynFlags SimplEnv
env
    case_depth :: Int
case_depth = SimplEnv -> Int
seCaseDepth SimplEnv
env
    logger :: Logger
logger     = SimplEnv -> Logger
seLogger SimplEnv
env
    (Bool
lone_variable, [ArgSummary]
arg_infos, SimplCont
call_cont) = SimplCont -> (Bool, [ArgSummary], SimplCont)
contArgs SimplCont
cont
    n_val_args :: Int
n_val_args       = forall (t :: * -> *) a. Foldable t => t a -> Int
length [ArgSummary]
arg_infos
    interesting_cont :: CallCtxt
interesting_cont = SimplEnv -> SimplCont -> CallCtxt
interestingCallContext SimplEnv
env SimplCont
call_cont
    active_unf :: Bool
active_unf       = SimplMode -> OutId -> Bool
activeUnfolding (SimplEnv -> SimplMode
getMode SimplEnv
env) OutId
var

    log_inlining :: SDoc -> SimplM ()
log_inlining SDoc
doc
      = forall (m :: * -> *) a. MonadIO m => IO a -> m a
liftIO forall a b. (a -> b) -> a -> b
$ Logger -> DumpAction
putDumpMsg Logger
logger DynFlags
dflags
           (PrintUnqualified -> PprStyle
mkDumpStyle PrintUnqualified
alwaysQualify)
           DumpFlag
Opt_D_dump_inlinings
           [Char]
"" DumpFormat
FormatText SDoc
doc

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

rebuildCall :: SimplEnv
            -> ArgInfo
            -> SimplCont
            -> SimplM (SimplFloats, OutExpr)
-- We decided not to inline, so
--    - simplify the arguments
--    - try rewrite rules
--    - and rebuild

---------- Bottoming applications --------------
rebuildCall :: SimplEnv -> ArgInfo -> SimplCont -> SimplM (SimplFloats, CoreExpr)
rebuildCall SimplEnv
env (ArgInfo { ai_fun :: ArgInfo -> OutId
ai_fun = OutId
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 seq :: forall a b. a -> b -> b
`seq`        -- See Note [Avoiding space leaks in OutType]
    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     = OutId -> [ArgSpec] -> CoreExpr
argInfoExpr OutId
fun [ArgSpec]
rev_args
    cont_ty :: Kind
cont_ty = SimplCont -> Kind
contResultType SimplCont
cont

---------- Try rewrite RULES --------------
-- See Note [Trying rewrite rules]
rebuildCall SimplEnv
env info :: ArgInfo
info@(ArgInfo { ai_fun :: ArgInfo -> OutId
ai_fun = OutId
fun, ai_args :: ArgInfo -> [ArgSpec]
ai_args = [ArgSpec]
rev_args
                              , ai_rules :: ArgInfo -> FunRules
ai_rules = Just (Int
nr_wanted, [CoreRule]
rules) }) SimplCont
cont
  | Int
nr_wanted forall a. Eq a => a -> a -> Bool
== Int
0 Bool -> Bool -> Bool
|| Bool
no_more_args
  , let info' :: ArgInfo
info' = ArgInfo
info { ai_rules :: FunRules
ai_rules = forall a. Maybe a
Nothing }
  = -- 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]
-> OutId
-> [ArgSpec]
-> SimplCont
-> SimplM (Maybe (SimplEnv, CoreExpr, SimplCont))
tryRules SimplEnv
env [CoreRule]
rules OutId
fun (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' SimplCont
cont }
  where
    no_more_args :: Bool
no_more_args = case SimplCont
cont of
                      ApplyToTy  {} -> Bool
False
                      ApplyToVal {} -> Bool
False
                      SimplCont
_             -> Bool
True


---------- Simplify 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 -> OutId
ai_fun = OutId
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 })
  | OutId
fun_id 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 OutId
s CoreExpr
body -> do { (SimplEnv
env', OutId
s') <- SimplEnv -> OutId -> SimplM (SimplEnv, OutId)
simplBinder SimplEnv
arg_env OutId
s
                            ; CoreExpr
body' <- SimplEnv -> CoreExpr -> SimplCont -> SimplM CoreExpr
simplExprC SimplEnv
env' CoreExpr
body SimplCont
cont
                            ; forall (m :: * -> *) a. Monad m => a -> m a
return (forall b. b -> Expr b -> Expr b
Lam OutId
s' CoreExpr
body') }
                            -- Important: do not try to eta-expand this lambda
                            -- See Note [No eta-expansion in runRW#]
           CoreExpr
_ -> do { OutId
s' <- FastString -> Kind -> Kind -> SimplM OutId
newId ([Char] -> FastString
fsLit [Char]
"s") Kind
Many Kind
realWorldStatePrimTy
                   ; let (Kind
m,Kind
_,Kind
_) = Kind -> (Kind, Kind, Kind)
splitFunTy Kind
fun_ty
                         env' :: SimplEnv
env'  = SimplEnv
arg_env SimplEnv -> [OutId] -> SimplEnv
`addNewInScopeIds` [OutId
s']
                         cont' :: SimplCont
cont' = ApplyToVal { sc_dup :: DupFlag
sc_dup = DupFlag
Simplified, sc_arg :: CoreExpr
sc_arg = forall b. OutId -> Expr b
Var OutId
s'
                                            , sc_env :: SimplEnv
sc_env = SimplEnv
env', sc_cont :: SimplCont
sc_cont = SimplCont
cont
                                            , sc_hole_ty :: Kind
sc_hole_ty = 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'
                   ; forall (m :: * -> *) a. Monad m => a -> m a
return (forall b. b -> Expr b -> Expr b
Lam OutId
s' CoreExpr
body') }

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

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
  , SimplMode -> Bool
sm_case_case (SimplEnv -> SimplMode
getMode 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 -> CallCtxt -> SimplCont
mkLazyArgStop Kind
arg_ty (ArgInfo -> CallCtxt
lazyArgContext 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 -> OutId
ai_fun = OutId
fun, ai_args :: ArgInfo -> [ArgSpec]
ai_args = [ArgSpec]
rev_args }) SimplCont
cont
  = SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
rebuild SimplEnv
env (OutId -> [ArgSpec] -> CoreExpr
argInfoExpr OutId
fun [ArgSpec]
rev_args) 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 [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]
         -> SimplCont
         -> SimplM (Maybe (SimplEnv, CoreExpr, SimplCont))

tryRules :: SimplEnv
-> [CoreRule]
-> OutId
-> [ArgSpec]
-> SimplCont
-> SimplM (Maybe (SimplEnv, CoreExpr, SimplCont))
tryRules SimplEnv
env [CoreRule]
rules OutId
fn [ArgSpec]
args SimplCont
call_cont
  | forall (t :: * -> *) a. Foldable t => t a -> Bool
null [CoreRule]
rules
  = forall (m :: * -> *) a. Monad m => a -> m a
return 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 dflags (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)
-> OutId
-> [CoreExpr]
-> [CoreRule]
-> Maybe (CoreRule, CoreExpr)
lookupRule RuleOpts
ropts (SimplEnv -> InScopeEnv
getUnfoldingInRuleMatch SimplEnv
env)
                                        (SimplMode -> Activation -> Bool
activeRule (SimplEnv -> SimplMode
getMode SimplEnv
env)) OutId
fn
                                        ([ArgSpec] -> [CoreExpr]
argInfoAppArgs [ArgSpec]
args) [CoreRule]
rules
  -- Fire a rule for the function
  = do { Tick -> SimplM ()
checkedTick (FastString -> Tick
RuleFired (CoreRule -> FastString
ruleName CoreRule
rule))
       ; let cont' :: SimplCont
cont' = SimplEnv -> [ArgSpec] -> SimplCont -> SimplCont
pushSimplifiedArgs SimplEnv
zapped_env
                                        (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]
       ; CoreRule -> CoreExpr -> SimplM ()
dump CoreRule
rule CoreExpr
rule_rhs
       ; forall (m :: * -> *) a. Monad m => a -> m a
return (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 { SimplM ()
nodump  -- This ensures that an empty file is written
       ; forall (m :: * -> *) a. Monad m => a -> m a
return forall a. Maybe a
Nothing }

