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

    The simplifier utilities
    -}

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

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

            -- The BindContext type
            BindContext(..), bindContextLevel,

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

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

            abstractFloats,

            -- Utilities
            isExitJoinId
        ) where

    import GHC.Prelude hiding (head, init, last, tail)
    import qualified GHC.Prelude as Partial (head)

    import GHC.Core
    import GHC.Types.Literal ( isLitRubbish )
    import GHC.Core.Opt.Simplify.Env
    import GHC.Core.Opt.Simplify.Inline( smallEnoughToInline )
    import GHC.Core.Opt.Stats ( Tick(..) )
    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.Rules( RuleEnv, getRules )
    import GHC.Core.Opt.Arity
    import GHC.Core.Unfold
    import GHC.Core.Unfold.Make
    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.Core.Opt.ConstantFold

    import GHC.Types.Name
    import GHC.Types.Id
    import GHC.Types.Id.Info
    import GHC.Types.Tickish
    import GHC.Types.Demand
    import GHC.Types.Var.Set
    import GHC.Types.Basic

    import GHC.Data.OrdList ( isNilOL )
    import GHC.Data.FastString ( fsLit )

    import GHC.Utils.Misc
    import GHC.Utils.Monad
    import GHC.Utils.Outputable
    import GHC.Utils.Panic

    import Control.Monad    ( when )
    import Data.List        ( sortBy )
    import GHC.Types.Name.Env
    import Data.Graph

    {- *********************************************************************
    *                                                                      *
                    The BindContext type
    *                                                                      *
    ********************************************************************* -}

    -- What sort of binding is this? A let-binding or a join-binding?
    data BindContext
      = BC_Let                 -- A regular let-binding
          TopLevelFlag RecFlag

      | BC_Join                -- A join point with continuation k
          RecFlag              -- See Note [Rules and unfolding for join points]
          SimplCont            -- in GHC.Core.Opt.Simplify

    bindContextLevel :: BindContext -> TopLevelFlag
    bindContextLevel :: BindContext -> TopLevelFlag
    bindContextLevel (BC_Let TopLevelFlag
    top_lvl RecFlag
    _) = TopLevelFlag
    top_lvl
    bindContextLevel (BC_Join {})       = TopLevelFlag
    NotTopLevel

    bindContextRec :: BindContext -> RecFlag
    bindContextRec :: BindContext -> RecFlag
    bindContextRec (BC_Let TopLevelFlag
    _ RecFlag
    rec_flag)  = RecFlag
    rec_flag
    bindContextRec (BC_Join RecFlag
    rec_flag SimplCont
    _) = RecFlag
    rec_flag

    isJoinBC :: BindContext -> Bool
    isJoinBC :: BindContext -> Bool
    isJoinBC (BC_Let {})  = Bool
    False
    isJoinBC (BC_Join {}) = Bool
    True

    {- *********************************************************************
    *                                                                      *
                    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 syntactic 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)
            SubDemand       -- ^ The evaluation context of e. Tells how e is evaluated.
                            -- This fuels eta-expansion or eta-reduction without looking
                            -- at lambda bodies, for example.
                            --
                            -- See Note [Eta reduction based on evaluation context]
                            -- The evaluation context for other SimplConts can be
                            -- reconstructed with 'contEvalContext'

      | CastIt              -- (CastIt co K)[e] = K[ e `cast` co ]
          { SimplCont -> OutCoercion
    sc_co   :: OutCoercion  -- The coercion simplified
                                    -- Invariant: never an identity coercion
          , SimplCont -> Bool
    sc_opt  :: Bool         -- True <=> sc_co has had optCoercion applied to it
                                    --      See Note [Avoid re-simplifying coercions]
                                    --      in GHC.Core.Opt.Simplify.Iteration
          , SimplCont -> SimplCont
    sc_cont :: 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]
          , SimplCont -> OutExpr
    sc_arg  :: InExpr       -- The argument,
          , SimplCont -> StaticEnv
    sc_env  :: StaticEnv    -- see Note [StaticEnv invariant]
          , 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]
          , 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 b K)[e] = let x = e in K[b]
                            --       or, equivalently,  = K[ (\x.b) e ]
          { sc_dup   :: DupFlag        -- See Note [DupFlag invariants]
          , SimplCont -> FromWhat
    sc_from  :: FromWhat
          , sc_bndr  :: InId
          , SimplCont -> OutExpr
    sc_body  :: InExpr
          , sc_env   :: StaticEnv      -- Static env for both sc_bndr (stable unfolding thereof)
                                       -- and sc_body.  Also 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 FromWhat = FromLet | FromBeta Levity

    -- See Note [DupFlag invariants]
    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        = HasDebugCallStack => StaticEnv -> OutType -> OutType
    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 { se_dup = dup, se_env = env, se_cont = k}
       and  Select { se_dup = dup, se_env = env, se_cont = 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,
                   or at least is always ignored; the payload is
                   already an OutThing
    -}

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

    instance Outputable SimplCont where
      ppr :: SimplCont -> SDoc
    ppr (Stop OutType
    ty CallCtxt
    interesting SubDemand
    eval_sd)
        = String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "Stop" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc
    brackets ([SDoc] -> SDoc
    forall doc. IsLine doc => [doc] -> doc
    sep ([SDoc] -> SDoc) -> [SDoc] -> SDoc
    forall a b. (a -> b) -> a -> b
    $ SDoc -> [SDoc] -> [SDoc]
    forall doc. IsLine doc => doc -> [doc] -> [doc]
    punctuate SDoc
    forall doc. IsLine doc => doc
    comma [SDoc]
    pps) SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> OutType -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr OutType
    ty
        where
          pps :: [SDoc]
    pps = [CallCtxt -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr CallCtxt
    interesting] [SDoc] -> [SDoc] -> [SDoc]
    forall a. [a] -> [a] -> [a]
    ++ [SubDemand -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr SubDemand
    eval_sd | SubDemand
    eval_sd SubDemand -> SubDemand -> Bool
    forall a. Eq a => a -> a -> Bool
    /= SubDemand
    topSubDmd]
      ppr (CastIt { sc_co :: SimplCont -> OutCoercion
    sc_co = OutCoercion
    co, sc_cont :: SimplCont -> SimplCont
    sc_cont = SimplCont
    cont })
        = (String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "CastIt" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> OutCoercion -> SDoc
    pprOptCo OutCoercion
    co) SDoc -> SDoc -> SDoc
    forall doc. IsDoc doc => doc -> doc -> doc
    $$ SimplCont -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr SimplCont
    cont
      ppr (TickIt CoreTickish
    t SimplCont
    cont)
        = (String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "TickIt" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> CoreTickish -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr CoreTickish
    t) SDoc -> SDoc -> SDoc
    forall doc. IsDoc doc => doc -> doc -> doc
    $$ SimplCont -> 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
    forall doc. IsLine doc => String -> doc
    text String
    "ApplyToTy" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> OutType -> SDoc
    pprParendType OutType
    ty) SDoc -> SDoc -> SDoc
    forall doc. IsDoc doc => doc -> doc -> doc
    $$ SimplCont -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr SimplCont
    cont
      ppr (ApplyToVal { sc_arg :: SimplCont -> OutExpr
    sc_arg = OutExpr
    arg, sc_dup :: SimplCont -> DupFlag
    sc_dup = DupFlag
    dup, sc_cont :: SimplCont -> SimplCont
    sc_cont = SimplCont
    cont, sc_hole_ty :: SimplCont -> OutType
    sc_hole_ty = OutType
    hole_ty })
        = (SDoc -> BranchCount -> SDoc -> SDoc
    hang (String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "ApplyToVal" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> DupFlag -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr DupFlag
    dup SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "hole" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> OutType -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr OutType
    hole_ty)
              BranchCount
    2 (OutExpr -> SDoc
    forall b. OutputableBndr b => Expr b -> SDoc
    pprParendExpr OutExpr
    arg))
          SDoc -> SDoc -> SDoc
    forall doc. IsDoc doc => doc -> doc -> doc
    $$ SimplCont -> 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
    forall doc. IsLine doc => String -> doc
    text String
    "StrictBind" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> Id -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Id
    b) SDoc -> SDoc -> SDoc
    forall doc. IsDoc doc => doc -> doc -> doc
    $$ SimplCont -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr SimplCont
    cont
      ppr (StrictArg { sc_fun :: SimplCont -> ArgInfo
    sc_fun = ArgInfo
    ai, sc_cont :: SimplCont -> SimplCont
    sc_cont = SimplCont
    cont })
        = (String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "StrictArg" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> Id -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr (ArgInfo -> Id
    ai_fun ArgInfo
    ai)) SDoc -> SDoc -> SDoc
    forall doc. IsDoc doc => doc -> doc -> doc
    $$ SimplCont -> 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_cont :: SimplCont -> SimplCont
    sc_cont = SimplCont
    cont })
        = (String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "Select" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> DupFlag -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr DupFlag
    dup SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> Id -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Id
    bndr) SDoc -> SDoc -> SDoc
    forall doc. IsDoc doc => doc -> doc -> doc
    $$
          SDoc -> SDoc
    forall doc. IsOutput doc => doc -> doc
    whenPprDebug (BranchCount -> SDoc -> SDoc
    nest BranchCount
    2 (SDoc -> SDoc) -> SDoc -> SDoc
    forall a b. (a -> b) -> a -> b
    $ [InAlt] -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr [InAlt]
    alts) SDoc -> SDoc -> SDoc
    forall doc. IsDoc doc => doc -> doc -> doc
    $$ SimplCont -> 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 -> RewriteCall
    ai_rewrite :: RewriteCall,  -- What transformation to try next for this call
                 -- See Note [Rewrite rules and inlining] in GHC.Core.Opt.Simplify.Iteration

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

    data RewriteCall  -- What rewriting to try next for this call
                      -- See Note [Rewrite rules and inlining] in GHC.Core.Opt.Simplify.Iteration
      = TryRules FullArgCount [CoreRule]
      | TryInlining
      | TryNothing

    data ArgSpec
      = ValArg { ArgSpec -> Demand
    as_dmd  :: Demand        -- Demand placed on this argument
               , ArgSpec -> OutExpr
    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
                                          -- Coercion is optimised

    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
    forall doc. IsLine doc => String -> doc
    text String
    "ArgInfo" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc
    braces
             ([SDoc] -> SDoc
    forall doc. IsLine doc => [doc] -> doc
    sep [ String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "fun =" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> Id -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Id
    fun
                  , String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "dmds(first 10) =" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> [Demand] -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr (BranchCount -> [Demand] -> [Demand]
    forall a. BranchCount -> [a] -> [a]
    take BranchCount
    10 [Demand]
    dmds)
                  , String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "args =" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> [ArgSpec] -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr [ArgSpec]
    args ])

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

    addValArgTo :: ArgInfo ->  OutExpr -> OutType -> ArgInfo
    addValArgTo :: ArgInfo -> OutExpr -> OutType -> ArgInfo
    addValArgTo ArgInfo
    ai OutExpr
    arg OutType
    hole_ty
      | ArgInfo { ai_dmds :: ArgInfo -> [Demand]
    ai_dmds = Demand
    dmd:[Demand]
    dmds, ai_discs :: ArgInfo -> [BranchCount]
    ai_discs = BranchCount
    _:[BranchCount]
    discs, ai_rewrite :: ArgInfo -> RewriteCall
    ai_rewrite = RewriteCall
    rew } <- ArgInfo
    ai
          -- Pop the top demand and and discounts off
      , let arg_spec :: ArgSpec
    arg_spec = ValArg { as_arg :: OutExpr
    as_arg = OutExpr
    arg, as_hole_ty :: OutType
    as_hole_ty = OutType
    hole_ty, as_dmd :: Demand
    as_dmd = Demand
    dmd }
      = ArgInfo
    ai { ai_args    = arg_spec : ai_args ai
           , ai_dmds    = dmds
           , ai_discs   = discs
           , ai_rewrite = decArgCount rew }
      | Bool
    otherwise
      = String -> SDoc -> ArgInfo
    forall a. HasCallStack => String -> SDoc -> a
    pprPanic String
    "addValArgTo" (ArgInfo -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr ArgInfo
    ai SDoc -> SDoc -> SDoc
    forall doc. IsDoc doc => doc -> doc -> doc
    $$ OutExpr -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr OutExpr
    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    = arg_spec : ai_args ai
                                      , ai_rewrite = decArgCount (ai_rewrite 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 = CastBy co : ai_args 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] -> [OutExpr]
    argInfoAppArgs []                              = []
    argInfoAppArgs (CastBy {}                : [ArgSpec]
    _)  = []  -- Stop at a cast
    argInfoAppArgs (ValArg { as_arg :: ArgSpec -> OutExpr
    as_arg = OutExpr
    arg }  : [ArgSpec]
    as) = OutExpr
    arg     OutExpr -> [OutExpr] -> [OutExpr]
    forall a. a -> [a] -> [a]
    : [ArgSpec] -> [OutExpr]
    argInfoAppArgs [ArgSpec]
    as
    argInfoAppArgs (TyArg { as_arg_ty :: ArgSpec -> OutType
    as_arg_ty = OutType
    ty } : [ArgSpec]
    as) = OutType -> OutExpr
    forall b. OutType -> Expr b
    Type OutType
    ty OutExpr -> [OutExpr] -> [OutExpr]
    forall a. a -> [a] -> [a]
    : [ArgSpec] -> [OutExpr]
    argInfoAppArgs [ArgSpec]
    as

