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

    The simplifier utilities
    -}

    {-# LANGUAGE CPP #-}

    module GHC.Core.Opt.Simplify.Utils (
            -- Rebuilding
            mkLam, mkCase, prepareAlts, tryEtaExpandRhs,

            -- Inlining,
            preInlineUnconditionally, postInlineUnconditionally,
            activeUnfolding, activeRule,
            getUnfoldingInRuleMatch,
            simplEnvForGHCi, updModeForStableUnfoldings, updModeForRules,

            -- The continuation type
            SimplCont(..), DupFlag(..), StaticEnv,
            isSimplified, contIsStop,
            contIsDupable, contResultType, contHoleType, contHoleScaling,
            contIsTrivial, contArgs,
            countArgs,
            mkBoringStop, mkRhsStop, mkLazyArgStop, contIsRhsOrArg,
            interestingCallContext,

            -- ArgInfo
            ArgInfo(..), ArgSpec(..), mkArgInfo,
            addValArgTo, addCastTo, addTyArgTo,
            argInfoExpr, argInfoAppArgs, pushSimplifiedArgs,
            isStrictArgInfo, lazyArgContext,

            abstractFloats,

            -- Utilities
            isExitJoinId
        ) where

    #include "HsVersions.h"

    import GHC.Prelude

    import GHC.Core.Opt.Simplify.Env
    import GHC.Core.Opt.Monad        ( SimplMode(..), Tick(..) )
    import GHC.Driver.Session
    import GHC.Driver.Ppr
    import GHC.Core
    import qualified GHC.Core.Subst
    import GHC.Core.Ppr
    import GHC.Core.TyCo.Ppr ( pprParendType )
    import GHC.Core.FVs
    import GHC.Core.Utils
    import GHC.Core.Opt.Arity
    import GHC.Core.Unfold
    import GHC.Core.Unfold.Make
    import GHC.Types.Name
    import GHC.Types.Id
    import GHC.Types.Id.Info
    import GHC.Types.Tickish
    import GHC.Types.Var
    import GHC.Types.Demand
    import GHC.Types.Var.Set
    import GHC.Types.Basic
    import GHC.Core.Opt.Simplify.Monad
    import GHC.Core.Type     hiding( substTy )
    import GHC.Core.Coercion hiding( substCo )
    import GHC.Core.DataCon ( dataConWorkId, isNullaryRepDataCon )
    import GHC.Core.Multiplicity
    import GHC.Utils.Misc
    import GHC.Data.OrdList ( isNilOL )
    import GHC.Utils.Monad
    import GHC.Utils.Outputable
    import GHC.Utils.Logger
    import GHC.Utils.Panic
    import GHC.Core.Opt.ConstantFold
    import GHC.Data.FastString ( fsLit )

    import Control.Monad    ( when )
    import Data.List        ( sortBy )

    {-
    ************************************************************************
    *                                                                      *
                    The SimplCont and DupFlag types
    *                                                                      *
    ************************************************************************

    A SimplCont allows the simplifier to traverse the expression in a
    zipper-like fashion.  The SimplCont represents the rest of the expression,
    "above" the point of interest.

    You can also think of a SimplCont as an "evaluation context", using
    that term in the way it is used for operational semantics. This is the
    way I usually think of it, For example you'll often see a syntax for
    evaluation context looking like
            C ::= []  |  C e   |  case C of alts  |  C `cast` co
    That's the kind of thing we are doing here, and I use that syntax in
    the comments.

    Key points:
      * A SimplCont describes a *strict* context (just like
        evaluation contexts do).  E.g. Just [] is not a SimplCont

      * A SimplCont describes a context that *does not* bind
        any variables.  E.g. \x. [] is not a SimplCont
    -}

    data SimplCont
      = Stop                -- Stop[e] = e
            OutType         -- Type of the <hole>
            CallCtxt        -- Tells if there is something interesting about
                            --          the context, and hence the inliner
                            --          should be a bit keener (see interestingCallContext)
                            -- Specifically:
                            --     This is an argument of a function that has RULES
                            --     Inlining the call might allow the rule to fire
                            -- Never ValAppCxt (use ApplyToVal instead)
                            -- or CaseCtxt (use Select instead)

      | CastIt              -- (CastIt co K)[e] = K[ e `cast` co ]
            OutCoercion             -- The coercion simplified
                                    -- Invariant: never an identity coercion
            SimplCont

      | ApplyToVal         -- (ApplyToVal arg K)[e] = K[ e arg ]
          { SimplCont -> DupFlag
    sc_dup     :: DupFlag   -- See Note [DupFlag invariants]
          , SimplCont -> OutType
    sc_hole_ty :: OutType   -- Type of the function, presumably (forall a. blah)
                                    -- See Note [The hole type in ApplyToTy/Val]
          , SimplCont -> Expr Id
    sc_arg  :: InExpr       -- The argument,
          , SimplCont -> StaticEnv
    sc_env  :: StaticEnv    -- see Note [StaticEnv invariant]
          , SimplCont -> SimplCont
    sc_cont :: SimplCont }

      | ApplyToTy          -- (ApplyToTy ty K)[e] = K[ e ty ]
          { SimplCont -> OutType
    sc_arg_ty  :: OutType     -- Argument type
          , sc_hole_ty :: OutType     -- Type of the function, presumably (forall a. blah)
                                      -- See Note [The hole type in ApplyToTy/Val]
          , sc_cont    :: SimplCont }

      | Select             -- (Select alts K)[e] = K[ case e of alts ]
          { sc_dup  :: DupFlag        -- See Note [DupFlag invariants]
          , SimplCont -> Id
    sc_bndr :: InId           -- case binder
          , SimplCont -> [InAlt]
    sc_alts :: [InAlt]        -- Alternatives
          , sc_env  :: StaticEnv      -- See Note [StaticEnv invariant]
          , sc_cont :: SimplCont }

      -- The two strict forms have no DupFlag, because we never duplicate them
      | StrictBind          -- (StrictBind x xs b K)[e] = let x = e in K[\xs.b]
                            --       or, equivalently,  = K[ (\x xs.b) e ]
          { sc_dup   :: DupFlag        -- See Note [DupFlag invariants]
          , sc_bndr  :: InId
          , SimplCont -> [Id]
    sc_bndrs :: [InBndr]
          , SimplCont -> Expr Id
    sc_body  :: InExpr
          , sc_env   :: StaticEnv      -- See Note [StaticEnv invariant]
          , sc_cont  :: SimplCont }

      | StrictArg           -- (StrictArg (f e1 ..en) K)[e] = K[ f e1 .. en e ]
          { sc_dup  :: DupFlag     -- Always Simplified or OkToDup
          , SimplCont -> ArgInfo
    sc_fun  :: ArgInfo     -- Specifies f, e1..en, Whether f has rules, etc
                                   --     plus demands and discount flags for *this* arg
                                   --          and further args
                                   --     So ai_dmds and ai_discs are never empty
          , SimplCont -> OutType
    sc_fun_ty :: OutType   -- Type of the function (f e1 .. en),
                                   -- presumably (arg_ty -> res_ty)
                                   -- where res_ty is expected by sc_cont
          , sc_cont :: SimplCont }

      | TickIt              -- (TickIt t K)[e] = K[ tick t e ]
            CoreTickish     -- Tick tickish <hole>
            SimplCont

    type StaticEnv = SimplEnv       -- Just the static part is relevant

    data DupFlag = NoDup       -- Unsimplified, might be big
                 | Simplified  -- Simplified
                 | OkToDup     -- Simplified and small

    isSimplified :: DupFlag -> Bool
    isSimplified :: DupFlag -> Bool
    isSimplified DupFlag
    NoDup = Bool
    False
    isSimplified DupFlag
    _     = Bool
    True       -- Invariant: the subst-env is empty

    perhapsSubstTy :: DupFlag -> StaticEnv -> Type -> Type
    perhapsSubstTy :: DupFlag -> StaticEnv -> OutType -> OutType
    perhapsSubstTy DupFlag
    dup StaticEnv
    env OutType
    ty
      | DupFlag -> Bool
    isSimplified DupFlag
    dup = OutType
    ty
      | Bool
    otherwise        = StaticEnv -> OutType -> OutType
    substTy StaticEnv
    env OutType
    ty

    {- Note [StaticEnv invariant]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    We pair up an InExpr or InAlts with a StaticEnv, which establishes the
    lexical scope for that InExpr.  When we simplify that InExpr/InAlts, we
    use
      - Its captured StaticEnv
      - Overriding its InScopeSet with the larger one at the
        simplification point.

    Why override the InScopeSet?  Example:
          (let y = ey in f) ex
    By the time we simplify ex, 'y' will be in scope.

    However the InScopeSet in the StaticEnv is not irrelevant: it should
    include all the free vars of applying the substitution to the InExpr.
    Reason: contHoleType uses perhapsSubstTy to apply the substitution to
    the expression, and that (rightly) gives ASSERT failures if the InScopeSet
    isn't big enough.

    Note [DupFlag invariants]
    ~~~~~~~~~~~~~~~~~~~~~~~~~
    In both (ApplyToVal dup _ env k)
       and  (Select dup _ _ env k)
    the following invariants hold

      (a) if dup = OkToDup, then continuation k is also ok-to-dup
      (b) if dup = OkToDup or Simplified, the subst-env is empty
          (and hence no need to re-simplify)
    -}

    instance Outputable DupFlag where
      ppr :: DupFlag -> SDoc
    ppr DupFlag
    OkToDup    = String -> SDoc
    text String
    "ok"
      ppr DupFlag
    NoDup      = String -> SDoc
    text String
    "nodup"
      ppr DupFlag
    Simplified = String -> SDoc
    text String
    "simpl"

    instance Outputable SimplCont where
      ppr :: SimplCont -> SDoc
    ppr (Stop OutType
    ty CallCtxt
    interesting) = String -> SDoc
    text String
    "Stop" SDoc -> SDoc -> SDoc
    <> SDoc -> SDoc
    brackets (forall a. Outputable a => a -> SDoc
    ppr CallCtxt
    interesting) SDoc -> SDoc -> SDoc
    <+> forall a. Outputable a => a -> SDoc
    ppr OutType
    ty
      ppr (CastIt OutCoercion
    co SimplCont
    cont  )    = (String -> SDoc
    text String
    "CastIt" SDoc -> SDoc -> SDoc
    <+> OutCoercion -> SDoc
    pprOptCo OutCoercion
    co) SDoc -> SDoc -> SDoc
    $$ forall a. Outputable a => a -> SDoc
    ppr SimplCont
    cont
      ppr (TickIt CoreTickish
    t SimplCont
    cont)       = (String -> SDoc
    text String
    "TickIt" SDoc -> SDoc -> SDoc
    <+> forall a. Outputable a => a -> SDoc
    ppr CoreTickish
    t) SDoc -> SDoc -> SDoc
    $$ forall a. Outputable a => a -> SDoc
    ppr SimplCont
    cont
      ppr (ApplyToTy  { sc_arg_ty :: SimplCont -> OutType
    sc_arg_ty = OutType
    ty, sc_cont :: SimplCont -> SimplCont
    sc_cont = SimplCont
    cont })
        = (String -> SDoc
    text String
    "ApplyToTy" SDoc -> SDoc -> SDoc
    <+> OutType -> SDoc
    pprParendType OutType
    ty) SDoc -> SDoc -> SDoc
    $$ forall a. Outputable a => a -> SDoc
    ppr SimplCont
    cont
      ppr (ApplyToVal { sc_arg :: SimplCont -> Expr Id
    sc_arg = Expr Id
    arg, sc_dup :: SimplCont -> DupFlag
    sc_dup = DupFlag
    dup, sc_cont :: SimplCont -> SimplCont
    sc_cont = SimplCont
    cont, sc_hole_ty :: SimplCont -> OutType
    sc_hole_ty = OutType
    hole_ty })
        = (SDoc -> Arity -> SDoc -> SDoc
    hang (String -> SDoc
    text String
    "ApplyToVal" SDoc -> SDoc -> SDoc
    <+> forall a. Outputable a => a -> SDoc
    ppr DupFlag
    dup SDoc -> SDoc -> SDoc
    <+> String -> SDoc
    text String
    "hole" SDoc -> SDoc -> SDoc
    <+> forall a. Outputable a => a -> SDoc
    ppr OutType
    hole_ty)
              Arity
    2 (forall b. OutputableBndr b => Expr b -> SDoc
    pprParendExpr Expr Id
    arg))
          SDoc -> SDoc -> SDoc
    $$ forall a. Outputable a => a -> SDoc
    ppr SimplCont
    cont
      ppr (StrictBind { sc_bndr :: SimplCont -> Id
    sc_bndr = Id
    b, sc_cont :: SimplCont -> SimplCont
    sc_cont = SimplCont
    cont })
        = (String -> SDoc
    text String
    "StrictBind" SDoc -> SDoc -> SDoc
    <+> forall a. Outputable a => a -> SDoc
    ppr Id
    b) SDoc -> SDoc -> SDoc
    $$ forall a. Outputable a => a -> SDoc
    ppr SimplCont
    cont
      ppr (StrictArg { sc_fun :: SimplCont -> ArgInfo
    sc_fun = ArgInfo
    ai, sc_cont :: SimplCont -> SimplCont
    sc_cont = SimplCont
    cont })
        = (String -> SDoc
    text String
    "StrictArg" SDoc -> SDoc -> SDoc
    <+> forall a. Outputable a => a -> SDoc
    ppr (ArgInfo -> Id
    ai_fun ArgInfo
    ai)) SDoc -> SDoc -> SDoc
    $$ forall a. Outputable a => a -> SDoc
    ppr SimplCont
    cont
      ppr (Select { sc_dup :: SimplCont -> DupFlag
    sc_dup = DupFlag
    dup, sc_bndr :: SimplCont -> Id
    sc_bndr = Id
    bndr, sc_alts :: SimplCont -> [InAlt]
    sc_alts = [InAlt]
    alts, sc_env :: SimplCont -> StaticEnv
    sc_env = StaticEnv
    se, sc_cont :: SimplCont -> SimplCont
    sc_cont = SimplCont
    cont })
        = (String -> SDoc
    text String
    "Select" SDoc -> SDoc -> SDoc
    <+> forall a. Outputable a => a -> SDoc
    ppr DupFlag
    dup SDoc -> SDoc -> SDoc
    <+> forall a. Outputable a => a -> SDoc
    ppr Id
    bndr) SDoc -> SDoc -> SDoc
    $$
           SDoc -> SDoc
    whenPprDebug (Arity -> SDoc -> SDoc
    nest Arity
    2 forall a b. (a -> b) -> a -> b
    $ [SDoc] -> SDoc
    vcat [forall a. Outputable a => a -> SDoc
    ppr (StaticEnv -> TvSubstEnv
    seTvSubst StaticEnv
    se), forall a. Outputable a => a -> SDoc
    ppr [InAlt]
    alts]) SDoc -> SDoc -> SDoc
    $$ forall a. Outputable a => a -> SDoc
    ppr SimplCont
    cont

    {- Note [The hole type in ApplyToTy]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    The sc_hole_ty field of ApplyToTy records the type of the "hole" in the
    continuation.  It is absolutely necessary to compute contHoleType, but it is
    not used for anything else (and hence may not be evaluated).

    Why is it necessary for contHoleType?  Consider the continuation
         ApplyToType Int (Stop Int)
    corresponding to
         (<hole> @Int) :: Int
    What is the type of <hole>?  It could be (forall a. Int) or (forall a. a),
    and there is no way to know which, so we must record it.

    In a chain of applications  (f @t1 @t2 @t3) we'll lazily compute exprType
    for (f @t1) and (f @t1 @t2), which is potentially non-linear; but it probably
    doesn't matter because we'll never compute them all.

    ************************************************************************
    *                                                                      *
                    ArgInfo and ArgSpec
    *                                                                      *
    ************************************************************************
    -}

    data ArgInfo
      = ArgInfo {
            ArgInfo -> Id
    ai_fun   :: OutId,      -- The function
            ArgInfo -> [ArgSpec]
    ai_args  :: [ArgSpec],  -- ...applied to these args (which are in *reverse* order)

            ArgInfo -> FunRules
    ai_rules :: FunRules,   -- Rules for this function

            ArgInfo -> Bool
    ai_encl :: Bool,        -- Flag saying whether this function
                                    -- or an enclosing one has rules (recursively)
                                    --      True => be keener to inline in all args

            ArgInfo -> [Demand]
    ai_dmds :: [Demand],    -- Demands on remaining value arguments (beyond ai_args)
                                    --   Usually infinite, but if it is finite it guarantees
                                    --   that the function diverges after being given
                                    --   that number of args

            ArgInfo -> [Arity]
    ai_discs :: [Int]       -- Discounts for remaining value arguments (beyong ai_args)
                                    --   non-zero => be keener to inline
                                    --   Always infinite
        }

    data ArgSpec
      = ValArg { ArgSpec -> Demand
    as_dmd  :: Demand        -- Demand placed on this argument
               , ArgSpec -> Expr Id
    as_arg  :: OutExpr       -- Apply to this (coercion or value); c.f. ApplyToVal
               , ArgSpec -> OutType
    as_hole_ty :: OutType }  -- Type of the function (presumably t1 -> t2)

      | TyArg { ArgSpec -> OutType
    as_arg_ty  :: OutType     -- Apply to this type; c.f. ApplyToTy
              , as_hole_ty :: OutType }   -- Type of the function (presumably forall a. blah)

      | CastBy OutCoercion                -- Cast by this; c.f. CastIt

    instance Outputable ArgInfo where
      ppr :: ArgInfo -> SDoc
    ppr (ArgInfo { ai_fun :: ArgInfo -> Id
    ai_fun = Id
    fun, ai_args :: ArgInfo -> [ArgSpec]
    ai_args = [ArgSpec]
    args, ai_dmds :: ArgInfo -> [Demand]
    ai_dmds = [Demand]
    dmds })
        = String -> SDoc
    text String
    "ArgInfo" SDoc -> SDoc -> SDoc
    <+> SDoc -> SDoc
    braces
             ([SDoc] -> SDoc
    sep [ String -> SDoc
    text String
    "fun =" SDoc -> SDoc -> SDoc
    <+> forall a. Outputable a => a -> SDoc
    ppr Id
    fun
                  , String -> SDoc
    text String
    "dmds =" SDoc -> SDoc -> SDoc
    <+> forall a. Outputable a => a -> SDoc
    ppr [Demand]
    dmds
                  , String -> SDoc
    text String
    "args =" SDoc -> SDoc -> SDoc
    <+> forall a. Outputable a => a -> SDoc
    ppr [ArgSpec]
    args ])

    instance Outputable ArgSpec where
      ppr :: ArgSpec -> SDoc
    ppr (ValArg { as_arg :: ArgSpec -> Expr Id
    as_arg = Expr Id
    arg })  = String -> SDoc
    text String
    "ValArg" SDoc -> SDoc -> SDoc
    <+> forall a. Outputable a => a -> SDoc
    ppr Expr Id
    arg
      ppr (TyArg { as_arg_ty :: ArgSpec -> OutType
    as_arg_ty = OutType
    ty }) = String -> SDoc
    text String
    "TyArg" SDoc -> SDoc -> SDoc
    <+> forall a. Outputable a => a -> SDoc
    ppr OutType
    ty
      ppr (CastBy OutCoercion
    c)                 = String -> SDoc
    text String
    "CastBy" SDoc -> SDoc -> SDoc
    <+> forall a. Outputable a => a -> SDoc
    ppr OutCoercion
    c

    addValArgTo :: ArgInfo ->  OutExpr -> OutType -> ArgInfo
    addValArgTo :: ArgInfo -> Expr Id -> OutType -> ArgInfo
    addValArgTo ArgInfo
    ai Expr Id
    arg OutType
    hole_ty
      | ArgInfo { ai_dmds :: ArgInfo -> [Demand]
    ai_dmds = Demand
    dmd:[Demand]
    dmds, ai_discs :: ArgInfo -> [Arity]
    ai_discs = Arity
    _:[Arity]
    discs, ai_rules :: ArgInfo -> FunRules
    ai_rules = FunRules
    rules } <- ArgInfo
    ai
          -- Pop the top demand and and discounts off
      , let arg_spec :: ArgSpec
    arg_spec = ValArg { as_arg :: Expr Id
    as_arg = Expr Id
    arg, as_hole_ty :: OutType
    as_hole_ty = OutType
    hole_ty, as_dmd :: Demand
    as_dmd = Demand
    dmd }
      = ArgInfo
    ai { ai_args :: [ArgSpec]
    ai_args  = ArgSpec
    arg_spec forall a. a -> [a] -> [a]
    : ArgInfo -> [ArgSpec]
    ai_args ArgInfo
    ai
           , ai_dmds :: [Demand]
    ai_dmds  = [Demand]
    dmds
           , ai_discs :: [Arity]
    ai_discs = [Arity]
    discs
           , ai_rules :: FunRules
    ai_rules = FunRules -> FunRules
    decRules FunRules
    rules }
      | Bool
    otherwise
      = forall a. HasCallStack => String -> SDoc -> a
    pprPanic String
    "addValArgTo" (forall a. Outputable a => a -> SDoc
    ppr ArgInfo
    ai SDoc -> SDoc -> SDoc
    $$ forall a. Outputable a => a -> SDoc
    ppr Expr Id
    arg)
        -- There should always be enough demands and discounts

