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

\section[SimplUtils]{The simplifier utilities}
-}

{-# LANGUAGE CPP #-}

module SimplUtils (
        -- Rebuilding
        mkLam, mkCase, prepareAlts, tryEtaExpandRhs,

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

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

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

        abstractFloats,

        -- Utilities
        isExitJoinId
    ) where

#include "HsVersions.h"

import GhcPrelude

import SimplEnv
import CoreMonad        ( SimplMode(..), Tick(..) )
import DynFlags
import CoreSyn
import qualified CoreSubst
import PprCore
import TyCoPpr          ( pprParendType )
import CoreFVs
import CoreUtils
import CoreArity
import CoreUnfold
import Name
import Id
import IdInfo
import Var
import Demand
import SimplMonad
import Type     hiding( substTy )
import Coercion hiding( substCo )
import DataCon          ( dataConWorkId, isNullaryRepDataCon )
import VarSet
import BasicTypes
import Util
import OrdList          ( isNilOL )
import MonadUtils
import Outputable
import Pair
import PrelRules
import FastString       ( fsLit )

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

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

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

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


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

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

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

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

  | ApplyToVal         -- (ApplyToVal arg K)[e] = K[ e arg ]
      { SimplCont -> DupFlag
sc_dup  :: DupFlag      -- See Note [DupFlag invariants]
      , SimplCont -> InExpr
sc_arg  :: InExpr       -- The argument,
      , SimplCont -> StaticEnv
sc_env  :: StaticEnv    -- see Note [StaticEnv invariant]
      , SimplCont -> SimplCont
sc_cont :: SimplCont }

  | ApplyToTy          -- (ApplyToTy ty K)[e] = K[ e ty ]
      { SimplCont -> OutType
sc_arg_ty  :: OutType     -- Argument type
      , SimplCont -> OutType
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 -> InId
sc_bndr :: InId           -- case binder
      , SimplCont -> [InAlt]
sc_alts :: [InAlt]        -- Alternatives
      , sc_env  :: StaticEnv      -- See Note [StaticEnv invariant]
      , sc_cont :: SimplCont }

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

  | StrictArg           -- (StrictArg (f e1 ..en) K)[e] = K[ f e1 .. en e ]
      { sc_dup  :: DupFlag     -- Always Simplified or OkToDup
      , SimplCont -> ArgInfo
sc_fun  :: ArgInfo     -- Specifies f, e1..en, Whether f has rules, etc
                               --     plus strictness flags for *further* args
      , SimplCont -> CallCtxt
sc_cci  :: CallCtxt    -- Whether *this* argument position is interesting
      , sc_cont :: SimplCont }