    pushSimplifiedArgs, pushSimplifiedRevArgs
      :: SimplEnv
      -> [ArgSpec]   -- In normal, forward order for pushSimplifiedArgs,
                     -- in /reverse/ order for pushSimplifiedRevArgs
      -> SimplCont -> SimplCont
    pushSimplifiedArgs :: StaticEnv -> [ArgSpec] -> SimplCont -> SimplCont
    pushSimplifiedArgs    StaticEnv
    env [ArgSpec]
    args SimplCont
    cont = (ArgSpec -> SimplCont -> SimplCont)
    -> SimplCont -> [ArgSpec] -> SimplCont
    forall a b. (a -> b -> b) -> b -> [a] -> b
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr  (StaticEnv -> ArgSpec -> SimplCont -> SimplCont
    pushSimplifiedArg StaticEnv
    env)             SimplCont
    cont [ArgSpec]
    args
    pushSimplifiedRevArgs :: StaticEnv -> [ArgSpec] -> SimplCont -> SimplCont
    pushSimplifiedRevArgs StaticEnv
    env [ArgSpec]
    args SimplCont
    cont = (SimplCont -> ArgSpec -> SimplCont)
    -> SimplCont -> [ArgSpec] -> SimplCont
    forall b a. (b -> a -> b) -> b -> [a] -> b
    forall (t :: * -> *) b a.
    Foldable t =>
    (b -> a -> b) -> b -> t a -> b
    foldl' (\SimplCont
    k ArgSpec
    a -> StaticEnv -> ArgSpec -> SimplCont -> SimplCont
    pushSimplifiedArg StaticEnv
    env ArgSpec
    a SimplCont
    k) SimplCont
    cont [ArgSpec]
    args

    pushSimplifiedArg :: SimplEnv -> ArgSpec -> SimplCont -> SimplCont
    pushSimplifiedArg :: StaticEnv -> ArgSpec -> SimplCont -> SimplCont
    pushSimplifiedArg StaticEnv
    _env (TyArg { as_arg_ty :: ArgSpec -> OutType
    as_arg_ty = OutType
    arg_ty, as_hole_ty :: ArgSpec -> OutType
    as_hole_ty = OutType
    hole_ty }) SimplCont
    cont
      = 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
    cont }
    pushSimplifiedArg StaticEnv
    env (ValArg { as_arg :: ArgSpec -> OutExpr
    as_arg = OutExpr
    arg, as_hole_ty :: ArgSpec -> OutType
    as_hole_ty = OutType
    hole_ty }) SimplCont
    cont
      = ApplyToVal { sc_arg :: OutExpr
    sc_arg = OutExpr
    arg, sc_env :: StaticEnv
    sc_env = StaticEnv
    env, sc_dup :: DupFlag
    sc_dup = DupFlag
    Simplified
                     -- The SubstEnv will be ignored since sc_dup=Simplified
                   , sc_hole_ty :: OutType
    sc_hole_ty = OutType
    hole_ty, sc_cont :: SimplCont
    sc_cont = SimplCont
    cont }
    pushSimplifiedArg StaticEnv
    _ (CastBy OutCoercion
    c) SimplCont
    cont
      = CastIt { sc_co :: OutCoercion
    sc_co = OutCoercion
    c, sc_cont :: SimplCont
    sc_cont = SimplCont
    cont, sc_opt :: Bool
    sc_opt = Bool
    True }

    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] -> OutExpr
    argInfoExpr Id
    fun [ArgSpec]
    rev_args
      = [ArgSpec] -> OutExpr
    go [ArgSpec]
    rev_args
      where
        go :: [ArgSpec] -> OutExpr
    go []                              = Id -> OutExpr
    forall b. Id -> Expr b
    Var Id
    fun
        go (ValArg { as_arg :: ArgSpec -> OutExpr
    as_arg = OutExpr
    arg }  : [ArgSpec]
    as) = [ArgSpec] -> OutExpr
    go [ArgSpec]
    as OutExpr -> OutExpr -> OutExpr
    forall b. Expr b -> Expr b -> Expr b
    `App` OutExpr
    arg
        go (TyArg { as_arg_ty :: ArgSpec -> OutType
    as_arg_ty = OutType
    ty } : [ArgSpec]
    as) = [ArgSpec] -> OutExpr
    go [ArgSpec]
    as OutExpr -> OutExpr -> OutExpr
    forall b. Expr b -> Expr b -> Expr b
    `App` OutType -> OutExpr
    forall b. OutType -> Expr b
    Type OutType
    ty
        go (CastBy OutCoercion
    co                : [ArgSpec]
    as) = HasDebugCallStack => OutExpr -> OutCoercion -> OutExpr
    OutExpr -> OutCoercion -> OutExpr
    mkCast ([ArgSpec] -> OutExpr
    go [ArgSpec]
    as) OutCoercion
    co

    decArgCount :: RewriteCall -> RewriteCall
    decArgCount :: RewriteCall -> RewriteCall
    decArgCount (TryRules BranchCount
    n [CoreRule]
    rules) = BranchCount -> [CoreRule] -> RewriteCall
    TryRules (BranchCount
    nBranchCount -> BranchCount -> BranchCount
    forall a. Num a => a -> a -> a
    -BranchCount
    1) [CoreRule]
    rules
    decArgCount RewriteCall
    rew                = RewriteCall
    rew

    mkRewriteCall :: Id -> RuleEnv -> RewriteCall
    -- See Note [Rewrite rules and inlining] in GHC.Core.Opt.Simplify.Iteration
    -- We try to skip any unnecessary stages:
    --    No rules     => skip TryRules
    --    No unfolding => skip TryInlining
    -- This skipping is "just" for efficiency.  But rebuildCall is
    -- quite a heavy hammer, so skipping stages is a good plan.
    -- And it's extremely simple to do.
    mkRewriteCall :: Id -> RuleEnv -> RewriteCall
    mkRewriteCall Id
    fun RuleEnv
    rule_env
      | Bool -> Bool
    not ([CoreRule] -> Bool
    forall a. [a] -> Bool
    forall (t :: * -> *) a. Foldable t => t a -> Bool
    null [CoreRule]
    rules) = BranchCount -> [CoreRule] -> RewriteCall
    TryRules BranchCount
    n_required [CoreRule]
    rules
      | Unfolding -> Bool
    canUnfold Unfolding
    unf    = RewriteCall
    TryInlining
      | Bool
    otherwise        = RewriteCall
    TryNothing
      where
        n_required :: BranchCount
    n_required = [BranchCount] -> BranchCount
    forall a. Ord a => [a] -> a
    forall (t :: * -> *) a. (Foldable t, Ord a) => t a -> a
    maximum ((CoreRule -> BranchCount) -> [CoreRule] -> [BranchCount]
    forall a b. (a -> b) -> [a] -> [b]
    map CoreRule -> BranchCount
    ruleArity [CoreRule]
    rules)
        rules :: [CoreRule]
    rules = RuleEnv -> Id -> [CoreRule]
    getRules RuleEnv
    rule_env Id
    fun
        unf :: Unfolding
    unf   = IdUnfoldingFun
    idUnfolding Id
    fun

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

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

    mkRhsStop :: OutType -> RecFlag -> Demand -> SimplCont
    -- See Note [RHS of lets] in GHC.Core.Unfold
    mkRhsStop :: OutType -> RecFlag -> Demand -> SimplCont
    mkRhsStop OutType
    ty RecFlag
    is_rec Demand
    bndr_dmd = OutType -> CallCtxt -> SubDemand -> SimplCont
    Stop OutType
    ty (RecFlag -> CallCtxt
    RhsCtxt RecFlag
    is_rec) (Demand -> SubDemand
    subDemandIfEvaluated Demand
    bndr_dmd)

    mkLazyArgStop :: OutType -> ArgInfo -> SimplCont
    mkLazyArgStop :: OutType -> ArgInfo -> SimplCont
    mkLazyArgStop OutType
    ty ArgInfo
    fun_info = OutType -> CallCtxt -> SubDemand -> SimplCont
    Stop OutType
    ty (ArgInfo -> CallCtxt
    lazyArgContext ArgInfo
    fun_info) SubDemand
    arg_sd
      where
        arg_sd :: SubDemand
    arg_sd = Demand -> SubDemand
    subDemandIfEvaluated ([Demand] -> Demand
    forall a. HasCallStack => [a] -> a
    Partial.head (ArgInfo -> [Demand]
    ai_dmds ArgInfo
    fun_info))

    -------------------
    contIsRhs :: SimplCont -> Maybe RecFlag
    contIsRhs :: SimplCont -> Maybe RecFlag
    contIsRhs (Stop OutType
    _ (RhsCtxt RecFlag
    is_rec) SubDemand
    _) = RecFlag -> Maybe RecFlag
    forall a. a -> Maybe a
    Just RecFlag
    is_rec
    contIsRhs (CastIt { sc_cont :: SimplCont -> SimplCont
    sc_cont = SimplCont
    k })    = SimplCont -> Maybe RecFlag
    contIsRhs SimplCont
    k   -- For f = e |> co, treat e as Rhs context
    contIsRhs SimplCont
    _                           = Maybe RecFlag
    forall a. Maybe a
    Nothing

    -------------------
    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 { sc_cont :: SimplCont -> SimplCont
    sc_cont = 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
    -- This one doesn't look right.  A value application is not trivial
    -- contIsTrivial (ApplyToVal { sc_arg = Coercion _, sc_cont = k }) = contIsTrivial k
    contIsTrivial (CastIt { sc_cont :: SimplCont -> SimplCont
    sc_cont = SimplCont
    k })                          = SimplCont -> Bool
    contIsTrivial SimplCont
    k
    contIsTrivial SimplCont
    _                                                 = Bool
    False

    -------------------
    contResultType :: SimplCont -> OutType
    contResultType :: SimplCont -> OutType
    contResultType (Stop OutType
    ty CallCtxt
    _ SubDemand
    _)                = OutType
    ty
    contResultType (CastIt { sc_cont :: SimplCont -> SimplCont
    sc_cont = 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
    _ SubDemand
    _)                    = OutType
    ty
    contHoleType (TickIt CoreTickish
    _ SimplCont
    k)                     = SimplCont -> OutType
    contHoleType SimplCont
    k
    contHoleType (CastIt { sc_co :: SimplCont -> OutCoercion
    sc_co = OutCoercion
    co })          = HasDebugCallStack => OutCoercion -> OutType
    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 })  = HasDebugCallStack => OutType -> OutType
    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]
    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
    _ SubDemand
    _) = OutType
    OneTy
    contHoleScaling (CastIt { sc_cont :: SimplCont -> SimplCont
    sc_cont = 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; skipping over casts.
    countArgs :: SimplCont -> BranchCount
    countArgs (ApplyToTy  { sc_cont :: SimplCont -> SimplCont
    sc_cont = SimplCont
    cont }) = BranchCount
    1 BranchCount -> BranchCount -> BranchCount
    forall a. Num a => a -> a -> a
    + SimplCont -> BranchCount
    countArgs SimplCont
    cont
    countArgs (ApplyToVal { sc_cont :: SimplCont -> SimplCont
    sc_cont = SimplCont
    cont }) = BranchCount
    1 BranchCount -> BranchCount -> BranchCount
    forall a. Num a => a -> a -> a
    + SimplCont -> BranchCount
    countArgs SimplCont
    cont
    countArgs (CastIt     { sc_cont :: SimplCont -> SimplCont
    sc_cont = SimplCont
    cont }) = SimplCont -> BranchCount
    countArgs SimplCont
    cont
    countArgs SimplCont
    _                               = BranchCount
    0

    countValArgs :: SimplCont -> Int
    -- Count value arguments only
    countValArgs :: SimplCont -> BranchCount
    countValArgs (ApplyToTy  { sc_cont :: SimplCont -> SimplCont
    sc_cont = SimplCont
    cont }) = SimplCont -> BranchCount
    countValArgs SimplCont
    cont
    countValArgs (ApplyToVal { sc_cont :: SimplCont -> SimplCont
    sc_cont = SimplCont
    cont }) = BranchCount
    1 BranchCount -> BranchCount -> BranchCount
    forall a. Num a => a -> a -> a
    + SimplCont -> BranchCount
    countValArgs SimplCont
    cont
    countValArgs (CastIt     { sc_cont :: SimplCont -> SimplCont
    sc_cont = SimplCont
    cont }) = SimplCont -> BranchCount
    countValArgs SimplCont
    cont
    countValArgs SimplCont
    _                               = BranchCount
    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 -> OutExpr
    sc_arg = OutExpr
    arg, sc_env :: SimplCont -> StaticEnv
    sc_env = StaticEnv
    se, sc_cont :: SimplCont -> SimplCont
    sc_cont = SimplCont
    k })
                                            = [ArgSummary] -> SimplCont -> (Bool, [ArgSummary], SimplCont)
    go (OutExpr -> StaticEnv -> ArgSummary
    is_interesting OutExpr
    arg StaticEnv
    se ArgSummary -> [ArgSummary] -> [ArgSummary]
    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 { sc_cont :: SimplCont -> SimplCont
    sc_cont = SimplCont
    k })    = [ArgSummary] -> SimplCont -> (Bool, [ArgSummary], SimplCont)
    go [ArgSummary]
    args SimplCont
    k
        go [ArgSummary]
    args SimplCont
    k                           = (Bool
    False, [ArgSummary] -> [ArgSummary]
    forall a. [a] -> [a]
    reverse [ArgSummary]
    args, SimplCont
    k)