  where
    -- Force this to avoid retaining DynFlags and hence SimplEnv
    !ropts :: RuleOpts
ropts     = DynFlags -> RuleOpts
initRuleOpts DynFlags
dflags
    dflags :: DynFlags
dflags     = SimplEnv -> DynFlags
seDynFlags SimplEnv
env
    logger :: Logger
logger     = SimplEnv -> Logger
seLogger SimplEnv
env
    zapped_env :: SimplEnv
zapped_env = SimplEnv -> SimplEnv
zapSubstEnv SimplEnv
env  -- See Note [zapSubstEnv]

    printRuleModule :: CoreRule -> SDoc
printRuleModule CoreRule
rule
      = SDoc -> SDoc
parens (forall b a. b -> (a -> b) -> Maybe a -> b
maybe ([Char] -> SDoc
text [Char]
"BUILTIN")
                      (ModuleName -> SDoc
pprModuleName forall b c a. (b -> c) -> (a -> b) -> a -> c
. forall unit. GenModule unit -> ModuleName
moduleName)
                      (CoreRule -> Maybe (GenModule Unit)
ruleModule CoreRule
rule))

    dump :: CoreRule -> CoreExpr -> SimplM ()
dump CoreRule
rule CoreExpr
rule_rhs
      | DumpFlag -> DynFlags -> Bool
dopt DumpFlag
Opt_D_dump_rule_rewrites DynFlags
dflags
      = DynFlags -> DumpFlag -> [Char] -> SDoc -> SimplM ()
log_rule DynFlags
dflags DumpFlag
Opt_D_dump_rule_rewrites [Char]
"Rule fired" forall a b. (a -> b) -> a -> b
$ [SDoc] -> SDoc
vcat
          [ [Char] -> SDoc
text [Char]
"Rule:" SDoc -> SDoc -> SDoc
<+> FastString -> SDoc
ftext (CoreRule -> FastString
ruleName CoreRule
rule)
          , [Char] -> SDoc
text [Char]
"Module:" SDoc -> SDoc -> SDoc
<+>  CoreRule -> SDoc
printRuleModule CoreRule
rule
          , [Char] -> SDoc
text [Char]
"Before:" SDoc -> SDoc -> SDoc
<+> SDoc -> Int -> SDoc -> SDoc
hang (forall a. Outputable a => a -> SDoc
ppr OutId
fn) Int
2 ([SDoc] -> SDoc
sep (forall a b. (a -> b) -> [a] -> [b]
map forall a. Outputable a => a -> SDoc
ppr [ArgSpec]
args))
          , [Char] -> SDoc
text [Char]
"After: " SDoc -> SDoc -> SDoc
<+> SDoc -> Int -> SDoc -> SDoc
hang (forall b. OutputableBndr b => Expr b -> SDoc
pprCoreExpr CoreExpr
rule_rhs) Int
2
                               ([SDoc] -> SDoc
sep forall a b. (a -> b) -> a -> b
$ forall a b. (a -> b) -> [a] -> [b]
map forall a. Outputable a => a -> SDoc
ppr forall a b. (a -> b) -> a -> b
$ forall a. Int -> [a] -> [a]
drop (CoreRule -> Int
ruleArity CoreRule
rule) [ArgSpec]
args)
          , [Char] -> SDoc
text [Char]
"Cont:  " SDoc -> SDoc -> SDoc
<+> forall a. Outputable a => a -> SDoc
ppr SimplCont
call_cont ]

      | DumpFlag -> DynFlags -> Bool
dopt DumpFlag
Opt_D_dump_rule_firings DynFlags
dflags
      = DynFlags -> DumpFlag -> [Char] -> SDoc -> SimplM ()
log_rule DynFlags
dflags DumpFlag
Opt_D_dump_rule_firings [Char]
"Rule fired:" forall a b. (a -> b) -> a -> b
$
          FastString -> SDoc
ftext (CoreRule -> FastString
ruleName CoreRule
rule)
            SDoc -> SDoc -> SDoc
<+> CoreRule -> SDoc
printRuleModule CoreRule
rule

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

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

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

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

    log_rule :: DynFlags -> DumpFlag -> [Char] -> SDoc -> SimplM ()
log_rule DynFlags
dflags DumpFlag
flag [Char]
hdr SDoc
details
      = forall (m :: * -> *) a. MonadIO m => IO a -> m a
liftIO forall a b. (a -> b) -> a -> b
$ do
          let sty :: PprStyle
sty = PrintUnqualified -> PprStyle
mkDumpStyle PrintUnqualified
alwaysQualify
          Logger -> DumpAction
putDumpMsg Logger
logger DynFlags
dflags PprStyle
sty DumpFlag
flag [Char]
"" DumpFormat
FormatText forall a b. (a -> b) -> a -> b
$
              [SDoc] -> SDoc
sep [[Char] -> SDoc
text [Char]
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]
-> OutId
-> [ArgSpec]
-> SimplCont
-> SimplM (Maybe (SimplEnv, CoreExpr, SimplCont))
tryRules SimplEnv
in_env (RuleEnv -> OutId -> [CoreRule]
getRules RuleEnv
rule_base OutId
seqId) OutId
seqId [ArgSpec]
out_args SimplCont
rule_cont }
  where
    no_cast_scrut :: CoreExpr
no_cast_scrut = forall {b}. Expr b -> Expr b
drop_casts CoreExpr
scrut
    scrut_ty :: Kind
scrut_ty  = CoreExpr -> Kind
exprType CoreExpr
no_cast_scrut
    seq_id_ty :: Kind
seq_id_ty = OutId -> Kind
idType OutId
seqId                    -- forall r a (b::TYPE r). a -> b -> b
    res1_ty :: Kind
res1_ty   = HasDebugCallStack => 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   = HasDebugCallStack => Kind -> Kind -> Kind
piResultTy Kind
res1_ty   Kind
scrut_ty   -- forall (b::TYPE rhs_rep). scrut_ty -> b -> b
    res3_ty :: Kind
res3_ty   = HasDebugCallStack => Kind -> Kind -> Kind
piResultTy Kind
res2_ty   Kind
rhs_ty     -- scrut_ty -> rhs_ty -> rhs_ty
    res4_ty :: Kind
res4_ty   = Kind -> Kind
funResultTy Kind
res3_ty             -- rhs_ty -> rhs_ty
    rhs_ty :: Kind
rhs_ty    = SimplEnv -> Kind -> Kind
substTy SimplEnv
in_env (CoreExpr -> Kind
exprType CoreExpr
rhs)
    rhs_rep :: Kind
rhs_rep   = HasDebugCallStack => 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.

Possible improvement: occ-anal the rules when putting them in the
database; and in the simplifier just occ-anal the OutExpr arguments.
But that's more complicated and the rule RHS is usually tiny; so I'm
just doing the simple thing.

Historical note: previously we did occ-anal the rules in Rule.hs,
but failed to occ-anal the OutExpr arguments, which led to the
nasty performance problem described above.


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/app 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]

  NB: absentError satisfies exprIsHNF: see Note [aBSENT_ERROR_ID] in GHC.Core.Make.
  We want to turn
     case (absentError "foo") of r -> ...MkT r...
  into
     let r = absentError "foo" in ...MkT r...


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 of an eval'd function] 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.
-}