    addTyArgTo :: ArgInfo -> OutType -> OutType -> ArgInfo
    addTyArgTo :: ArgInfo -> OutType -> OutType -> ArgInfo
    addTyArgTo ArgInfo
    ai OutType
    arg_ty OutType
    hole_ty = ArgInfo
    ai { ai_args :: [ArgSpec]
    ai_args = ArgSpec
    arg_spec forall a. a -> [a] -> [a]
    : ArgInfo -> [ArgSpec]
    ai_args ArgInfo
    ai
                                      , ai_rules :: FunRules
    ai_rules = FunRules -> FunRules
    decRules (ArgInfo -> FunRules
    ai_rules ArgInfo
    ai) }
      where
        arg_spec :: ArgSpec
    arg_spec = TyArg { as_arg_ty :: OutType
    as_arg_ty = OutType
    arg_ty, as_hole_ty :: OutType
    as_hole_ty = OutType
    hole_ty }

    addCastTo :: ArgInfo -> OutCoercion -> ArgInfo
    addCastTo :: ArgInfo -> OutCoercion -> ArgInfo
    addCastTo ArgInfo
    ai OutCoercion
    co = ArgInfo
    ai { ai_args :: [ArgSpec]
    ai_args = OutCoercion -> ArgSpec
    CastBy OutCoercion
    co forall a. a -> [a] -> [a]
    : ArgInfo -> [ArgSpec]
    ai_args ArgInfo
    ai }

    isStrictArgInfo :: ArgInfo -> Bool
    -- True if the function is strict in the next argument
    isStrictArgInfo :: ArgInfo -> Bool
    isStrictArgInfo (ArgInfo { ai_dmds :: ArgInfo -> [Demand]
    ai_dmds = [Demand]
    dmds })
      | Demand
    dmd:[Demand]
    _ <- [Demand]
    dmds = Demand -> Bool
    isStrUsedDmd Demand
    dmd
      | Bool
    otherwise     = Bool
    False

    argInfoAppArgs :: [ArgSpec] -> [OutExpr]
    argInfoAppArgs :: [ArgSpec] -> [Expr Id]
    argInfoAppArgs []                              = []
    argInfoAppArgs (CastBy {}                : [ArgSpec]
    _)  = []  -- Stop at a cast
    argInfoAppArgs (ValArg { as_arg :: ArgSpec -> Expr Id
    as_arg = Expr Id
    arg }  : [ArgSpec]
    as) = Expr Id
    arg     forall a. a -> [a] -> [a]
    : [ArgSpec] -> [Expr Id]
    argInfoAppArgs [ArgSpec]
    as
    argInfoAppArgs (TyArg { as_arg_ty :: ArgSpec -> OutType
    as_arg_ty = OutType
    ty } : [ArgSpec]
    as) = forall b. OutType -> Expr b
    Type OutType
    ty forall a. a -> [a] -> [a]
    : [ArgSpec] -> [Expr Id]
    argInfoAppArgs [ArgSpec]
    as

    pushSimplifiedArgs :: SimplEnv -> [ArgSpec] -> SimplCont -> SimplCont
    pushSimplifiedArgs :: StaticEnv -> [ArgSpec] -> SimplCont -> SimplCont
    pushSimplifiedArgs StaticEnv
    _env []           SimplCont
    k = SimplCont
    k
    pushSimplifiedArgs StaticEnv
    env  (ArgSpec
    arg : [ArgSpec]
    args) SimplCont
    k
      = case ArgSpec
    arg of
          TyArg { as_arg_ty :: ArgSpec -> OutType
    as_arg_ty = OutType
    arg_ty, as_hole_ty :: ArgSpec -> OutType
    as_hole_ty = OutType
    hole_ty }
                   -> ApplyToTy  { sc_arg_ty :: OutType
    sc_arg_ty = OutType
    arg_ty, sc_hole_ty :: OutType
    sc_hole_ty = OutType
    hole_ty, sc_cont :: SimplCont
    sc_cont = SimplCont
    rest }
          ValArg { as_arg :: ArgSpec -> Expr Id
    as_arg = Expr Id
    arg, as_hole_ty :: ArgSpec -> OutType
    as_hole_ty = OutType
    hole_ty }
                 -> ApplyToVal { sc_arg :: Expr Id
    sc_arg = Expr Id
    arg, sc_env :: StaticEnv
    sc_env = StaticEnv
    env, sc_dup :: DupFlag
    sc_dup = DupFlag
    Simplified
                               , sc_hole_ty :: OutType
    sc_hole_ty = OutType
    hole_ty, sc_cont :: SimplCont
    sc_cont = SimplCont
    rest }
          CastBy OutCoercion
    c -> OutCoercion -> SimplCont -> SimplCont
    CastIt OutCoercion
    c SimplCont
    rest
      where
        rest :: SimplCont
    rest = StaticEnv -> [ArgSpec] -> SimplCont -> SimplCont
    pushSimplifiedArgs StaticEnv
    env [ArgSpec]
    args SimplCont
    k
               -- The env has an empty SubstEnv

    argInfoExpr :: OutId -> [ArgSpec] -> OutExpr
    -- NB: the [ArgSpec] is reversed so that the first arg
    -- in the list is the last one in the application
    argInfoExpr :: Id -> [ArgSpec] -> Expr Id
    argInfoExpr Id
    fun [ArgSpec]
    rev_args
      = [ArgSpec] -> Expr Id
    go [ArgSpec]
    rev_args
      where
        go :: [ArgSpec] -> Expr Id
    go []                              = forall b. Id -> Expr b
    Var Id
    fun
        go (ValArg { as_arg :: ArgSpec -> Expr Id
    as_arg = Expr Id
    arg }  : [ArgSpec]
    as) = [ArgSpec] -> Expr Id
    go [ArgSpec]
    as forall b. Expr b -> Expr b -> Expr b
    `App` Expr Id
    arg
        go (TyArg { as_arg_ty :: ArgSpec -> OutType
    as_arg_ty = OutType
    ty } : [ArgSpec]
    as) = [ArgSpec] -> Expr Id
    go [ArgSpec]
    as forall b. Expr b -> Expr b -> Expr b
    `App` forall b. OutType -> Expr b
    Type OutType
    ty
        go (CastBy OutCoercion
    co                : [ArgSpec]
    as) = Expr Id -> OutCoercion -> Expr Id
    mkCast ([ArgSpec] -> Expr Id
    go [ArgSpec]
    as) OutCoercion
    co

    type FunRules = Maybe (Int, [CoreRule]) -- Remaining rules for this function
         -- Nothing => No rules
         -- Just (n, rules) => some rules, requiring at least n more type/value args

    decRules :: FunRules -> FunRules
    decRules :: FunRules -> FunRules
    decRules (Just (Arity
    n, [CoreRule]
    rules)) = forall a. a -> Maybe a
    Just (Arity
    nforall a. Num a => a -> a -> a
    -Arity
    1, [CoreRule]
    rules)
    decRules FunRules
    Nothing           = forall a. Maybe a
    Nothing

    mkFunRules :: [CoreRule] -> FunRules
    mkFunRules :: [CoreRule] -> FunRules
    mkFunRules [] = forall a. Maybe a
    Nothing
    mkFunRules [CoreRule]
    rs = forall a. a -> Maybe a
    Just (Arity
    n_required, [CoreRule]
    rs)
      where
        n_required :: Arity
    n_required = forall (t :: * -> *) a. (Foldable t, Ord a) => t a -> a
    maximum (forall a b. (a -> b) -> [a] -> [b]
    map CoreRule -> Arity
    ruleArity [CoreRule]
    rs)

    {-
    ************************************************************************
    *                                                                      *
                    Functions on SimplCont
    *                                                                      *
    ************************************************************************
    -}

    mkBoringStop :: OutType -> SimplCont
    mkBoringStop :: OutType -> SimplCont
    mkBoringStop OutType
    ty = OutType -> CallCtxt -> SimplCont
    Stop OutType
    ty CallCtxt
    BoringCtxt

    mkRhsStop :: OutType -> SimplCont       -- See Note [RHS of lets] in GHC.Core.Unfold
    mkRhsStop :: OutType -> SimplCont
    mkRhsStop OutType
    ty = OutType -> CallCtxt -> SimplCont
    Stop OutType
    ty CallCtxt
    RhsCtxt

    mkLazyArgStop :: OutType -> CallCtxt -> SimplCont
    mkLazyArgStop :: OutType -> CallCtxt -> SimplCont
    mkLazyArgStop OutType
    ty CallCtxt
    cci = OutType -> CallCtxt -> SimplCont
    Stop OutType
    ty CallCtxt
    cci

    -------------------
    contIsRhsOrArg :: SimplCont -> Bool
    contIsRhsOrArg :: SimplCont -> Bool
    contIsRhsOrArg (Stop {})       = Bool
    True
    contIsRhsOrArg (StrictBind {}) = Bool
    True
    contIsRhsOrArg (StrictArg {})  = Bool
    True
    contIsRhsOrArg SimplCont
    _               = Bool
    False

    contIsRhs :: SimplCont -> Bool
    contIsRhs :: SimplCont -> Bool
    contIsRhs (Stop OutType
    _ CallCtxt
    RhsCtxt) = Bool
    True
    contIsRhs SimplCont
    _                = Bool
    False

    -------------------
    contIsStop :: SimplCont -> Bool
    contIsStop :: SimplCont -> Bool
    contIsStop (Stop {}) = Bool
    True
    contIsStop SimplCont
    _         = Bool
    False

    contIsDupable :: SimplCont -> Bool
    contIsDupable :: SimplCont -> Bool
    contIsDupable (Stop {})                         = Bool
    True
    contIsDupable (ApplyToTy  { sc_cont :: SimplCont -> SimplCont
    sc_cont = SimplCont
    k })      = SimplCont -> Bool
    contIsDupable SimplCont
    k
    contIsDupable (ApplyToVal { sc_dup :: SimplCont -> DupFlag
    sc_dup = DupFlag
    OkToDup }) = Bool
    True -- See Note [DupFlag invariants]
    contIsDupable (Select { sc_dup :: SimplCont -> DupFlag
    sc_dup = DupFlag
    OkToDup })     = Bool
    True -- ...ditto...
    contIsDupable (StrictArg { sc_dup :: SimplCont -> DupFlag
    sc_dup = DupFlag
    OkToDup })  = Bool
    True -- ...ditto...
    contIsDupable (CastIt OutCoercion
    _ SimplCont
    k)                      = SimplCont -> Bool
    contIsDupable SimplCont
    k
    contIsDupable SimplCont
    _                                 = Bool
    False

    -------------------
    contIsTrivial :: SimplCont -> Bool
    contIsTrivial :: SimplCont -> Bool
    contIsTrivial (Stop {})                                         = Bool
    True
    contIsTrivial (ApplyToTy { sc_cont :: SimplCont -> SimplCont
    sc_cont = SimplCont
    k })                       = SimplCont -> Bool
    contIsTrivial SimplCont
    k
    contIsTrivial (ApplyToVal { sc_arg :: SimplCont -> Expr Id
    sc_arg = Coercion OutCoercion
    _, sc_cont :: SimplCont -> SimplCont
    sc_cont = SimplCont
    k }) = SimplCont -> Bool
    contIsTrivial SimplCont
    k
    contIsTrivial (CastIt OutCoercion
    _ SimplCont
    k)                                      = SimplCont -> Bool
    contIsTrivial SimplCont
    k
    contIsTrivial SimplCont
    _                                                 = Bool
    False

    -------------------
    contResultType :: SimplCont -> OutType
    contResultType :: SimplCont -> OutType
    contResultType (Stop OutType
    ty CallCtxt
    _)                  = OutType
    ty
    contResultType (CastIt OutCoercion
    _ SimplCont
    k)                 = SimplCont -> OutType
    contResultType SimplCont
    k
    contResultType (StrictBind { sc_cont :: SimplCont -> SimplCont
    sc_cont = SimplCont
    k }) = SimplCont -> OutType
    contResultType SimplCont
    k
    contResultType (StrictArg { sc_cont :: SimplCont -> SimplCont
    sc_cont = SimplCont
    k })  = SimplCont -> OutType
    contResultType SimplCont
    k
    contResultType (Select { sc_cont :: SimplCont -> SimplCont
    sc_cont = SimplCont
    k })     = SimplCont -> OutType
    contResultType SimplCont
    k
    contResultType (ApplyToTy  { sc_cont :: SimplCont -> SimplCont
    sc_cont = SimplCont
    k }) = SimplCont -> OutType
    contResultType SimplCont
    k
    contResultType (ApplyToVal { sc_cont :: SimplCont -> SimplCont
    sc_cont = SimplCont
    k }) = SimplCont -> OutType
    contResultType SimplCont
    k
    contResultType (TickIt CoreTickish
    _ SimplCont
    k)                 = SimplCont -> OutType
    contResultType SimplCont
    k

    contHoleType :: SimplCont -> OutType
    contHoleType :: SimplCont -> OutType
    contHoleType (Stop OutType
    ty CallCtxt
    _)                      = OutType
    ty
    contHoleType (TickIt CoreTickish
    _ SimplCont
    k)                     = SimplCont -> OutType
    contHoleType SimplCont
    k
    contHoleType (CastIt OutCoercion
    co SimplCont
    _)                    = OutCoercion -> OutType
    coercionLKind OutCoercion
    co
    contHoleType (StrictBind { sc_bndr :: SimplCont -> Id
    sc_bndr = Id
    b, sc_dup :: SimplCont -> DupFlag
    sc_dup = DupFlag
    dup, sc_env :: SimplCont -> StaticEnv
    sc_env = StaticEnv
    se })
      = DupFlag -> StaticEnv -> OutType -> OutType
    perhapsSubstTy DupFlag
    dup StaticEnv
    se (Id -> OutType
    idType Id
    b)
    contHoleType (StrictArg  { sc_fun_ty :: SimplCont -> OutType
    sc_fun_ty = OutType
    ty })  = OutType -> OutType
    funArgTy OutType
    ty
    contHoleType (ApplyToTy  { sc_hole_ty :: SimplCont -> OutType
    sc_hole_ty = OutType
    ty }) = OutType
    ty  -- See Note [The hole type in ApplyToTy]
    contHoleType (ApplyToVal { sc_hole_ty :: SimplCont -> OutType
    sc_hole_ty = OutType
    ty }) = OutType
    ty  -- See Note [The hole type in ApplyToTy/Val]
    contHoleType (Select { sc_dup :: SimplCont -> DupFlag
    sc_dup = DupFlag
    d, sc_bndr :: SimplCont -> Id
    sc_bndr =  Id
    b, sc_env :: SimplCont -> StaticEnv
    sc_env = StaticEnv
    se })
      = DupFlag -> StaticEnv -> OutType -> OutType
    perhapsSubstTy DupFlag
    d StaticEnv
    se (Id -> OutType
    idType Id
    b)

    -- Computes the multiplicity scaling factor at the hole. That is, in (case [] of
    -- x ::(p) _ { … }) (respectively for arguments of functions), the scaling
    -- factor is p. And in E[G[]], the scaling factor is the product of the scaling
    -- factor of E and that of G.
    --
    -- The scaling factor at the hole of E[] is used to determine how a binder
    -- should be scaled if it commutes with E. This appears, in particular, in the
    -- case-of-case transformation.
    contHoleScaling :: SimplCont -> Mult
    contHoleScaling :: SimplCont -> OutType
    contHoleScaling (Stop OutType
    _ CallCtxt
    _) = OutType
    One
    contHoleScaling (CastIt OutCoercion
    _ SimplCont
    k) = SimplCont -> OutType
    contHoleScaling SimplCont
    k
    contHoleScaling (StrictBind { sc_bndr :: SimplCont -> Id
    sc_bndr = Id
    id, sc_cont :: SimplCont -> SimplCont
    sc_cont = SimplCont
    k })
      = Id -> OutType
    idMult Id
    id OutType -> OutType -> OutType
    `mkMultMul` SimplCont -> OutType
    contHoleScaling SimplCont
    k
    contHoleScaling (Select { sc_bndr :: SimplCont -> Id
    sc_bndr = Id
    id, sc_cont :: SimplCont -> SimplCont
    sc_cont = SimplCont
    k })
      = Id -> OutType
    idMult Id
    id OutType -> OutType -> OutType
    `mkMultMul` SimplCont -> OutType
    contHoleScaling SimplCont
    k
    contHoleScaling (StrictArg { sc_fun_ty :: SimplCont -> OutType
    sc_fun_ty = OutType
    fun_ty, sc_cont :: SimplCont -> SimplCont
    sc_cont = SimplCont
    k })
      = OutType
    w OutType -> OutType -> OutType
    `mkMultMul` SimplCont -> OutType
    contHoleScaling SimplCont
    k
      where
        (OutType
    w, OutType
    _, OutType
    _) = OutType -> (OutType, OutType, OutType)
    splitFunTy OutType
    fun_ty
    contHoleScaling (ApplyToTy { sc_cont :: SimplCont -> SimplCont
    sc_cont = SimplCont
    k }) = SimplCont -> OutType
    contHoleScaling SimplCont
    k
    contHoleScaling (ApplyToVal { sc_cont :: SimplCont -> SimplCont
    sc_cont = SimplCont
    k }) = SimplCont -> OutType
    contHoleScaling SimplCont
    k
    contHoleScaling (TickIt CoreTickish
    _ SimplCont
    k) = SimplCont -> OutType
    contHoleScaling SimplCont
    k
    -------------------
    countArgs :: SimplCont -> Int
    -- Count all arguments, including types, coercions, and other values
    countArgs :: SimplCont -> Arity
    countArgs (ApplyToTy  { sc_cont :: SimplCont -> SimplCont
    sc_cont = SimplCont
    cont }) = Arity
    1 forall a. Num a => a -> a -> a
    + SimplCont -> Arity
    countArgs SimplCont
    cont
    countArgs (ApplyToVal { sc_cont :: SimplCont -> SimplCont
    sc_cont = SimplCont
    cont }) = Arity
    1 forall a. Num a => a -> a -> a
    + SimplCont -> Arity
    countArgs SimplCont
    cont
    countArgs SimplCont
    _                               = Arity
    0

    contArgs :: SimplCont -> (Bool, [ArgSummary], SimplCont)
    -- Summarises value args, discards type args and coercions
    -- The returned continuation of the call is only used to
    -- answer questions like "are you interesting?"
    contArgs :: SimplCont -> (Bool, [ArgSummary], SimplCont)
    contArgs SimplCont
    cont
      | SimplCont -> Bool
    lone SimplCont
    cont = (Bool
    True, [], SimplCont
    cont)
      | Bool
    otherwise = [ArgSummary] -> SimplCont -> (Bool, [ArgSummary], SimplCont)
    go [] SimplCont
    cont
      where
        lone :: SimplCont -> Bool
    lone (ApplyToTy  {}) = Bool
    False  -- See Note [Lone variables] in GHC.Core.Unfold
        lone (ApplyToVal {}) = Bool
    False  -- NB: even a type application or cast
        lone (CastIt {})     = Bool
    False  --     stops it being "lone"
        lone SimplCont
    _               = Bool
    True

        go :: [ArgSummary] -> SimplCont -> (Bool, [ArgSummary], SimplCont)
    go [ArgSummary]
    args (ApplyToVal { sc_arg :: SimplCont -> Expr Id
    sc_arg = Expr Id
    arg, sc_env :: SimplCont -> StaticEnv
    sc_env = StaticEnv
    se, sc_cont :: SimplCont -> SimplCont
    sc_cont = SimplCont
    k })
                                            = [ArgSummary] -> SimplCont -> (Bool, [ArgSummary], SimplCont)
    go (Expr Id -> StaticEnv -> ArgSummary
    is_interesting Expr Id
    arg StaticEnv
    se forall a. a -> [a] -> [a]
    : [ArgSummary]
    args) SimplCont
    k
        go [ArgSummary]
    args (ApplyToTy { sc_cont :: SimplCont -> SimplCont
    sc_cont = SimplCont
    k }) = [ArgSummary] -> SimplCont -> (Bool, [ArgSummary], SimplCont)
    go [ArgSummary]
    args SimplCont
    k
        go [ArgSummary]
    args (CastIt OutCoercion
    _ SimplCont
    k)                = [ArgSummary] -> SimplCont -> (Bool, [ArgSummary], SimplCont)
    go [ArgSummary]
    args SimplCont
    k
        go [ArgSummary]
    args SimplCont
    k                           = (Bool
    False, forall a. [a] -> [a]
    reverse [ArgSummary]
    args, SimplCont
    k)

        is_interesting :: Expr Id -> StaticEnv -> ArgSummary
    is_interesting Expr Id
    arg StaticEnv
    se = StaticEnv -> Expr Id -> ArgSummary
    interestingArg StaticEnv
    se Expr Id
    arg
                       -- Do *not* use short-cutting substitution here
                       -- because we want to get as much IdInfo as possible