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

    -- | Describes how the 'SimplCont' will evaluate the hole as a 'SubDemand'.
    -- This can be more insightful than the limited syntactic context that
    -- 'SimplCont' provides, because the 'Stop' constructor might carry a useful
    -- 'SubDemand'.
    -- For example, when simplifying the argument `e` in `f e` and `f` has the
    -- demand signature `<MP(S,A)>`, this function will give you back `P(S,A)` when
    -- simplifying `e`.
    --
    -- PRECONDITION: Don't call with 'ApplyToVal'. We haven't thoroughly thought
    -- about what to do then and no call sites so far seem to care.
    contEvalContext :: SimplCont -> SubDemand
    contEvalContext :: SimplCont -> SubDemand
    contEvalContext SimplCont
    k = case SimplCont
    k of
      Stop OutType
    _ CallCtxt
    _ SubDemand
    sd              -> SubDemand
    sd
      TickIt CoreTickish
    _ SimplCont
    k               -> SimplCont -> SubDemand
    contEvalContext SimplCont
    k
      CastIt   { sc_cont :: SimplCont -> SimplCont
    sc_cont = SimplCont
    k } -> SimplCont -> SubDemand
    contEvalContext SimplCont
    k
      ApplyToTy{ sc_cont :: SimplCont -> SimplCont
    sc_cont = SimplCont
    k } -> SimplCont -> SubDemand
    contEvalContext SimplCont
    k
        --  ApplyToVal{sc_cont=k}      -> mkCalledOnceDmd $ contEvalContext k
        -- Not 100% sure that's correct, . Here's an example:
        --   f (e x) and f :: <SC(S,C(1,L))>
        -- then what is the evaluation context of 'e' when we simplify it? E.g.,
        --   simpl e (ApplyToVal x $ Stop "C(S,C(1,L))")
        -- then it *should* be "C(1,C(S,C(1,L))", so perhaps correct after all.
        -- But for now we just panic:
      ApplyToVal{}               -> String -> SDoc -> SubDemand
    forall a. HasCallStack => String -> SDoc -> a
    pprPanic String
    "contEvalContext" (SimplCont -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr SimplCont
    k)
      StrictArg{sc_fun :: SimplCont -> ArgInfo
    sc_fun=ArgInfo
    fun_info} -> Demand -> SubDemand
    subDemandIfEvaluated ([Demand] -> Demand
    forall a. HasCallStack => [a] -> a
    Partial.head (ArgInfo -> [Demand]
    ai_dmds ArgInfo
    fun_info))
      StrictBind{sc_bndr :: SimplCont -> Id
    sc_bndr=Id
    bndr}   -> Demand -> SubDemand
    subDemandIfEvaluated (Id -> Demand
    idDemandInfo Id
    bndr)
      Select{}                   -> SubDemand
    topSubDmd
        -- Perhaps reconstruct the demand on the scrutinee by looking at field
        -- and case binder dmds, see addCaseBndrDmd. No priority right now.

    -------------------
    mkArgInfo :: SimplEnv -> RuleEnv -> Id -> SimplCont -> ArgInfo

    mkArgInfo :: StaticEnv -> RuleEnv -> Id -> SimplCont -> ArgInfo
    mkArgInfo StaticEnv
    env RuleEnv
    rule_base Id
    fun SimplCont
    cont
      | BranchCount
    n_val_args BranchCount -> BranchCount -> Bool
    forall a. Ord a => a -> a -> Bool
    < Id -> BranchCount
    idArity Id
    fun            -- Note [Unsaturated functions]
      = ArgInfo { ai_fun :: Id
    ai_fun = Id
    fun, ai_args :: [ArgSpec]
    ai_args = []
                , ai_rewrite :: RewriteCall
    ai_rewrite = RewriteCall
    fun_rewrite
                , ai_encl :: Bool
    ai_encl = Bool
    False
                , ai_dmds :: [Demand]
    ai_dmds = [Demand]
    vanilla_dmds
                , ai_discs :: [BranchCount]
    ai_discs = [BranchCount]
    vanilla_discounts }
      | Bool
    otherwise
      = ArgInfo { ai_fun :: Id
    ai_fun   = Id
    fun
                , ai_args :: [ArgSpec]
    ai_args  = []
                , ai_rewrite :: RewriteCall
    ai_rewrite = RewriteCall
    fun_rewrite
                , ai_encl :: Bool
    ai_encl  = Bool
    fun_has_rules Bool -> Bool -> Bool
    || SimplCont -> Bool
    contHasRules SimplCont
    cont
                , ai_dmds :: [Demand]
    ai_dmds  = OutType -> [Demand] -> [Demand]
    add_type_strictness (Id -> OutType
    idType Id
    fun) [Demand]
    arg_dmds
                , ai_discs :: [BranchCount]
    ai_discs = [BranchCount]
    arg_discounts }
      where
        n_val_args :: BranchCount
    n_val_args    = SimplCont -> BranchCount
    countValArgs SimplCont
    cont
        fun_rewrite :: RewriteCall
    fun_rewrite   = Id -> RuleEnv -> RewriteCall
    mkRewriteCall Id
    fun RuleEnv
    rule_base
        fun_has_rules :: Bool
    fun_has_rules = case RewriteCall
    fun_rewrite of
                          TryRules {} -> Bool
    True
                          RewriteCall
    _           -> Bool
    False

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

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

        arg_dmds :: [Demand]
    arg_dmds
          | Bool -> Bool
    not (StaticEnv -> Bool
    seInline StaticEnv
    env)
          = [Demand]
    vanilla_dmds -- See Note [Do not expose strictness if sm_inline=False]
          | Bool
    otherwise
          = -- add_type_str fun_ty $
            case DmdSig -> ([Demand], Divergence)
    splitDmdSig (Id -> DmdSig
    idDmdSig Id
    fun) of
              ([Demand]
    demands, Divergence
    result_info)
                    | Bool -> Bool
    not ([Demand]
    demands [Demand] -> BranchCount -> Bool
    forall a. [a] -> BranchCount -> Bool
    `lengthExceeds` BranchCount
    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 [Demand] -> [Demand] -> [Demand]
    forall a. [a] -> [a] -> [a]
    ++ [Demand]
    vanilla_dmds
                   | Bool
    otherwise
                   -> Bool -> String -> SDoc -> [Demand] -> [Demand]
    forall a. HasCallStack => Bool -> String -> SDoc -> a -> a
    warnPprTrace Bool
    True String
    "More demands than arity" (Id -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Id
    fun SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> BranchCount -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr (Id -> BranchCount
    idArity Id
    fun)
                                    SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> BranchCount -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr BranchCount
    n_val_args SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> [Demand] -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr [Demand]
    demands) ([Demand] -> [Demand]) -> [Demand] -> [Demand]
    forall a b. (a -> b) -> a -> b
    $
                      [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
          | [Demand] -> Bool
    forall a. [a] -> Bool
    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 (FunTyFlag
    _, OutType
    _, OutType
    arg_ty, OutType
    fun_ty') <- OutType -> Maybe (FunTyFlag, OutType, OutType, OutType)
    splitFunTy_maybe OutType
    fun_ty        -- Add strict-type info
          , Demand
    dmd : [Demand]
    rest_dmds <- [Demand]
    dmds
          , let dmd' :: Demand
    dmd'
                 | OutType -> Bool
    definitelyUnliftedType OutType
    arg_ty
                 = Demand -> Demand
    strictifyDmd Demand
    dmd
                 | Bool
    otherwise
                 -- Something that's not definitely unlifted.
                 -- If the type is representation-polymorphic, we can't know whether
                 -- it's strict.
                 = Demand
    dmd
          = Demand
    dmd' Demand -> [Demand] -> [Demand]
    forall a. a -> [a] -> [a]
    : OutType -> [Demand] -> [Demand]
    add_type_strictness OutType
    fun_ty' [Demand]
    rest_dmds

          | 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 that isn't just a seq, 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.

    Note [Seq is boring]
    ~~~~~~~~~~~~~~~~~~~~
    Suppose
      f x = case v of
              True  -> Just x
              False -> Just (x-1)

    Now consider these variants of
       case (f x) of ...

    1. [Dead case binder]: inline f
          case f x of b{-dead-} { DEFAULT -> blah[no b] }
       Inlining (f x) will allow us to avoid ever allocating (Just x),
       since the case binder `b` is dead.  We will end up with a
         join point for blah, thus
             join j = blah in
             case v of { True -> j; False -> j }
       which will turn into (case v of DEFAULT -> blah)
       All good

    2. [Live case binder, live alt binders]: inline f
           case f x of b { Just y -> blah[y,b] }
       Inlining (f x) will mean we still allocate (Just x),
       but we also get to bind `y` without fetching it out of the Just, thus
             join j y b = blah[y,b]
             case v of { True -> j x (Just x)
                       ; False -> let y = x-1 in j y (Just y) }
       Inlining (f x) has a small benefit, perhaps.
       (To T14955 it makes a surprisingly large difference of ~30% to inline here.)

    3. [Live case binder, dead alt binders]: maybe don't inline f
          case f x of b { DEFAULT -> blah[b] }
       Inlining (f x) will still mean we allocate (Just x). We'd get:
             join j b = blah[b]
             case v of { True -> j (Just x); False -> j (Just (x-1)) }
       No new optimisations are revealed. Nothing is gained.
       (This is the situation in T22317.)

       A variant is when we have a data constructor with dead binders:
           case g x of b { (x{-dead-}, x{-dead-}) -> blah[b, no x, no y] }
       Instead of DEFAULT we have a single constructor alternative
       with all dead binders.  Again, no gain from inlining (f x)

    4. [Live case binder, dead alt binders]: small f
       Suppose f is CPR'd, so it looks like
           f x = case $wf x of (# a #) -> Just a
       Then even in case (3) we want to inline:
          case f x of b { DEFAULT -> blah[b] }
       -->
          case $wf x of (# a #) ->
          let b = Just a in blah[b]
       This is very good; we now know a lot about `b` (instead of nothing)
       and `blah` might benefit.  Similarly if `f` has a join point
          f x = join $j y = Just y in ...
       Again the case (f x) is now consuming a constructor (Just y).

       This is very like the situation described in Note [RHS of lets]
       in GHC.Core.Opt.Simplify.Inline; (case e of b -> blah) is just
       like a strict `let`.

    Conclusion: in interestingCallCtxt, a case-expression (i.e. Select continuation)
    usually gives a CaseCtxt (cases 1,2); but when (cases 3,4):
      * It has a non-dead case-binder
      * It has one alternative
      * All the binders in the alternative are dead
    then the `case` is just a strict let-binding, so use RhsCtxt NonRecursive.
    This RhsCtxt gives a small incentive for small functions to inline.
    That incentive is what is needed in case (4).

    Wrinkle (SB1).  The 'small incentive' is implemented by `calc_some_benefit` in
    GHC.Core.Opt.Simplify.Inline.tryUnfolding.  We restrict the incentive just to
    funtions that have unfolding guidance of `UnfWhen`, which particularly includes
    wrappers created by CPR, exactly case (4) above.  Without this limitation I
    got too much fruitless inlining, which led to regressions (#22317 is an example).

    A good example of a function where this 'small incentive' is important is
    GHC.Num.Integer where we ended up with calls like this:
         case (integerSignum a b) of r -> ...
    but were failing to inline integerSignum, even though it always returns
    a single constructor, so it is very helpful to inline it. There is also an
    issue of confluence-of-the-simplifier.  Suppose we have
        f x = case x of r -> ...
    and the Simplifier sees
        f (integerSigNum a b)
    Because `f` scrutines `x`, the unfolding guidance for f gives a discount
    for `x`; and that discount makes interestingCallContext for the context
    `f <>` return DiscArgCtxt, which again gives that incentive.  We don't want
    the incentive to disappear when we inline `f`!
    -}

    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 -> [BranchCount]
    ai_discs = [BranchCount]
    discs })
      | Bool
    encl_rules                = CallCtxt
    RuleArgCtxt
      | BranchCount
    disc:[BranchCount]
    _ <- [BranchCount]
    discs, BranchCount
    disc BranchCount -> BranchCount -> Bool
    forall a. Ord a => a -> a -> Bool
    > BranchCount
    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 -> [BranchCount]
    ai_discs = [BranchCount]
    discs })
    -- Use this for strict arguments
      | Bool
    encl_rules                = CallCtxt
    RuleArgCtxt
      | BranchCount
    disc:[BranchCount]
    _ <- [BranchCount]
    discs, BranchCount
    disc BranchCount -> BranchCount -> Bool
    forall a. Ord a => a -> a -> Bool
    > BranchCount
    0 = CallCtxt
    DiscArgCtxt  -- Be keener here
      | Bool
    otherwise                 = RecFlag -> CallCtxt
    RhsCtxt RecFlag
    NonRecursive
          -- Why RhsCtxt?  if we see f (g 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'
          --
          -- Why NonRecursive?  Becuase it's a bit like
          --   let a = g x in f a

    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 {sc_alts :: SimplCont -> [InAlt]
    sc_alts=[InAlt]
    alts, sc_bndr :: SimplCont -> Id
    sc_bndr=Id
    case_bndr})
          | Bool -> Bool
    not (StaticEnv -> Bool
    seCaseCase StaticEnv
    env)         = CallCtxt
    BoringCtxt -- See Note [No case of case is boring]
          | [Alt AltCon
    _ [Id]
    bs OutExpr
    _] <- [InAlt]
    alts
          , (Id -> Bool) -> [Id] -> Bool
    forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
    all Id -> Bool
    isDeadBinder [Id]
    bs
          , Bool -> Bool
    not (Id -> Bool
    isDeadBinder Id
    case_bndr) = RecFlag -> CallCtxt
    RhsCtxt RecFlag
    NonRecursive -- See Note [Seq is boring]
          | Bool
    otherwise                    = CallCtxt
    CaseCtxt