---------------------------------------------------------
--      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
-> OutId
-> [Alt OutId]
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
rebuildCase SimplEnv
env CoreExpr
scrut OutId
case_bndr [Alt OutId]
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 (OutId -> Tick
KnownBranch OutId
case_bndr)
        ; case forall b. AltCon -> [Alt b] -> Maybe (Alt b)
findAlt (Literal -> AltCon
LitAlt Literal
lit) [Alt OutId]
alts of
            Maybe (Alt OutId)
Nothing             -> SimplEnv
-> OutId
-> [Alt OutId]
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
missingAlt SimplEnv
env OutId
case_bndr [Alt OutId]
alts SimplCont
cont
            Just (Alt AltCon
_ [OutId]
bs CoreExpr
rhs) -> SimplEnv
-> [FloatBind]
-> CoreExpr
-> [OutId]
-> CoreExpr
-> SimplM (SimplFloats, CoreExpr)
simple_rhs SimplEnv
env [] CoreExpr
scrut [OutId]
bs CoreExpr
rhs }

  | Just (InScopeSet
in_scope', [FloatBind]
wfloats, DataCon
con, [Kind]
ty_args, [CoreExpr]
other_args)
      <- HasDebugCallStack =>
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 (OutId -> Tick
KnownBranch OutId
case_bndr)
        ; let scaled_wfloats :: [FloatBind]
scaled_wfloats = forall a b. (a -> b) -> [a] -> [b]
map FloatBind -> FloatBind
scale_float [FloatBind]
wfloats
        ; case forall b. AltCon -> [Alt b] -> Maybe (Alt b)
findAlt (DataCon -> AltCon
DataAlt DataCon
con) [Alt OutId]
alts of
            Maybe (Alt OutId)
Nothing  -> SimplEnv
-> OutId
-> [Alt OutId]
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
missingAlt SimplEnv
env0 OutId
case_bndr [Alt OutId]
alts SimplCont
cont
            Just (Alt AltCon
DEFAULT [OutId]
bs CoreExpr
rhs) -> let con_app :: CoreExpr
con_app = forall b. OutId -> Expr b
Var (DataCon -> OutId
dataConWorkId DataCon
con)
                                                 forall b. Expr b -> [Kind] -> Expr b
`mkTyApps` [Kind]
ty_args
                                                 forall b. Expr b -> [Expr b] -> Expr b
`mkApps`   [CoreExpr]
other_args
                                         in SimplEnv
-> [FloatBind]
-> CoreExpr
-> [OutId]
-> CoreExpr
-> SimplM (SimplFloats, CoreExpr)
simple_rhs SimplEnv
env0 [FloatBind]
scaled_wfloats CoreExpr
con_app [OutId]
bs CoreExpr
rhs
            Just (Alt AltCon
_ [OutId]
bs CoreExpr
rhs)       -> SimplEnv
-> CoreExpr
-> [FloatBind]
-> DataCon
-> [Kind]
-> [CoreExpr]
-> OutId
-> [OutId]
-> CoreExpr
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
knownCon SimplEnv
env0 CoreExpr
scrut [FloatBind]
scaled_wfloats DataCon
con [Kind]
ty_args [CoreExpr]
other_args
                                                  OutId
case_bndr [OutId]
bs CoreExpr
rhs SimplCont
cont
        }
  where
    simple_rhs :: SimplEnv
-> [FloatBind]
-> CoreExpr
-> [OutId]
-> CoreExpr
-> SimplM (SimplFloats, CoreExpr)
simple_rhs SimplEnv
env [FloatBind]
wfloats CoreExpr
scrut' [OutId]
bs CoreExpr
rhs =
      ASSERT( null bs )
      do { (SimplFloats
floats1, SimplEnv
env') <- SimplEnv -> OutId -> CoreExpr -> SimplM (SimplFloats, SimplEnv)
simplNonRecX SimplEnv
env OutId
case_bndr CoreExpr
scrut'
             -- scrut is a constructor application,
             -- hence satisfies let/app invariant
         ; (SimplFloats
floats2, CoreExpr
expr') <- SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF SimplEnv
env' CoreExpr
rhs SimplCont
cont
         ; case [FloatBind]
wfloats of
             [] -> forall (m :: * -> *) a. Monad m => a -> m a
return (SimplFloats
floats1 SimplFloats -> SimplFloats -> SimplFloats
`addFloats` SimplFloats
floats2, CoreExpr
expr')
             [FloatBind]
_ -> 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 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 OutId
case_bndr AltCon
con [OutId]
vars) =
      let
        scale_id :: OutId -> OutId
scale_id OutId
id = Kind -> OutId -> OutId
scaleVarBy Kind
holeScaling OutId
id
      in
      CoreExpr -> OutId -> AltCon -> [OutId] -> FloatBind
GHC.Core.Make.FloatCase CoreExpr
scrut (OutId -> OutId
scale_id OutId
case_bndr) AltCon
con (forall a b. (a -> b) -> [a] -> [b]
map OutId -> OutId
scale_id [OutId]
vars)
    scale_float FloatBind
f = FloatBind
f

    holeScaling :: Kind
holeScaling = SimplCont -> Kind
contHoleScaling SimplCont
cont Kind -> Kind -> Kind
`mkMultMul` OutId -> Kind
idMult OutId
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 OutId
case_bndr alts :: [Alt OutId]
alts@[Alt AltCon
_ [OutId]
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 -> OutId -> Bool
doCaseToLet CoreExpr
scrut OutId
case_bndr
  = do { Tick -> SimplM ()
tick (OutId -> Tick
CaseElim OutId
case_bndr)
       ; (SimplFloats
floats1, SimplEnv
env') <- SimplEnv -> OutId -> CoreExpr -> SimplM (SimplFloats, SimplEnv)
simplNonRecX SimplEnv
env OutId
case_bndr CoreExpr
scrut
       ; (SimplFloats
floats2, CoreExpr
expr') <- SimplEnv -> CoreExpr -> SimplCont -> SimplM (SimplFloats, CoreExpr)
simplExprF SimplEnv
env' CoreExpr
rhs SimplCont
cont
       ; 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
-> OutId
-> [Alt OutId]
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
reallyRebuildCase SimplEnv
env CoreExpr
scrut OutId
case_bndr [Alt OutId]
alts SimplCont
cont }
  where
    all_dead_bndrs :: Bool
all_dead_bndrs = forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
all OutId -> Bool
isDeadBinder [OutId]
bndrs       -- bndrs are [InId]
    is_plain_seq :: Bool
is_plain_seq   = Bool
all_dead_bndrs Bool -> Bool -> Bool
&& OutId -> Bool
isDeadBinder OutId
case_bndr -- Evaluation *only* for effect

rebuildCase SimplEnv
env CoreExpr
scrut OutId
case_bndr [Alt OutId]
alts SimplCont
cont
  = SimplEnv
-> CoreExpr
-> OutId
-> [Alt OutId]
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
reallyRebuildCase SimplEnv
env CoreExpr
scrut OutId
case_bndr [Alt OutId]
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 -> OutId -> Bool
doCaseToLet CoreExpr
scrut OutId
case_bndr
  | OutId -> Bool
isTyCoVar OutId
case_bndr    -- Respect GHC.Core
  = forall {b}. Expr b -> Bool
isTyCoArg CoreExpr
scrut        -- Note [Core type and coercion invariant]

  | HasDebugCallStack => Kind -> Bool
isUnliftedType (OutId -> Kind
idType OutId
case_bndr)
  = CoreExpr -> Bool
exprOkForSpeculation CoreExpr
scrut

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

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

reallyRebuildCase :: SimplEnv
-> CoreExpr
-> OutId
-> [Alt OutId]
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
reallyRebuildCase SimplEnv
env CoreExpr
scrut OutId
case_bndr [Alt OutId]
alts SimplCont
cont
  | Bool -> Bool
not (SimplMode -> Bool
sm_case_case (SimplEnv -> SimplMode
getMode SimplEnv
env))
  = do { CoreExpr
case_expr <- SimplEnv
-> CoreExpr -> OutId -> [Alt OutId] -> SimplCont -> SimplM CoreExpr
simplAlts SimplEnv
env CoreExpr
scrut OutId
case_bndr [Alt OutId]
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 OutId]
-> SimplCont
-> SimplM (SimplFloats, SimplEnv, SimplCont)
mkDupableCaseCont SimplEnv
env [Alt OutId]
alts SimplCont
cont
       ; CoreExpr
case_expr <- SimplEnv
-> CoreExpr -> OutId -> [Alt OutId] -> SimplCont -> SimplM CoreExpr
simplAlts SimplEnv
env' CoreExpr
scrut
                                (Kind -> OutId -> OutId
scaleIdBy Kind
holeScaling OutId
case_bndr)
                                (Kind -> [Alt OutId] -> [Alt OutId]
scaleAltsBy Kind
holeScaling [Alt OutId]
alts)
                                SimplCont
cont'
       ; 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 -> OutId -> [Alt OutId] -> SimplCont -> SimplM CoreExpr
simplAlts SimplEnv
env0 CoreExpr
scrut OutId
case_bndr [Alt OutId]
alts SimplCont
cont'
  = do  { [Char] -> SDoc -> SimplM ()
traceSmpl [Char]
"simplAlts" ([SDoc] -> SDoc
vcat [ forall a. Outputable a => a -> SDoc
ppr OutId
case_bndr
                                      , [Char] -> SDoc
text [Char]
"cont':" SDoc -> SDoc -> SDoc
<+> forall a. Outputable a => a -> SDoc
ppr SimplCont
cont'
                                      , [Char] -> SDoc
text [Char]
"in_scope" SDoc -> SDoc -> SDoc
<+> forall a. Outputable a => a -> SDoc
ppr (SimplEnv -> InScopeSet
seInScope SimplEnv
env0) ])
        ; (SimplEnv
env1, OutId
case_bndr1) <- SimplEnv -> OutId -> SimplM (SimplEnv, OutId)
simplBinder SimplEnv
env0 OutId
case_bndr
        ; let case_bndr2 :: OutId
case_bndr2 = OutId
case_bndr1 OutId -> Unfolding -> OutId
`setIdUnfolding` Unfolding
evaldUnfolding
              env2 :: SimplEnv
env2       = SimplEnv -> OutId -> SimplEnv
modifyInScope SimplEnv
env1 OutId
case_bndr2
              -- See Note [Case binder evaluated-ness]