    -------------------
    mkArgInfo :: SimplEnv
              -> Id
              -> [CoreRule] -- Rules for function
              -> Int        -- Number of value args
              -> SimplCont  -- Context of the call
              -> ArgInfo

    mkArgInfo :: StaticEnv -> Id -> [CoreRule] -> Arity -> SimplCont -> ArgInfo
    mkArgInfo StaticEnv
    env Id
    fun [CoreRule]
    rules Arity
    n_val_args SimplCont
    call_cont
      | Arity
    n_val_args forall a. Ord a => a -> a -> Bool
    < Id -> Arity
    idArity Id
    fun            -- Note [Unsaturated functions]
      = ArgInfo { ai_fun :: Id
    ai_fun = Id
    fun, ai_args :: [ArgSpec]
    ai_args = []
                , ai_rules :: FunRules
    ai_rules = FunRules
    fun_rules
                , ai_encl :: Bool
    ai_encl = Bool
    False
                , ai_dmds :: [Demand]
    ai_dmds = [Demand]
    vanilla_dmds
                , ai_discs :: [Arity]
    ai_discs = [Arity]
    vanilla_discounts }
      | Bool
    otherwise
      = ArgInfo { ai_fun :: Id
    ai_fun   = Id
    fun
                , ai_args :: [ArgSpec]
    ai_args = []
                , ai_rules :: FunRules
    ai_rules = FunRules
    fun_rules
                , ai_encl :: Bool
    ai_encl  = [CoreRule] -> SimplCont -> Bool
    interestingArgContext [CoreRule]
    rules SimplCont
    call_cont
                , ai_dmds :: [Demand]
    ai_dmds  = OutType -> [Demand] -> [Demand]
    add_type_strictness (Id -> OutType
    idType Id
    fun) [Demand]
    arg_dmds
                , ai_discs :: [Arity]
    ai_discs = [Arity]
    arg_discounts }
      where
        fun_rules :: FunRules
    fun_rules = [CoreRule] -> FunRules
    mkFunRules [CoreRule]
    rules

        vanilla_discounts, arg_discounts :: [Int]
        vanilla_discounts :: [Arity]
    vanilla_discounts = forall a. a -> [a]
    repeat Arity
    0
        arg_discounts :: [Arity]
    arg_discounts = case Id -> Unfolding
    idUnfolding Id
    fun of
                            CoreUnfolding {uf_guidance :: Unfolding -> UnfoldingGuidance
    uf_guidance = UnfIfGoodArgs {ug_args :: UnfoldingGuidance -> [Arity]
    ug_args = [Arity]
    discounts}}
                                  -> [Arity]
    discounts forall a. [a] -> [a] -> [a]
    ++ [Arity]
    vanilla_discounts
                            Unfolding
    _     -> [Arity]
    vanilla_discounts

        vanilla_dmds, arg_dmds :: [Demand]
        vanilla_dmds :: [Demand]
    vanilla_dmds  = forall a. a -> [a]
    repeat Demand
    topDmd

        arg_dmds :: [Demand]
    arg_dmds
          | Bool -> Bool
    not (SimplMode -> Bool
    sm_inline (StaticEnv -> SimplMode
    seMode StaticEnv
    env))
          = [Demand]
    vanilla_dmds -- See Note [Do not expose strictness if sm_inline=False]
          | Bool
    otherwise
          = -- add_type_str fun_ty $
            case StrictSig -> ([Demand], Divergence)
    splitStrictSig (Id -> StrictSig
    idStrictness Id
    fun) of
              ([Demand]
    demands, Divergence
    result_info)
                    | Bool -> Bool
    not ([Demand]
    demands forall a. [a] -> Arity -> Bool
    `lengthExceeds` Arity
    n_val_args)
                    ->      -- Enough args, use the strictness given.
                            -- For bottoming functions we used to pretend that the arg
                            -- is lazy, so that we don't treat the arg as an
                            -- interesting context.  This avoids substituting
                            -- top-level bindings for (say) strings into
                            -- calls to error.  But now we are more careful about
                            -- inlining lone variables, so its ok
                            -- (see GHC.Core.Op.Simplify.Utils.analyseCont)
                       if Divergence -> Bool
    isDeadEndDiv Divergence
    result_info then
                            [Demand]
    demands  -- Finite => result is bottom
                       else
                            [Demand]
    demands forall a. [a] -> [a] -> [a]
    ++ [Demand]
    vanilla_dmds
                   | Bool
    otherwise
                   -> WARN( True, text "More demands than arity" <+> ppr fun <+> ppr (idArity fun)
                                    <+> ppr n_val_args <+> ppr demands )
                      [Demand]
    vanilla_dmds      -- Not enough args, or no strictness

        add_type_strictness :: Type -> [Demand] -> [Demand]
        -- If the function arg types are strict, record that in the 'strictness bits'
        -- No need to instantiate because unboxed types (which dominate the strict
        --   types) can't instantiate type variables.
        -- add_type_strictness is done repeatedly (for each call);
        --   might be better once-for-all in the function
        -- But beware primops/datacons with no strictness

        add_type_strictness :: OutType -> [Demand] -> [Demand]
    add_type_strictness OutType
    fun_ty [Demand]
    dmds
          | forall (t :: * -> *) a. Foldable t => t a -> Bool
    null [Demand]
    dmds = []

          | Just (Id
    _, OutType
    fun_ty') <- OutType -> Maybe (Id, OutType)
    splitForAllTyCoVar_maybe OutType
    fun_ty
          = OutType -> [Demand] -> [Demand]
    add_type_strictness OutType
    fun_ty' [Demand]
    dmds     -- Look through foralls

          | Just (OutType
    _, OutType
    arg_ty, OutType
    fun_ty') <- OutType -> Maybe (OutType, OutType, OutType)
    splitFunTy_maybe OutType
    fun_ty        -- Add strict-type info
          , Demand
    dmd : [Demand]
    rest_dmds <- [Demand]
    dmds
          , let dmd' :: Demand
    dmd' = case HasDebugCallStack => OutType -> Maybe Bool
    isLiftedType_maybe OutType
    arg_ty of
                           Just Bool
    False -> Demand -> Demand
    strictifyDmd Demand
    dmd
                           Maybe Bool
    _          -> Demand
    dmd
          = Demand
    dmd' forall a. a -> [a] -> [a]
    : OutType -> [Demand] -> [Demand]
    add_type_strictness OutType
    fun_ty' [Demand]
    rest_dmds
              -- If the type is levity-polymorphic, we can't know whether it's
              -- strict. isLiftedType_maybe will return Just False only when
              -- we're sure the type is unlifted.

          | Bool
    otherwise
          = [Demand]
    dmds

    {- Note [Unsaturated functions]
      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider (test eyeball/inline4)
            x = a:as
            y = f x
    where f has arity 2.  Then we do not want to inline 'x', because
    it'll just be floated out again.  Even if f has lots of discounts
    on its first argument -- it must be saturated for these to kick in

    Note [Do not expose strictness if sm_inline=False]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    #15163 showed a case in which we had

      {-# INLINE [1] zip #-}
      zip = undefined

      {-# RULES "foo" forall as bs. stream (zip as bs) = ..blah... #-}

    If we expose zip's bottoming nature when simplifying the LHS of the
    RULE we get
      {-# RULES "foo" forall as bs.
                       stream (case zip of {}) = ..blah... #-}
    discarding the arguments to zip.  Usually this is fine, but on the
    LHS of a rule it's not, because 'as' and 'bs' are now not bound on
    the LHS.

    This is a pretty pathological example, so I'm not losing sleep over
    it, but the simplest solution was to check sm_inline; if it is False,
    which it is on the LHS of a rule (see updModeForRules), then don't
    make use of the strictness info for the function.
    -}

    {-
    ************************************************************************
    *                                                                      *
            Interesting arguments
    *                                                                      *
    ************************************************************************

    Note [Interesting call context]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    We want to avoid inlining an expression where there can't possibly be
    any gain, such as in an argument position.  Hence, if the continuation
    is interesting (eg. a case scrutinee, application etc.) then we
    inline, otherwise we don't.

    Previously some_benefit used to return True only if the variable was
    applied to some value arguments.  This didn't work:

            let x = _coerce_ (T Int) Int (I# 3) in
            case _coerce_ Int (T Int) x of
                    I# y -> ....

    we want to inline x, but can't see that it's a constructor in a case
    scrutinee position, and some_benefit is False.

    Another example:

    dMonadST = _/\_ t -> :Monad (g1 _@_ t, g2 _@_ t, g3 _@_ t)

    ....  case dMonadST _@_ x0 of (a,b,c) -> ....

    we'd really like to inline dMonadST here, but we *don't* want to
    inline if the case expression is just

            case x of y { DEFAULT -> ... }

    since we can just eliminate this case instead (x is in WHNF).  Similar
    applies when x is bound to a lambda expression.  Hence
    contIsInteresting looks for case expressions with just a single
    default case.

    Note [No case of case is boring]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    If we see
       case f x of <alts>

    we'd usually treat the context as interesting, to encourage 'f' to
    inline.  But if case-of-case is off, it's really not so interesting
    after all, because we are unlikely to be able to push the case
    expression into the branches of any case in f's unfolding.  So, to
    reduce unnecessary code expansion, we just make the context look boring.
    This made a small compile-time perf improvement in perf/compiler/T6048,
    and it looks plausible to me.
    -}

    lazyArgContext :: ArgInfo -> CallCtxt
    -- Use this for lazy arguments
    lazyArgContext :: ArgInfo -> CallCtxt
    lazyArgContext (ArgInfo { ai_encl :: ArgInfo -> Bool
    ai_encl = Bool
    encl_rules, ai_discs :: ArgInfo -> [Arity]
    ai_discs = [Arity]
    discs })
      | Bool
    encl_rules                = CallCtxt
    RuleArgCtxt
      | Arity
    disc:[Arity]
    _ <- [Arity]
    discs, Arity
    disc forall a. Ord a => a -> a -> Bool
    > Arity
    0 = CallCtxt
    DiscArgCtxt  -- Be keener here
      | Bool
    otherwise                 = CallCtxt
    BoringCtxt   -- Nothing interesting

    strictArgContext :: ArgInfo -> CallCtxt
    strictArgContext :: ArgInfo -> CallCtxt
    strictArgContext (ArgInfo { ai_encl :: ArgInfo -> Bool
    ai_encl = Bool
    encl_rules, ai_discs :: ArgInfo -> [Arity]
    ai_discs = [Arity]
    discs })
    -- Use this for strict arguments
      | Bool
    encl_rules                = CallCtxt
    RuleArgCtxt
      | Arity
    disc:[Arity]
    _ <- [Arity]
    discs, Arity
    disc forall a. Ord a => a -> a -> Bool
    > Arity
    0 = CallCtxt
    DiscArgCtxt  -- Be keener here
      | Bool
    otherwise                 = CallCtxt
    RhsCtxt
          -- Why RhsCtxt?  if we see f (g x) (h x), and f is strict, we
          -- want to be a bit more eager to inline g, because it may
          -- expose an eval (on x perhaps) that can be eliminated or
          -- shared. I saw this in nofib 'boyer2', RewriteFuns.onewayunify1
          -- It's worth an 18% improvement in allocation for this
          -- particular benchmark; 5% on 'mate' and 1.3% on 'multiplier'

    interestingCallContext :: SimplEnv -> SimplCont -> CallCtxt
    -- See Note [Interesting call context]
    interestingCallContext :: StaticEnv -> SimplCont -> CallCtxt
    interestingCallContext StaticEnv
    env SimplCont
    cont
      = SimplCont -> CallCtxt
    interesting SimplCont
    cont
      where
        interesting :: SimplCont -> CallCtxt
    interesting (Select {})
           | SimplMode -> Bool
    sm_case_case (StaticEnv -> SimplMode
    getMode StaticEnv
    env) = CallCtxt
    CaseCtxt
           | Bool
    otherwise                  = CallCtxt
    BoringCtxt
           -- See Note [No case of case is boring]

        interesting (ApplyToVal {}) = CallCtxt
    ValAppCtxt
            -- Can happen if we have (f Int |> co) y
            -- If f has an INLINE prag we need to give it some
            -- motivation to inline. See Note [Cast then apply]
            -- in GHC.Core.Unfold

        interesting (StrictArg { sc_fun :: SimplCont -> ArgInfo
    sc_fun = ArgInfo
    fun }) = ArgInfo -> CallCtxt
    strictArgContext ArgInfo
    fun
        interesting (StrictBind {})              = CallCtxt
    BoringCtxt
        interesting (Stop OutType
    _ CallCtxt
    cci)                 = CallCtxt
    cci
        interesting (TickIt CoreTickish
    _ SimplCont
    k)                 = SimplCont -> CallCtxt
    interesting SimplCont
    k
        interesting (ApplyToTy { sc_cont :: SimplCont -> SimplCont
    sc_cont = SimplCont
    k })  = SimplCont -> CallCtxt
    interesting SimplCont
    k
        interesting (CastIt OutCoercion
    _ SimplCont
    k)                 = SimplCont -> CallCtxt
    interesting SimplCont
    k
            -- If this call is the arg of a strict function, the context
            -- is a bit interesting.  If we inline here, we may get useful
            -- evaluation information to avoid repeated evals: e.g.
            --      x + (y * z)
            -- Here the contIsInteresting makes the '*' keener to inline,
            -- which in turn exposes a constructor which makes the '+' inline.
            -- Assuming that +,* aren't small enough to inline regardless.
            --
            -- It's also very important to inline in a strict context for things
            -- like
            --              foldr k z (f x)
            -- Here, the context of (f x) is strict, and if f's unfolding is
            -- a build it's *great* to inline it here.  So we must ensure that
            -- the context for (f x) is not totally uninteresting.

    interestingArgContext :: [CoreRule] -> SimplCont -> Bool
    -- If the argument has form (f x y), where x,y are boring,
    -- and f is marked INLINE, then we don't want to inline f.
    -- But if the context of the argument is
    --      g (f x y)
    -- where g has rules, then we *do* want to inline f, in case it
    -- exposes a rule that might fire.  Similarly, if the context is
    --      h (g (f x x))
    -- where h has rules, then we do want to inline f; hence the
    -- call_cont argument to interestingArgContext
    --
    -- The ai-rules flag makes this happen; if it's
    -- set, the inliner gets just enough keener to inline f
    -- regardless of how boring f's arguments are, if it's marked INLINE
    --
    -- The alternative would be to *always* inline an INLINE function,
    -- regardless of how boring its context is; but that seems overkill
    -- For example, it'd mean that wrapper functions were always inlined
    --
    -- The call_cont passed to interestingArgContext is the context of
    -- the call itself, e.g. g <hole> in the example above
    interestingArgContext :: [CoreRule] -> SimplCont -> Bool
    interestingArgContext [CoreRule]
    rules SimplCont
    call_cont
      = forall (f :: * -> *) a. Foldable f => f a -> Bool
    notNull [CoreRule]
    rules Bool -> Bool -> Bool
    || Bool
    enclosing_fn_has_rules
      where
        enclosing_fn_has_rules :: Bool
    enclosing_fn_has_rules = SimplCont -> Bool
    go SimplCont
    call_cont

        go :: SimplCont -> Bool
    go (Select {})                  = Bool
    False
        go (ApplyToVal {})              = Bool
    False  -- Shouldn't really happen
        go (ApplyToTy  {})              = Bool
    False  -- Ditto
        go (StrictArg { sc_fun :: SimplCont -> ArgInfo
    sc_fun = ArgInfo
    fun }) = ArgInfo -> Bool
    ai_encl ArgInfo
    fun
        go (StrictBind {})              = Bool
    False      -- ??
        go (CastIt OutCoercion
    _ SimplCont
    c)                 = SimplCont -> Bool
    go SimplCont
    c
        go (Stop OutType
    _ CallCtxt
    RuleArgCtxt)         = Bool
    True
        go (Stop OutType
    _ CallCtxt
    _)                   = Bool
    False
        go (TickIt CoreTickish
    _ SimplCont
    c)                 = SimplCont -> Bool
    go SimplCont
    c

    {- Note [Interesting arguments]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    An argument is interesting if it deserves a discount for unfoldings
    with a discount in that argument position.  The idea is to avoid
    unfolding a function that is applied only to variables that have no
    unfolding (i.e. they are probably lambda bound): f x y z There is
    little point in inlining f here.

    Generally, *values* (like (C a b) and (\x.e)) deserve discounts.  But
    we must look through lets, eg (let x = e in C a b), because the let will
    float, exposing the value, if we inline.  That makes it different to
    exprIsHNF.

    Before 2009 we said it was interesting if the argument had *any* structure
    at all; i.e. (hasSomeUnfolding v).  But does too much inlining; see #3016.

    But we don't regard (f x y) as interesting, unless f is unsaturated.
    If it's saturated and f hasn't inlined, then it's probably not going
    to now!