        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 SubDemand
    _)               = 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 { sc_cont :: SimplCont -> SimplCont
    sc_cont = 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.

    contHasRules :: 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.  So contHasRules
    -- tries to see if the context of the f-call is a call to a function
    -- with rules.
    --
    -- The ai_encl 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
    contHasRules :: SimplCont -> Bool
    contHasRules SimplCont
    cont
      = SimplCont -> Bool
    go SimplCont
    cont
      where
        go :: SimplCont -> Bool
    go (ApplyToVal { sc_cont :: SimplCont -> SimplCont
    sc_cont = SimplCont
    cont }) = SimplCont -> Bool
    go SimplCont
    cont
        go (ApplyToTy  { sc_cont :: SimplCont -> SimplCont
    sc_cont = SimplCont
    cont }) = SimplCont -> Bool
    go SimplCont
    cont
        go (CastIt { sc_cont :: SimplCont -> SimplCont
    sc_cont = SimplCont
    cont })     = SimplCont -> Bool
    go SimplCont
    cont
        go (StrictArg { sc_fun :: SimplCont -> ArgInfo
    sc_fun = ArgInfo
    fun })    = ArgInfo -> Bool
    ai_encl ArgInfo
    fun
        go (Stop OutType
    _ CallCtxt
    RuleArgCtxt SubDemand
    _)          = Bool
    True
        go (TickIt CoreTickish
    _ SimplCont
    c)                    = SimplCont -> Bool
    go SimplCont
    c
        go (Select {})                     = Bool
    False
        go (StrictBind {})                 = Bool
    False      -- ??
        go (Stop OutType
    _ CallCtxt
    _ SubDemand
    _)                    = Bool
    False

    {- 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 -> OutExpr -> ArgSummary
    interestingArg StaticEnv
    env OutExpr
    e = StaticEnv -> BranchCount -> OutExpr -> ArgSummary
    go StaticEnv
    env BranchCount
    0 OutExpr
    e
      where
        -- n is # value args to which the expression is applied
        go :: StaticEnv -> BranchCount -> OutExpr -> ArgSummary
    go StaticEnv
    env BranchCount
    n (Var Id
    v)
           = case StaticEnv -> Id -> SimplSR
    substId StaticEnv
    env Id
    v of
               DoneId Id
    v'            -> BranchCount -> Id -> ArgSummary
    go_var BranchCount
    n Id
    v'
               DoneEx OutExpr
    e JoinPointHood
    _           -> StaticEnv -> BranchCount -> OutExpr -> ArgSummary
    go (StaticEnv -> StaticEnv
    zapSubstEnv StaticEnv
    env)             BranchCount
    n OutExpr
    e
               ContEx TvSubstEnv
    tvs CvSubstEnv
    cvs SimplIdSubst
    ids OutExpr
    e -> StaticEnv -> BranchCount -> OutExpr -> ArgSummary
    go (StaticEnv -> TvSubstEnv -> CvSubstEnv -> SimplIdSubst -> StaticEnv
    setSubstEnv StaticEnv
    env TvSubstEnv
    tvs CvSubstEnv
    cvs SimplIdSubst
    ids) BranchCount
    n OutExpr
    e

        go StaticEnv
    _   BranchCount
    _ (Lit Literal
    l)
           | Literal -> Bool
    isLitRubbish Literal
    l        = ArgSummary
    TrivArg -- Leads to unproductive inlining in WWRec, #20035
           | Bool
    otherwise             = ArgSummary
    ValueArg
        go StaticEnv
    _   BranchCount
    _ (Type OutType
    _)          = ArgSummary
    TrivArg
        go StaticEnv
    _   BranchCount
    _ (Coercion OutCoercion
    _)      = ArgSummary
    TrivArg
        go StaticEnv
    env BranchCount
    n (App OutExpr
    fn (Type OutType
    _)) = StaticEnv -> BranchCount -> OutExpr -> ArgSummary
    go StaticEnv
    env BranchCount
    n OutExpr
    fn
        go StaticEnv
    env BranchCount
    n (App OutExpr
    fn OutExpr
    _)        = StaticEnv -> BranchCount -> OutExpr -> ArgSummary
    go StaticEnv
    env (BranchCount
    nBranchCount -> BranchCount -> BranchCount
    forall a. Num a => a -> a -> a
    +BranchCount
    1) OutExpr
    fn
        go StaticEnv
    env BranchCount
    n (Tick CoreTickish
    _ OutExpr
    a)        = StaticEnv -> BranchCount -> OutExpr -> ArgSummary
    go StaticEnv
    env BranchCount
    n OutExpr
    a
        go StaticEnv
    env BranchCount
    n (Cast OutExpr
    e OutCoercion
    _)        = StaticEnv -> BranchCount -> OutExpr -> ArgSummary
    go StaticEnv
    env BranchCount
    n OutExpr
    e
        go StaticEnv
    env BranchCount
    n (Lam Id
    v OutExpr
    e)
           | Id -> Bool
    isTyVar Id
    v             = StaticEnv -> BranchCount -> OutExpr -> ArgSummary
    go StaticEnv
    env BranchCount
    n OutExpr
    e
           | BranchCount
    nBranchCount -> BranchCount -> Bool
    forall a. Ord a => a -> a -> Bool
    >BranchCount
    0                   = ArgSummary
    NonTrivArg     -- (\x.b) e   is NonTriv
           | Bool
    otherwise             = ArgSummary
    ValueArg
        go StaticEnv
    _ BranchCount
    _ (Case {})           = ArgSummary
    NonTrivArg
        go StaticEnv
    env BranchCount
    n (Let Bind Id
    b OutExpr
    e)         = case StaticEnv -> BranchCount -> OutExpr -> ArgSummary
    go StaticEnv
    env' BranchCount
    n OutExpr
    e of
                                       ArgSummary
    ValueArg -> ArgSummary
    ValueArg
                                       ArgSummary
    _        -> ArgSummary
    NonTrivArg
                                   where
                                     env' :: StaticEnv
    env' = StaticEnv
    env StaticEnv -> [Id] -> StaticEnv
    `addNewInScopeIds` Bind Id -> [Id]
    forall b. Bind b -> [b]
    bindersOf Bind Id
    b

        go_var :: BranchCount -> Id -> ArgSummary
    go_var BranchCount
    n Id
    v
           | Id -> Bool
    isConLikeId Id
    v = ArgSummary
    ValueArg   -- Experimenting with 'conlike' rather that
                                        --    data constructors here
                                        -- DFuns are con-like; see Note [Conlike is interesting]
           | Id -> BranchCount
    idArity Id
    v BranchCount -> BranchCount -> Bool
    forall a. Ord a => a -> a -> Bool
    > BranchCount
    n = ArgSummary
    ValueArg   -- Catches (eg) primops with arity but no unfolding
           | BranchCount
    n BranchCount -> BranchCount -> Bool
    forall a. Ord a => a -> a -> Bool
    > BranchCount
    0         = ArgSummary
    NonTrivArg -- Saturated or unknown call
           | Bool
    otherwise  -- n==0, no value arguments; look for an interesting unfolding
           = case IdUnfoldingFun
    idUnfolding Id
    v of
               OtherCon [] -> ArgSummary
    NonTrivArg   -- It's evaluated, but that's all we know
               OtherCon [AltCon]
    _  -> ArgSummary
    ValueArg     -- Evaluated and we know it isn't these constructors
                  -- See Note [OtherCon and interestingArg]
               DFunUnfolding {} -> ArgSummary
    ValueArg   -- We konw that idArity=0
               CoreUnfolding{ uf_cache :: Unfolding -> UnfoldingCache
    uf_cache = UnfoldingCache
    cache }
                 | UnfoldingCache -> Bool
    uf_is_conlike UnfoldingCache
    cache -> ArgSummary
    ValueArg    -- Includes constructor applications
                 | UnfoldingCache -> Bool
    uf_is_value UnfoldingCache
    cache   -> ArgSummary
    NonTrivArg  -- Things like partial applications
                 | Bool
    otherwise           -> ArgSummary
    TrivArg
               Unfolding
    BootUnfolding           -> ArgSummary
    TrivArg
               Unfolding
    NoUnfolding             -> ArgSummary
    TrivArg

    {- Note [OtherCon and interestingArg]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    interstingArg returns
       (a) NonTrivArg for an arg with an OtherCon [] unfolding
       (b) ValueArg for an arg with an OtherCon [c1,c2..] unfolding.

    Reason for (a): I found (in the GHC.Num.Integer library) that I was
    inlining a pretty big function when all we knew was that its arguments
    were evaluated, nothing more.  That in turn make the enclosing function
    too big to inline elsewhere.

    Reason for (b): we want to inline integerCompare here
      integerLt# :: Integer -> Integer -> Bool#
      integerLt# (IS x) (IS y)                  = x <# y
      integerLt# x y | LT <- integerCompare x y = 1#
      integerLt# _ _                            = 0#

    ************************************************************************
    *                                                                      *
                      SimplMode
    *                                                                      *
    ************************************************************************
    -}

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

    updModeForRules :: SimplMode -> SimplMode
    -- See Note [Simplifying rules]
    -- See Note [The environments of the Simplify pass]
    updModeForRules :: SimplMode -> SimplMode
    updModeForRules SimplMode
    current_mode
      = SimplMode
    current_mode { sm_phase        = InitialPhase
                     , sm_inline       = False
                          -- See Note [Do not expose strictness if sm_inline=False]
                     , sm_rules        = False
                     , sm_cast_swizzle = False
                          -- See Note [Cast swizzling on rule LHSs]
                     , sm_eta_expand   = 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.

    * sm_inline, sm_rules: 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.

      See also Note [Do not expose strictness if sm_inline=False]

    * sm_eta_expand: the template (LHS) of a rule must only mention coercion
      /variables/ not arbitrary coercions.  See Note [Casts in the template] in
      GHC.Core.Rules.  Eta expansion can create new coercions; so we switch
      it off.

    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 and rules]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    SPJ Jul 22: whether or not eta-expansion is switched on in a stable
    unfolding, or the RHS of a RULE, seems to be a bit moot. But switching
    it on adds clutter, so I'm experimenting with switching off
    eta-expansion in such places.

    In the olden days, we really /wanted/ to switch it off.

        Old note: If we have a stable unfolding
          f :: Ord a => a -> IO ()
          -- Unfolding template
          --    = /\a \(d:Ord a) (x:a). bla
        we do 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 now specialisation of the overloading doesn't work properly
        (see Note [Specialisation shape] in GHC.Core.Opt.Specialise), #9509.
        So we disable eta-expansion in stable unfoldings.

    But this old note is no longer relevant because the specialiser has
    improved: see Note [Account for casts in binding] in
    GHC.Core.Opt.Specialise.  So we seem to have a free choice.

    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.
    -}

    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 -> IdUnfoldingFun -> InScopeEnv
    ISE InScopeSet
    in_scope IdUnfoldingFun
    id_unf
      where
        in_scope :: InScopeSet
    in_scope = StaticEnv -> InScopeSet
    seInScope StaticEnv
    env
        phase :: CompilerPhase
    phase    = StaticEnv -> CompilerPhase
    sePhase StaticEnv
    env
        id_unf :: IdUnfoldingFun
    id_unf   = (Activation -> Bool) -> IdUnfoldingFun
    whenActiveUnfoldingFun (CompilerPhase -> Activation -> Bool
    isActive CompilerPhase
    phase)
         -- When sm_rules was off we used to test for a /stable/ unfolding,
         -- but that seems wrong (#20941)

    ----------------------
    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-can-float invariant
    -- See Note [Core let-can-float 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 -> OutExpr -> StaticEnv -> Maybe StaticEnv
    preInlineUnconditionally StaticEnv
    env TopLevelFlag
    top_lvl Id
    bndr OutExpr
    rhs StaticEnv
    rhs_env
      | Bool -> Bool
    not Bool
    pre_inline_unconditionally           = Maybe StaticEnv
    forall a. Maybe a
    Nothing
      | Bool -> Bool
    not Bool
    active                               = Maybe StaticEnv
    forall a. Maybe a
    Nothing
      | TopLevelFlag -> Bool
    isTopLevel TopLevelFlag
    top_lvl Bool -> Bool -> Bool
    && Id -> Bool
    isDeadEndId Id
    bndr   = Maybe StaticEnv
    forall a. Maybe a
    Nothing -- Note [Top-level bottoming Ids]
      | Id -> Bool
    isCoVar Id
    bndr                             = Maybe StaticEnv
    forall a. Maybe a
    Nothing -- Note [Do not inline CoVars unconditionally]
      | Id -> Bool
    isExitJoinId Id
    bndr                        = Maybe StaticEnv
    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))           = Maybe StaticEnv
    forall a. Maybe a
    Nothing
      | Bool -> Bool
    not (Unfolding -> Bool
    isStableUnfolding Unfolding
    unf)              = StaticEnv -> Maybe StaticEnv
    forall a. a -> Maybe a
    Just (StaticEnv -> Maybe StaticEnv) -> StaticEnv -> Maybe StaticEnv
    forall a b. (a -> b) -> a -> b
    $! (OutExpr -> StaticEnv
    extend_subst_with OutExpr
    rhs)