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

        ; ([AltCon]
imposs_deflt_cons, [Alt OutId]
in_alts) <- CoreExpr -> OutId -> [Alt OutId] -> SimplM ([AltCon], [Alt OutId])
prepareAlts CoreExpr
scrut' OutId
case_bndr' [Alt OutId]
alts
          -- NB: it's possible that the returned in_alts is empty: this is handled
          -- by the caller (rebuildCase) in the missingAlt function

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

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


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

improveSeq (FamInstEnv, FamInstEnv)
_ SimplEnv
env CoreExpr
scrut OutId
_ OutId
case_bndr1 [Alt OutId]
_
  = forall (m :: * -> *) a. Monad m => a -> m a
return (SimplEnv
env, CoreExpr
scrut, OutId
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]
-> OutId
-> SimplCont
-> Alt OutId
-> SimplM (Alt OutId)
simplAlt SimplEnv
env Maybe CoreExpr
_ ![AltCon]
imposs_deflt_cons OutId
case_bndr' SimplCont
cont' (Alt AltCon
DEFAULT [OutId]
bndrs CoreExpr
rhs)
  = ASSERT( null bndrs )
    do  { let env' :: SimplEnv
env' = SimplEnv -> OutId -> Unfolding -> SimplEnv
addBinderUnfolding SimplEnv
env OutId
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'
        ; forall (m :: * -> *) a. Monad m => a -> m a
return (forall b. AltCon -> [b] -> Expr b -> Alt b
Alt AltCon
DEFAULT [] CoreExpr
rhs') }

simplAlt SimplEnv
env Maybe CoreExpr
scrut' [AltCon]
_ OutId
case_bndr' SimplCont
cont' (Alt (LitAlt Literal
lit) [OutId]
bndrs CoreExpr
rhs)
  = ASSERT( null bndrs )
    do  { SimplEnv
env' <- SimplEnv -> Maybe CoreExpr -> OutId -> CoreExpr -> SimplM SimplEnv
addAltUnfoldings SimplEnv
env Maybe CoreExpr
scrut' OutId
case_bndr' (forall b. Literal -> Expr b
Lit Literal
lit)
        ; CoreExpr
rhs' <- SimplEnv -> CoreExpr -> SimplCont -> SimplM CoreExpr
simplExprC SimplEnv
env' CoreExpr
rhs SimplCont
cont'
        ; forall (m :: * -> *) a. Monad m => a -> m a
return (forall b. AltCon -> [b] -> Expr b -> Alt b
Alt (Literal -> AltCon
LitAlt Literal
lit) [] CoreExpr
rhs') }

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

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

        ; SimplEnv
env'' <- SimplEnv -> Maybe CoreExpr -> OutId -> CoreExpr -> SimplM SimplEnv
addAltUnfoldings SimplEnv
env' Maybe CoreExpr
scrut' OutId
case_bndr' CoreExpr
con_app
        -- Forced so that simplExprC forces wrapFloats which means we don't
        -- retain the InScopeSet in SimplFloats
        ; !CoreExpr
rhs' <- SimplEnv -> CoreExpr -> SimplCont -> SimplM CoreExpr
simplExprC SimplEnv
env'' CoreExpr
rhs SimplCont
cont'
        ; forall (m :: * -> *) a. Monad m => a -> m a
return (forall b. AltCon -> [b] -> Expr b -> Alt b
Alt (DataCon -> AltCon
DataAlt DataCon
con) [OutId]
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 -> [OutId] -> [OutId]
addEvals Maybe CoreExpr
scrut DataCon
con [OutId]
vs
  -- Deal with seq# applications
  | Just CoreExpr
scr <- Maybe CoreExpr
scrut
  , DataCon -> Bool
isUnboxedTupleDataCon DataCon
con
  , [OutId
s,OutId
x] <- [OutId]
vs
    -- Use stripNArgs rather than collectArgsTicks to avoid building
    -- a list of arguments only to throw it away immediately.
  , Just (Var OutId
f) <- forall a. Word -> Expr a -> Maybe (Expr a)
stripNArgs Word
4 CoreExpr
scr
  , Just PrimOp
SeqOp <- OutId -> Maybe PrimOp
isPrimOpId_maybe OutId
f
  , let x' :: OutId
x' = StrictnessMark -> OutId -> OutId
zapIdOccInfoAndSetEvald StrictnessMark
MarkedStrict OutId
x
  = [OutId
s, OutId
x']

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

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

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

addAltUnfoldings :: SimplEnv -> Maybe OutExpr -> OutId -> OutExpr -> SimplM SimplEnv
addAltUnfoldings :: SimplEnv -> Maybe CoreExpr -> OutId -> CoreExpr -> SimplM SimplEnv
addAltUnfoldings SimplEnv
env Maybe CoreExpr
scrut OutId
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 -> OutId -> Unfolding -> SimplEnv
addBinderUnfolding SimplEnv
env OutId
case_bndr Unfolding
con_app_unf

             -- See Note [Add unfolding for scrutinee]
             env2 :: SimplEnv
env2 | Kind
Many <- OutId -> Kind
idMult OutId
case_bndr = case Maybe CoreExpr
scrut of
                      Just (Var OutId
v)           -> SimplEnv -> OutId -> Unfolding -> SimplEnv
addBinderUnfolding SimplEnv
env1 OutId
v Unfolding
con_app_unf
                      Just (Cast (Var OutId
v) Coercion
co) -> SimplEnv -> OutId -> Unfolding -> SimplEnv
addBinderUnfolding SimplEnv
env1 OutId
v forall a b. (a -> b) -> a -> b
$
                                                CoreExpr -> Unfolding
mk_simple_unf (forall b. Expr b -> Coercion -> Expr b
Cast CoreExpr
con_app (Coercion -> Coercion
mkSymCo Coercion
co))
                      Maybe CoreExpr
_                      -> SimplEnv
env1
                  | Bool
otherwise = SimplEnv
env1

       ; [Char] -> SDoc -> SimplM ()
traceSmpl [Char]
"addAltUnf" ([SDoc] -> SDoc
vcat [forall a. Outputable a => a -> SDoc
ppr OutId
case_bndr SDoc -> SDoc -> SDoc
<+> forall a. Outputable a => a -> SDoc
ppr Maybe CoreExpr
scrut, forall a. Outputable a => a -> SDoc
ppr CoreExpr
con_app])
       ; 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 -> OutId -> Unfolding -> SimplEnv
addBinderUnfolding SimplEnv
env OutId
bndr Unfolding
unf
  | Bool
debugIsOn, Just CoreExpr
tmpl <- Unfolding -> Maybe CoreExpr
maybeUnfoldingTemplate Unfolding
unf
  = WARN( not (eqType (idType bndr) (exprType tmpl)),
          ppr bndr $$ ppr (idType bndr) $$ ppr tmpl $$ ppr (exprType tmpl) )
    SimplEnv -> OutId -> SimplEnv
modifyInScope SimplEnv
env (OutId
bndr OutId -> Unfolding -> OutId
`setIdUnfolding` Unfolding
unf)

  | Bool
otherwise
  = SimplEnv -> OutId -> SimplEnv
modifyInScope SimplEnv
env (OutId
bndr OutId -> Unfolding -> OutId
`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 -> OutId -> OutId
zapBndrOccInfo Bool
keep_occ_info OutId
pat_id
  | Bool
keep_occ_info = OutId
pat_id
  | Bool
otherwise     = OutId -> OutId
zapIdOccInfo OutId
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/app invariant.  Example
    case e of b { DEFAULT -> let v = reallyUnsafePtrEq# b y in ....
                ; K       -> blah }

The let/app invariant requires that y is evaluated in the call to
reallyUnsafePtrEq#, 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.