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

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

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

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

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

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

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

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

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

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

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

instance Outputable SimplCont where
  ppr :: SimplCont -> SDoc
ppr (Stop OutType
ty CallCtxt
interesting) = String -> SDoc
text String
"Stop" SDoc -> SDoc -> SDoc
<> SDoc -> SDoc
brackets (CallCtxt -> SDoc
forall a. Outputable a => a -> SDoc
ppr CallCtxt
interesting) SDoc -> SDoc -> SDoc
<+> OutType -> SDoc
forall a. Outputable a => a -> SDoc
ppr OutType
ty
  ppr (CastIt OutCoercion
co SimplCont
cont  )    = (String -> SDoc
text String
"CastIt" SDoc -> SDoc -> SDoc
<+> OutCoercion -> SDoc
pprOptCo OutCoercion
co) SDoc -> SDoc -> SDoc
$$ SimplCont -> SDoc
forall a. Outputable a => a -> SDoc
ppr SimplCont
cont
  ppr (TickIt Tickish InId
t SimplCont
cont)       = (String -> SDoc
text String
"TickIt" SDoc -> SDoc -> SDoc
<+> Tickish InId -> SDoc
forall a. Outputable a => a -> SDoc
ppr Tickish InId
t) SDoc -> SDoc -> SDoc
$$ 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
text String
"ApplyToTy" SDoc -> SDoc -> SDoc
<+> OutType -> SDoc
pprParendType OutType
ty) SDoc -> SDoc -> SDoc
$$ SimplCont -> SDoc
forall a. Outputable a => a -> SDoc
ppr SimplCont
cont
  ppr (ApplyToVal { sc_arg :: SimplCont -> InExpr
sc_arg = InExpr
arg, sc_dup :: SimplCont -> DupFlag
sc_dup = DupFlag
dup, sc_cont :: SimplCont -> SimplCont
sc_cont = SimplCont
cont })
    = (String -> SDoc
text String
"ApplyToVal" SDoc -> SDoc -> SDoc
<+> DupFlag -> SDoc
forall a. Outputable a => a -> SDoc
ppr DupFlag
dup SDoc -> SDoc -> SDoc
<+> InExpr -> SDoc
forall b. OutputableBndr b => Expr b -> SDoc
pprParendExpr InExpr
arg)
                                        SDoc -> SDoc -> SDoc
$$ SimplCont -> SDoc
forall a. Outputable a => a -> SDoc
ppr SimplCont
cont
  ppr (StrictBind { sc_bndr :: SimplCont -> InId
sc_bndr = InId
b, sc_cont :: SimplCont -> SimplCont
sc_cont = SimplCont
cont })
    = (String -> SDoc
text String
"StrictBind" SDoc -> SDoc -> SDoc
<+> InId -> SDoc
forall a. Outputable a => a -> SDoc
ppr InId
b) SDoc -> SDoc -> SDoc
$$ SimplCont -> SDoc
forall a. Outputable a => a -> SDoc
ppr SimplCont
cont
  ppr (StrictArg { sc_fun :: SimplCont -> ArgInfo
sc_fun = ArgInfo
ai, sc_cont :: SimplCont -> SimplCont
sc_cont = SimplCont
cont })
    = (String -> SDoc
text String
"StrictArg" SDoc -> SDoc -> SDoc
<+> InId -> SDoc
forall a. Outputable a => a -> SDoc
ppr (ArgInfo -> InId
ai_fun ArgInfo
ai)) SDoc -> SDoc -> SDoc
$$ SimplCont -> SDoc
forall a. Outputable a => a -> SDoc
ppr SimplCont
cont
  ppr (Select { sc_dup :: SimplCont -> DupFlag
sc_dup = DupFlag
dup, sc_bndr :: SimplCont -> InId
sc_bndr = InId
bndr, sc_alts :: SimplCont -> [InAlt]
sc_alts = [InAlt]
alts, sc_env :: SimplCont -> StaticEnv
sc_env = StaticEnv
se, sc_cont :: SimplCont -> SimplCont
sc_cont = SimplCont
cont })
    = (String -> SDoc
text String
"Select" SDoc -> SDoc -> SDoc
<+> DupFlag -> SDoc
forall a. Outputable a => a -> SDoc
ppr DupFlag
dup SDoc -> SDoc -> SDoc
<+> InId -> SDoc
forall a. Outputable a => a -> SDoc
ppr InId
bndr) SDoc -> SDoc -> SDoc
$$
       SDoc -> SDoc
whenPprDebug (Int -> SDoc -> SDoc
nest Int
2 (SDoc -> SDoc) -> SDoc -> SDoc
forall a b. (a -> b) -> a -> b
$ [SDoc] -> SDoc
vcat [TvSubstEnv -> SDoc
forall a. Outputable a => a -> SDoc
ppr (StaticEnv -> TvSubstEnv
seTvSubst StaticEnv
se), [InAlt] -> SDoc
forall a. Outputable a => a -> SDoc
ppr [InAlt]
alts]) SDoc -> SDoc -> SDoc
$$ 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 -> InId
ai_fun   :: OutId,      -- The function
        ArgInfo -> [ArgSpec]
ai_args  :: [ArgSpec],  -- ...applied to these args (which are in *reverse* order)