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

        one_occ :: OccInfo -> Bool
    one_occ OccInfo
    IAmDead = Bool
    True -- Happens in ((\x.1) v)
        one_occ OneOcc{ occ_n_br :: OccInfo -> BranchCount
    occ_n_br   = BranchCount
    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 -> BranchCount
    occ_n_br   = BranchCount
    1
                      , occ_in_lam :: OccInfo -> InsideLam
    occ_in_lam = InsideLam
    IsInsideLam
                      , occ_int_cxt :: OccInfo -> InterestingCxt
    occ_int_cxt = InterestingCxt
    IsInteresting } = OutExpr -> Bool
    canInlineInLam OutExpr
    rhs
        one_occ OccInfo
    _                                     = Bool
    False

        pre_inline_unconditionally :: Bool
    pre_inline_unconditionally = StaticEnv -> Bool
    sePreInline StaticEnv
    env
        active :: Bool
    active = CompilerPhase -> Activation -> Bool
    isActive (StaticEnv -> CompilerPhase
    sePhase StaticEnv
    env) (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 :: OutExpr -> Bool
    canInlineInLam (Lit Literal
    _)    = Bool
    True
        canInlineInLam (Lam Id
    b OutExpr
    e)  = Id -> Bool
    isRuntimeVar Id
    b Bool -> Bool -> Bool
    || OutExpr -> Bool
    canInlineInLam OutExpr
    e
        canInlineInLam (Tick CoreTickish
    t OutExpr
    e) = Bool -> Bool
    not (CoreTickish -> Bool
    forall (pass :: TickishPass). GenTickish pass -> Bool
    tickishIsCode CoreTickish
    t) Bool -> Bool -> Bool
    && OutExpr -> Bool
    canInlineInLam OutExpr
    e
        canInlineInLam OutExpr
    _          = Bool
    False
          -- not ticks.  Counting ticks cannot be duplicated, and non-counting
          -- ticks around a Lam will disappear anyway.

        early_phase :: Bool
    early_phase = StaticEnv -> CompilerPhase
    sePhase StaticEnv
    env CompilerPhase -> CompilerPhase -> Bool
    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.
        --
        -- What exactly to check in `early_phase` above is the subject of #17910.
        --
        -- !10088 introduced an additional Simplifier iteration in LargeRecord
        -- because we first FloatOut `case unsafeEqualityProof of ... -> I# 2#`
        -- (a non-trivial value) which we immediately inline back in.
        -- Ideally, we'd never have inlined it because the binding turns out to
        -- be expandable; unfortunately we need an iteration of the Simplifier to
        -- attach the proper unfolding and can't check isExpandableUnfolding right
        -- here.
        -- (Nor can we check for `exprIsExpandable rhs`, because that needs to look
        -- at the non-existent unfolding for the `I# 2#` which is also floated out.)

    {-
    ************************************************************************
    *                                                                      *
                      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 [Simplifying
    rules] for details.
    -}

    postInlineUnconditionally
        :: SimplEnv -> BindContext
        -> InId -> OutId    -- The binder (*not* a CoVar), including its unfolding
        -> OutExpr
        -> Bool
    -- Precondition: rhs satisfies the let-can-float invariant
    -- See Note [Core let-can-float 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 -> BindContext -> Id -> Id -> OutExpr -> Bool
    postInlineUnconditionally StaticEnv
    env BindContext
    bind_cxt Id
    old_bndr Id
    bndr OutExpr
    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 (BindContext -> TopLevelFlag
    bindContextLevel BindContext
    bind_cxt)
                                    = Bool
    False -- Note [Top level and postInlineUnconditionally]
      | OutExpr -> Bool
    exprIsTrivial OutExpr
    rhs           = Bool
    True
      | BC_Join {} <- BindContext
    bind_cxt      = Bool
    False -- See point (1) of Note [Duplicating join points]
                                            --     in GHC.Core.Opt.Simplify.Iteration
      | 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 -> BranchCount
    occ_n_br = BranchCount
    n_br }
            -- See Note [Inline small things to avoid creating a thunk]

            | BranchCount
    n_br BranchCount -> BranchCount -> Bool
    forall a. Ord a => a -> a -> Bool
    >= BranchCount
    100 -> Bool
    False  -- See #23627

            | BranchCount
    n_br BranchCount -> BranchCount -> Bool
    forall a. Eq a => a -> a -> Bool
    == BranchCount
    1, InsideLam
    NotInsideLam <- InsideLam
    in_lam  -- One syntactic occurrence
            -> Bool
    True                              -- See Note [Post-inline for single-use things]

    --        | is_unlifted                        -- Unlifted binding, hence ok-for-spec
    --        -> True                              -- hence cheap to inline probably just a primop
    --                                             -- Not a big deal either way
    -- No, this is wrong.  {v = p +# q; x = K v}.
    -- Don't inline v; it'll just get floated out again. Stupid.

            | Bool
    is_demanded
            -> Bool
    False                            -- No allocation (it'll be a case expression in the end)
                                                -- so inlining duplicates code but nothing more

            | Bool
    otherwise
            -> InsideLam -> InterestingCxt -> Bool
    work_ok InsideLam
    in_lam InterestingCxt
    int_cxt Bool -> Bool -> Bool
    && UnfoldingOpts -> Unfolding -> Bool
    smallEnoughToInline UnfoldingOpts
    uf_opts Unfolding
    unfolding
                  -- Multiple syntactic occurences; but lazy, and small enough to dup
                  -- ToDo: consider discount on smallEnoughToInline if int_cxt is true

          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

      where
        work_ok :: InsideLam -> InterestingCxt -> Bool
    work_ok InsideLam
    NotInsideLam InterestingCxt
    _              = Bool
    True
        work_ok InsideLam
    IsInsideLam  InterestingCxt
    IsInteresting  = Unfolding -> Bool
    isCheapUnfolding Unfolding
    unfolding
        work_ok InsideLam
    IsInsideLam  InterestingCxt
    NotInteresting = Bool
    False
          -- NotInsideLam: 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'

          -- InsideLam: check for acceptable work duplication, using isCheapUnfoldign
          -- int_cxt to prevent us inlining inside a lambda without some
          -- good reason.  See the notes on int_cxt in preInlineUnconditionally

    --    is_unlifted = isUnliftedType (idType bndr)
        is_demanded :: Bool
    is_demanded = Demand -> Bool
    isStrUsedDmd (Id -> Demand
    idDemandInfo Id
    bndr)
        occ_info :: OccInfo
    occ_info    = Id -> OccInfo
    idOccInfo Id
    old_bndr
        unfolding :: Unfolding
    unfolding   = IdUnfoldingFun
    idUnfolding Id
    bndr
        uf_opts :: UnfoldingOpts
    uf_opts     = StaticEnv -> UnfoldingOpts
    seUnfoldingOpts StaticEnv
    env
        phase :: CompilerPhase
    phase       = StaticEnv -> CompilerPhase
    sePhase 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 [Post-inline for single-use things]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    If we have

       let x = rhs in ...x...

    and `x` is used exactly once, and not inside a lambda, then we will usually
    preInlineUnconditinally. But we can still get this situation in
    postInlineUnconditionally:

      case K rhs of K x -> ...x....

    Here we'll use `simplAuxBind` to bind `x` to (the already-simplified) `rhs`;
    and `x` is used exactly once.  It's beneficial to inline right away; otherwise
    we risk creating

       let x = rhs in ...x...

    which will take another iteration of the Simplifier to eliminate.  We do this in
    two places

    1. In the full `postInlineUnconditionally` look for the special case
       of "one occurrence, not under a lambda", and inline unconditionally then.

       This is a bit risky: see Note [Avoiding simplifying repeatedly] in
       Simplify.Iteration.  But in practice it seems to be a small win.

    2. `simplAuxBind` does a kind of poor-man's `postInlineUnconditionally`.  It
       does not need to account for many of the cases (e.g. top level) that the
       full `postInlineUnconditionally` does.  Moreover, we don't have an
       OutId, which `postInlineUnconditionally` needs.  I got a slight improvement
       in compiler performance when I added this test.

    Here's an example that we don't currently 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!

    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
    *                                                                      *
    ************************************************************************
    -}

    rebuildLam :: SimplEnv
               -> [OutBndr] -> OutExpr
               -> SimplCont
               -> SimplM OutExpr
    -- (rebuildLam env bndrs body cont)
    -- returns expr which means the same as \bndrs. body
    --
    -- But it tries
    --      a) eta reduction, if that gives a trivial expression
    --      b) eta expansion [only if there are some value lambdas]
    --
    -- NB: the SimplEnv already includes the [OutBndr] in its in-scope set

    rebuildLam :: StaticEnv -> [Id] -> OutExpr -> SimplCont -> SimplM OutExpr
    rebuildLam StaticEnv
    _env [] OutExpr
    body SimplCont
    _cont
      = OutExpr -> SimplM OutExpr
    forall a. a -> SimplM a
    forall (m :: * -> *) a. Monad m => a -> m a
    return OutExpr
    body

    rebuildLam StaticEnv
    env bndrs :: [Id]
    bndrs@(Id
    bndr:[Id]
    _) OutExpr
    body SimplCont
    cont
      = {-# SCC "rebuildLam" #-} [Id] -> OutExpr -> SimplM OutExpr
    try_eta [Id]
    bndrs OutExpr
    body
      where
        rec_ids :: UnVarSet
    rec_ids  = StaticEnv -> UnVarSet
    seRecIds StaticEnv
    env
        in_scope :: InScopeSet
    in_scope = StaticEnv -> InScopeSet
    getInScope StaticEnv
    env  -- Includes 'bndrs'
        mb_rhs :: Maybe RecFlag
    mb_rhs   = SimplCont -> Maybe RecFlag
    contIsRhs SimplCont
    cont

        -- See Note [Eta reduction based on evaluation context]
        eval_sd :: SubDemand
    eval_sd = SimplCont -> SubDemand
    contEvalContext SimplCont
    cont
            -- NB: cont is never ApplyToVal, because beta-reduction would
            -- have happened.  So contEvalContext can panic on ApplyToVal.

        try_eta :: [OutBndr] -> OutExpr -> SimplM OutExpr
        try_eta :: [Id] -> OutExpr -> SimplM OutExpr
    try_eta [Id]
    bndrs OutExpr
    body
          | -- Try eta reduction
            StaticEnv -> Bool
    seDoEtaReduction StaticEnv
    env
          , Just OutExpr
    etad_lam <- UnVarSet -> [Id] -> OutExpr -> SubDemand -> Maybe OutExpr
    tryEtaReduce UnVarSet
    rec_ids [Id]
    bndrs OutExpr
    body SubDemand
    eval_sd
          = do { Tick -> SimplM ()
    tick (Id -> Tick
    EtaReduction Id
    bndr)
               ; OutExpr -> SimplM OutExpr
    forall a. a -> SimplM a
    forall (m :: * -> *) a. Monad m => a -> m a
    return OutExpr
    etad_lam }

          | -- Try eta expansion
            Maybe RecFlag
    Nothing <- Maybe RecFlag
    mb_rhs  -- See Note [Eta expanding lambdas]
          , StaticEnv -> Bool
    seEtaExpand StaticEnv
    env
          , (Id -> Bool) -> [Id] -> Bool
    forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
    any Id -> Bool
    isRuntimeVar [Id]
    bndrs  -- Only when there is at least one value lambda already
          , Just SafeArityType
    body_arity <- HasDebugCallStack => ArityOpts -> OutExpr -> Maybe SafeArityType
    ArityOpts -> OutExpr -> Maybe SafeArityType
    exprEtaExpandArity (StaticEnv -> ArityOpts
    seArityOpts StaticEnv
    env) OutExpr
    body
          = do { Tick -> SimplM ()
    tick (Id -> Tick
    EtaExpansion Id
    bndr)
               ; let body' :: OutExpr
    body' = InScopeSet -> SafeArityType -> OutExpr -> OutExpr
    etaExpandAT InScopeSet
    in_scope SafeArityType
    body_arity OutExpr
    body
               ; String -> SDoc -> SimplM ()
    traceSmpl String
    "eta expand" ([SDoc] -> SDoc
    forall doc. IsDoc doc => [doc] -> doc
    vcat [String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "before" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> OutExpr -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr OutExpr
    body
                                              , String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "after" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> OutExpr -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr OutExpr
    body'])
               -- NB: body' might have an outer Cast, but if so
               --     mk_lams will pull it further out, past 'bndrs' to the top
               ; OutExpr -> SimplM OutExpr
    forall a. a -> SimplM a
    forall (m :: * -> *) a. Monad m => a -> m a
    return ([Id] -> OutExpr -> OutExpr
    mk_lams [Id]
    bndrs OutExpr
    body') }

          | Bool
    otherwise
          = OutExpr -> SimplM OutExpr
    forall a. a -> SimplM a
    forall (m :: * -> *) a. Monad m => a -> m a
    return ([Id] -> OutExpr -> OutExpr
    mk_lams [Id]
    bndrs OutExpr
    body)

        mk_lams :: [OutBndr] -> OutExpr -> OutExpr
        -- mk_lams pulls casts and ticks to the top
        mk_lams :: [Id] -> OutExpr -> OutExpr
    mk_lams [Id]
    bndrs body :: OutExpr
    body@(Lam {})
          = [Id] -> OutExpr -> OutExpr
    mk_lams ([Id]
    bndrs [Id] -> [Id] -> [Id]
    forall a. [a] -> [a] -> [a]
    ++ [Id]
    bndrs1) OutExpr
    body1
          where
            ([Id]
    bndrs1, OutExpr
    body1) = OutExpr -> ([Id], OutExpr)
    forall b. Expr b -> ([b], Expr b)
    collectBinders OutExpr
    body

        mk_lams [Id]
    bndrs (Tick CoreTickish
    t OutExpr
    expr)
          | CoreTickish -> Bool
    forall (pass :: TickishPass). GenTickish pass -> Bool
    tickishFloatable CoreTickish
    t
          = CoreTickish -> OutExpr -> OutExpr
    mkTick CoreTickish
    t ([Id] -> OutExpr -> OutExpr
    mk_lams [Id]
    bndrs OutExpr
    expr)

        mk_lams [Id]
    bndrs (Cast OutExpr
    body OutCoercion
    co)
          | -- Note [Casts and lambdas]
            StaticEnv -> Bool
    seCastSwizzle StaticEnv
    env
          , Bool -> Bool
    not ((Id -> Bool) -> [Id] -> Bool
    forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
    any Id -> Bool
    bad [Id]
    bndrs)
          = HasDebugCallStack => OutExpr -> OutCoercion -> OutExpr
    OutExpr -> OutCoercion -> OutExpr
    mkCast ([Id] -> OutExpr -> OutExpr
    mk_lams [Id]
    bndrs OutExpr
    body) (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

        mk_lams [Id]
    bndrs OutExpr
    body
          = [Id] -> OutExpr -> OutExpr
    forall b. [b] -> Expr b -> Expr b
    mkLams [Id]
    bndrs OutExpr
    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.