    Note [Conlike is interesting]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider
            f d = ...((*) d x y)...
            ... f (df d')...
    where df is con-like. Then we'd really like to inline 'f' so that the
    rule for (*) (df d) can fire.  To do this
      a) we give a discount for being an argument of a class-op (eg (*) d)
      b) we say that a con-like argument (eg (df d)) is interesting
    -}

    interestingArg :: SimplEnv -> CoreExpr -> ArgSummary
    -- See Note [Interesting arguments]
    interestingArg :: StaticEnv -> Expr Id -> ArgSummary
    interestingArg StaticEnv
    env Expr Id
    e = StaticEnv -> Arity -> Expr Id -> ArgSummary
    go StaticEnv
    env Arity
    0 Expr Id
    e
      where
        -- n is # value args to which the expression is applied
        go :: StaticEnv -> Arity -> Expr Id -> ArgSummary
    go StaticEnv
    env Arity
    n (Var Id
    v)
           = case StaticEnv -> Id -> SimplSR
    substId StaticEnv
    env Id
    v of
               DoneId Id
    v'            -> Arity -> Id -> ArgSummary
    go_var Arity
    n Id
    v'
               DoneEx Expr Id
    e Maybe Arity
    _           -> StaticEnv -> Arity -> Expr Id -> ArgSummary
    go (StaticEnv -> StaticEnv
    zapSubstEnv StaticEnv
    env)             Arity
    n Expr Id
    e
               ContEx TvSubstEnv
    tvs CvSubstEnv
    cvs SimplIdSubst
    ids Expr Id
    e -> StaticEnv -> Arity -> Expr Id -> ArgSummary
    go (StaticEnv -> TvSubstEnv -> CvSubstEnv -> SimplIdSubst -> StaticEnv
    setSubstEnv StaticEnv
    env TvSubstEnv
    tvs CvSubstEnv
    cvs SimplIdSubst
    ids) Arity
    n Expr Id
    e

        go StaticEnv
    _   Arity
    _ (Lit {})          = ArgSummary
    ValueArg
        go StaticEnv
    _   Arity
    _ (Type OutType
    _)          = ArgSummary
    TrivArg
        go StaticEnv
    _   Arity
    _ (Coercion OutCoercion
    _)      = ArgSummary
    TrivArg
        go StaticEnv
    env Arity
    n (App Expr Id
    fn (Type OutType
    _)) = StaticEnv -> Arity -> Expr Id -> ArgSummary
    go StaticEnv
    env Arity
    n Expr Id
    fn
        go StaticEnv
    env Arity
    n (App Expr Id
    fn Expr Id
    _)        = StaticEnv -> Arity -> Expr Id -> ArgSummary
    go StaticEnv
    env (Arity
    nforall a. Num a => a -> a -> a
    +Arity
    1) Expr Id
    fn
        go StaticEnv
    env Arity
    n (Tick CoreTickish
    _ Expr Id
    a)        = StaticEnv -> Arity -> Expr Id -> ArgSummary
    go StaticEnv
    env Arity
    n Expr Id
    a
        go StaticEnv
    env Arity
    n (Cast Expr Id
    e OutCoercion
    _)        = StaticEnv -> Arity -> Expr Id -> ArgSummary
    go StaticEnv
    env Arity
    n Expr Id
    e
        go StaticEnv
    env Arity
    n (Lam Id
    v Expr Id
    e)
           | Id -> Bool
    isTyVar Id
    v             = StaticEnv -> Arity -> Expr Id -> ArgSummary
    go StaticEnv
    env Arity
    n Expr Id
    e
           | Arity
    nforall a. Ord a => a -> a -> Bool
    >Arity
    0                   = ArgSummary
    NonTrivArg     -- (\x.b) e   is NonTriv
           | Bool
    otherwise             = ArgSummary
    ValueArg
        go StaticEnv
    _ Arity
    _ (Case {})           = ArgSummary
    NonTrivArg
        go StaticEnv
    env Arity
    n (Let Bind Id
    b Expr Id
    e)         = case StaticEnv -> Arity -> Expr Id -> ArgSummary
    go StaticEnv
    env' Arity
    n Expr Id
    e of
                                       ArgSummary
    ValueArg -> ArgSummary
    ValueArg
                                       ArgSummary
    _        -> ArgSummary
    NonTrivArg
                                   where
                                     env' :: StaticEnv
    env' = StaticEnv
    env StaticEnv -> [Id] -> StaticEnv
    `addNewInScopeIds` forall b. Bind b -> [b]
    bindersOf Bind Id
    b

        go_var :: Arity -> Id -> ArgSummary
    go_var Arity
    n Id
    v
           | Id -> Bool
    isConLikeId Id
    v     = ArgSummary
    ValueArg   -- Experimenting with 'conlike' rather that
                                            --    data constructors here
           | Id -> Arity
    idArity Id
    v forall a. Ord a => a -> a -> Bool
    > Arity
    n     = ArgSummary
    ValueArg   -- Catches (eg) primops with arity but no unfolding
           | Arity
    n forall a. Ord a => a -> a -> Bool
    > Arity
    0             = ArgSummary
    NonTrivArg -- Saturated or unknown call
           | Bool
    conlike_unfolding = ArgSummary
    ValueArg   -- n==0; look for an interesting unfolding
                                            -- See Note [Conlike is interesting]
           | Bool
    otherwise         = ArgSummary
    TrivArg    -- n==0, no useful unfolding
           where
             conlike_unfolding :: Bool
    conlike_unfolding = Unfolding -> Bool
    isConLikeUnfolding (Id -> Unfolding
    idUnfolding Id
    v)

    {-
    ************************************************************************
    *                                                                      *
                      SimplMode
    *                                                                      *
    ************************************************************************

    The SimplMode controls several switches; see its definition in
    GHC.Core.Opt.Monad
            sm_rules      :: Bool     -- Whether RULES are enabled
            sm_inline     :: Bool     -- Whether inlining is enabled
            sm_case_case  :: Bool     -- Whether case-of-case is enabled
            sm_eta_expand :: Bool     -- Whether eta-expansion is enabled
    -}

    simplEnvForGHCi :: Logger -> DynFlags -> SimplEnv
    simplEnvForGHCi :: Logger -> DynFlags -> StaticEnv
    simplEnvForGHCi Logger
    logger DynFlags
    dflags
      = SimplMode -> StaticEnv
    mkSimplEnv forall a b. (a -> b) -> a -> b
    $ SimplMode { sm_names :: [String]
    sm_names  = [String
    "GHCi"]
                               , sm_phase :: CompilerPhase
    sm_phase  = CompilerPhase
    InitialPhase
                               , sm_logger :: Logger
    sm_logger = Logger
    logger
                               , sm_dflags :: DynFlags
    sm_dflags = DynFlags
    dflags
                               , sm_uf_opts :: UnfoldingOpts
    sm_uf_opts = UnfoldingOpts
    uf_opts
                               , sm_rules :: Bool
    sm_rules  = Bool
    rules_on
                               , sm_inline :: Bool
    sm_inline = Bool
    False
                                  -- Do not do any inlining, in case we expose some
                                  -- unboxed tuple stuff that confuses the bytecode
                                  -- interpreter
                               , sm_eta_expand :: Bool
    sm_eta_expand = Bool
    eta_expand_on
                               , sm_cast_swizzle :: Bool
    sm_cast_swizzle = Bool
    True
                               , sm_case_case :: Bool
    sm_case_case  = Bool
    True
                               , sm_pre_inline :: Bool
    sm_pre_inline = Bool
    pre_inline_on
                               }
      where
        rules_on :: Bool
    rules_on      = GeneralFlag -> DynFlags -> Bool
    gopt GeneralFlag
    Opt_EnableRewriteRules   DynFlags
    dflags
        eta_expand_on :: Bool
    eta_expand_on = GeneralFlag -> DynFlags -> Bool
    gopt GeneralFlag
    Opt_DoLambdaEtaExpansion DynFlags
    dflags
        pre_inline_on :: Bool
    pre_inline_on = GeneralFlag -> DynFlags -> Bool
    gopt GeneralFlag
    Opt_SimplPreInlining     DynFlags
    dflags
        uf_opts :: UnfoldingOpts
    uf_opts       = DynFlags -> UnfoldingOpts
    unfoldingOpts                 DynFlags
    dflags

    updModeForStableUnfoldings :: Activation -> SimplMode -> SimplMode
    updModeForStableUnfoldings :: Activation -> SimplMode -> SimplMode
    updModeForStableUnfoldings Activation
    unf_act SimplMode
    current_mode
      = SimplMode
    current_mode { sm_phase :: CompilerPhase
    sm_phase      = Activation -> CompilerPhase
    phaseFromActivation Activation
    unf_act
                     , sm_eta_expand :: Bool
    sm_eta_expand = Bool
    False
                     , sm_inline :: Bool
    sm_inline     = Bool
    True }
        -- sm_phase: see Note [Simplifying inside stable unfoldings]
        -- sm_eta_expand: see Note [Eta-expansion in stable unfoldings]
        -- sm_rules: just inherit; sm_rules might be "off"
        --           because of -fno-enable-rewrite-rules
      where
        phaseFromActivation :: Activation -> CompilerPhase
    phaseFromActivation (ActiveAfter SourceText
    _ Arity
    n) = Arity -> CompilerPhase
    Phase Arity
    n
        phaseFromActivation Activation
    _                 = CompilerPhase
    InitialPhase

    updModeForRules :: SimplMode -> SimplMode
    -- See Note [Simplifying rules]
    updModeForRules :: SimplMode -> SimplMode
    updModeForRules SimplMode
    current_mode
      = SimplMode
    current_mode { sm_phase :: CompilerPhase
    sm_phase        = CompilerPhase
    InitialPhase
                     , sm_inline :: Bool
    sm_inline       = Bool
    False
                          -- See Note [Do not expose strictness if sm_inline=False]
                     , sm_rules :: Bool
    sm_rules        = Bool
    False
                     , sm_cast_swizzle :: Bool
    sm_cast_swizzle = Bool
    False
                          -- See Note [Cast swizzling on rule LHSs]
                     , sm_eta_expand :: Bool
    sm_eta_expand   = Bool
    False }

    {- Note [Simplifying rules]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    When simplifying a rule LHS, refrain from /any/ inlining or applying
    of other RULES.

    Doing anything to the LHS is plain confusing, because it means that what the
    rule matches is not what the user wrote. c.f. #10595, and #10528.
    Moreover, inlining (or applying rules) on rule LHSs risks introducing
    Ticks into the LHS, which makes matching trickier. #10665, #10745.

    Doing this to either side confounds tools like HERMIT, which seek to reason
    about and apply the RULES as originally written. See #10829.

    There is, however, one case where we are pretty much /forced/ to transform the
    LHS of a rule: postInlineUnconditionally. For instance, in the case of

        let f = g @Int in f

    We very much want to inline f into the body of the let. However, to do so (and
    be able to safely drop f's binding) we must inline into all occurrences of f,
    including those in the LHS of rules.

    This can cause somewhat surprising results; for instance, in #18162 we found
    that a rule template contained ticks in its arguments, because
    postInlineUnconditionally substituted in a trivial expression that contains
    ticks. See Note [Tick annotations in RULE matching] in GHC.Core.Rules for
    details.

    Note [Cast swizzling on rule LHSs]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    In the LHS of a RULE we may have
           (\x. blah |> CoVar cv)
    where `cv` is a coercion variable.  Critically, we really only want
    coercion /variables/, not general coercions, on the LHS of a RULE.  So
    we don't want to swizzle this to
          (\x. blah) |> (Refl xty `FunCo` CoVar cv)
    So we switch off cast swizzling in updModeForRules.

    Note [Eta-expansion in stable unfoldings]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    We don't do eta-expansion inside stable unfoldings.  It's extra work,
    and can be expensive (the bizarre T18223 is a case in point).

    See Note [Occurrence analysis for lambda binders] in GHC.Core.Opt.OccurAnal.

    Historical note. There was /previously/ another reason not to do eta
    expansion in stable unfoldings.  If we have a stable unfolding

      f :: Ord a => a -> IO ()
      -- Unfolding template
      --    = /\a \(d:Ord a) (x:a). bla

    we previously did not want to eta-expand to

      f :: Ord a => a -> IO ()
      -- Unfolding template
      --    = (/\a \(d:Ord a) (x:a) (eta:State#). bla eta) |> co

    because not specialisation of the overloading didn't work properly (#9509).
    But now it does: see Note [Account for casts in binding] in GHC.Core.Opt.Specialise

    Note [Inlining in gentle mode]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Something is inlined if
       (i)   the sm_inline flag is on, AND
       (ii)  the thing has an INLINE pragma, AND
       (iii) the thing is inlinable in the earliest phase.

    Example of why (iii) is important:
      {-# INLINE [~1] g #-}
      g = ...

      {-# INLINE f #-}
      f x = g (g x)

    If we were to inline g into f's inlining, then an importing module would
    never be able to do
            f e --> g (g e) ---> RULE fires
    because the stable unfolding for f has had g inlined into it.

    On the other hand, it is bad not to do ANY inlining into an
    stable unfolding, because then recursive knots in instance declarations
    don't get unravelled.

    However, *sometimes* SimplGently must do no call-site inlining at all
    (hence sm_inline = False).  Before full laziness we must be careful
    not to inline wrappers, because doing so inhibits floating
        e.g. ...(case f x of ...)...
        ==> ...(case (case x of I# x# -> fw x#) of ...)...
        ==> ...(case x of I# x# -> case fw x# of ...)...
    and now the redex (f x) isn't floatable any more.

    The no-inlining thing is also important for Template Haskell.  You might be
    compiling in one-shot mode with -O2; but when TH compiles a splice before
    running it, we don't want to use -O2.  Indeed, we don't want to inline
    anything, because the byte-code interpreter might get confused about
    unboxed tuples and suchlike.

    Note [Simplifying inside stable unfoldings]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    We must take care with simplification inside stable unfoldings (which come from
    INLINE pragmas).

    First, consider the following example
            let f = \pq -> BIG
            in
            let g = \y -> f y y
                {-# INLINE g #-}
            in ...g...g...g...g...g...
    Now, if that's the ONLY occurrence of f, it might be inlined inside g,
    and thence copied multiple times when g is inlined. HENCE we treat
    any occurrence in a stable unfolding as a multiple occurrence, not a single
    one; see OccurAnal.addRuleUsage.

    Second, we do want *do* to some modest rules/inlining stuff in stable
    unfoldings, partly to eliminate senseless crap, and partly to break
    the recursive knots generated by instance declarations.

    However, suppose we have
            {-# INLINE <act> f #-}
            f = <rhs>
    meaning "inline f in phases p where activation <act>(p) holds".
    Then what inlinings/rules can we apply to the copy of <rhs> captured in
    f's stable unfolding?  Our model is that literally <rhs> is substituted for
    f when it is inlined.  So our conservative plan (implemented by
    updModeForStableUnfoldings) is this:

      -------------------------------------------------------------
      When simplifying the RHS of a stable unfolding, set the phase
      to the phase in which the stable unfolding first becomes active
      -------------------------------------------------------------

    That ensures that

      a) Rules/inlinings that *cease* being active before p will
         not apply to the stable unfolding, consistent with it being
         inlined in its *original* form in phase p.

      b) Rules/inlinings that only become active *after* p will
         not apply to the stable unfolding, again to be consistent with
         inlining the *original* rhs in phase p.

    For example,
            {-# INLINE f #-}
            f x = ...g...

            {-# NOINLINE [1] g #-}
            g y = ...

            {-# RULE h g = ... #-}
    Here we must not inline g into f's RHS, even when we get to phase 0,
    because when f is later inlined into some other module we want the
    rule for h to fire.

    Similarly, consider
            {-# INLINE f #-}
            f x = ...g...

            g y = ...
    and suppose that there are auto-generated specialisations and a strictness
    wrapper for g.  The specialisations get activation AlwaysActive, and the
    strictness wrapper get activation (ActiveAfter 0).  So the strictness
    wrepper fails the test and won't be inlined into f's stable unfolding. That
    means f can inline, expose the specialised call to g, so the specialisation
    rules can fire.

    A note about wrappers
    ~~~~~~~~~~~~~~~~~~~~~
    It's also important not to inline a worker back into a wrapper.
    A wrapper looks like
            wraper = inline_me (\x -> ...worker... )
    Normally, the inline_me prevents the worker getting inlined into
    the wrapper (initially, the worker's only call site!).  But,
    if the wrapper is sure to be called, the strictness analyser will
    mark it 'demanded', so when the RHS is simplified, it'll get an ArgOf
    continuation.
    -}

    activeUnfolding :: SimplMode -> Id -> Bool
    activeUnfolding :: SimplMode -> Id -> Bool
    activeUnfolding SimplMode
    mode Id
    id
      | Unfolding -> Bool
    isCompulsoryUnfolding (Id -> Unfolding
    realIdUnfolding Id
    id)
      = Bool
    True   -- Even sm_inline can't override compulsory unfoldings
      | Bool
    otherwise
      = CompilerPhase -> Activation -> Bool
    isActive (SimplMode -> CompilerPhase
    sm_phase SimplMode
    mode) (Id -> Activation
    idInlineActivation Id
    id)
      Bool -> Bool -> Bool
    && SimplMode -> Bool
    sm_inline SimplMode
    mode
          -- `or` isStableUnfolding (realIdUnfolding id)
          -- Inline things when
          --  (a) they are active
          --  (b) sm_inline says so, except that for stable unfoldings
          --                         (ie pragmas) we inline anyway

    getUnfoldingInRuleMatch :: SimplEnv -> InScopeEnv
    -- When matching in RULE, we want to "look through" an unfolding
    -- (to see a constructor) if *rules* are on, even if *inlinings*
    -- are not.  A notable example is DFuns, which really we want to
    -- match in rules like (op dfun) in gentle mode. Another example
    -- is 'otherwise' which we want exprIsConApp_maybe to be able to
    -- see very early on
    getUnfoldingInRuleMatch :: StaticEnv -> InScopeEnv
    getUnfoldingInRuleMatch StaticEnv
    env
      = (InScopeSet
    in_scope, Id -> Unfolding
    id_unf)
      where
        in_scope :: InScopeSet
    in_scope = StaticEnv -> InScopeSet
    seInScope StaticEnv
    env
        mode :: SimplMode
    mode = StaticEnv -> SimplMode
    getMode StaticEnv
    env
        id_unf :: Id -> Unfolding
    id_unf Id
    id | Id -> Bool
    unf_is_active Id
    id = Id -> Unfolding
    idUnfolding Id
    id
                  | Bool
    otherwise        = Unfolding
    NoUnfolding
        unf_is_active :: Id -> Bool
    unf_is_active Id
    id
         | Bool -> Bool
    not (SimplMode -> Bool
    sm_rules SimplMode
    mode) = -- active_unfolding_minimal id
                                 Unfolding -> Bool
    isStableUnfolding (Id -> Unfolding
    realIdUnfolding Id
    id)
            -- Do we even need to test this?  I think this InScopeEnv
            -- is only consulted if activeRule returns True, which
            -- never happens if sm_rules is False
         | Bool
    otherwise           = CompilerPhase -> Activation -> Bool
    isActive (SimplMode -> CompilerPhase
    sm_phase SimplMode
    mode) (Id -> Activation
    idInlineActivation Id
    id)

    ----------------------
    activeRule :: SimplMode -> Activation -> Bool
    -- Nothing => No rules at all
    activeRule :: SimplMode -> Activation -> Bool
    activeRule SimplMode
    mode
      | Bool -> Bool
    not (SimplMode -> Bool
    sm_rules SimplMode
    mode) = \Activation
    _ -> Bool
    False     -- Rewriting is off
      | Bool
    otherwise           = CompilerPhase -> Activation -> Bool
    isActive (SimplMode -> CompilerPhase
    sm_phase SimplMode
    mode)

    {-
    ************************************************************************
    *                                                                      *
                      preInlineUnconditionally
    *                                                                      *
    ************************************************************************

    preInlineUnconditionally
    ~~~~~~~~~~~~~~~~~~~~~~~~
    @preInlineUnconditionally@ examines a bndr to see if it is used just
    once in a completely safe way, so that it is safe to discard the
    binding inline its RHS at the (unique) usage site, REGARDLESS of how
    big the RHS might be.  If this is the case we don't simplify the RHS
    first, but just inline it un-simplified.

    This is much better than first simplifying a perhaps-huge RHS and then
    inlining and re-simplifying it.  Indeed, it can be at least quadratically
    better.  Consider

            x1 = e1
            x2 = e2[x1]
            x3 = e3[x2]
            ...etc...
            xN = eN[xN-1]

    We may end up simplifying e1 N times, e2 N-1 times, e3 N-3 times etc.
    This can happen with cascades of functions too:

            f1 = \x1.e1
            f2 = \xs.e2[f1]
            f3 = \xs.e3[f3]
            ...etc...

    THE MAIN INVARIANT is this:

            ----  preInlineUnconditionally invariant -----
       IF preInlineUnconditionally chooses to inline x = <rhs>
       THEN doing the inlining should not change the occurrence
            info for the free vars of <rhs>
            ----------------------------------------------

    For example, it's tempting to look at trivial binding like
            x = y
    and inline it unconditionally.  But suppose x is used many times,
    but this is the unique occurrence of y.  Then inlining x would change
    y's occurrence info, which breaks the invariant.  It matters: y
    might have a BIG rhs, which will now be dup'd at every occurrence of x.

    Even RHSs labelled InlineMe aren't caught here, because there might be
    no benefit from inlining at the call site.

    [Sept 01] Don't unconditionally inline a top-level thing, because that
    can simply make a static thing into something built dynamically.  E.g.
            x = (a,b)
            main = \s -> h x

    [Remember that we treat \s as a one-shot lambda.]  No point in
    inlining x unless there is something interesting about the call site.

    But watch out: if you aren't careful, some useful foldr/build fusion
    can be lost (most notably in spectral/hartel/parstof) because the
    foldr didn't see the build.  Doing the dynamic allocation isn't a big
    deal, in fact, but losing the fusion can be.  But the right thing here
    seems to be to do a callSiteInline based on the fact that there is
    something interesting about the call site (it's strict).  Hmm.  That
    seems a bit fragile.

    Conclusion: inline top level things gaily until FinalPhase (the last
    phase), at which point don't.

    Note [pre/postInlineUnconditionally in gentle mode]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Even in gentle mode we want to do preInlineUnconditionally.  The
    reason is that too little clean-up happens if you don't inline
    use-once things.  Also a bit of inlining is *good* for full laziness;
    it can expose constant sub-expressions.  Example in
    spectral/mandel/Mandel.hs, where the mandelset function gets a useful
    let-float if you inline windowToViewport

    However, as usual for Gentle mode, do not inline things that are
    inactive in the initial stages.  See Note [Gentle mode].

    Note [Stable unfoldings and preInlineUnconditionally]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Surprisingly, do not pre-inline-unconditionally Ids with INLINE pragmas!
    Example

       {-# INLINE f #-}
       f :: Eq a => a -> a
       f x = ...

       fInt :: Int -> Int
       fInt = f Int dEqInt

       ...fInt...fInt...fInt...