        ArgInfo -> OutType
ai_type  :: OutType,    -- Type of (f a1 ... an)

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

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

        ArgInfo -> [Bool]
ai_strs :: [Bool],      -- Strictness of remaining arguments
                                --   Usually infinite, but if it is finite it guarantees
                                --   that the function diverges after being given
                                --   that number of args
        ArgInfo -> [Int]
ai_discs :: [Int]       -- Discounts for remaining arguments; non-zero => be keener to inline
                                --   Always infinite
    }

data ArgSpec
  = ValArg OutExpr                    -- Apply to this (coercion or value); c.f. ApplyToVal
  | TyArg { ArgSpec -> OutType
as_arg_ty  :: OutType     -- Apply to this type; c.f. ApplyToTy
          , ArgSpec -> OutType
as_hole_ty :: OutType }   -- Type of the function (presumably forall a. blah)
  | CastBy OutCoercion                -- Cast by this; c.f. CastIt

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

addValArgTo :: ArgInfo -> OutExpr -> ArgInfo
addValArgTo :: ArgInfo -> InExpr -> ArgInfo
addValArgTo ArgInfo
ai InExpr
arg = ArgInfo
ai { ai_args :: [ArgSpec]
ai_args = InExpr -> ArgSpec
ValArg InExpr
arg ArgSpec -> [ArgSpec] -> [ArgSpec]
forall a. a -> [a] -> [a]
: ArgInfo -> [ArgSpec]
ai_args ArgInfo
ai
                        , ai_type :: OutType
ai_type = OutType -> InExpr -> OutType
applyTypeToArg (ArgInfo -> OutType
ai_type ArgInfo
ai) InExpr
arg
                        , ai_rules :: FunRules
ai_rules = FunRules -> FunRules
decRules (ArgInfo -> FunRules
ai_rules ArgInfo
ai) }

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

addCastTo :: ArgInfo -> OutCoercion -> ArgInfo
addCastTo :: ArgInfo -> OutCoercion -> ArgInfo
addCastTo ArgInfo
ai OutCoercion
co = ArgInfo
ai { ai_args :: [ArgSpec]
ai_args = OutCoercion -> ArgSpec
CastBy OutCoercion
co ArgSpec -> [ArgSpec] -> [ArgSpec]
forall a. a -> [a] -> [a]
: ArgInfo -> [ArgSpec]
ai_args ArgInfo
ai
                     , ai_type :: OutType
ai_type = Pair OutType -> OutType
forall a. Pair a -> a
pSnd (OutCoercion -> Pair OutType
coercionKind OutCoercion
co) }

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

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

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


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

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

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

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

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

mkRhsStop :: OutType -> SimplCont       -- See Note [RHS of lets] in CoreUnfold
mkRhsStop :: OutType -> SimplCont
mkRhsStop OutType
ty = OutType -> CallCtxt -> SimplCont
Stop OutType
ty CallCtxt
RhsCtxt