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

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, the same caveat as in
Note [Suppressing binder-swaps on linear case] in OccurAnal apply.


************************************************************************
*                                                                      *
\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]
-> OutId
-> [OutId]
-> CoreExpr
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
knownCon SimplEnv
env CoreExpr
scrut [FloatBind]
dc_floats DataCon
dc [Kind]
dc_ty_args [CoreExpr]
dc_args OutId
bndr [OutId]
bs CoreExpr
rhs SimplCont
cont
  = do  { (SimplFloats
floats1, SimplEnv
env1)  <- SimplEnv -> [OutId] -> [CoreExpr] -> SimplM (SimplFloats, SimplEnv)
bind_args SimplEnv
env [OutId]
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
            [] ->
              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]
_ ->
              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 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 :: OutId -> OutId
zap_occ = Bool -> OutId -> OutId
zapBndrOccInfo (OutId -> Bool
isDeadBinder OutId
bndr)    -- bndr is an InId

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

    bind_args SimplEnv
env' (OutId
b:[OutId]
bs') (Type Kind
ty : [CoreExpr]
args)
      = ASSERT( isTyVar b )
        SimplEnv -> [OutId] -> [CoreExpr] -> SimplM (SimplFloats, SimplEnv)
bind_args (SimplEnv -> OutId -> Kind -> SimplEnv
extendTvSubst SimplEnv
env' OutId
b Kind
ty) [OutId]
bs' [CoreExpr]
args

    bind_args SimplEnv
env' (OutId
b:[OutId]
bs') (Coercion Coercion
co : [CoreExpr]
args)
      = ASSERT( isCoVar b )
        SimplEnv -> [OutId] -> [CoreExpr] -> SimplM (SimplFloats, SimplEnv)
bind_args (SimplEnv -> OutId -> Coercion -> SimplEnv
extendCvSubst SimplEnv
env' OutId
b Coercion
co) [OutId]
bs' [CoreExpr]
args

    bind_args SimplEnv
env' (OutId
b:[OutId]
bs') (CoreExpr
arg : [CoreExpr]
args)
      = ASSERT( isId b )
        do { let b' :: OutId
b' = OutId -> OutId
zap_occ OutId
b
             -- Note that the binder might be "dead", because it doesn't
             -- occur in the RHS; and simplNonRecX may therefore discard
             -- it via postInlineUnconditionally.
             -- 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 -> OutId -> CoreExpr -> SimplM (SimplFloats, SimplEnv)
simplNonRecX SimplEnv
env' OutId
b' CoreExpr
arg  -- arg satisfies let/app invariant
           ; (SimplFloats
floats2, SimplEnv
env3)  <- SimplEnv -> [OutId] -> [CoreExpr] -> SimplM (SimplFloats, SimplEnv)
bind_args SimplEnv
env2 [OutId]
bs' [CoreExpr]
args
           ; forall (m :: * -> *) a. Monad m => a -> m a
return (SimplFloats
floats1 SimplFloats -> SimplFloats -> SimplFloats
`addFloats` SimplFloats
floats2, SimplEnv
env3) }

    bind_args SimplEnv
_ [OutId]
_ [CoreExpr]
_ =
      forall a. HasCallStack => [Char] -> SDoc -> a
pprPanic [Char]
"bind_args" forall a b. (a -> b) -> a -> b
$ forall a. Outputable a => a -> SDoc
ppr DataCon
dc SDoc -> SDoc -> SDoc
$$ forall a. Outputable a => a -> SDoc
ppr [OutId]
bs SDoc -> SDoc -> SDoc
$$ forall a. Outputable a => a -> SDoc
ppr [CoreExpr]
dc_args SDoc -> SDoc -> SDoc
$$
                             [Char] -> SDoc
text [Char]
"scrut:" SDoc -> SDoc -> 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
      | OutId -> Bool
isDeadBinder OutId
bndr   = forall (m :: * -> *) a. Monad m => a -> m a
return (SimplEnv -> SimplFloats
emptyFloats SimplEnv
env, SimplEnv
env)
      | CoreExpr -> Bool
exprIsTrivial CoreExpr
scrut = forall (m :: * -> *) a. Monad m => a -> m a
return (SimplEnv -> SimplFloats
emptyFloats SimplEnv
env
                                     , SimplEnv -> OutId -> SimplSR -> SimplEnv
extendIdSubst SimplEnv
env OutId
bndr (CoreExpr -> Maybe Int -> SimplSR
DoneEx CoreExpr
scrut forall a. Maybe a
Nothing))
      | Bool
otherwise           = do { [CoreExpr]
dc_args <- forall (t :: * -> *) (m :: * -> *) a b.
(Traversable t, Monad m) =>
(a -> m b) -> t a -> m (t b)
mapM (SimplEnv -> OutId -> SimplM CoreExpr
simplVar SimplEnv
env) [OutId]
bs
                                         -- dc_ty_args are already OutTypes,
                                         -- but bs are InBndrs
                                 ; let con_app :: CoreExpr
con_app = forall b. OutId -> Expr b
Var (DataCon -> OutId
dataConWorkId DataCon
dc)
                                                 forall b. Expr b -> [Kind] -> Expr b
`mkTyApps` [Kind]
dc_ty_args
                                                 forall b. Expr b -> [Expr b] -> Expr b
`mkApps`   [CoreExpr]
dc_args
                                 ; SimplEnv -> OutId -> CoreExpr -> SimplM (SimplFloats, SimplEnv)
simplNonRecX SimplEnv
env OutId
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
-> OutId
-> [Alt OutId]
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
missingAlt SimplEnv
env OutId
case_bndr [Alt OutId]
_ SimplCont
cont
  = WARN( True, text "missingAlt" <+> ppr case_bndr )
    -- See Note [Avoiding space leaks in OutType]
    let cont_ty :: Kind
cont_ty = SimplCont -> Kind
contResultType SimplCont
cont
    in Kind -> ()
seqType Kind
cont_ty seq :: forall a b. a -> b -> b
`seq`
       forall (m :: * -> *) a. Monad m => a -> m a
return (SimplEnv -> SimplFloats
emptyFloats SimplEnv
env, Kind -> CoreExpr
mkImpossibleExpr Kind
cont_ty)

{-
************************************************************************
*                                                                      *
\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 OutId]
-> SimplCont
-> SimplM (SimplFloats, SimplEnv, SimplCont)
mkDupableCaseCont SimplEnv
env [Alt OutId]
alts SimplCont
cont
  | [Alt OutId] -> Bool
altsWouldDup [Alt OutId]
alts = do { (SimplFloats
floats, SimplCont
cont) <- SimplEnv -> SimplCont -> SimplM (SimplFloats, SimplCont)
mkDupableCont SimplEnv
env SimplCont
cont
                           ; let env' :: SimplEnv
env' = SimplEnv -> SimplEnv
bumpCaseDepth forall a b. (a -> b) -> a -> b
$
                                        SimplEnv
env SimplEnv -> SimplFloats -> SimplEnv
`setInScopeFromF` SimplFloats
floats
                           ; forall (m :: * -> *) a. Monad m => a -> m a
return (SimplFloats
floats, SimplEnv
env', SimplCont
cont) }
  | Bool
otherwise         = 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 OutId] -> Bool
altsWouldDup []  = Bool
False        -- See Note [Bottom alternatives]
altsWouldDup [Alt OutId
_] = Bool
False
altsWouldDup (Alt OutId
alt:[Alt OutId]
alts)
  | Alt OutId -> Bool
is_bot_alt Alt OutId
alt = [Alt OutId] -> Bool
altsWouldDup [Alt OutId]
alts
  | Bool
otherwise      = Bool -> Bool
not (forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
all Alt OutId -> Bool
is_bot_alt [Alt OutId]
alts)
    -- otherwise case: first alt is non-bot, so all the rest must be bot
  where
    is_bot_alt :: Alt OutId -> Bool
is_bot_alt (Alt AltCon
_ [OutId]
_ 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 (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
  = forall (m :: * -> *) a. Monad m => a -> m a
return (SimplEnv -> SimplFloats
emptyFloats SimplEnv
env, SimplCont
cont)