    Here f occurs just once, in the RHS of fInt. But if we inline it there
    it might make fInt look big, and we'll lose the opportunity to inline f
    at each of fInt's call sites.  The INLINE pragma will only inline when
    the application is saturated for exactly this reason; and we don't
    want PreInlineUnconditionally to second-guess it. A live example is #3736.
        c.f. Note [Stable unfoldings and postInlineUnconditionally]

    NB: this only applies for INLINE things. Do /not/ switch off
    preInlineUnconditionally for

    * INLINABLE. It just says to GHC "inline this if you like".  If there
      is a unique occurrence, we want to inline the stable unfolding, not
      the RHS.

    * NONLINE[n] just switches off inlining until phase n.  We should
      respect that, but after phase n, just behave as usual.

    * NoUserInlinePrag.  There is no pragma at all. This ends up on wrappers.
      (See #18815.)

    Note [Top-level bottoming Ids]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Don't inline top-level Ids that are bottoming, even if they are used just
    once, because FloatOut has gone to some trouble to extract them out.
    Inlining them won't make the program run faster!

    Note [Do not inline CoVars unconditionally]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Coercion variables appear inside coercions, and the RHS of a let-binding
    is a term (not a coercion) so we can't necessarily inline the latter in
    the former.
    -}

    preInlineUnconditionally
        :: SimplEnv -> TopLevelFlag -> InId
        -> InExpr -> StaticEnv  -- These two go together
        -> Maybe SimplEnv       -- Returned env has extended substitution
    -- Precondition: rhs satisfies the let/app invariant
    -- See Note [Core let/app invariant] in GHC.Core
    -- Reason: we don't want to inline single uses, or discard dead bindings,
    --         for unlifted, side-effect-ful bindings
    preInlineUnconditionally :: StaticEnv
    -> TopLevelFlag -> Id -> Expr Id -> StaticEnv -> Maybe StaticEnv
    preInlineUnconditionally StaticEnv
    env TopLevelFlag
    top_lvl Id
    bndr Expr Id
    rhs StaticEnv
    rhs_env
      | Bool -> Bool
    not Bool
    pre_inline_unconditionally           = forall a. Maybe a
    Nothing
      | Bool -> Bool
    not Bool
    active                               = forall a. Maybe a
    Nothing
      | TopLevelFlag -> Bool
    isTopLevel TopLevelFlag
    top_lvl Bool -> Bool -> Bool
    && Id -> Bool
    isDeadEndId Id
    bndr   = forall a. Maybe a
    Nothing -- Note [Top-level bottoming Ids]
      | Id -> Bool
    isCoVar Id
    bndr                             = forall a. Maybe a
    Nothing -- Note [Do not inline CoVars unconditionally]
      | Id -> Bool
    isExitJoinId Id
    bndr                        = forall a. Maybe a
    Nothing -- Note [Do not inline exit join points]
                                                           -- in module Exitify
      | Bool -> Bool
    not (OccInfo -> Bool
    one_occ (Id -> OccInfo
    idOccInfo Id
    bndr))           = forall a. Maybe a
    Nothing
      | Bool -> Bool
    not (Unfolding -> Bool
    isStableUnfolding Unfolding
    unf)              = forall a. a -> Maybe a
    Just forall a b. (a -> b) -> a -> b
    $! (Expr Id -> StaticEnv
    extend_subst_with Expr Id
    rhs)

      -- Note [Stable unfoldings and preInlineUnconditionally]
      | Bool -> Bool
    not (InlinePragma -> Bool
    isInlinePragma InlinePragma
    inline_prag)
      , Just Expr Id
    inl <- Unfolding -> Maybe (Expr Id)
    maybeUnfoldingTemplate Unfolding
    unf   = forall a. a -> Maybe a
    Just forall a b. (a -> b) -> a -> b
    $! (Expr Id -> StaticEnv
    extend_subst_with Expr Id
    inl)
      | Bool
    otherwise                                = forall a. Maybe a
    Nothing
      where
        unf :: Unfolding
    unf = Id -> Unfolding
    idUnfolding Id
    bndr
        extend_subst_with :: Expr Id -> StaticEnv
    extend_subst_with Expr Id
    inl_rhs = StaticEnv -> Id -> SimplSR -> StaticEnv
    extendIdSubst StaticEnv
    env Id
    bndr forall a b. (a -> b) -> a -> b
    $! (StaticEnv -> Expr Id -> SimplSR
    mkContEx StaticEnv
    rhs_env Expr Id
    inl_rhs)

        one_occ :: OccInfo -> Bool
    one_occ OccInfo
    IAmDead = Bool
    True -- Happens in ((\x.1) v)
        one_occ OneOcc{ occ_n_br :: OccInfo -> Arity
    occ_n_br   = Arity
    1
                      , occ_in_lam :: OccInfo -> InsideLam
    occ_in_lam = InsideLam
    NotInsideLam }   = TopLevelFlag -> Bool
    isNotTopLevel TopLevelFlag
    top_lvl Bool -> Bool -> Bool
    || Bool
    early_phase
        one_occ OneOcc{ occ_n_br :: OccInfo -> Arity
    occ_n_br   = Arity
    1
                      , occ_in_lam :: OccInfo -> InsideLam
    occ_in_lam = InsideLam
    IsInsideLam
                      , occ_int_cxt :: OccInfo -> InterestingCxt
    occ_int_cxt = InterestingCxt
    IsInteresting } = Expr Id -> Bool
    canInlineInLam Expr Id
    rhs
        one_occ OccInfo
    _                                     = Bool
    False

        pre_inline_unconditionally :: Bool
    pre_inline_unconditionally = SimplMode -> Bool
    sm_pre_inline SimplMode
    mode
        mode :: SimplMode
    mode   = StaticEnv -> SimplMode
    getMode StaticEnv
    env
        active :: Bool
    active = CompilerPhase -> Activation -> Bool
    isActive (SimplMode -> CompilerPhase
    sm_phase SimplMode
    mode) (InlinePragma -> Activation
    inlinePragmaActivation InlinePragma
    inline_prag)
                 -- See Note [pre/postInlineUnconditionally in gentle mode]
        inline_prag :: InlinePragma
    inline_prag = Id -> InlinePragma
    idInlinePragma Id
    bndr

    -- Be very careful before inlining inside a lambda, because (a) we must not
    -- invalidate occurrence information, and (b) we want to avoid pushing a
    -- single allocation (here) into multiple allocations (inside lambda).
    -- Inlining a *function* with a single *saturated* call would be ok, mind you.
    --      || (if is_cheap && not (canInlineInLam rhs) then pprTrace "preinline" (ppr bndr <+> ppr rhs) ok else ok)
    --      where
    --              is_cheap = exprIsCheap rhs
    --              ok = is_cheap && int_cxt

            --      int_cxt         The context isn't totally boring
            -- E.g. let f = \ab.BIG in \y. map f xs
            --      Don't want to substitute for f, because then we allocate
            --      its closure every time the \y is called
            -- But: let f = \ab.BIG in \y. map (f y) xs
            --      Now we do want to substitute for f, even though it's not
            --      saturated, because we're going to allocate a closure for
            --      (f y) every time round the loop anyhow.

            -- canInlineInLam => free vars of rhs are (Once in_lam) or Many,
            -- so substituting rhs inside a lambda doesn't change the occ info.
            -- Sadly, not quite the same as exprIsHNF.
        canInlineInLam :: Expr Id -> Bool
    canInlineInLam (Lit Literal
    _)    = Bool
    True
        canInlineInLam (Lam Id
    b Expr Id
    e)  = Id -> Bool
    isRuntimeVar Id
    b Bool -> Bool -> Bool
    || Expr Id -> Bool
    canInlineInLam Expr Id
    e
        canInlineInLam (Tick CoreTickish
    t Expr Id
    e) = Bool -> Bool
    not (forall (pass :: TickishPass). GenTickish pass -> Bool
    tickishIsCode CoreTickish
    t) Bool -> Bool -> Bool
    && Expr Id -> Bool
    canInlineInLam Expr Id
    e
        canInlineInLam Expr Id
    _          = Bool
    False
          -- not ticks.  Counting ticks cannot be duplicated, and non-counting
          -- ticks around a Lam will disappear anyway.

        early_phase :: Bool
    early_phase = SimplMode -> CompilerPhase
    sm_phase SimplMode
    mode forall a. Eq a => a -> a -> Bool
    /= CompilerPhase
    FinalPhase
        -- If we don't have this early_phase test, consider
        --      x = length [1,2,3]
        -- The full laziness pass carefully floats all the cons cells to
        -- top level, and preInlineUnconditionally floats them all back in.
        -- Result is (a) static allocation replaced by dynamic allocation
        --           (b) many simplifier iterations because this tickles
        --               a related problem; only one inlining per pass
        --
        -- On the other hand, I have seen cases where top-level fusion is
        -- lost if we don't inline top level thing (e.g. string constants)
        -- Hence the test for phase zero (which is the phase for all the final
        -- simplifications).  Until phase zero we take no special notice of
        -- top level things, but then we become more leery about inlining
        -- them.

    {-
    ************************************************************************
    *                                                                      *
                      postInlineUnconditionally
    *                                                                      *
    ************************************************************************

    postInlineUnconditionally
    ~~~~~~~~~~~~~~~~~~~~~~~~~
    @postInlineUnconditionally@ decides whether to unconditionally inline
    a thing based on the form of its RHS; in particular if it has a
    trivial RHS.  If so, we can inline and discard the binding altogether.

    NB: a loop breaker has must_keep_binding = True and non-loop-breakers
    only have *forward* references. Hence, it's safe to discard the binding

    NOTE: This isn't our last opportunity to inline.  We're at the binding
    site right now, and we'll get another opportunity when we get to the
    occurrence(s)

    Note that we do this unconditional inlining only for trivial RHSs.
    Don't inline even WHNFs inside lambdas; doing so may simply increase
    allocation when the function is called. This isn't the last chance; see
    NOTE above.

    NB: Even inline pragmas (e.g. IMustBeINLINEd) are ignored here Why?
    Because we don't even want to inline them into the RHS of constructor
    arguments. See NOTE above

    NB: At one time even NOINLINE was ignored here: if the rhs is trivial
    it's best to inline it anyway.  We often get a=E; b=a from desugaring,
    with both a and b marked NOINLINE.  But that seems incompatible with
    our new view that inlining is like a RULE, so I'm sticking to the 'active'
    story for now.

    NB: unconditional inlining of this sort can introduce ticks in places that
    may seem surprising; for instance, the LHS of rules. See Note [Simplfying
    rules] for details.
    -}

    postInlineUnconditionally
        :: SimplEnv -> TopLevelFlag
        -> OutId            -- The binder (*not* a CoVar), including its unfolding
        -> OccInfo          -- From the InId
        -> OutExpr
        -> Bool
    -- Precondition: rhs satisfies the let/app invariant
    -- See Note [Core let/app invariant] in GHC.Core
    -- Reason: we don't want to inline single uses, or discard dead bindings,
    --         for unlifted, side-effect-ful bindings
    postInlineUnconditionally :: StaticEnv -> TopLevelFlag -> Id -> OccInfo -> Expr Id -> Bool
    postInlineUnconditionally StaticEnv
    env TopLevelFlag
    top_lvl Id
    bndr OccInfo
    occ_info Expr Id
    rhs
      | Bool -> Bool
    not Bool
    active                  = Bool
    False
      | OccInfo -> Bool
    isWeakLoopBreaker OccInfo
    occ_info  = Bool
    False -- If it's a loop-breaker of any kind, don't inline
                                            -- because it might be referred to "earlier"
      | Unfolding -> Bool
    isStableUnfolding Unfolding
    unfolding = Bool
    False -- Note [Stable unfoldings and postInlineUnconditionally]
      | TopLevelFlag -> Bool
    isTopLevel TopLevelFlag
    top_lvl          = Bool
    False -- Note [Top level and postInlineUnconditionally]
      | Expr Id -> Bool
    exprIsTrivial Expr Id
    rhs           = Bool
    True
      | Id -> Bool
    isJoinId Id
    bndr                       -- See point (1) of Note [Duplicating join points]
      , Bool -> Bool
    not (CompilerPhase
    phase forall a. Eq a => a -> a -> Bool
    == CompilerPhase
    FinalPhase)   = Bool
    False -- in Simplify.hs
      | Bool
    otherwise
      = case OccInfo
    occ_info of
          OneOcc { occ_in_lam :: OccInfo -> InsideLam
    occ_in_lam = InsideLam
    in_lam, occ_int_cxt :: OccInfo -> InterestingCxt
    occ_int_cxt = InterestingCxt
    int_cxt, occ_n_br :: OccInfo -> Arity
    occ_n_br = Arity
    n_br }
            -- See Note [Inline small things to avoid creating a thunk]

            -> Arity
    n_br forall a. Ord a => a -> a -> Bool
    < Arity
    100  -- See Note [Suppress exponential blowup]

               Bool -> Bool -> Bool
    && UnfoldingOpts -> Unfolding -> Bool
    smallEnoughToInline UnfoldingOpts
    uf_opts Unfolding
    unfolding     -- Small enough to dup
                            -- ToDo: consider discount on smallEnoughToInline if int_cxt is true
                            --
                            -- NB: Do NOT inline arbitrarily big things, even if occ_n_br=1
                            -- Reason: doing so risks exponential behaviour.  We simplify a big
                            --         expression, inline it, and simplify it again.  But if the
                            --         very same thing happens in the big expression, we get
                            --         exponential cost!
                            -- PRINCIPLE: when we've already simplified an expression once,
                            -- make sure that we only inline it if it's reasonably small.

               Bool -> Bool -> Bool
    && (InsideLam
    in_lam forall a. Eq a => a -> a -> Bool
    == InsideLam
    NotInsideLam Bool -> Bool -> Bool
    ||
                            -- Outside a lambda, we want to be reasonably aggressive
                            -- about inlining into multiple branches of case
                            -- e.g. let x = <non-value>
                            --      in case y of { C1 -> ..x..; C2 -> ..x..; C3 -> ... }
                            -- Inlining can be a big win if C3 is the hot-spot, even if
                            -- the uses in C1, C2 are not 'interesting'
                            -- An example that gets worse if you add int_cxt here is 'clausify'

                    (Unfolding -> Bool
    isCheapUnfolding Unfolding
    unfolding Bool -> Bool -> Bool
    && InterestingCxt
    int_cxt forall a. Eq a => a -> a -> Bool
    == InterestingCxt
    IsInteresting))
                            -- isCheap => acceptable work duplication; in_lam may be true
                            -- int_cxt to prevent us inlining inside a lambda without some
                            -- good reason.  See the notes on int_cxt in preInlineUnconditionally

          OccInfo
    IAmDead -> Bool
    True   -- This happens; for example, the case_bndr during case of
                            -- known constructor:  case (a,b) of x { (p,q) -> ... }
                            -- Here x isn't mentioned in the RHS, so we don't want to
                            -- create the (dead) let-binding  let x = (a,b) in ...

          OccInfo
    _ -> Bool
    False

    -- Here's an example that we don't handle well:
    --      let f = if b then Left (\x.BIG) else Right (\y.BIG)
    --      in \y. ....case f of {...} ....
    -- Here f is used just once, and duplicating the case work is fine (exprIsCheap).
    -- But
    --  - We can't preInlineUnconditionally because that would invalidate
    --    the occ info for b.
    --  - We can't postInlineUnconditionally because the RHS is big, and
    --    that risks exponential behaviour
    --  - We can't call-site inline, because the rhs is big
    -- Alas!

      where
        unfolding :: Unfolding
    unfolding = Id -> Unfolding
    idUnfolding Id
    bndr
        uf_opts :: UnfoldingOpts
    uf_opts   = StaticEnv -> UnfoldingOpts
    seUnfoldingOpts StaticEnv
    env
        phase :: CompilerPhase
    phase     = SimplMode -> CompilerPhase
    sm_phase (StaticEnv -> SimplMode
    getMode StaticEnv
    env)
        active :: Bool
    active    = CompilerPhase -> Activation -> Bool
    isActive CompilerPhase
    phase (Id -> Activation
    idInlineActivation Id
    bndr)
            -- See Note [pre/postInlineUnconditionally in gentle mode]

    {- Note [Inline small things to avoid creating a thunk]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    The point of examining occ_info here is that for *non-values* that
    occur outside a lambda, the call-site inliner won't have a chance
    (because it doesn't know that the thing only occurs once).  The
    pre-inliner won't have gotten it either, if the thing occurs in more
    than one branch So the main target is things like

         let x = f y in
         case v of
            True  -> case x of ...
            False -> case x of ...

    This is very important in practice; e.g. wheel-seive1 doubles
    in allocation if you miss this out.  And bits of GHC itself start
    to allocate more.  An egregious example is test perf/compiler/T14697,
    where GHC.Driver.CmdLine.$wprocessArgs allocated hugely more.

    Note [Suppress exponential blowup]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    In #13253, and several related tickets, we got an exponential blowup
    in code size from postInlineUnconditionally.  The trouble comes when
    we have
      let j1a = case f y     of { True -> p;   False -> q }
          j1b = case f y     of { True -> q;   False -> p }
          j2a = case f (y+1) of { True -> j1a; False -> j1b }
          j2b = case f (y+1) of { True -> j1b; False -> j1a }
          ...
      in case f (y+10) of { True -> j10a; False -> j10b }

    when there are many branches. In pass 1, postInlineUnconditionally
    inlines j10a and j10b (they are both small).  Now we have two calls
    to j9a and two to j9b.  In pass 2, postInlineUnconditionally inlines
    all four of these calls, leaving four calls to j8a and j8b. Etc.
    Yikes!  This is exponential!

    A possible plan: stop doing postInlineUnconditionally
    for some fixed, smallish number of branches, say 4. But that turned
    out to be bad: see Note [Inline small things to avoid creating a thunk].
    And, as it happened, the problem with #13253 was solved in a
    different way (Note [Duplicating StrictArg] in Simplify).

    So I just set an arbitrary, high limit of 100, to stop any
    totally exponential behaviour.

    This still leaves the nasty possibility that /ordinary/ inlining (not
    postInlineUnconditionally) might inline these join points, each of
    which is individually quiet small.  I'm still not sure what to do
    about this (e.g. see #15488).

    Note [Top level and postInlineUnconditionally]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    We don't do postInlineUnconditionally for top-level things (even for
    ones that are trivial):

      * Doing so will inline top-level error expressions that have been
        carefully floated out by FloatOut.  More generally, it might
        replace static allocation with dynamic.

      * Even for trivial expressions there's a problem.  Consider
          {-# RULE "foo" forall (xs::[T]). reverse xs = ruggle xs #-}
          blah xs = reverse xs
          ruggle = sort
        In one simplifier pass we might fire the rule, getting
          blah xs = ruggle xs
        but in *that* simplifier pass we must not do postInlineUnconditionally
        on 'ruggle' because then we'll have an unbound occurrence of 'ruggle'

        If the rhs is trivial it'll be inlined by callSiteInline, and then
        the binding will be dead and discarded by the next use of OccurAnal

      * There is less point, because the main goal is to get rid of local
        bindings used in multiple case branches.

      * The inliner should inline trivial things at call sites anyway.

      * The Id might be exported.  We could check for that separately,
        but since we aren't going to postInlineUnconditionally /any/
        top-level bindings, we don't need to test.