    Note [Casts and lambdas]
    ~~~~~~~~~~~~~~~~~~~~~~~~
    Consider
            (\(x:tx). (\(y:ty). e) `cast` co)

    We float the cast out, thus
            (\(x:tx) (y:ty). e) `cast` (tx -> co)

    We do this for at least three reasons:

    1. There is a danger here that the two lambdas look separated, and the
       full laziness pass might float an expression to between the two.

    2. The occurrence analyser will mark x as InsideLam if the Lam nodes
       are separated (see the Lam case of occAnal).  By floating the cast
       out we put the two Lams together, so x can get a vanilla Once
       annotation.  If this lambda is the RHS of a let, which we inline,
       we can do preInlineUnconditionally on that x=arg binding.  With the
       InsideLam OccInfo, we can't do that, which results in an extra
       iteration of the Simplifier.

    3. It may cancel with another cast.  E.g
          (\x. e |> co1) |> co2
       If we float out co1 it might cancel with co2.  Similarly
          let f = (\x. e |> co1) in ...
       If we float out co1, and then do cast worker/wrapper, we get
          let f1 = \x.e; f = f1 |> co1 in ...
       and now we can inline f, hoping that co1 may cancel at a call site.

    TL;DR: put the lambdas together if at all possible.

    In general, here's the transformation:
            \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 :: SimplEnv -> BindContext -> OutId -> OutExpr
                    -> SimplM (ArityType, OutExpr)
    -- See Note [Eta-expanding at let bindings]
    tryEtaExpandRhs :: StaticEnv
    -> BindContext -> Id -> OutExpr -> SimplM (SafeArityType, OutExpr)
    tryEtaExpandRhs StaticEnv
    env BindContext
    bind_cxt Id
    bndr OutExpr
    rhs
      | StaticEnv -> Bool
    seEtaExpand StaticEnv
    env         -- If Eta-expansion is on
      , OutExpr -> Bool
    wantEtaExpansion OutExpr
    rhs    -- and we'd like to eta-expand e
      , Bool
    do_eta_expand           -- and e's manifest arity is lower than
                                --     what it could be
                                --     (never true for join points)
      =                         -- Do eta-expansion.
        Bool
    -> SDoc
    -> SimplM (SafeArityType, OutExpr)
    -> SimplM (SafeArityType, OutExpr)
    forall a. HasCallStack => Bool -> SDoc -> a -> a
    assertPpr( Bool -> Bool
    not (BindContext -> Bool
    isJoinBC BindContext
    bind_cxt) ) (Id -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Id
    bndr) (SimplM (SafeArityType, OutExpr)
     -> SimplM (SafeArityType, OutExpr))
    -> SimplM (SafeArityType, OutExpr)
    -> SimplM (SafeArityType, OutExpr)
    forall a b. (a -> b) -> a -> b
    $
           -- assert: this never happens for join points; see GHC.Core.Opt.Arity
           --         Note [Do not eta-expand join points]
        do { Tick -> SimplM ()
    tick (Id -> Tick
    EtaExpansion Id
    bndr)
           ; (SafeArityType, OutExpr) -> SimplM (SafeArityType, OutExpr)
    forall a. a -> SimplM a
    forall (m :: * -> *) a. Monad m => a -> m a
    return (SafeArityType
    arity_type, InScopeSet -> SafeArityType -> OutExpr -> OutExpr
    etaExpandAT InScopeSet
    in_scope SafeArityType
    arity_type OutExpr
    rhs) }

      | Bool
    otherwise
      = (SafeArityType, OutExpr) -> SimplM (SafeArityType, OutExpr)
    forall a. a -> SimplM a
    forall (m :: * -> *) a. Monad m => a -> m a
    return (SafeArityType
    arity_type, OutExpr
    rhs)

      where
        in_scope :: InScopeSet
    in_scope   = StaticEnv -> InScopeSet
    getInScope StaticEnv
    env
        arity_opts :: ArityOpts
    arity_opts = StaticEnv -> ArityOpts
    seArityOpts StaticEnv
    env
        is_rec :: RecFlag
    is_rec     = BindContext -> RecFlag
    bindContextRec BindContext
    bind_cxt
        (Bool
    do_eta_expand, SafeArityType
    arity_type) = ArityOpts -> RecFlag -> Id -> OutExpr -> (Bool, SafeArityType)
    findRhsArity ArityOpts
    arity_opts RecFlag
    is_rec Id
    bndr OutExpr
    rhs

    wantEtaExpansion :: CoreExpr -> Bool
    -- Mostly True; but False of PAPs which will immediately eta-reduce again
    -- See Note [Which RHSs do we eta-expand?]
    wantEtaExpansion :: OutExpr -> Bool
    wantEtaExpansion (Cast OutExpr
    e OutCoercion
    _)             = OutExpr -> Bool
    wantEtaExpansion OutExpr
    e
    wantEtaExpansion (Tick CoreTickish
    _ OutExpr
    e)             = OutExpr -> Bool
    wantEtaExpansion OutExpr
    e
    wantEtaExpansion (Lam Id
    b OutExpr
    e) | Id -> Bool
    isTyVar Id
    b  = OutExpr -> Bool
    wantEtaExpansion OutExpr
    e
    wantEtaExpansion (App OutExpr
    e OutExpr
    _)              = OutExpr -> Bool
    wantEtaExpansion OutExpr
    e
    wantEtaExpansion (Var {})               = Bool
    False
    wantEtaExpansion (Lit {})               = Bool
    False
    wantEtaExpansion OutExpr
    _                      = Bool
    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 to
        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?

    ************************************************************************
    *                                                                      *
    \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.  Several points worth noting

    (AB1) 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*)

    (AB2) 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.

    (AB3) We get the variables to abstract over by filtering down the
          the main_tvs for the original function, picking only ones
          mentioned in the abstracted body. This means:
          - they are automatically in dependency order, because main_tvs is
          - there is no issue about non-determinism
          - we don't gratuitously change order, which may help (in a tiny
            way) with CSE and/or the compiler-debugging experience

    (AB4) 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'.
          Remember this bizarre case too:
               x::a = x
          Here, we must abstract 'x' over 'a'.

          Why is it worth doing this?  Partly tidiness; and partly #22459
          which showed that it's harder to do polymorphic specialisation well
          if there are dictionaries abstracted over unnecessary type variables.
          See Note [Weird special case for SpecDict] in GHC.Core.Opt.Specialise

    (AB5) We do dependency analysis on recursive groups prior to determining
          which variables to abstract over.
          This is useful, because ANFisation in prepareBinding may float out
          values out of a complex recursive binding, e.g.,
              letrec { xs = g @a "blah"# ((:) 1 []) xs } in ...
            ==> { prepareBinding }
              letrec { foo = "blah"#
                       bar = [42]
                       xs = g @a foo bar xs } in
              ...
          and we don't want to abstract foo and bar over @a.

          (Why is it OK to float the unlifted `foo` there?
          See Note [Core top-level string literals] in GHC.Core;
          it is controlled by GHC.Core.Opt.Simplify.Env.unitLetFloat.)

          It is also necessary to do dependency analysis, because
          otherwise (in #24551) we might get `foo = \@_ -> "missing"#` at the
          top-level, and that triggers a CoreLint error because `foo` is *not*
          manifestly a literal string.
    -}

    abstractFloats :: UnfoldingOpts -> TopLevelFlag -> [OutTyVar] -> SimplFloats
                  -> OutExpr -> SimplM ([OutBind], OutExpr)
    abstractFloats :: UnfoldingOpts
    -> TopLevelFlag
    -> [Id]
    -> SimplFloats
    -> OutExpr
    -> SimplM ([Bind Id], OutExpr)
    abstractFloats UnfoldingOpts
    uf_opts TopLevelFlag
    top_lvl [Id]
    main_tvs SimplFloats
    floats OutExpr
    body
      = Bool -> SimplM ([Bind Id], OutExpr) -> SimplM ([Bind Id], OutExpr)
    forall a. HasCallStack => Bool -> a -> a
    assert ([Bind Id] -> Bool
    forall (f :: * -> *) a. Foldable f => f a -> Bool
    notNull [Bind Id]
    body_floats) (SimplM ([Bind Id], OutExpr) -> SimplM ([Bind Id], OutExpr))
    -> SimplM ([Bind Id], OutExpr) -> SimplM ([Bind Id], OutExpr)
    forall a b. (a -> b) -> a -> b
    $
        Bool -> SimplM ([Bind Id], OutExpr) -> SimplM ([Bind Id], OutExpr)
    forall a. HasCallStack => Bool -> a -> a
    assert (OrdList (Bind Id) -> Bool
    forall a. OrdList a -> Bool
    isNilOL (SimplFloats -> OrdList (Bind Id)
    sfJoinFloats SimplFloats
    floats)) (SimplM ([Bind Id], OutExpr) -> SimplM ([Bind Id], OutExpr))
    -> SimplM ([Bind Id], OutExpr) -> SimplM ([Bind Id], OutExpr)
    forall a b. (a -> b) -> a -> b
    $
        do  { let sccs :: [SCC (Id, OutExpr, TyCoVarSet)]
    sccs = (Bind Id -> [SCC (Id, OutExpr, TyCoVarSet)])
    -> [Bind Id] -> [SCC (Id, OutExpr, TyCoVarSet)]
    forall (t :: * -> *) a b. Foldable t => (a -> [b]) -> t a -> [b]
    concatMap Bind Id -> [SCC (Id, OutExpr, TyCoVarSet)]
    to_sccs [Bind Id]
    body_floats
            ; (subst, float_binds) <- (Subst -> SCC (Id, OutExpr, TyCoVarSet) -> SimplM (Subst, Bind Id))
    -> Subst
    -> [SCC (Id, OutExpr, TyCoVarSet)]
    -> SimplM (Subst, [Bind Id])
    forall (m :: * -> *) (t :: * -> *) acc x y.
    (Monad m, Traversable t) =>
    (acc -> x -> m (acc, y)) -> acc -> t x -> m (acc, t y)
    mapAccumLM Subst -> SCC (Id, OutExpr, TyCoVarSet) -> SimplM (Subst, Bind Id)
    abstract Subst
    empty_subst [SCC (Id, OutExpr, TyCoVarSet)]
    sccs
            ; return (float_binds, GHC.Core.Subst.substExpr subst body) }
      where
        is_top_lvl :: Bool
    is_top_lvl  = TopLevelFlag -> Bool
    isTopLevel TopLevelFlag
    top_lvl
        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)

        -- See wrinkle (AB5) in Note [Which type variables to abstract over]
        -- for why we need to re-do dependency analysis
        to_sccs :: OutBind -> [SCC (Id, CoreExpr, VarSet)]
        to_sccs :: Bind Id -> [SCC (Id, OutExpr, TyCoVarSet)]
    to_sccs (NonRec Id
    id OutExpr
    e) = [(Id, OutExpr, TyCoVarSet) -> SCC (Id, OutExpr, TyCoVarSet)
    forall vertex. vertex -> SCC vertex
    AcyclicSCC (Id
    id, OutExpr
    e, TyCoVarSet
    emptyVarSet)] -- emptyVarSet: abstract doesn't need it
        to_sccs (Rec [(Id, OutExpr)]
    prs)     = [SCC (Id, OutExpr, TyCoVarSet)]
    sccs
          where
            ([Id]
    ids,[OutExpr]
    rhss) = [(Id, OutExpr)] -> ([Id], [OutExpr])
    forall a b. [(a, b)] -> ([a], [b])
    unzip [(Id, OutExpr)]
    prs
            sccs :: [SCC (Id, OutExpr, TyCoVarSet)]
    sccs = ((Id, OutExpr, TyCoVarSet) -> [Name])
    -> ((Id, OutExpr, TyCoVarSet) -> [Name])
    -> [(Id, OutExpr, TyCoVarSet)]
    -> [SCC (Id, OutExpr, TyCoVarSet)]
    forall node.
    (node -> [Name]) -> (node -> [Name]) -> [node] -> [SCC node]
    depAnal (\(Id
    id,OutExpr
    _rhs,TyCoVarSet
    _fvs) -> [Id -> Name
    forall a. NamedThing a => a -> Name
    getName Id
    id])
                           (\(Id
    _id,OutExpr
    _rhs,TyCoVarSet
    fvs) -> (Id -> [Name] -> [Name]) -> [Name] -> TyCoVarSet -> [Name]
    forall a. (Id -> a -> a) -> a -> TyCoVarSet -> a
    nonDetStrictFoldVarSet ((:) (Name -> [Name] -> [Name])
    -> (Id -> Name) -> Id -> [Name] -> [Name]
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . Id -> Name
    forall a. NamedThing a => a -> Name
    getName) [] TyCoVarSet
    fvs) -- Wrinkle (AB3)
                           ([Id] -> [OutExpr] -> [TyCoVarSet] -> [(Id, OutExpr, TyCoVarSet)]
    forall a b c. [a] -> [b] -> [c] -> [(a, b, c)]
    zip3 [Id]
    ids [OutExpr]
    rhss ((OutExpr -> TyCoVarSet) -> [OutExpr] -> [TyCoVarSet]
    forall a b. (a -> b) -> [a] -> [b]
    map OutExpr -> TyCoVarSet
    exprFreeVars [OutExpr]
    rhss))

        abstract :: GHC.Core.Subst.Subst -> SCC (Id, CoreExpr, VarSet) -> SimplM (GHC.Core.Subst.Subst, OutBind)
        abstract :: Subst -> SCC (Id, OutExpr, TyCoVarSet) -> SimplM (Subst, Bind Id)
    abstract Subst
    subst (AcyclicSCC (Id
    id, OutExpr
    rhs, TyCoVarSet
    _empty_var_set))
          = do { (poly_id1, poly_app) <- [Id] -> Id -> SimplM (Id, OutExpr)
    mk_poly1 [Id]
    tvs_here Id
    id
               ; let (poly_id2, poly_rhs) = mk_poly2 poly_id1 tvs_here rhs'
                     !subst' = Subst -> Id -> OutExpr -> Subst
    GHC.Core.Subst.extendIdSubst Subst
    subst Id
    id OutExpr
    poly_app
               ; return (subst', NonRec poly_id2 poly_rhs) }
          where
            rhs' :: OutExpr
    rhs' = HasDebugCallStack => Subst -> OutExpr -> OutExpr
    Subst -> OutExpr -> OutExpr
    GHC.Core.Subst.substExpr Subst
    subst OutExpr
    rhs