mkDupableContWithDmds SimplEnv
_ [Demand]
_ (Stop {}) = forall a. [Char] -> a
panic [Char]
"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
        ; 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
        ; 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 -> OutId
sc_bndr = OutId
bndr, sc_bndrs :: SimplCont -> [OutId]
sc_bndrs = [OutId]
bndrs
                 , sc_body :: SimplCont -> CoreExpr
sc_body = CoreExpr
body, 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, OutId
bndr')      <- SimplEnv -> OutId -> SimplM (SimplEnv, OutId)
simplBinder SimplEnv
sb_env OutId
bndr
       ; (SimplFloats
floats1, CoreExpr
join_inner) <- SimplEnv
-> [OutId]
-> CoreExpr
-> SimplCont
-> SimplM (SimplFloats, CoreExpr)
simplLam SimplEnv
sb_env1 [OutId]
bndrs CoreExpr
body SimplCont
cont
          -- No need to use mkDupableCont before simplLam; 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
-> OutId -> CoreExpr -> Kind -> SimplM (SimplFloats, SimplCont)
mkDupableStrictBind SimplEnv
env OutId
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
  | forall a. Maybe a -> Bool
isNothing (OutId -> Maybe DataCon
isDataConId_maybe (ArgInfo -> OutId
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') <- forall (m :: * -> *) a b c.
Applicative m =>
(a -> m (b, c)) -> [a] -> m ([b], [c])
mapAndUnzipM (SimplMode -> ArgSpec -> SimplM (LetFloats, ArgSpec)
makeTrivialArg (SimplEnv -> SimplMode
getMode SimplEnv
env))
                                           (ArgInfo -> [ArgSpec]
ai_args ArgInfo
fun)
       ; forall (m :: * -> *) a. Monad m => a -> m a
return ( 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 :: [ArgSpec]
ai_args = [ArgSpec]
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
       ; OutId
arg_bndr <- FastString -> Kind -> Kind -> SimplM OutId
newId ([Char] -> FastString
fsLit [Char]
"arg") Kind
m Kind
arg_ty
       ; let env' :: SimplEnv
env' = SimplEnv
env SimplEnv -> [OutId] -> SimplEnv
`addNewInScopeIds` [OutId
arg_bndr]
       ; (SimplFloats
floats, CoreExpr
join_rhs) <- SimplEnv -> ArgInfo -> SimplCont -> SimplM (SimplFloats, CoreExpr)
rebuildCall SimplEnv
env' (ArgInfo -> CoreExpr -> Kind -> ArgInfo
addValArgTo ArgInfo
fun (forall b. OutId -> Expr b
Var OutId
arg_bndr) Kind
fun_ty) SimplCont
cont
       ; SimplEnv
-> OutId -> CoreExpr -> Kind -> SimplM (SimplFloats, SimplCont)
mkDupableStrictBind SimplEnv
env' OutId
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
        ; 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]
_) = [Demand]
dmds   -- Never fails
        ; (SimplFloats
floats1, SimplCont
cont') <- SimplEnv
-> [Demand] -> SimplCont -> SimplM (SimplFloats, SimplCont)
mkDupableContWithDmds SimplEnv
env [Demand]
dmds SimplCont
cont
        ; let env' :: SimplEnv
env' = SimplEnv
env SimplEnv -> SimplFloats -> SimplEnv
`setInScopeFromF` SimplFloats
floats1
        ; (DupFlag
_, SimplEnv
se', CoreExpr
arg') <- SimplEnv
-> DupFlag
-> SimplEnv
-> CoreExpr
-> SimplM (DupFlag, SimplEnv, CoreExpr)
simplArg SimplEnv
env' DupFlag
dup SimplEnv
se CoreExpr
arg
        ; (LetFloats
let_floats2, CoreExpr
arg'') <- SimplMode
-> TopLevelFlag
-> Demand
-> FastString
-> CoreExpr
-> SimplM (LetFloats, CoreExpr)
makeTrivial (SimplEnv -> SimplMode
getMode SimplEnv
env) TopLevelFlag
NotTopLevel Demand
dmd ([Char] -> FastString
fsLit [Char]
"karg") CoreExpr
arg'
        ; let all_floats :: SimplFloats
all_floats = SimplFloats
floats1 SimplFloats -> LetFloats -> SimplFloats
`addLetFloats` LetFloats
let_floats2
        ; 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 -> OutId
sc_bndr = OutId
case_bndr, sc_alts :: SimplCont -> [Alt OutId]
sc_alts = [Alt OutId]
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 (OutId -> Tick
CaseOfCase OutId
case_bndr)
        ; (SimplFloats
floats, SimplEnv
alt_env, SimplCont
alt_cont) <- SimplEnv
-> [Alt OutId]
-> SimplCont
-> SimplM (SimplFloats, SimplEnv, SimplCont)
mkDupableCaseCont (SimplEnv
se SimplEnv -> SimplEnv -> SimplEnv
`setInScopeFromE` SimplEnv
env) [Alt OutId]
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', OutId
case_bndr') <- SimplEnv -> OutId -> SimplM (SimplEnv, OutId)
simplBinder SimplEnv
alt_env (Kind -> OutId -> OutId
scaleIdBy Kind
cont_scaling OutId
case_bndr)
        ; [Alt OutId]
alts' <- forall (t :: * -> *) (m :: * -> *) a b.
(Traversable t, Monad m) =>
(a -> m b) -> t a -> m (t b)
mapM (SimplEnv
-> Maybe CoreExpr
-> [AltCon]
-> OutId
-> SimplCont
-> Alt OutId
-> SimplM (Alt OutId)
simplAlt SimplEnv
alt_env' forall a. Maybe a
Nothing [] OutId
case_bndr' SimplCont
alt_cont) (Kind -> [Alt OutId] -> [Alt OutId]
scaleAltsBy Kind
cont_scaling [Alt OutId]
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

        ; (JoinFloats
join_floats, [Alt OutId]
alts'') <- forall (m :: * -> *) acc x y.
Monad m =>
(acc -> x -> m (acc, y)) -> acc -> [x] -> m (acc, [y])
mapAccumLM (Platform
-> OutId
-> JoinFloats
-> Alt OutId
-> SimplM (JoinFloats, Alt OutId)
mkDupableAlt (DynFlags -> Platform
targetPlatform (SimplEnv -> DynFlags
seDynFlags SimplEnv
env)) OutId
case_bndr')
                                              JoinFloats
emptyJoinFloats [Alt OutId]
alts'

        ; let all_floats :: SimplFloats
all_floats = SimplFloats
floats SimplFloats -> JoinFloats -> SimplFloats
`addJoinFloats` JoinFloats
join_floats
                           -- Note [Duplicated env]
        ; forall (m :: * -> *) a. Monad m => a -> m a
return (SimplFloats
all_floats
                 , Select { sc_dup :: DupFlag
sc_dup  = DupFlag
OkToDup
                          , sc_bndr :: OutId
sc_bndr = OutId
case_bndr'
                          , sc_alts :: [Alt OutId]
sc_alts = [Alt OutId]
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
-> OutId -> CoreExpr -> Kind -> SimplM (SimplFloats, SimplCont)
mkDupableStrictBind SimplEnv
env OutId
arg_bndr CoreExpr
join_rhs Kind
res_ty
  | CoreExpr -> Bool
exprIsTrivial CoreExpr
join_rhs   -- See point (2) of Note [Duplicating join points]
  = forall (m :: * -> *) a. Monad m => a -> m a
return (SimplEnv -> SimplFloats
emptyFloats SimplEnv
env
           , StrictBind { sc_bndr :: OutId
sc_bndr = OutId
arg_bndr, sc_bndrs :: [OutId]
sc_bndrs = []
                        , sc_body :: CoreExpr
sc_body = CoreExpr
join_rhs
                        , sc_env :: SimplEnv
sc_env  = SimplEnv -> SimplEnv
zapSubstEnv SimplEnv
env
                          -- 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 { OutId
join_bndr <- [OutId] -> Kind -> SimplM OutId
newJoinId [OutId
arg_bndr] Kind
res_ty
       ; let arg_info :: ArgInfo
arg_info = ArgInfo { ai_fun :: OutId
ai_fun   = OutId
join_bndr
                                , ai_rules :: FunRules
ai_rules = forall a. Maybe a
Nothing, ai_args :: [ArgSpec]
ai_args  = []
                                , ai_encl :: Bool
ai_encl  = Bool
False, ai_dmds :: [Demand]
ai_dmds  = forall a. a -> [a]
repeat Demand
topDmd
                                , ai_discs :: [Int]
ai_discs = forall a. a -> [a]
repeat Int
0 }
       ; forall (m :: * -> *) a. Monad m => a -> m a
return ( SimplFloats -> JoinFloats -> SimplFloats
addJoinFloats (SimplEnv -> SimplFloats
emptyFloats SimplEnv
env) forall a b. (a -> b) -> a -> b
$
                  InBind -> JoinFloats
unitJoinFloat                   forall a b. (a -> b) -> a -> b
$
                  forall b. b -> Expr b -> Bind b
NonRec OutId
join_bndr                forall a b. (a -> b) -> a -> b
$
                  forall b. b -> Expr b -> Expr b
Lam (OutId -> OutId
setOneShotLambda OutId
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 = OutId -> Kind
idType OutId
join_bndr
                            , sc_cont :: SimplCont
sc_cont   = Kind -> SimplCont
mkBoringStop Kind
res_ty
                            } ) }