    Note [Stable unfoldings and postInlineUnconditionally]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Do not do postInlineUnconditionally if the Id has a stable unfolding,
    otherwise we lose the unfolding.  Example

         -- f has stable unfolding with rhs (e |> co)
         --   where 'e' is big
         f = e |> co

    Then there's a danger we'll optimise to

         f' = e
         f = f' |> co

    and now postInlineUnconditionally, losing the stable unfolding on f.  Now f'
    won't inline because 'e' is too big.

        c.f. Note [Stable unfoldings and preInlineUnconditionally]

    ************************************************************************
    *                                                                      *
            Rebuilding a lambda
    *                                                                      *
    ************************************************************************
    -}

    mkLam :: SimplEnv -> [OutBndr] -> OutExpr -> SimplCont -> SimplM OutExpr
    -- mkLam tries three things
    --      a) eta reduction, if that gives a trivial expression
    --      b) eta expansion [only if there are some value lambdas]

    mkLam :: StaticEnv -> [Id] -> Expr Id -> SimplCont -> SimplM (Expr Id)
    mkLam StaticEnv
    _env [] Expr Id
    body SimplCont
    _cont
      = forall (m :: * -> *) a. Monad m => a -> m a
    return Expr Id
    body
    mkLam StaticEnv
    env [Id]
    bndrs Expr Id
    body SimplCont
    cont
      = do { DynFlags
    dflags <- forall (m :: * -> *). HasDynFlags m => m DynFlags
    getDynFlags
           ; DynFlags -> [Id] -> Expr Id -> SimplM (Expr Id)
    mkLam' DynFlags
    dflags [Id]
    bndrs Expr Id
    body }
      where
        mode :: SimplMode
    mode = StaticEnv -> SimplMode
    getMode StaticEnv
    env

        mkLam' :: DynFlags -> [OutBndr] -> OutExpr -> SimplM OutExpr
        mkLam' :: DynFlags -> [Id] -> Expr Id -> SimplM (Expr Id)
    mkLam' DynFlags
    dflags [Id]
    bndrs body :: Expr Id
    body@(Lam {})
          = DynFlags -> [Id] -> Expr Id -> SimplM (Expr Id)
    mkLam' DynFlags
    dflags ([Id]
    bndrs forall a. [a] -> [a] -> [a]
    ++ [Id]
    bndrs1) Expr Id
    body1
          where
            ([Id]
    bndrs1, Expr Id
    body1) = forall b. Expr b -> ([b], Expr b)
    collectBinders Expr Id
    body

        mkLam' DynFlags
    dflags [Id]
    bndrs (Tick CoreTickish
    t Expr Id
    expr)
          | forall (pass :: TickishPass). GenTickish pass -> Bool
    tickishFloatable CoreTickish
    t
          = CoreTickish -> Expr Id -> Expr Id
    mkTick CoreTickish
    t forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
    <$> DynFlags -> [Id] -> Expr Id -> SimplM (Expr Id)
    mkLam' DynFlags
    dflags [Id]
    bndrs Expr Id
    expr

        mkLam' DynFlags
    dflags [Id]
    bndrs (Cast Expr Id
    body OutCoercion
    co)
          | -- Note [Casts and lambdas]
            SimplMode -> Bool
    sm_cast_swizzle SimplMode
    mode
          , Bool -> Bool
    not (forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
    any Id -> Bool
    bad [Id]
    bndrs)
          = do { Expr Id
    lam <- DynFlags -> [Id] -> Expr Id -> SimplM (Expr Id)
    mkLam' DynFlags
    dflags [Id]
    bndrs Expr Id
    body
               ; forall (m :: * -> *) a. Monad m => a -> m a
    return (Expr Id -> OutCoercion -> Expr Id
    mkCast Expr Id
    lam (Role -> [Id] -> OutCoercion -> OutCoercion
    mkPiCos Role
    Representational [Id]
    bndrs OutCoercion
    co)) }
          where
            co_vars :: TyCoVarSet
    co_vars  = OutCoercion -> TyCoVarSet
    tyCoVarsOfCo OutCoercion
    co
            bad :: Id -> Bool
    bad Id
    bndr = Id -> Bool
    isCoVar Id
    bndr Bool -> Bool -> Bool
    && Id
    bndr Id -> TyCoVarSet -> Bool
    `elemVarSet` TyCoVarSet
    co_vars

        mkLam' DynFlags
    dflags [Id]
    bndrs Expr Id
    body
          | GeneralFlag -> DynFlags -> Bool
    gopt GeneralFlag
    Opt_DoEtaReduction DynFlags
    dflags
          , Just Expr Id
    etad_lam <- {-# SCC "tryee" #-} [Id] -> Expr Id -> Maybe (Expr Id)
    tryEtaReduce [Id]
    bndrs Expr Id
    body
          = do { Tick -> SimplM ()
    tick (Id -> Tick
    EtaReduction (forall a. [a] -> a
    head [Id]
    bndrs))
               ; forall (m :: * -> *) a. Monad m => a -> m a
    return Expr Id
    etad_lam }

          | Bool -> Bool
    not (SimplCont -> Bool
    contIsRhs SimplCont
    cont)   -- See Note [Eta-expanding lambdas]
          , SimplMode -> Bool
    sm_eta_expand SimplMode
    mode
          , forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
    any Id -> Bool
    isRuntimeVar [Id]
    bndrs
          , let body_arity :: ArityType
    body_arity = {-# SCC "eta" #-} DynFlags -> Expr Id -> ArityType
    exprEtaExpandArity DynFlags
    dflags Expr Id
    body
          , ArityType -> Bool
    expandableArityType ArityType
    body_arity
          = do { Tick -> SimplM ()
    tick (Id -> Tick
    EtaExpansion (forall a. [a] -> a
    head [Id]
    bndrs))
               ; let res :: Expr Id
    res = {-# SCC "eta3" #-}
                           forall b. [b] -> Expr b -> Expr b
    mkLams [Id]
    bndrs forall a b. (a -> b) -> a -> b
    $
                           ArityType -> Expr Id -> Expr Id
    etaExpandAT ArityType
    body_arity Expr Id
    body
               ; String -> SDoc -> SimplM ()
    traceSmpl String
    "eta expand" ([SDoc] -> SDoc
    vcat [String -> SDoc
    text String
    "before" SDoc -> SDoc -> SDoc
    <+> forall a. Outputable a => a -> SDoc
    ppr (forall b. [b] -> Expr b -> Expr b
    mkLams [Id]
    bndrs Expr Id
    body)
                                              , String -> SDoc
    text String
    "after" SDoc -> SDoc -> SDoc
    <+> forall a. Outputable a => a -> SDoc
    ppr Expr Id
    res])
               ; forall (m :: * -> *) a. Monad m => a -> m a
    return Expr Id
    res }

          | Bool
    otherwise
          = forall (m :: * -> *) a. Monad m => a -> m a
    return (forall b. [b] -> Expr b -> Expr b
    mkLams [Id]
    bndrs Expr Id
    body)

    {-
    Note [Eta expanding lambdas]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    In general we *do* want to eta-expand lambdas. Consider
       f (\x -> case x of (a,b) -> \s -> blah)
    where 's' is a state token, and hence can be eta expanded.  This
    showed up in the code for GHc.IO.Handle.Text.hPutChar, a rather
    important function!

    The eta-expansion will never happen unless we do it now.  (Well, it's
    possible that CorePrep will do it, but CorePrep only has a half-baked
    eta-expander that can't deal with casts.  So it's much better to do it
    here.)

    However, when the lambda is let-bound, as the RHS of a let, we have a
    better eta-expander (in the form of tryEtaExpandRhs), so we don't
    bother to try expansion in mkLam in that case; hence the contIsRhs
    guard.

    NB: We check the SimplEnv (sm_eta_expand), not DynFlags.
        See Note [Eta-expansion in stable unfoldings]

    Note [Casts and lambdas]
    ~~~~~~~~~~~~~~~~~~~~~~~~
    Consider
            (\x. (\y. e) `cast` g1) `cast` g2
    There is a danger here that the two lambdas look separated, and the
    full laziness pass might float an expression to between the two.

    So this equation in mkLam' floats the g1 out, thus:
            (\x. e `cast` g1)  -->  (\x.e) `cast` (tx -> g1)
    where x:tx.

    In general, this floats casts outside lambdas, where (I hope) they
    might meet and cancel with some other cast:
            \x. e `cast` co   ===>   (\x. e) `cast` (tx -> co)
            /\a. e `cast` co  ===>   (/\a. e) `cast` (/\a. co)
            /\g. e `cast` co  ===>   (/\g. e) `cast` (/\g. co)
                              (if not (g `in` co))

    We call this "cast swizzling". It is controlled by sm_cast_swizzle.
    See also Note [Cast swizzling on rule LHSs]

    Wrinkles

    * Notice that it works regardless of 'e'.  Originally it worked only
      if 'e' was itself a lambda, but in some cases that resulted in
      fruitless iteration in the simplifier.  A good example was when
      compiling Text.ParserCombinators.ReadPrec, where we had a definition
      like    (\x. Get `cast` g)
      where Get is a constructor with nonzero arity.  Then mkLam eta-expanded
      the Get, and the next iteration eta-reduced it, and then eta-expanded
      it again.

    * Note also the side condition for the case of coercion binders, namely
      not (any bad bndrs).  It does not make sense to transform
              /\g. e `cast` g  ==>  (/\g.e) `cast` (/\g.g)
      because the latter is not well-kinded.

    ************************************************************************
    *                                                                      *
                  Eta expansion
    *                                                                      *
    ************************************************************************
    -}

    tryEtaExpandRhs :: SimplMode -> OutId -> OutExpr
                    -> SimplM (ArityType, OutExpr)
    -- See Note [Eta-expanding at let bindings]
    -- If tryEtaExpandRhs rhs = (n, is_bot, rhs') then
    --   (a) rhs' has manifest arity n
    --   (b) if is_bot is True then rhs' applied to n args is guaranteed bottom
    tryEtaExpandRhs :: SimplMode -> Id -> Expr Id -> SimplM (ArityType, Expr Id)
    tryEtaExpandRhs SimplMode
    mode Id
    bndr Expr Id
    rhs
      | Just Arity
    join_arity <- Id -> Maybe Arity
    isJoinId_maybe Id
    bndr
      = do { let ([Id]
    join_bndrs, Expr Id
    join_body) = forall b. Arity -> Expr b -> ([b], Expr b)
    collectNBinders Arity
    join_arity Expr Id
    rhs
                 oss :: [OneShotInfo]
    oss   = [Id -> OneShotInfo
    idOneShotInfo Id
    id | Id
    id <- [Id]
    join_bndrs, Id -> Bool
    isId Id
    id]
                 arity_type :: ArityType
    arity_type | Expr Id -> Bool
    exprIsDeadEnd Expr Id
    join_body = [OneShotInfo] -> ArityType
    mkBotArityType [OneShotInfo]
    oss
                            | Bool
    otherwise               = [OneShotInfo] -> ArityType
    mkTopArityType [OneShotInfo]
    oss
           ; forall (m :: * -> *) a. Monad m => a -> m a
    return (ArityType
    arity_type, Expr Id
    rhs) }
             -- Note [Do not eta-expand join points]
             -- But do return the correct arity and bottom-ness, because
             -- these are used to set the bndr's IdInfo (#15517)
             -- Note [Invariants on join points] invariant 2b, in GHC.Core

      | SimplMode -> Bool
    sm_eta_expand SimplMode
    mode      -- Provided eta-expansion is on
      , Arity
    new_arity forall a. Ord a => a -> a -> Bool
    > Arity
    old_arity   -- And the current manifest arity isn't enough
      , Expr Id -> Bool
    want_eta Expr Id
    rhs
      = do { Tick -> SimplM ()
    tick (Id -> Tick
    EtaExpansion Id
    bndr)
           ; forall (m :: * -> *) a. Monad m => a -> m a
    return (ArityType
    arity_type, ArityType -> Expr Id -> Expr Id
    etaExpandAT ArityType
    arity_type Expr Id
    rhs) }

      | Bool
    otherwise
      = forall (m :: * -> *) a. Monad m => a -> m a
    return (ArityType
    arity_type, Expr Id
    rhs)

      where
        dflags :: DynFlags
    dflags    = SimplMode -> DynFlags
    sm_dflags SimplMode
    mode
        old_arity :: Arity
    old_arity = Expr Id -> Arity
    exprArity Expr Id
    rhs

        arity_type :: ArityType
    arity_type = DynFlags -> Id -> Expr Id -> Arity -> ArityType
    findRhsArity DynFlags
    dflags Id
    bndr Expr Id
    rhs Arity
    old_arity
                     ArityType -> Arity -> ArityType
    `maxWithArity` Id -> Arity
    idCallArity Id
    bndr
        new_arity :: Arity
    new_arity = ArityType -> Arity
    arityTypeArity ArityType
    arity_type

        -- See Note [Which RHSs do we eta-expand?]
        want_eta :: Expr Id -> Bool
    want_eta (Cast Expr Id
    e OutCoercion
    _)                  = Expr Id -> Bool
    want_eta Expr Id
    e
        want_eta (Tick CoreTickish
    _ Expr Id
    e)                  = Expr Id -> Bool
    want_eta Expr Id
    e
        want_eta (Lam Id
    b Expr Id
    e) | Id -> Bool
    isTyVar Id
    b       = Expr Id -> Bool
    want_eta Expr Id
    e
        want_eta (App Expr Id
    e Expr Id
    a) | Expr Id -> Bool
    exprIsTrivial Expr Id
    a = Expr Id -> Bool
    want_eta Expr Id
    e
        want_eta (Var {})                    = Bool
    False
        want_eta (Lit {})                    = Bool
    False
        want_eta Expr Id
    _ = Bool
    True
    {-
        want_eta _ = case arity_type of
                       ATop (os:_) -> isOneShotInfo os
                       ATop []     -> False
                       ABot {}     -> True
    -}

    {-
    Note [Eta-expanding at let bindings]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    We now eta expand at let-bindings, which is where the payoff comes.
    The most significant thing is that we can do a simple arity analysis
    (in GHC.Core.Opt.Arity.findRhsArity), which we can't do for free-floating lambdas

    One useful consequence of not eta-expanding lambdas is this example:
       genMap :: C a => ...
       {-# INLINE genMap #-}
       genMap f xs = ...

       myMap :: D a => ...
       {-# INLINE myMap #-}
       myMap = genMap

    Notice that 'genMap' should only inline if applied to two arguments.
    In the stable unfolding for myMap we'll have the unfolding
        (\d -> genMap Int (..d..))
    We do not want to eta-expand to
        (\d f xs -> genMap Int (..d..) f xs)
    because then 'genMap' will inline, and it really shouldn't: at least
    as far as the programmer is concerned, it's not applied to two
    arguments!

    Note [Which RHSs do we eta-expand?]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    We don't eta-expand:

    * Trivial RHSs, e.g.     f = g
      If we eta expand do
        f = \x. g x
      we'll just eta-reduce again, and so on; so the
      simplifier never terminates.

    * PAPs: see Note [Do not eta-expand PAPs]

    What about things like this?
       f = case y of p -> \x -> blah

    Here we do eta-expand.  This is a change (Jun 20), but if we have
    really decided that f has arity 1, then putting that lambda at the top
    seems like a Good idea.

    Note [Do not eta-expand PAPs]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    We used to have old_arity = manifestArity rhs, which meant that we
    would eta-expand even PAPs.  But this gives no particular advantage,
    and can lead to a massive blow-up in code size, exhibited by #9020.
    Suppose we have a PAP
        foo :: IO ()
        foo = returnIO ()
    Then we can eta-expand do
        foo = (\eta. (returnIO () |> sym g) eta) |> g
    where
        g :: IO () ~ State# RealWorld -> (# State# RealWorld, () #)

    But there is really no point in doing this, and it generates masses of
    coercions and whatnot that eventually disappear again. For T9020, GHC
    allocated 6.6G before, and 0.8G afterwards; and residency dropped from
    1.8G to 45M.

    Moreover, if we eta expand
            f = g d  ==>  f = \x. g d x
    that might in turn make g inline (if it has an inline pragma), which
    we might not want.  After all, INLINE pragmas say "inline only when
    saturated" so we don't want to be too gung-ho about saturating!

    But note that this won't eta-expand, say
      f = \g -> map g
    Does it matter not eta-expanding such functions?  I'm not sure.  Perhaps
    strictness analysis will have less to bite on?

    Note [Do not eta-expand join points]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Similarly to CPR (see Note [Don't w/w join points for CPR] in
    GHC.Core.Opt.WorkWrap), a join point stands well to gain from its outer binding's
    eta-expansion, and eta-expanding a join point is fraught with issues like how to
    deal with a cast:

        let join $j1 :: IO ()
                 $j1 = ...
                 $j2 :: Int -> IO ()
                 $j2 n = if n > 0 then $j1
                                  else ...

        =>

        let join $j1 :: IO ()
                 $j1 = (\eta -> ...)
                         `cast` N:IO :: State# RealWorld -> (# State# RealWorld, ())
                                     ~  IO ()
                 $j2 :: Int -> IO ()
                 $j2 n = (\eta -> if n > 0 then $j1
                                           else ...)
                         `cast` N:IO :: State# RealWorld -> (# State# RealWorld, ())
                                     ~  IO ()

    The cast here can't be pushed inside the lambda (since it's not casting to a
    function type), so the lambda has to stay, but it can't because it contains a
    reference to a join point. In fact, $j2 can't be eta-expanded at all. Rather
    than try and detect this situation (and whatever other situations crop up!), we
    don't bother; again, any surrounding eta-expansion will improve these join
    points anyway, since an outer cast can *always* be pushed inside. By the time
    CorePrep comes around, the code is very likely to look more like this:

        let join $j1 :: State# RealWorld -> (# State# RealWorld, ())
                 $j1 = (...) eta
                 $j2 :: Int -> State# RealWorld -> (# State# RealWorld, ())
                 $j2 = if n > 0 then $j1
                                else (...) eta

    ************************************************************************
    *                                                                      *
    \subsection{Floating lets out of big lambdas}
    *                                                                      *
    ************************************************************************

    Note [Floating and type abstraction]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider this:
            x = /\a. C e1 e2
    We'd like to float this to
            y1 = /\a. e1
            y2 = /\a. e2
            x  = /\a. C (y1 a) (y2 a)
    for the usual reasons: we want to inline x rather vigorously.

    You may think that this kind of thing is rare.  But in some programs it is
    common.  For example, if you do closure conversion you might get:

            data a :-> b = forall e. (e -> a -> b) :$ e

            f_cc :: forall a. a :-> a
            f_cc = /\a. (\e. id a) :$ ()

    Now we really want to inline that f_cc thing so that the
    construction of the closure goes away.

    So I have elaborated simplLazyBind to understand right-hand sides that look
    like
            /\ a1..an. body

    and treat them specially. The real work is done in
    GHC.Core.Opt.Simplify.Utils.abstractFloats, but there is quite a bit of plumbing
    in simplLazyBind as well.

    The same transformation is good when there are lets in the body:

            /\abc -> let(rec) x = e in b
       ==>
            let(rec) x' = /\abc -> let x = x' a b c in e
            in
            /\abc -> let x = x' a b c in b

    This is good because it can turn things like:

            let f = /\a -> letrec g = ... g ... in g
    into
            letrec g' = /\a -> ... g' a ...
            in
            let f = /\ a -> g' a

    which is better.  In effect, it means that big lambdas don't impede
    let-floating.

    This optimisation is CRUCIAL in eliminating the junk introduced by
    desugaring mutually recursive definitions.  Don't eliminate it lightly!

    [May 1999]  If we do this transformation *regardless* then we can
    end up with some pretty silly stuff.  For example,

            let
                st = /\ s -> let { x1=r1 ; x2=r2 } in ...
            in ..
    becomes
            let y1 = /\s -> r1
                y2 = /\s -> r2
                st = /\s -> ...[y1 s/x1, y2 s/x2]
            in ..

    Unless the "..." is a WHNF there is really no point in doing this.
    Indeed it can make things worse.  Suppose x1 is used strictly,
    and is of the form

            x1* = case f y of { (a,b) -> e }

    If we abstract this wrt the tyvar we then can't do the case inline
    as we would normally do.

    That's why the whole transformation is part of the same process that
    floats let-bindings and constructor arguments out of RHSs.  In particular,
    it is guarded by the doFloatFromRhs call in simplLazyBind.