            -- tvs_here: see Note [Which type variables to abstract over]
            tvs_here :: [Id]
    tvs_here = TyCoVarSet -> [Id]
    choose_tvs ((Id -> Bool) -> OutExpr -> TyCoVarSet
    exprSomeFreeVars Id -> Bool
    isTyVar OutExpr
    rhs')

        abstract Subst
    subst (CyclicSCC [(Id, OutExpr, TyCoVarSet)]
    trpls)
          = do { (poly_ids, poly_apps) <- (Id -> SimplM (Id, OutExpr)) -> [Id] -> SimplM ([Id], [OutExpr])
    forall (m :: * -> *) a b c.
    Applicative m =>
    (a -> m (b, c)) -> [a] -> m ([b], [c])
    mapAndUnzipM ([Id] -> Id -> SimplM (Id, OutExpr)
    mk_poly1 [Id]
    tvs_here) [Id]
    ids
               ; let subst' = Subst -> [(Id, OutExpr)] -> Subst
    GHC.Core.Subst.extendSubstList Subst
    subst ([Id]
    ids [Id] -> [OutExpr] -> [(Id, OutExpr)]
    forall a b. [a] -> [b] -> [(a, b)]
    `zip` [OutExpr]
    poly_apps)
                     poly_pairs = [ Id -> [Id] -> OutExpr -> (Id, OutExpr)
    mk_poly2 Id
    poly_id [Id]
    tvs_here OutExpr
    rhs'
                                  | (Id
    poly_id, OutExpr
    rhs) <- [Id]
    poly_ids [Id] -> [OutExpr] -> [(Id, OutExpr)]
    forall a b. [a] -> [b] -> [(a, b)]
    `zip` [OutExpr]
    rhss
                                  , let rhs' :: OutExpr
    rhs' = HasDebugCallStack => Subst -> OutExpr -> OutExpr
    Subst -> OutExpr -> OutExpr
    GHC.Core.Subst.substExpr Subst
    subst' OutExpr
    rhs ]
               ; return (subst', Rec poly_pairs) }
          where
            ([Id]
    ids,[OutExpr]
    rhss,[TyCoVarSet]
    _fvss) = [(Id, OutExpr, TyCoVarSet)] -> ([Id], [OutExpr], [TyCoVarSet])
    forall a b c. [(a, b, c)] -> ([a], [b], [c])
    unzip3 [(Id, OutExpr, TyCoVarSet)]
    trpls

            -- tvs_here: see Note [Which type variables to abstract over]
            tvs_here :: [Id]
    tvs_here = TyCoVarSet -> [Id]
    choose_tvs (((Id, OutExpr, TyCoVarSet) -> TyCoVarSet)
    -> [(Id, OutExpr, TyCoVarSet)] -> TyCoVarSet
    forall a. (a -> TyCoVarSet) -> [a] -> TyCoVarSet
    mapUnionVarSet (Id, OutExpr, TyCoVarSet) -> TyCoVarSet
    forall {b}. (Id, b, TyCoVarSet) -> TyCoVarSet
    get_bind_fvs [(Id, OutExpr, TyCoVarSet)]
    trpls)

            -- See wrinkle (AB4) in Note [Which type variables to abstract over]
            get_bind_fvs :: (Id, b, TyCoVarSet) -> TyCoVarSet
    get_bind_fvs (Id
    id,b
    _rhs,TyCoVarSet
    rhs_fvs) = OutType -> TyCoVarSet
    tyCoVarsOfType (Id -> OutType
    idType Id
    id) TyCoVarSet -> TyCoVarSet -> TyCoVarSet
    `unionVarSet` TyCoVarSet -> TyCoVarSet
    get_rec_rhs_tvs TyCoVarSet
    rhs_fvs
            get_rec_rhs_tvs :: TyCoVarSet -> TyCoVarSet
    get_rec_rhs_tvs TyCoVarSet
    rhs_fvs        = (Id -> TyCoVarSet -> TyCoVarSet)
    -> TyCoVarSet -> TyCoVarSet -> TyCoVarSet
    forall a. (Id -> a -> a) -> a -> TyCoVarSet -> a
    nonDetStrictFoldVarSet Id -> TyCoVarSet -> TyCoVarSet
    get_tvs TyCoVarSet
    emptyVarSet TyCoVarSet
    rhs_fvs
                                      -- nonDet is safe because of wrinkle (AB3)

            get_tvs :: Var -> VarSet -> VarSet
            get_tvs :: Id -> TyCoVarSet -> TyCoVarSet
    get_tvs Id
    var TyCoVarSet
    free_tvs
               | Id -> Bool
    isTyVar Id
    var      -- CoVars have been substituted away
               = TyCoVarSet -> Id -> TyCoVarSet
    extendVarSet TyCoVarSet
    free_tvs Id
    var
               | Id -> Bool
    isCoVar Id
    var  -- CoVars can be free in the RHS, but they are never let-bound;
               = TyCoVarSet
    free_tvs     -- Do not call lookupIdSubst_maybe, though (#23426)
                              --    because it has a non-CoVar precondition
               | Just OutExpr
    poly_app <- HasDebugCallStack => Subst -> Id -> Maybe OutExpr
    Subst -> Id -> Maybe OutExpr
    GHC.Core.Subst.lookupIdSubst_maybe Subst
    subst Id
    var
               = -- 'var' is like 'x' in (AB4)
                 (Id -> Bool) -> OutExpr -> TyCoVarSet
    exprSomeFreeVars Id -> Bool
    isTyVar OutExpr
    poly_app TyCoVarSet -> TyCoVarSet -> TyCoVarSet
    `unionVarSet` TyCoVarSet
    free_tvs
               | Bool
    otherwise
               = TyCoVarSet
    free_tvs

        choose_tvs :: TyCoVarSet -> [Id]
    choose_tvs TyCoVarSet
    free_tvs
           = (Id -> Bool) -> [Id] -> [Id]
    forall a. (a -> Bool) -> [a] -> [a]
    filter (Id -> TyCoVarSet -> Bool
    `elemVarSet` TyCoVarSet
    all_free_tvs) [Id]
    main_tvs  -- (AB3)
           where
             all_free_tvs :: TyCoVarSet
    all_free_tvs = TyCoVarSet -> TyCoVarSet
    closeOverKinds TyCoVarSet
    free_tvs       -- (AB2)

        mk_poly1 :: [TyVar] -> Id -> SimplM (Id, CoreExpr)
        mk_poly1 :: [Id] -> Id -> SimplM (Id, OutExpr)
    mk_poly1 [Id]
    tvs_here Id
    var
          = do { uniq <- SimplM Unique
    forall (m :: * -> *). MonadUnique m => m Unique
    getUniqueM
               ; let  poly_name = Name -> Unique -> Name
    setNameUnique (Id -> Name
    idName Id
    var) Unique
    uniq      -- Keep same name
                      poly_ty   = [Id] -> OutType -> OutType
    mkInfForAllTys [Id]
    tvs_here (Id -> OutType
    idType Id
    var) -- But new type of course
                      poly_id   = Id -> [Id] -> Id -> Id
    transferPolyIdInfo Id
    var [Id]
    tvs_here (Id -> Id) -> Id -> Id
    forall a b. (a -> b) -> a -> b
    $ -- Note [transferPolyIdInfo] in GHC.Types.Id
                                  HasDebugCallStack => Name -> OutType -> OutType -> Id
    Name -> OutType -> OutType -> Id
    mkLocalId Name
    poly_name (Id -> OutType
    idMult Id
    var) OutType
    poly_ty
               ; return (poly_id, mkTyApps (Var poly_id) (mkTyVarTys 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] -> OutExpr -> (Id, OutExpr)
    mk_poly2 Id
    poly_id [Id]
    tvs_here OutExpr
    rhs
          = (Id
    poly_id Id -> Unfolding -> Id
    `setIdUnfolding` Unfolding
    unf, OutExpr
    poly_rhs)
          where
            poly_rhs :: OutExpr
    poly_rhs = [Id] -> OutExpr -> OutExpr
    forall b. [b] -> Expr b -> Expr b
    mkLams [Id]
    tvs_here OutExpr
    rhs
            unf :: Unfolding
    unf = UnfoldingOpts
    -> UnfoldingSource
    -> Bool
    -> Bool
    -> Bool
    -> OutExpr
    -> Maybe UnfoldingCache
    -> Unfolding
    mkUnfolding UnfoldingOpts
    uf_opts UnfoldingSource
    VanillaSrc Bool
    is_top_lvl Bool
    False Bool
    False OutExpr
    poly_rhs Maybe UnfoldingCache
    forall a. Maybe a
    Nothing

            -- 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 GHC.Core.Utils 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!

    Note [Shadowing in prepareAlts]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Note that we pass case_bndr::InId to prepareAlts; an /InId/, not an
    /OutId/.  This is vital, because `refineDefaultAlt` uses `tys` to build
    a new /InAlt/.  If you pass an OutId, we'll end up applying the
    substitution twice: disaster (#23012).

    However this does mean that filling in the default alt might be
    delayed by a simplifier cycle, because an InId has less info than an
    OutId.  Test simplCore/should_compile/simpl013 apparently shows this
    up, although I'm not sure exactly how..
    -}

    prepareAlts :: OutExpr -> InId -> [InAlt] -> SimplM ([AltCon], [InAlt])
    -- The returned alternatives can be empty, none are possible
    --
    -- Note that case_bndr is an InId; see Note [Shadowing in prepareAlts]
    prepareAlts :: OutExpr -> Id -> [InAlt] -> SimplM ([AltCon], [InAlt])
    prepareAlts OutExpr
    scrut Id
    case_bndr [InAlt]
    alts
      | Just (TyCon
    tc, [OutType]
    tys) <- HasDebugCallStack => OutType -> Maybe (TyCon, [OutType])
    OutType -> Maybe (TyCon, [OutType])
    splitTyConApp_maybe (Id -> OutType
    idType Id
    case_bndr)
      = do { us <- SimplM [Unique]
    forall (m :: * -> *). MonadUnique m => m [Unique]
    getUniquesM
           ; let (idcs1, alts1) = filterAlts tc tys imposs_cons alts
                 (yes2,  alts2) = refineDefaultAlt us (idMult case_bndr) tc tys idcs1 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
                 (yes3, idcs3, alts3) = combineIdenticalAlts idcs1 alts2
                 -- "idcs" stands for "impossible default data constructors"
                 -- i.e. the constructors that can't match the default case
           ; when yes2 $ tick (FillInCaseDefault case_bndr)
           ; when yes3 $ tick (AltMerge case_bndr)
           ; return (idcs3, alts3) }

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

    {- Note [Merging nested cases]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    The basic case-merge stuff is described in Note [Merge Nested Cases] in GHC.Core.Utils

    We do it here in `prepareAlts` (on InAlts) rather than after (on OutAlts) for two reasons:

    * It "belongs" here with `filterAlts`, `refineDefaultAlt` and `combineIdenticalAlts`.

    * In test perf/compiler/T22428 I found that I was getting extra Simplifer iterations:
        1. Create a join point
        2. That join point gets inlined at all call sites, so it is now dead.
        3. Case-merge happened, but left behind some trivial bindings (see `mergeCaseAlts`)
        4. Get rid of the trivial bindings
      The first two seem reasonable.  It's imaginable that we could do better on
      (3), by making case-merge join-point-aware, but it's not trivial.  But the
      fourth is just stupid.  Rather than always do an extra iteration, it's better
      to do the transformation on the input-end of teh Simplifier.
    -}

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

    mkCase tries these things

    * Note [Eliminate Identity Case]
    * Note [Scrutinee Constant Folding]

    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.