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

  | Bool
otherwise
  = do  { SimpleOpts
simpl_opts <- DynFlags -> SimpleOpts
initSimpleOpts forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
<$> forall (m :: * -> *). HasDynFlags m => m DynFlags
getDynFlags
        ; let rhs_ty' :: Kind
rhs_ty'  = CoreExpr -> Kind
exprType CoreExpr
rhs'
              scrut_ty :: Kind
scrut_ty = OutId -> Kind
idType OutId
case_bndr
              case_bndr_w_unf :: OutId
case_bndr_w_unf
                = case AltCon
con of
                      AltCon
DEFAULT    -> OutId
case_bndr
                      DataAlt DataCon
dc -> OutId -> Unfolding -> OutId
setIdUnfolding OutId
case_bndr Unfolding
unf
                          where
                                 -- See Note [Case binders and join points]
                             unf :: Unfolding
unf = SimpleOpts -> CoreExpr -> Unfolding
mkInlineUnfolding SimpleOpts
simpl_opts CoreExpr
rhs
                             rhs :: CoreExpr
rhs = forall b. DataCon -> [Kind] -> [OutId] -> Expr b
mkConApp2 DataCon
dc (Kind -> [Kind]
tyConAppArgs Kind
scrut_ty) [OutId]
bndrs'

                      LitAlt {} -> WARN( True, text "mkDupableAlt"
                                                <+> ppr case_bndr <+> ppr con )
                                   OutId
case_bndr
                           -- The case binder is alive but trivial, so why has
                           -- it not been substituted away?

              final_bndrs' :: [OutId]
final_bndrs'
                | OutId -> Bool
isDeadBinder OutId
case_bndr = forall a. (a -> Bool) -> [a] -> [a]
filter OutId -> Bool
abstract_over [OutId]
bndrs'
                | Bool
otherwise              = [OutId]
bndrs' forall a. [a] -> [a] -> [a]
++ [OutId
case_bndr_w_unf]

              abstract_over :: OutId -> Bool
abstract_over OutId
bndr
                  | OutId -> Bool
isTyVar OutId
bndr = Bool
True -- Abstract over all type variables just in case
                  | Bool
otherwise    = Bool -> Bool
not (OutId -> Bool
isDeadBinder OutId
bndr)
                        -- The deadness info on the new Ids is preserved by simplBinders
              final_args :: [CoreExpr]
final_args = forall b. [OutId] -> [Expr b]
varsToCoreExprs [OutId]
final_bndrs'
                           -- 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
              really_final_bndrs :: [OutId]
really_final_bndrs     = forall a b. (a -> b) -> [a] -> [b]
map OutId -> OutId
one_shot [OutId]
final_bndrs'
              one_shot :: OutId -> OutId
one_shot OutId
v | OutId -> Bool
isId OutId
v    = OutId -> OutId
setOneShotLambda OutId
v
                         | Bool
otherwise = OutId
v
              join_rhs :: CoreExpr
join_rhs   = forall b. [b] -> Expr b -> Expr b
mkLams [OutId]
really_final_bndrs CoreExpr
rhs'

        ; OutId
join_bndr <- [OutId] -> Kind -> SimplM OutId
newJoinId [OutId]
final_bndrs' Kind
rhs_ty'

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

        ; forall (m :: * -> *) a. Monad m => a -> m a
return ( JoinFloats
jfloats JoinFloats -> JoinFloats -> JoinFloats
`addJoinFlts` InBind -> JoinFloats
unitJoinFloat (forall b. b -> Expr b -> Bind b
NonRec OutId
join_bndr CoreExpr
join_rhs)
                 , Alt OutId
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.

Note [Case binders and join points]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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-> TopLevelFlag
                  -> MaybeJoinCont
                  -> InId
                  -> OutExpr -> OutType -> ArityType
                  -> Unfolding -> SimplM Unfolding
simplLetUnfolding :: SimplEnv
-> TopLevelFlag
-> MaybeJoinCont
-> OutId
-> CoreExpr
-> Kind
-> ArityType
-> Unfolding
-> SimplM Unfolding
simplLetUnfolding SimplEnv
env TopLevelFlag
top_lvl MaybeJoinCont
cont_mb OutId
id CoreExpr
new_rhs Kind
rhs_ty ArityType
arity Unfolding
unf
  | Unfolding -> Bool
isStableUnfolding Unfolding
unf
  = SimplEnv
-> TopLevelFlag
-> MaybeJoinCont
-> OutId
-> Kind
-> ArityType
-> Unfolding
-> SimplM Unfolding
simplStableUnfolding SimplEnv
env TopLevelFlag
top_lvl MaybeJoinCont
cont_mb OutId
id Kind
rhs_ty ArityType
arity Unfolding
unf
  | OutId -> Bool
isExitJoinId OutId
id
  = 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
-> OutId
-> CoreExpr
-> SimplM Unfolding
mkLetUnfolding UnfoldingOpts
opts TopLevelFlag
top_lvl UnfoldingSource
InlineRhs OutId
id CoreExpr
new_rhs

-------------------
mkLetUnfolding :: UnfoldingOpts -> TopLevelFlag -> UnfoldingSource
               -> InId -> OutExpr -> SimplM Unfolding
mkLetUnfolding :: UnfoldingOpts
-> TopLevelFlag
-> UnfoldingSource
-> OutId
-> CoreExpr
-> SimplM Unfolding
mkLetUnfolding !UnfoldingOpts
uf_opts TopLevelFlag
top_lvl UnfoldingSource
src OutId
id CoreExpr
new_rhs
  = forall (m :: * -> *) a. Monad m => a -> m a
return (UnfoldingOpts
-> UnfoldingSource -> Bool -> Bool -> CoreExpr -> Unfolding
mkUnfolding UnfoldingOpts
uf_opts UnfoldingSource
src Bool
is_top_lvl Bool
is_bottoming CoreExpr
new_rhs)
            -- 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 = OutId -> Bool
isDeadEndId OutId
id

-------------------
simplStableUnfolding :: SimplEnv -> TopLevelFlag
                     -> MaybeJoinCont  -- Just k => a join point with continuation k
                     -> InId
                     -> OutType
                     -> ArityType      -- Used to eta expand, but only for non-join-points
                     -> Unfolding
                     ->SimplM Unfolding
-- Note [Setting the new unfolding]
simplStableUnfolding :: SimplEnv
-> TopLevelFlag
-> MaybeJoinCont
-> OutId
-> Kind
-> ArityType
-> Unfolding
-> SimplM Unfolding
simplStableUnfolding SimplEnv
env TopLevelFlag
top_lvl MaybeJoinCont
mb_cont OutId
id Kind
rhs_ty ArityType
id_arity Unfolding
unf
  = case Unfolding
unf of
      Unfolding
NoUnfolding   -> forall (m :: * -> *) a. Monad m => a -> m a
return Unfolding
unf
      Unfolding
BootUnfolding -> forall (m :: * -> *) a. Monad m => a -> m a
return Unfolding
unf
      OtherCon {}   -> forall (m :: * -> *) a. Monad m => a -> m a
return Unfolding
unf