    Note [Which type variables to abstract over]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Abstract only over the type variables free in the rhs wrt which the
    new binding is abstracted.  Note that

      * The naive approach of abstracting wrt the
        tyvars free in the Id's /type/ fails. Consider:
            /\ a b -> let t :: (a,b) = (e1, e2)
                          x :: a     = fst t
                      in ...
        Here, b isn't free in x's type, but we must nevertheless
        abstract wrt b as well, because t's type mentions b.
        Since t is floated too, we'd end up with the bogus:
             poly_t = /\ a b -> (e1, e2)
             poly_x = /\ a   -> fst (poly_t a *b*)

      * We must do closeOverKinds.  Example (#10934):
           f = /\k (f:k->*) (a:k). let t = AccFailure @ (f a) in ...
        Here we want to float 't', but we must remember to abstract over
        'k' as well, even though it is not explicitly mentioned in the RHS,
        otherwise we get
           t = /\ (f:k->*) (a:k). AccFailure @ (f a)
        which is obviously bogus.
    -}

    abstractFloats :: UnfoldingOpts -> TopLevelFlag -> [OutTyVar] -> SimplFloats
                  -> OutExpr -> SimplM ([OutBind], OutExpr)
    abstractFloats :: UnfoldingOpts
    -> TopLevelFlag
    -> [Id]
    -> SimplFloats
    -> Expr Id
    -> SimplM ([Bind Id], Expr Id)
    abstractFloats UnfoldingOpts
    uf_opts TopLevelFlag
    top_lvl [Id]
    main_tvs SimplFloats
    floats Expr Id
    body
      = ASSERT( notNull body_floats )
        ASSERT( isNilOL (sfJoinFloats floats) )
        do  { (Subst
    subst, [Bind Id]
    float_binds) <- forall (m :: * -> *) acc x y.
    Monad m =>
    (acc -> x -> m (acc, y)) -> acc -> [x] -> m (acc, [y])
    mapAccumLM Subst -> Bind Id -> SimplM (Subst, Bind Id)
    abstract Subst
    empty_subst [Bind Id]
    body_floats
            ; forall (m :: * -> *) a. Monad m => a -> m a
    return ([Bind Id]
    float_binds, HasDebugCallStack => Subst -> Expr Id -> Expr Id
    GHC.Core.Subst.substExpr Subst
    subst Expr Id
    body) }
      where
        is_top_lvl :: Bool
    is_top_lvl  = TopLevelFlag -> Bool
    isTopLevel TopLevelFlag
    top_lvl
        main_tv_set :: TyCoVarSet
    main_tv_set = [Id] -> TyCoVarSet
    mkVarSet [Id]
    main_tvs
        body_floats :: [Bind Id]
    body_floats = LetFloats -> [Bind Id]
    letFloatBinds (SimplFloats -> LetFloats
    sfLetFloats SimplFloats
    floats)
        empty_subst :: Subst
    empty_subst = InScopeSet -> Subst
    GHC.Core.Subst.mkEmptySubst (SimplFloats -> InScopeSet
    sfInScope SimplFloats
    floats)

        abstract :: GHC.Core.Subst.Subst -> OutBind -> SimplM (GHC.Core.Subst.Subst, OutBind)
        abstract :: Subst -> Bind Id -> SimplM (Subst, Bind Id)
    abstract Subst
    subst (NonRec Id
    id Expr Id
    rhs)
          = do { (Id
    poly_id1, Expr Id
    poly_app) <- [Id] -> Id -> SimplM (Id, Expr Id)
    mk_poly1 [Id]
    tvs_here Id
    id
               ; let (Id
    poly_id2, Expr Id
    poly_rhs) = Id -> [Id] -> Expr Id -> (Id, Expr Id)
    mk_poly2 Id
    poly_id1 [Id]
    tvs_here Expr Id
    rhs'
                     !subst' :: Subst
    subst' = Subst -> Id -> Expr Id -> Subst
    GHC.Core.Subst.extendIdSubst Subst
    subst Id
    id Expr Id
    poly_app
               ; forall (m :: * -> *) a. Monad m => a -> m a
    return (Subst
    subst', forall b. b -> Expr b -> Bind b
    NonRec Id
    poly_id2 Expr Id
    poly_rhs) }
          where
            rhs' :: Expr Id
    rhs' = HasDebugCallStack => Subst -> Expr Id -> Expr Id
    GHC.Core.Subst.substExpr Subst
    subst Expr Id
    rhs

            -- tvs_here: see Note [Which type variables to abstract over]
            tvs_here :: [Id]
    tvs_here = [Id] -> [Id]
    scopedSort forall a b. (a -> b) -> a -> b
    $
                       forall a. (a -> Bool) -> [a] -> [a]
    filter (Id -> TyCoVarSet -> Bool
    `elemVarSet` TyCoVarSet
    main_tv_set) forall a b. (a -> b) -> a -> b
    $
                       [Id] -> [Id]
    closeOverKindsList forall a b. (a -> b) -> a -> b
    $
                       (Id -> Bool) -> Expr Id -> [Id]
    exprSomeFreeVarsList Id -> Bool
    isTyVar Expr Id
    rhs'

        abstract Subst
    subst (Rec [(Id, Expr Id)]
    prs)
           = do { ([Id]
    poly_ids, [Expr Id]
    poly_apps) <- forall (m :: * -> *) a b c.
    Applicative m =>
    (a -> m (b, c)) -> [a] -> m ([b], [c])
    mapAndUnzipM ([Id] -> Id -> SimplM (Id, Expr Id)
    mk_poly1 [Id]
    tvs_here) [Id]
    ids
                ; let subst' :: Subst
    subst' = Subst -> [(Id, Expr Id)] -> Subst
    GHC.Core.Subst.extendSubstList Subst
    subst ([Id]
    ids forall a b. [a] -> [b] -> [(a, b)]
    `zip` [Expr Id]
    poly_apps)
                      poly_pairs :: [(Id, Expr Id)]
    poly_pairs = [ Id -> [Id] -> Expr Id -> (Id, Expr Id)
    mk_poly2 Id
    poly_id [Id]
    tvs_here Expr Id
    rhs'
                                   | (Id
    poly_id, Expr Id
    rhs) <- [Id]
    poly_ids forall a b. [a] -> [b] -> [(a, b)]
    `zip` [Expr Id]
    rhss
                                   , let rhs' :: Expr Id
    rhs' = HasDebugCallStack => Subst -> Expr Id -> Expr Id
    GHC.Core.Subst.substExpr Subst
    subst' Expr Id
    rhs ]
                ; forall (m :: * -> *) a. Monad m => a -> m a
    return (Subst
    subst', forall b. [(b, Expr b)] -> Bind b
    Rec [(Id, Expr Id)]
    poly_pairs) }
           where
             ([Id]
    ids,[Expr Id]
    rhss) = forall a b. [(a, b)] -> ([a], [b])
    unzip [(Id, Expr Id)]
    prs
                    -- For a recursive group, it's a bit of a pain to work out the minimal
                    -- set of tyvars over which to abstract:
                    --      /\ a b c.  let x = ...a... in
                    --                 letrec { p = ...x...q...
                    --                          q = .....p...b... } in
                    --                 ...
                    -- Since 'x' is abstracted over 'a', the {p,q} group must be abstracted
                    -- over 'a' (because x is replaced by (poly_x a)) as well as 'b'.
                    -- Since it's a pain, we just use the whole set, which is always safe
                    --
                    -- If you ever want to be more selective, remember this bizarre case too:
                    --      x::a = x
                    -- Here, we must abstract 'x' over 'a'.
             tvs_here :: [Id]
    tvs_here = [Id] -> [Id]
    scopedSort [Id]
    main_tvs

        mk_poly1 :: [TyVar] -> Id -> SimplM (Id, CoreExpr)
        mk_poly1 :: [Id] -> Id -> SimplM (Id, Expr Id)
    mk_poly1 [Id]
    tvs_here Id
    var
          = do { Unique
    uniq <- forall (m :: * -> *). MonadUnique m => m Unique
    getUniqueM
               ; let  poly_name :: Name
    poly_name = Name -> Unique -> Name
    setNameUnique (Id -> Name
    idName Id
    var) Unique
    uniq      -- Keep same name
                      poly_ty :: OutType
    poly_ty   = [Id] -> OutType -> OutType
    mkInfForAllTys [Id]
    tvs_here (Id -> OutType
    idType Id
    var) -- But new type of course
                      poly_id :: Id
    poly_id   = Id -> [Id] -> Id -> Id
    transferPolyIdInfo Id
    var [Id]
    tvs_here forall a b. (a -> b) -> a -> b
    $ -- Note [transferPolyIdInfo] in GHC.Types.Id
                                  HasDebugCallStack => Name -> OutType -> OutType -> Id
    mkLocalId Name
    poly_name (Id -> OutType
    idMult Id
    var) OutType
    poly_ty
               ; forall (m :: * -> *) a. Monad m => a -> m a
    return (Id
    poly_id, forall b. Expr b -> [OutType] -> Expr b
    mkTyApps (forall b. Id -> Expr b
    Var Id
    poly_id) ([Id] -> [OutType]
    mkTyVarTys [Id]
    tvs_here)) }
                    -- In the olden days, it was crucial to copy the occInfo of the original var,
                    -- because we were looking at occurrence-analysed but as yet unsimplified code!
                    -- In particular, we mustn't lose the loop breakers.  BUT NOW we are looking
                    -- at already simplified code, so it doesn't matter
                    --
                    -- It's even right to retain single-occurrence or dead-var info:
                    -- Suppose we started with  /\a -> let x = E in B
                    -- where x occurs once in B. Then we transform to:
                    --      let x' = /\a -> E in /\a -> let x* = x' a in B
                    -- where x* has an INLINE prag on it.  Now, once x* is inlined,
                    -- the occurrences of x' will be just the occurrences originally
                    -- pinned on x.

        mk_poly2 :: Id -> [TyVar] -> CoreExpr -> (Id, CoreExpr)
        mk_poly2 :: Id -> [Id] -> Expr Id -> (Id, Expr Id)
    mk_poly2 Id
    poly_id [Id]
    tvs_here Expr Id
    rhs
          = (Id
    poly_id Id -> Unfolding -> Id
    `setIdUnfolding` Unfolding
    unf, Expr Id
    poly_rhs)
          where
            poly_rhs :: Expr Id
    poly_rhs = forall b. [b] -> Expr b -> Expr b
    mkLams [Id]
    tvs_here Expr Id
    rhs
            unf :: Unfolding
    unf = UnfoldingOpts
    -> UnfoldingSource -> Bool -> Bool -> Expr Id -> Unfolding
    mkUnfolding UnfoldingOpts
    uf_opts UnfoldingSource
    InlineRhs Bool
    is_top_lvl Bool
    False Expr Id
    poly_rhs

            -- We want the unfolding.  Consider
            --      let
            --            x = /\a. let y = ... in Just y
            --      in body
            -- Then we float the y-binding out (via abstractFloats and addPolyBind)
            -- but 'x' may well then be inlined in 'body' in which case we'd like the
            -- opportunity to inline 'y' too.

    {-
    Note [Abstract over coercions]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    If a coercion variable (g :: a ~ Int) is free in the RHS, then so is the
    type variable a.  Rather than sort this mess out, we simply bale out and abstract
    wrt all the type variables if any of them are coercion variables.

    Historical note: if you use let-bindings instead of a substitution, beware of this:

                    -- Suppose we start with:
                    --
                    --      x = /\ a -> let g = G in E
                    --
                    -- Then we'll float to get
                    --
                    --      x = let poly_g = /\ a -> G
                    --          in /\ a -> let g = poly_g a in E
                    --
                    -- But now the occurrence analyser will see just one occurrence
                    -- of poly_g, not inside a lambda, so the simplifier will
                    -- PreInlineUnconditionally poly_g back into g!  Badk to square 1!
                    -- (I used to think that the "don't inline lone occurrences" stuff
                    --  would stop this happening, but since it's the *only* occurrence,
                    --  PreInlineUnconditionally kicks in first!)
                    --
                    -- Solution: put an INLINE note on g's RHS, so that poly_g seems
                    --           to appear many times.  (NB: mkInlineMe eliminates
                    --           such notes on trivial RHSs, so do it manually.)

    ************************************************************************
    *                                                                      *
                    prepareAlts
    *                                                                      *
    ************************************************************************

    prepareAlts tries these things:

    1.  filterAlts: eliminate alternatives that cannot match, including
        the DEFAULT alternative.  Here "cannot match" includes knowledge
        from GADTs

    2.  refineDefaultAlt: if the DEFAULT alternative can match only one
        possible constructor, then make that constructor explicit.
        e.g.
            case e of x { DEFAULT -> rhs }
         ===>
            case e of x { (a,b) -> rhs }
        where the type is a single constructor type.  This gives better code
        when rhs also scrutinises x or e.
        See CoreUtils Note [Refine DEFAULT case alternatives]

    3. combineIdenticalAlts: combine identical alternatives into a DEFAULT.
       See CoreUtils Note [Combine identical alternatives], which also
       says why we do this on InAlts not on OutAlts

    4. Returns a list of the constructors that cannot holds in the
       DEFAULT alternative (if there is one)

    It's a good idea to do this stuff before simplifying the alternatives, to
    avoid simplifying alternatives we know can't happen, and to come up with
    the list of constructors that are handled, to put into the IdInfo of the
    case binder, for use when simplifying the alternatives.

    Eliminating the default alternative in (1) isn't so obvious, but it can
    happen:

    data Colour = Red | Green | Blue

    f x = case x of
            Red -> ..
            Green -> ..
            DEFAULT -> h x

    h y = case y of
            Blue -> ..
            DEFAULT -> [ case y of ... ]

    If we inline h into f, the default case of the inlined h can't happen.
    If we don't notice this, we may end up filtering out *all* the cases
    of the inner case y, which give us nowhere to go!
    -}

    prepareAlts :: OutExpr -> OutId -> [InAlt] -> SimplM ([AltCon], [InAlt])
    -- The returned alternatives can be empty, none are possible
    prepareAlts :: Expr Id -> Id -> [InAlt] -> SimplM ([AltCon], [InAlt])
    prepareAlts Expr Id
    scrut Id
    case_bndr' [InAlt]
    alts
      | Just (TyCon
    tc, [OutType]
    tys) <- HasDebugCallStack => OutType -> Maybe (TyCon, [OutType])
    splitTyConApp_maybe (Id -> OutType
    varType Id
    case_bndr')
               -- Case binder is needed just for its type. Note that as an
               --   OutId, it has maximum information; this is important.
               --   Test simpl013 is an example
      = do { [Unique]
    us <- forall (m :: * -> *). MonadUnique m => m [Unique]
    getUniquesM
           ; let ([AltCon]
    idcs1, [InAlt]
    alts1)       = forall b.
    TyCon -> [OutType] -> [AltCon] -> [Alt b] -> ([AltCon], [Alt b])
    filterAlts TyCon
    tc [OutType]
    tys [AltCon]
    imposs_cons [InAlt]
    alts
                 (Bool
    yes2,  [InAlt]
    alts2)       = [Unique]
    -> OutType
    -> TyCon
    -> [OutType]
    -> [AltCon]
    -> [InAlt]
    -> (Bool, [InAlt])
    refineDefaultAlt [Unique]
    us (Id -> OutType
    idMult Id
    case_bndr') TyCon
    tc [OutType]
    tys [AltCon]
    idcs1 [InAlt]
    alts1
                   -- the multiplicity on case_bndr's is the multiplicity of the
                   -- case expression The newly introduced patterns in
                   -- refineDefaultAlt must be scaled by this multiplicity
                 (Bool
    yes3, [AltCon]
    idcs3, [InAlt]
    alts3) = [AltCon] -> [InAlt] -> (Bool, [AltCon], [InAlt])
    combineIdenticalAlts [AltCon]
    idcs1 [InAlt]
    alts2
                 -- "idcs" stands for "impossible default data constructors"
                 -- i.e. the constructors that can't match the default case
           ; forall (f :: * -> *). Applicative f => Bool -> f () -> f ()
    when Bool
    yes2 forall a b. (a -> b) -> a -> b
    $ Tick -> SimplM ()
    tick (Id -> Tick
    FillInCaseDefault Id
    case_bndr')
           ; forall (f :: * -> *). Applicative f => Bool -> f () -> f ()
    when Bool
    yes3 forall a b. (a -> b) -> a -> b
    $ Tick -> SimplM ()
    tick (Id -> Tick
    AltMerge Id
    case_bndr')
           ; forall (m :: * -> *) a. Monad m => a -> m a
    return ([AltCon]
    idcs3, [InAlt]
    alts3) }

      | Bool
    otherwise  -- Not a data type, so nothing interesting happens
      = forall (m :: * -> *) a. Monad m => a -> m a
    return ([], [InAlt]
    alts)
      where
        imposs_cons :: [AltCon]
    imposs_cons = case Expr Id
    scrut of
                        Var Id
    v -> Unfolding -> [AltCon]
    otherCons (Id -> Unfolding
    idUnfolding Id
    v)
                        Expr Id
    _     -> []

    {-
    ************************************************************************
    *                                                                      *
                    mkCase
    *                                                                      *
    ************************************************************************

    mkCase tries these things

    * Note [Nerge nested cases]
    * Note [Eliminate identity case]
    * Note [Scrutinee constant folding]

    Note [Merge Nested Cases]
    ~~~~~~~~~~~~~~~~~~~~~~~~~
           case e of b {             ==>   case e of b {
             p1 -> rhs1                      p1 -> rhs1
             ...                             ...
             pm -> rhsm                      pm -> rhsm
             _  -> case b of b' {            pn -> let b'=b in rhsn
                         pn -> rhsn          ...
                         ...                 po -> let b'=b in rhso
                         po -> rhso          _  -> let b'=b in rhsd
                         _  -> rhsd
           }

    which merges two cases in one case when -- the default alternative of
    the outer case scrutises the same variable as the outer case. This
    transformation is called Case Merging.  It avoids that the same
    variable is scrutinised multiple times.

    Note [Eliminate Identity Case]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
            case e of               ===> e
                    True  -> True;
                    False -> False

    and similar friends.

    Note [Scrutinee Constant Folding]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
         case x op# k# of _ {  ===> case x of _ {
            a1# -> e1                  (a1# inv_op# k#) -> e1
            a2# -> e2                  (a2# inv_op# k#) -> e2
            ...                        ...
            DEFAULT -> ed              DEFAULT -> ed

         where (x op# k#) inv_op# k# == x

    And similarly for commuted arguments and for some unary operations.

    The purpose of this transformation is not only to avoid an arithmetic
    operation at runtime but to allow other transformations to apply in cascade.

    Example with the "Merge Nested Cases" optimization (from #12877):

          main = case t of t0
             0##     -> ...
             DEFAULT -> case t0 `minusWord#` 1## of t1
                0##     -> ...
                DEFAULT -> case t1 `minusWord#` 1## of t2
                   0##     -> ...
                   DEFAULT -> case t2 `minusWord#` 1## of _
                      0##     -> ...
                      DEFAULT -> ...

      becomes:

          main = case t of _
          0##     -> ...
          1##     -> ...
          2##     -> ...
          3##     -> ...
          DEFAULT -> ...

    There are some wrinkles

    * Do not apply caseRules if there is just a single DEFAULT alternative
         case e +# 3# of b { DEFAULT -> rhs }
      If we applied the transformation here we would (stupidly) get
         case a of b' { DEFAULT -> let b = e +# 3# in rhs }
      and now the process may repeat, because that let will really
      be a case.

    * The type of the scrutinee might change.  E.g.
            case tagToEnum (x :: Int#) of (b::Bool)
              False -> e1
              True -> e2
      ==>
            case x of (b'::Int#)
              DEFAULT -> e1
              1#      -> e2

    * The case binder may be used in the right hand sides, so we need
      to make a local binding for it, if it is alive.  e.g.
             case e +# 10# of b
               DEFAULT -> blah...b...
               44#     -> blah2...b...
      ===>
             case e of b'
               DEFAULT -> let b = b' +# 10# in blah...b...
               34#     -> let b = 44# in blah2...b...

      Note that in the non-DEFAULT cases we know what to bind 'b' to,
      whereas in the DEFAULT case we must reconstruct the original value.
      But NB: we use b'; we do not duplicate 'e'.