    Wrinkle 1:
      Do not apply caseRules if there is just a single DEFAULT alternative,
      unless the case-binder is dead. Example:
         case e +# 3# of b { DEFAULT -> rhs }
      If we applied the transformation here we would (stupidly) get
         case e of b' { DEFAULT -> let b = b' +# 3# in rhs }
      and now the process may repeat, because that let will really
      be a case. But if the original case binder b is dead, we instead get
         case e of b' { DEFAULT -> rhs }
      and there is no such problem.

      See Note [Example of case-merging and caseRules] for a compelling
      example of why this dead-binder business can be really important.

    Wrinkle 2:
      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

    Wrinkle 3:
      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'.

    Wrinkle 4:
      In dataToTag we might need to make up some fake binders;
      see Note [caseRules for dataToTag] in GHC.Core.Opt.ConstantFold

    Note [Example of case-merging and caseRules]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    The case-transformation rules are quite powerful. Here's a
    subtle example from #22375.  We start with

      data T = A | B | ...
        deriving Eq

      f :: T -> String
      f x = if | x==A -> "one"
               | x==B -> "two"
               | ...

    In Core after a bit of simplification we get:

        f x = case dataToTagLarge# x of a# { _DEFAULT ->
              case a# of
                _DEFAULT -> case dataToTagLarge# x of b# { _DEFAULT ->
                            case b# of
                               _DEFAULT -> ...
                               1# -> "two"
                            }
                0# -> "one"
              }

    Now consider what mkCase does to these case expressions.
    The case-merge transformation Note [Merge Nested Cases]
    does this (affecting both pairs of cases):

        f x = case dataToTagLarge# x of a# {
                 _DEFAULT -> case dataToTagLarge# x of b# {
                              _DEFAULT -> ...
                              1# -> "two"
                             }
                 0# -> "one"
              }

    Now Note [caseRules for dataToTag] does its work, again
    on both dataToTagLarge# cases:

        f x = case x of x1 {
                 _DEFAULT -> case dataToTagLarge# x1 of a# { _DEFAULT ->
                             case x of x2 {
                               _DEFAULT -> case dataToTagLarge# x2 of b# { _DEFAULT -> ... }
                               B -> "two"
                             }}
                 A -> "one"
              }

    The new dataToTagLarge# calls come from the "reconstruct scrutinee" part of
    caseRules (note that a# and b# were not dead in the original program
    before all this merging).  However, since a# and b# /are/ in fact dead
    in the resulting program, we are left with redundant dataToTagLarge# calls.
    But they are easily eliminated by doing caseRules again, in
    the next Simplifier iteration, this time noticing that a# and b# are
    dead.  Hence the "dead-binder" sub-case of Wrinkle 1 of Note
    [Scrutinee Constant Folding] above.  Once we do this we get

        f x = case x of x1 {
                 _DEFAULT -> case x1 of x2 { _DEFAULT ->
                             case x1 of x2 {
                                _DEFAULT -> case x2 of x3 { _DEFAULT -> ... }
                                B -> "two"
                             }}
                 A -> "one"
              }

    and now we can do case-merge again, getting the desired

        f x = case x of
                A -> "one"
                B -> "two"
                ...

    -}

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

    --------------------------------------------------
    --      1. Merge Nested Cases
    --         See Note [Merge Nested Cases]
    --             Note [Example of case-merging and caseRules]
    --             Note [Cascading case merge]
    --------------------------------------------------

    mkCase :: SimplMode -> OutExpr -> Id -> OutType -> [InAlt] -> SimplM OutExpr
    mkCase SimplMode
    mode OutExpr
    scrut Id
    outer_bndr OutType
    alts_ty [InAlt]
    alts
      | SimplMode -> Bool
    sm_case_merge SimplMode
    mode
      , Just ([Bind Id]
    joins, [InAlt]
    alts') <- Id -> [InAlt] -> Maybe ([Bind Id], [InAlt])
    mergeCaseAlts Id
    outer_bndr [InAlt]
    alts
      = do  { Tick -> SimplM ()
    tick (Id -> Tick
    CaseMerge Id
    outer_bndr)
            ; case_expr <- SimplMode -> OutExpr -> Id -> OutType -> [InAlt] -> SimplM OutExpr
    mkCase1 SimplMode
    mode OutExpr
    scrut Id
    outer_bndr OutType
    alts_ty [InAlt]
    alts'
            ; return (mkLets joins case_expr) }
            -- mkCase1: 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!
      | Bool
    otherwise
      = SimplMode -> OutExpr -> Id -> OutType -> [InAlt] -> SimplM OutExpr
    mkCase1 SimplMode
    mode OutExpr
    scrut Id
    outer_bndr OutType
    alts_ty [InAlt]
    alts

    --------------------------------------------------
    --      2. Eliminate Identity Case
    --         See Note [Eliminate Identity Case]
    --------------------------------------------------

    mkCase1 :: SimplMode -> OutExpr -> Id -> OutType -> [InAlt] -> SimplM OutExpr
    mkCase1 SimplMode
    _mode OutExpr
    scrut Id
    case_bndr OutType
    _ alts :: [InAlt]
    alts@(Alt AltCon
    _ [Id]
    _ OutExpr
    rhs1 : [InAlt]
    alts')      -- Identity case
      | (InAlt -> Bool) -> [InAlt] -> Bool
    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)
           ; OutExpr -> SimplM OutExpr
    forall a. a -> SimplM a
    forall (m :: * -> *) a. Monad m => a -> m a
    return ([CoreTickish] -> OutExpr -> OutExpr
    mkTicks [CoreTickish]
    ticks (OutExpr -> OutExpr) -> OutExpr -> OutExpr
    forall a b. (a -> b) -> a -> b
    $ OutExpr -> OutExpr -> OutExpr
    forall {b} {b}. Expr b -> Expr b -> Expr b
    re_cast OutExpr
    scrut OutExpr
    rhs1) }
      where
        ticks :: [CoreTickish]
    ticks = (InAlt -> [CoreTickish]) -> [InAlt] -> [CoreTickish]
    forall (t :: * -> *) a b. Foldable t => (a -> [b]) -> t a -> [b]
    concatMap (\(Alt AltCon
    _ [Id]
    _ OutExpr
    rhs) -> (CoreTickish -> Bool) -> OutExpr -> [CoreTickish]
    forall b. (CoreTickish -> Bool) -> Expr b -> [CoreTickish]
    stripTicksT CoreTickish -> Bool
    forall (pass :: TickishPass). GenTickish pass -> Bool
    tickishFloatable OutExpr
    rhs) [InAlt]
    alts'
        identity_alt :: InAlt -> Bool
    identity_alt (Alt AltCon
    con [Id]
    args OutExpr
    rhs) = OutExpr -> AltCon -> [Id] -> Bool
    check_eq OutExpr
    rhs AltCon
    con [Id]
    args

        check_eq :: OutExpr -> AltCon -> [Id] -> Bool
    check_eq (Cast OutExpr
    rhs OutCoercion
    co) AltCon
    con [Id]
    args        -- See Note [RHS casts]
          = Bool -> Bool
    not ((Id -> Bool) -> [Id] -> Bool
    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
    && OutExpr -> AltCon -> [Id] -> Bool
    check_eq OutExpr
    rhs AltCon
    con [Id]
    args
        check_eq (Tick CoreTickish
    t OutExpr
    e) AltCon
    alt [Id]
    args
          = CoreTickish -> Bool
    forall (pass :: TickishPass). GenTickish pass -> Bool
    tickishFloatable CoreTickish
    t Bool -> Bool -> Bool
    && OutExpr -> AltCon -> [Id] -> Bool
    check_eq OutExpr
    e AltCon
    alt [Id]
    args

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

        arg_tys :: [OutType]
    arg_tys = HasDebugCallStack => OutType -> [OutType]
    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) = Expr b -> OutCoercion -> Expr b
    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 SimplMode
    mode OutExpr
    scrut Id
    bndr OutType
    alts_ty [InAlt]
    alts = SimplMode -> OutExpr -> Id -> OutType -> [InAlt] -> SimplM OutExpr
    mkCase2 SimplMode
    mode OutExpr
    scrut Id
    bndr OutType
    alts_ty [InAlt]
    alts

    --------------------------------------------------
    --      2. Scrutinee Constant Folding
    --         See Note [Scrutinee Constant Folding]
    --------------------------------------------------

    mkCase2 :: SimplMode -> OutExpr -> Id -> OutType -> [InAlt] -> SimplM OutExpr
    mkCase2 SimplMode
    mode OutExpr
    scrut Id
    bndr OutType
    alts_ty [InAlt]
    alts
      | -- See Note [Scrutinee Constant Folding]
        case [InAlt]
    alts of
          [Alt AltCon
    DEFAULT [Id]
    _ OutExpr
    _] -> Id -> Bool
    isDeadBinder Id
    bndr -- see wrinkle 1
          [InAlt]
    _                 -> Bool
    True
      , SimplMode -> Bool
    sm_case_folding SimplMode
    mode
      , Just (OutExpr
    scrut', AltCon -> Maybe AltCon
    tx_con, Id -> OutExpr
    mk_orig) <- Platform
    -> OutExpr
    -> Maybe (OutExpr, AltCon -> Maybe AltCon, Id -> OutExpr)
    caseRules (SimplMode -> Platform
    smPlatform SimplMode
    mode) OutExpr
    scrut
      = do { bndr' <- FastString -> OutType -> OutType -> SimplM Id
    newId (String -> FastString
    fsLit String
    "lwild") OutType
    ManyTy (HasDebugCallStack => OutExpr -> OutType
    OutExpr -> OutType
    exprType OutExpr
    scrut')

           ; alts' <- mapMaybeM (tx_alt tx_con mk_orig bndr') alts
                      -- mapMaybeM: discard unreachable alternatives
                      -- See Note [Unreachable caseRules alternatives]
                      -- in GHC.Core.Opt.ConstantFold

           ; mkCase3 mode scrut' bndr' alts_ty $
             add_default (re_sort alts')
           }

      | Bool
    otherwise
      = SimplMode -> OutExpr -> Id -> OutType -> [InAlt] -> SimplM OutExpr
    mkCase3 SimplMode
    mode OutExpr
    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 = 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 -> OutExpr) -> Id -> InAlt -> SimplM (Maybe InAlt)
    tx_alt AltCon -> Maybe AltCon
    tx_con Id -> OutExpr
    mk_orig Id
    new_bndr (Alt AltCon
    con [Id]
    bs OutExpr
    rhs)
          = case AltCon -> Maybe AltCon
    tx_con AltCon
    con of
              Maybe AltCon
    Nothing   -> Maybe InAlt -> SimplM (Maybe InAlt)
    forall a. a -> SimplM a
    forall (m :: * -> *) a. Monad m => a -> m a
    return Maybe InAlt
    forall a. Maybe a
    Nothing
              Just AltCon
    con' -> do { bs' <- Id -> AltCon -> SimplM [Id]
    forall {m :: * -> *}. MonadUnique m => Id -> AltCon -> m [Id]
    mk_new_bndrs Id
    new_bndr AltCon
    con'
                              ; return (Just (Alt con' bs' rhs')) }
          where
            rhs' :: OutExpr
    rhs' | Id -> Bool
    isDeadBinder Id
    bndr = OutExpr
    rhs
                 | Bool
    otherwise         = HasDebugCallStack => Id -> OutExpr -> OutExpr -> OutExpr
    Id -> OutExpr -> OutExpr -> OutExpr
    bindNonRec Id
    bndr OutExpr
    orig_val OutExpr
    rhs

            orig_val :: OutExpr
    orig_val = case AltCon
    con of
                          AltCon
    DEFAULT    -> Id -> OutExpr
    mk_orig Id
    new_bndr
                          LitAlt Literal
    l   -> Literal -> OutExpr
    forall b. Literal -> Expr b
    Lit Literal
    l
                          DataAlt DataCon
    dc -> DataCon -> [OutType] -> [Id] -> OutExpr
    forall b. DataCon -> [OutType] -> [Id] -> Expr b
    mkConApp2 DataCon
    dc (HasDebugCallStack => OutType -> [OutType]
    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 { us <- m [Unique]
    forall (m :: * -> *). MonadUnique m => m [Unique]
    getUniquesM
               ; let (ex_tvs, arg_ids) = dataConRepInstPat us (idMult new_bndr) dc
                                            (tyConAppArgs (idType new_bndr))
               ; return (ex_tvs ++ arg_ids) }
        mk_new_bndrs Id
    _ AltCon
    _ = [Id] -> m [Id]
    forall a. a -> m a
    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 = (InAlt -> InAlt -> Ordering) -> [InAlt] -> [InAlt]
    forall a. (a -> a -> Ordering) -> [a] -> [a]
    sortBy InAlt -> InAlt -> Ordering
    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 OutExpr
    rhs : [InAlt]
    alts) = AltCon -> [Id] -> OutExpr -> InAlt
    forall b. AltCon -> [b] -> Expr b -> Alt b
    Alt AltCon
    DEFAULT [Id]
    bs OutExpr
    rhs InAlt -> [InAlt] -> [InAlt]
    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 slightly 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 :: SimplMode -> OutExpr -> Id -> OutType -> [InAlt] -> SimplM OutExpr
    mkCase3 SimplMode
    _mode OutExpr
    scrut Id
    bndr OutType
    alts_ty [InAlt]
    alts
      = OutExpr -> SimplM OutExpr
    forall a. a -> SimplM a
    forall (m :: * -> *) a. Monad m => a -> m a
    return (OutExpr -> Id -> OutType -> [InAlt] -> OutExpr
    forall b. Expr b -> b -> OutType -> [Alt b] -> Expr b
    Case OutExpr
    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) InsideLam -> InsideLam -> Bool
    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.

    -}