      DFunUnfolding { df_bndrs :: Unfolding -> [OutId]
df_bndrs = [OutId]
bndrs, df_con :: Unfolding -> DataCon
df_con = DataCon
con, df_args :: Unfolding -> [CoreExpr]
df_args = [CoreExpr]
args }
        -> do { (SimplEnv
env', [OutId]
bndrs') <- SimplEnv -> [OutId] -> SimplM (SimplEnv, [OutId])
simplBinders SimplEnv
unf_env [OutId]
bndrs
              ; [CoreExpr]
args' <- forall (t :: * -> *) (m :: * -> *) a b.
(Traversable t, Monad m) =>
(a -> m b) -> t a -> m (t b)
mapM (SimplEnv -> CoreExpr -> SimplM CoreExpr
simplExpr SimplEnv
env') [CoreExpr]
args
              ; forall (m :: * -> *) a. Monad m => a -> m a
return ([OutId] -> DataCon -> [CoreExpr] -> Unfolding
mkDFunUnfolding [OutId]
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 MaybeJoinCont
mb_cont of
                           Just SimplCont
cont -> -- Binder is a join point
                                        -- See Note [Rules and unfolding for join points]
                                        SimplEnv -> OutId -> CoreExpr -> SimplCont -> SimplM CoreExpr
simplJoinRhs SimplEnv
unf_env OutId
id CoreExpr
expr SimplCont
cont
                           MaybeJoinCont
Nothing   -> -- Binder is not a join point
                                        do { CoreExpr
expr' <- SimplEnv -> CoreExpr -> SimplCont -> SimplM CoreExpr
simplExprC SimplEnv
unf_env CoreExpr
expr (Kind -> SimplCont
mkBoringStop Kind
rhs_ty)
                                           ; forall (m :: * -> *) a. Monad m => a -> m a
return (CoreExpr -> CoreExpr
eta_expand CoreExpr
expr') }
              ; case UnfoldingGuidance
guide of
                  UnfWhen { ug_arity :: UnfoldingGuidance -> Int
ug_arity = Int
arity
                          , ug_unsat_ok :: UnfoldingGuidance -> Bool
ug_unsat_ok = Bool
sat_ok
                          , ug_boring_ok :: UnfoldingGuidance -> Bool
ug_boring_ok = Bool
boring_ok
                          }
                          -- Happens for INLINE things
                        -- Really important to force new_boring_ok as 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' =
                              UnfWhen { ug_arity :: Int
ug_arity = Int
arity
                                      , ug_unsat_ok :: Bool
ug_unsat_ok = Bool
sat_ok
                                      , ug_boring_ok :: Bool
ug_boring_ok = Bool
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 forall (m :: * -> *) a. Monad m => a -> m a
return (UnfoldingSource
-> Bool -> CoreExpr -> UnfoldingGuidance -> Unfolding
mkCoreUnfolding UnfoldingSource
src Bool
is_top_lvl CoreExpr
expr' UnfoldingGuidance
guide')
                            -- See Note [Top-level flag on inline rules] in GHC.Core.Unfold

                  UnfoldingGuidance
_other              -- Happens for INLINABLE things
                     -> UnfoldingOpts
-> TopLevelFlag
-> UnfoldingSource
-> OutId
-> CoreExpr
-> SimplM Unfolding
mkLetUnfolding UnfoldingOpts
uf_opts TopLevelFlag
top_lvl UnfoldingSource
src OutId
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 -> 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.
    !is_top_lvl :: Bool
is_top_lvl = TopLevelFlag -> Bool
isTopLevel TopLevelFlag
top_lvl
    act :: Activation
act        = OutId -> Activation
idInlineActivation OutId
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]
    eta_expand :: CoreExpr -> CoreExpr
eta_expand CoreExpr
expr
      | Bool -> Bool
not Bool
eta_on         = CoreExpr
expr
      | CoreExpr -> Bool
exprIsTrivial CoreExpr
expr = CoreExpr
expr
      | Bool
otherwise          = ArityType -> CoreExpr -> CoreExpr
etaExpandAT ArityType
id_arity CoreExpr
expr
    eta_on :: Bool
eta_on = SimplMode -> Bool
sm_eta_expand (SimplEnv -> SimplMode
getMode SimplEnv
env)

{- 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 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 [Do not eta-expand trivial expressions]
  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 (mb_cont = Just _) 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
             -> MaybeJoinCont   -- Just k for a join point binder
                                -- Nothing otherwise
             -> SimplM (SimplEnv, OutBndr)
-- Rules are added back into the bin
addBndrRules :: SimplEnv
-> OutId -> OutId -> MaybeJoinCont -> SimplM (SimplEnv, OutId)
addBndrRules SimplEnv
env OutId
in_id OutId
out_id MaybeJoinCont
mb_cont
  | forall (t :: * -> *) a. Foldable t => t a -> Bool
null [CoreRule]
old_rules
  = forall (m :: * -> *) a. Monad m => a -> m a
return (SimplEnv
env, OutId
out_id)
  | Bool
otherwise
  = do { [CoreRule]
new_rules <- SimplEnv
-> Maybe OutId -> [CoreRule] -> MaybeJoinCont -> SimplM [CoreRule]
simplRules SimplEnv
env (forall a. a -> Maybe a
Just OutId
out_id) [CoreRule]
old_rules MaybeJoinCont
mb_cont
       ; let final_id :: OutId
final_id  = OutId
out_id OutId -> RuleInfo -> OutId
`setIdSpecialisation` [CoreRule] -> RuleInfo
mkRuleInfo [CoreRule]
new_rules
       ; forall (m :: * -> *) a. Monad m => a -> m a
return (SimplEnv -> OutId -> SimplEnv
modifyInScope SimplEnv
env OutId
final_id, OutId
final_id) }
  where
    old_rules :: [CoreRule]
old_rules = RuleInfo -> [CoreRule]
ruleInfoRules (OutId -> RuleInfo
idSpecialisation OutId
in_id)

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

    simpl_rule rule :: CoreRule
rule@(Rule { ru_bndrs :: CoreRule -> [OutId]
ru_bndrs = [OutId]
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', [OutId]
bndrs') <- SimplEnv -> [OutId] -> SimplM (SimplEnv, [OutId])
simplBinders SimplEnv
env [OutId]
bndrs
           ; let rhs_ty :: Kind
rhs_ty = SimplEnv -> Kind -> Kind
substTy SimplEnv
env' (CoreExpr -> Kind
exprType CoreExpr
rhs)
                 rhs_cont :: SimplCont
rhs_cont = case MaybeJoinCont
mb_cont of  -- See Note [Rules and unfolding for join points]
                                MaybeJoinCont
Nothing   -> Kind -> SimplCont
mkBoringStop Kind
rhs_ty
                                Just SimplCont
cont -> ASSERT2( join_ok, 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]
                 fn_name' :: Name
fn_name' = case Maybe OutId
mb_new_id of
                              Just OutId
id -> OutId -> Name
idName OutId
id
                              Maybe OutId
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 OutId
mb_new_id of
                             Just OutId
id | Just Int
join_arity <- OutId -> Maybe Int
isJoinId_maybe OutId
id
                                     -> forall (t :: * -> *) a. Foldable t => t a -> Int
length [CoreExpr]
args forall a. Eq a => a -> a -> Bool
== Int
join_arity
                             Maybe OutId
_ -> Bool
False
                 bad_join_msg :: SDoc
bad_join_msg = [SDoc] -> SDoc
vcat [ forall a. Outputable a => a -> SDoc
ppr Maybe OutId
mb_new_id, forall a. Outputable a => a -> SDoc
ppr CoreRule
rule
                                     , forall a. Outputable a => a -> SDoc
ppr (forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
fmap OutId -> Maybe Int
isJoinId_maybe Maybe OutId
mb_new_id) ]

           ; [CoreExpr]
args' <- forall (t :: * -> *) (m :: * -> *) a b.
(Traversable t, Monad m) =>
(a -> m b) -> t a -> m (t 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
           ; forall (m :: * -> *) a. Monad m => a -> m a
return (CoreRule
rule { ru_bndrs :: [OutId]
ru_bndrs = [OutId]
bndrs'
                          , ru_fn :: Name
ru_fn    = Name
fn_name'
                          , ru_args :: [CoreExpr]
ru_args  = [CoreExpr]
args'
                          , ru_rhs :: CoreExpr
ru_rhs   = CoreExpr
rhs' }) }

{- 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.
-}