    * In dataToTag we might need to make up some fake binders;
      see Note [caseRules for dataToTag] in GHC.Core.Opt.ConstantFold
    -}

    mkCase, mkCase1, mkCase2, mkCase3
       :: DynFlags
       -> OutExpr -> OutId
       -> OutType -> [OutAlt]               -- Alternatives in standard (increasing) order
       -> SimplM OutExpr

    --------------------------------------------------
    --      1. Merge Nested Cases
    --------------------------------------------------

    mkCase :: DynFlags -> Expr Id -> Id -> OutType -> [InAlt] -> SimplM (Expr Id)
    mkCase DynFlags
    dflags Expr Id
    scrut Id
    outer_bndr OutType
    alts_ty (Alt AltCon
    DEFAULT [Id]
    _ Expr Id
    deflt_rhs : [InAlt]
    outer_alts)
      | GeneralFlag -> DynFlags -> Bool
    gopt GeneralFlag
    Opt_CaseMerge DynFlags
    dflags
      , ([CoreTickish]
    ticks, Case (Var Id
    inner_scrut_var) Id
    inner_bndr OutType
    _ [InAlt]
    inner_alts)
           <- forall b.
    (CoreTickish -> Bool) -> Expr b -> ([CoreTickish], Expr b)
    stripTicksTop forall (pass :: TickishPass). GenTickish pass -> Bool
    tickishFloatable Expr Id
    deflt_rhs
      , Id
    inner_scrut_var forall a. Eq a => a -> a -> Bool
    == Id
    outer_bndr
      = do  { Tick -> SimplM ()
    tick (Id -> Tick
    CaseMerge Id
    outer_bndr)

            ; let wrap_alt :: InAlt -> InAlt
    wrap_alt (Alt AltCon
    con [Id]
    args Expr Id
    rhs) = ASSERT( outer_bndr `notElem` args )
                                                (forall b. AltCon -> [b] -> Expr b -> Alt b
    Alt AltCon
    con [Id]
    args (Expr Id -> Expr Id
    wrap_rhs Expr Id
    rhs))
                    -- Simplifier's no-shadowing invariant should ensure
                    -- that outer_bndr is not shadowed by the inner patterns
                  wrap_rhs :: Expr Id -> Expr Id
    wrap_rhs Expr Id
    rhs = forall b. Bind b -> Expr b -> Expr b
    Let (forall b. b -> Expr b -> Bind b
    NonRec Id
    inner_bndr (forall b. Id -> Expr b
    Var Id
    outer_bndr)) Expr Id
    rhs
                    -- The let is OK even for unboxed binders,

                  wrapped_alts :: [InAlt]
    wrapped_alts | Id -> Bool
    isDeadBinder Id
    inner_bndr = [InAlt]
    inner_alts
                               | Bool
    otherwise               = forall a b. (a -> b) -> [a] -> [b]
    map InAlt -> InAlt
    wrap_alt [InAlt]
    inner_alts

                  merged_alts :: [InAlt]
    merged_alts = forall a. [Alt a] -> [Alt a] -> [Alt a]
    mergeAlts [InAlt]
    outer_alts [InAlt]
    wrapped_alts
                    -- NB: mergeAlts gives priority to the left
                    --      case x of
                    --        A -> e1
                    --        DEFAULT -> case x of
                    --                      A -> e2
                    --                      B -> e3
                    -- When we merge, we must ensure that e1 takes
                    -- precedence over e2 as the value for A!

            ; forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
    fmap ([CoreTickish] -> Expr Id -> Expr Id
    mkTicks [CoreTickish]
    ticks) forall a b. (a -> b) -> a -> b
    $
              DynFlags -> Expr Id -> Id -> OutType -> [InAlt] -> SimplM (Expr Id)
    mkCase1 DynFlags
    dflags Expr Id
    scrut Id
    outer_bndr OutType
    alts_ty [InAlt]
    merged_alts
            }
            -- Warning: don't call mkCase recursively!
            -- Firstly, there's no point, because inner alts have already had
            -- mkCase applied to them, so they won't have a case in their default
            -- Secondly, if you do, you get an infinite loop, because the bindCaseBndr
            -- in munge_rhs may put a case into the DEFAULT branch!

    mkCase DynFlags
    dflags Expr Id
    scrut Id
    bndr OutType
    alts_ty [InAlt]
    alts = DynFlags -> Expr Id -> Id -> OutType -> [InAlt] -> SimplM (Expr Id)
    mkCase1 DynFlags
    dflags Expr Id
    scrut Id
    bndr OutType
    alts_ty [InAlt]
    alts

    --------------------------------------------------
    --      2. Eliminate Identity Case
    --------------------------------------------------

    mkCase1 :: DynFlags -> Expr Id -> Id -> OutType -> [InAlt] -> SimplM (Expr Id)
    mkCase1 DynFlags
    _dflags Expr Id
    scrut Id
    case_bndr OutType
    _ alts :: [InAlt]
    alts@(Alt AltCon
    _ [Id]
    _ Expr Id
    rhs1 : [InAlt]
    _)      -- Identity case
      | forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
    all InAlt -> Bool
    identity_alt [InAlt]
    alts
      = do { Tick -> SimplM ()
    tick (Id -> Tick
    CaseIdentity Id
    case_bndr)
           ; forall (m :: * -> *) a. Monad m => a -> m a
    return ([CoreTickish] -> Expr Id -> Expr Id
    mkTicks [CoreTickish]
    ticks forall a b. (a -> b) -> a -> b
    $ forall {b} {b}. Expr b -> Expr b -> Expr b
    re_cast Expr Id
    scrut Expr Id
    rhs1) }
      where
        ticks :: [CoreTickish]
    ticks = forall (t :: * -> *) a b. Foldable t => (a -> [b]) -> t a -> [b]
    concatMap (\(Alt AltCon
    _ [Id]
    _ Expr Id
    rhs) -> forall b. (CoreTickish -> Bool) -> Expr b -> [CoreTickish]
    stripTicksT forall (pass :: TickishPass). GenTickish pass -> Bool
    tickishFloatable Expr Id
    rhs) (forall a. [a] -> [a]
    tail [InAlt]
    alts)
        identity_alt :: InAlt -> Bool
    identity_alt (Alt AltCon
    con [Id]
    args Expr Id
    rhs) = Expr Id -> AltCon -> [Id] -> Bool
    check_eq Expr Id
    rhs AltCon
    con [Id]
    args

        check_eq :: Expr Id -> AltCon -> [Id] -> Bool
    check_eq (Cast Expr Id
    rhs OutCoercion
    co) AltCon
    con [Id]
    args        -- See Note [RHS casts]
          = Bool -> Bool
    not (forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
    any (Id -> TyCoVarSet -> Bool
    `elemVarSet` OutCoercion -> TyCoVarSet
    tyCoVarsOfCo OutCoercion
    co) [Id]
    args) Bool -> Bool -> Bool
    && Expr Id -> AltCon -> [Id] -> Bool
    check_eq Expr Id
    rhs AltCon
    con [Id]
    args
        check_eq (Tick CoreTickish
    t Expr Id
    e) AltCon
    alt [Id]
    args
          = forall (pass :: TickishPass). GenTickish pass -> Bool
    tickishFloatable CoreTickish
    t Bool -> Bool -> Bool
    && Expr Id -> AltCon -> [Id] -> Bool
    check_eq Expr Id
    e AltCon
    alt [Id]
    args

        check_eq (Lit Literal
    lit) (LitAlt Literal
    lit') [Id]
    _     = Literal
    lit forall a. Eq a => a -> a -> Bool
    == Literal
    lit'
        check_eq (Var Id
    v) AltCon
    _ [Id]
    _  | Id
    v forall a. Eq a => a -> a -> Bool
    == Id
    case_bndr = Bool
    True
        check_eq (Var Id
    v)   (DataAlt DataCon
    con) [Id]
    args
          | forall (t :: * -> *) a. Foldable t => t a -> Bool
    null [OutType]
    arg_tys, forall (t :: * -> *) a. Foldable t => t a -> Bool
    null [Id]
    args            = Id
    v forall a. Eq a => a -> a -> Bool
    == DataCon -> Id
    dataConWorkId DataCon
    con
                                                 -- Optimisation only
        check_eq Expr Id
    rhs        (DataAlt DataCon
    con) [Id]
    args = forall b. (CoreTickish -> Bool) -> Expr b -> Expr b -> Bool
    cheapEqExpr' forall (pass :: TickishPass). GenTickish pass -> Bool
    tickishFloatable Expr Id
    rhs forall a b. (a -> b) -> a -> b
    $
                                                 forall b. DataCon -> [OutType] -> [Id] -> Expr b
    mkConApp2 DataCon
    con [OutType]
    arg_tys [Id]
    args
        check_eq Expr Id
    _          AltCon
    _             [Id]
    _    = Bool
    False

        arg_tys :: [OutType]
    arg_tys = OutType -> [OutType]
    tyConAppArgs (Id -> OutType
    idType Id
    case_bndr)

            -- Note [RHS casts]
            -- ~~~~~~~~~~~~~~~~
            -- We've seen this:
            --      case e of x { _ -> x `cast` c }
            -- And we definitely want to eliminate this case, to give
            --      e `cast` c
            -- So we throw away the cast from the RHS, and reconstruct
            -- it at the other end.  All the RHS casts must be the same
            -- if (all identity_alt alts) holds.
            --
            -- Don't worry about nested casts, because the simplifier combines them

        re_cast :: Expr b -> Expr b -> Expr b
    re_cast Expr b
    scrut (Cast Expr b
    rhs OutCoercion
    co) = forall b. Expr b -> OutCoercion -> Expr b
    Cast (Expr b -> Expr b -> Expr b
    re_cast Expr b
    scrut Expr b
    rhs) OutCoercion
    co
        re_cast Expr b
    scrut Expr b
    _             = Expr b
    scrut

    mkCase1 DynFlags
    dflags Expr Id
    scrut Id
    bndr OutType
    alts_ty [InAlt]
    alts = DynFlags -> Expr Id -> Id -> OutType -> [InAlt] -> SimplM (Expr Id)
    mkCase2 DynFlags
    dflags Expr Id
    scrut Id
    bndr OutType
    alts_ty [InAlt]
    alts

    --------------------------------------------------
    --      2. Scrutinee Constant Folding
    --------------------------------------------------

    mkCase2 :: DynFlags -> Expr Id -> Id -> OutType -> [InAlt] -> SimplM (Expr Id)
    mkCase2 DynFlags
    dflags Expr Id
    scrut Id
    bndr OutType
    alts_ty [InAlt]
    alts
      | -- See Note [Scrutinee Constant Folding]
        case [InAlt]
    alts of  -- Not if there is just a DEFAULT alternative
          [Alt AltCon
    DEFAULT [Id]
    _ Expr Id
    _] -> Bool
    False
          [InAlt]
    _                 -> Bool
    True
      , GeneralFlag -> DynFlags -> Bool
    gopt GeneralFlag
    Opt_CaseFolding DynFlags
    dflags
      , Just (Expr Id
    scrut', AltCon -> Maybe AltCon
    tx_con, Id -> Expr Id
    mk_orig) <- Platform
    -> Expr Id
    -> Maybe (Expr Id, AltCon -> Maybe AltCon, Id -> Expr Id)
    caseRules (DynFlags -> Platform
    targetPlatform DynFlags
    dflags) Expr Id
    scrut
      = do { Id
    bndr' <- FastString -> OutType -> OutType -> SimplM Id
    newId (String -> FastString
    fsLit String
    "lwild") OutType
    Many (Expr Id -> OutType
    exprType Expr Id
    scrut')

           ; [InAlt]
    alts' <- forall (m :: * -> *) a b.
    Applicative m =>
    (a -> m (Maybe b)) -> [a] -> m [b]
    mapMaybeM ((AltCon -> Maybe AltCon)
    -> (Id -> Expr Id) -> Id -> InAlt -> SimplM (Maybe InAlt)
    tx_alt AltCon -> Maybe AltCon
    tx_con Id -> Expr Id
    mk_orig Id
    bndr') [InAlt]
    alts
                      -- mapMaybeM: discard unreachable alternatives
                      -- See Note [Unreachable caseRules alternatives]
                      -- in GHC.Core.Opt.ConstantFold

           ; DynFlags -> Expr Id -> Id -> OutType -> [InAlt] -> SimplM (Expr Id)
    mkCase3 DynFlags
    dflags Expr Id
    scrut' Id
    bndr' OutType
    alts_ty forall a b. (a -> b) -> a -> b
    $
             [InAlt] -> [InAlt]
    add_default ([InAlt] -> [InAlt]
    re_sort [InAlt]
    alts')
           }

      | Bool
    otherwise
      = DynFlags -> Expr Id -> Id -> OutType -> [InAlt] -> SimplM (Expr Id)
    mkCase3 DynFlags
    dflags Expr Id
    scrut Id
    bndr OutType
    alts_ty [InAlt]
    alts
      where
        -- We need to keep the correct association between the scrutinee and its
        -- binder if the latter isn't dead. Hence we wrap rhs of alternatives with
        -- "let bndr = ... in":
        --
        --     case v + 10 of y        =====> case v of y
        --        20      -> e1                 10      -> let y = 20     in e1
        --        DEFAULT -> e2                 DEFAULT -> let y = v + 10 in e2
        --
        -- Other transformations give: =====> case v of y'
        --                                      10      -> let y = 20      in e1
        --                                      DEFAULT -> let y = y' + 10 in e2
        --
        -- This wrapping is done in tx_alt; we use mk_orig, returned by caseRules,
        -- to construct an expression equivalent to the original one, for use
        -- in the DEFAULT case

        tx_alt :: (AltCon -> Maybe AltCon) -> (Id -> CoreExpr) -> Id
               -> CoreAlt -> SimplM (Maybe CoreAlt)
        tx_alt :: (AltCon -> Maybe AltCon)
    -> (Id -> Expr Id) -> Id -> InAlt -> SimplM (Maybe InAlt)
    tx_alt AltCon -> Maybe AltCon
    tx_con Id -> Expr Id
    mk_orig Id
    new_bndr (Alt AltCon
    con [Id]
    bs Expr Id
    rhs)
          = case AltCon -> Maybe AltCon
    tx_con AltCon
    con of
              Maybe AltCon
    Nothing   -> forall (m :: * -> *) a. Monad m => a -> m a
    return forall a. Maybe a
    Nothing
              Just AltCon
    con' -> do { [Id]
    bs' <- forall {m :: * -> *}. MonadUnique m => Id -> AltCon -> m [Id]
    mk_new_bndrs Id
    new_bndr AltCon
    con'
                              ; forall (m :: * -> *) a. Monad m => a -> m a
    return (forall a. a -> Maybe a
    Just (forall b. AltCon -> [b] -> Expr b -> Alt b
    Alt AltCon
    con' [Id]
    bs' Expr Id
    rhs')) }
          where
            rhs' :: Expr Id
    rhs' | Id -> Bool
    isDeadBinder Id
    bndr = Expr Id
    rhs
                 | Bool
    otherwise         = Id -> Expr Id -> Expr Id -> Expr Id
    bindNonRec Id
    bndr Expr Id
    orig_val Expr Id
    rhs

            orig_val :: Expr Id
    orig_val = case AltCon
    con of
                          AltCon
    DEFAULT    -> Id -> Expr Id
    mk_orig Id
    new_bndr
                          LitAlt Literal
    l   -> forall b. Literal -> Expr b
    Lit Literal
    l
                          DataAlt DataCon
    dc -> forall b. DataCon -> [OutType] -> [Id] -> Expr b
    mkConApp2 DataCon
    dc (OutType -> [OutType]
    tyConAppArgs (Id -> OutType
    idType Id
    bndr)) [Id]
    bs

        mk_new_bndrs :: Id -> AltCon -> m [Id]
    mk_new_bndrs Id
    new_bndr (DataAlt DataCon
    dc)
          | Bool -> Bool
    not (DataCon -> Bool
    isNullaryRepDataCon DataCon
    dc)
          = -- For non-nullary data cons we must invent some fake binders
            -- See Note [caseRules for dataToTag] in GHC.Core.Opt.ConstantFold
            do { [Unique]
    us <- forall (m :: * -> *). MonadUnique m => m [Unique]
    getUniquesM
               ; let ([Id]
    ex_tvs, [Id]
    arg_ids) = [Unique] -> OutType -> DataCon -> [OutType] -> ([Id], [Id])
    dataConRepInstPat [Unique]
    us (Id -> OutType
    idMult Id
    new_bndr) DataCon
    dc
                                            (OutType -> [OutType]
    tyConAppArgs (Id -> OutType
    idType Id
    new_bndr))
               ; forall (m :: * -> *) a. Monad m => a -> m a
    return ([Id]
    ex_tvs forall a. [a] -> [a] -> [a]
    ++ [Id]
    arg_ids) }
        mk_new_bndrs Id
    _ AltCon
    _ = forall (m :: * -> *) a. Monad m => a -> m a
    return []

        re_sort :: [CoreAlt] -> [CoreAlt]
        -- Sort the alternatives to re-establish
        -- GHC.Core Note [Case expression invariants]
        re_sort :: [InAlt] -> [InAlt]
    re_sort [InAlt]
    alts = forall a. (a -> a -> Ordering) -> [a] -> [a]
    sortBy forall a. Alt a -> Alt a -> Ordering
    cmpAlt [InAlt]
    alts

        add_default :: [CoreAlt] -> [CoreAlt]
        -- See Note [Literal cases]
        add_default :: [InAlt] -> [InAlt]
    add_default (Alt (LitAlt {}) [Id]
    bs Expr Id
    rhs : [InAlt]
    alts) = forall b. AltCon -> [b] -> Expr b -> Alt b
    Alt AltCon
    DEFAULT [Id]
    bs Expr Id
    rhs forall a. a -> [a] -> [a]
    : [InAlt]
    alts
        add_default [InAlt]
    alts                            = [InAlt]
    alts

    {- Note [Literal cases]
    ~~~~~~~~~~~~~~~~~~~~~~~
    If we have
      case tagToEnum (a ># b) of
         False -> e1
         True  -> e2

    then caseRules for TagToEnum will turn it into
      case tagToEnum (a ># b) of
         0# -> e1
         1# -> e2

    Since the case is exhaustive (all cases are) we can convert it to
      case tagToEnum (a ># b) of
         DEFAULT -> e1
         1#      -> e2

    This may generate sligthtly better code (although it should not, since
    all cases are exhaustive) and/or optimise better.  I'm not certain that
    it's necessary, but currently we do make this change.  We do it here,
    NOT in the TagToEnum rules (see "Beware" in Note [caseRules for tagToEnum]
    in GHC.Core.Opt.ConstantFold)
    -}

    --------------------------------------------------
    --      Catch-all
    --------------------------------------------------
    mkCase3 :: DynFlags -> Expr Id -> Id -> OutType -> [InAlt] -> SimplM (Expr Id)
    mkCase3 DynFlags
    _dflags Expr Id
    scrut Id
    bndr OutType
    alts_ty [InAlt]
    alts
      = forall (m :: * -> *) a. Monad m => a -> m a
    return (forall b. Expr b -> b -> OutType -> [Alt b] -> Expr b
    Case Expr Id
    scrut Id
    bndr OutType
    alts_ty [InAlt]
    alts)

    -- See Note [Exitification] and Note [Do not inline exit join points] in
    -- GHC.Core.Opt.Exitify
    -- This lives here (and not in Id) because occurrence info is only valid on
    -- InIds, so it's crucial that isExitJoinId is only called on freshly
    -- occ-analysed code. It's not a generic function you can call anywhere.
    isExitJoinId :: Var -> Bool
    isExitJoinId :: Id -> Bool
    isExitJoinId Id
    id
      = Id -> Bool
    isJoinId Id
    id
      Bool -> Bool -> Bool
    && OccInfo -> Bool
    isOneOcc (Id -> OccInfo
    idOccInfo Id
    id)
      Bool -> Bool -> Bool
    && OccInfo -> InsideLam
    occ_in_lam (Id -> OccInfo
    idOccInfo Id
    id) forall a. Eq a => a -> a -> Bool
    == InsideLam
    IsInsideLam

    {-
    Note [Dead binders]
    ~~~~~~~~~~~~~~~~~~~~
    Note that dead-ness is maintained by the simplifier, so that it is
    accurate after simplification as well as before.

    Note [Cascading case merge]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Case merging should cascade in one sweep, because it
    happens bottom-up

          case e of a {
            DEFAULT -> case a of b
                          DEFAULT -> case b of c {
                                         DEFAULT -> e
                                         A -> ea
                          B -> eb
            C -> ec
    ==>
          case e of a {
            DEFAULT -> case a of b
                          DEFAULT -> let c = b in e
                          A -> let c = b in ea
                          B -> eb
            C -> ec
    ==>
          case e of a {
            DEFAULT -> let b = a in let c = b in e
            A -> let b = a in let c = b in ea
            B -> let b = a in eb
            C -> ec

    However here's a tricky case that we still don't catch, and I don't
    see how to catch it in one pass:

      case x of c1 { I# a1 ->
      case a1 of c2 ->
        0 -> ...
        DEFAULT -> case x of c3 { I# a2 ->
                   case a2 of ...

    After occurrence analysis (and its binder-swap) we get this

      case x of c1 { I# a1 ->
      let x = c1 in         -- Binder-swap addition
      case a1 of c2 ->
        0 -> ...
        DEFAULT -> case x of c3 { I# a2 ->
                   case a2 of ...

    When we simplify the inner case x, we'll see that
    x=c1=I# a1.  So we'll bind a2 to a1, and get

      case x of c1 { I# a1 ->
      case a1 of c2 ->
        0 -> ...
        DEFAULT -> case a1 of ...

    This is correct, but we can't do a case merge in this sweep
    because c2 /= a1.  Reason: the binding c1=I# a1 went inwards
    without getting changed to c1=I# c2.

    I don't think this is worth fixing, even if I knew how. It'll
    all come out in the next pass anyway.
    -}