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

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

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

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

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

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

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

contHoleType :: SimplCont -> OutType
contHoleType :: SimplCont -> OutType
contHoleType (Stop OutType
ty CallCtxt
_)                      = OutType
ty
contHoleType (TickIt Tickish InId
_ SimplCont
k)                     = SimplCont -> OutType
contHoleType SimplCont
k
contHoleType (CastIt OutCoercion
co SimplCont
_)                    = Pair OutType -> OutType
forall a. Pair a -> a
pFst (OutCoercion -> Pair OutType
coercionKind OutCoercion
co)
contHoleType (StrictBind { sc_bndr :: SimplCont -> InId
sc_bndr = InId
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 (InId -> OutType
idType InId
b)
contHoleType (StrictArg { sc_fun :: SimplCont -> ArgInfo
sc_fun = ArgInfo
ai })      = OutType -> OutType
funArgTy (ArgInfo -> OutType
ai_type ArgInfo
ai)
contHoleType (ApplyToTy  { sc_hole_ty :: SimplCont -> OutType
sc_hole_ty = OutType
ty }) = OutType
ty  -- See Note [The hole type in ApplyToTy]
contHoleType (ApplyToVal { sc_arg :: SimplCont -> InExpr
sc_arg = InExpr
e, sc_env :: SimplCont -> StaticEnv
sc_env = StaticEnv
se, sc_dup :: SimplCont -> DupFlag
sc_dup = DupFlag
dup, sc_cont :: SimplCont -> SimplCont
sc_cont = SimplCont
k })
  = OutType -> OutType -> OutType
mkVisFunTy (DupFlag -> StaticEnv -> OutType -> OutType
perhapsSubstTy DupFlag
dup StaticEnv
se (InExpr -> OutType
exprType InExpr
e))
               (SimplCont -> OutType
contHoleType SimplCont
k)
contHoleType (Select { sc_dup :: SimplCont -> DupFlag
sc_dup = DupFlag
d, sc_bndr :: SimplCont -> InId
sc_bndr =  InId
b, sc_env :: SimplCont -> StaticEnv
sc_env = StaticEnv
se })
  = DupFlag -> StaticEnv -> OutType -> OutType
perhapsSubstTy DupFlag
d StaticEnv
se (InId -> OutType
idType InId
b)

-------------------
countArgs :: SimplCont -> Int
-- Count all arguments, including types, coercions, and other values
countArgs :: SimplCont -> Int
countArgs (ApplyToTy  { sc_cont :: SimplCont -> SimplCont
sc_cont = SimplCont
cont }) = Int
1 Int -> Int -> Int
forall a. Num a => a -> a -> a
+ SimplCont -> Int
countArgs SimplCont
cont
countArgs (ApplyToVal { sc_cont :: SimplCont -> SimplCont
sc_cont = SimplCont
cont }) = Int
1 Int -> Int -> Int
forall a. Num a => a -> a -> a
+ SimplCont -> Int
countArgs SimplCont
cont
countArgs SimplCont
_                               = Int
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 CoreUnfold
    lone (ApplyToVal {}) = Bool
False
    lone (CastIt {})     = Bool
False
    lone SimplCont
_               = Bool
True

    go :: [ArgSummary] -> SimplCont -> (Bool, [ArgSummary], SimplCont)
go [ArgSummary]
args (ApplyToVal { sc_arg :: SimplCont -> InExpr
sc_arg = InExpr
arg, sc_env :: SimplCont -> StaticEnv
sc_env = StaticEnv
se, sc_cont :: SimplCont -> SimplCont
sc_cont = SimplCont
k })
                                        = [ArgSummary] -> SimplCont -> (Bool, [ArgSummary], SimplCont)
go (InExpr -> StaticEnv -> ArgSummary
is_interesting InExpr
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 OutCoercion
_ 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 :: InExpr -> StaticEnv -> ArgSummary
is_interesting InExpr
arg StaticEnv
se = StaticEnv -> InExpr -> ArgSummary
interestingArg StaticEnv
se InExpr
arg
                   -- Do *not* use short-cutting substitution here
                   -- because we want to get as much IdInfo as possible


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

mkArgInfo :: StaticEnv -> InId -> [CoreRule] -> Int -> SimplCont -> ArgInfo
mkArgInfo StaticEnv
env InId
fun [CoreRule]
rules Int
n_val_args SimplCont
call_cont
  | Int
n_val_args Int -> Int -> Bool
forall a. Ord a => a -> a -> Bool
< InId -> Int
idArity InId
fun            -- Note [Unsaturated functions]
  = ArgInfo :: InId
-> [ArgSpec]
-> OutType
-> FunRules
-> Bool
-> [Bool]
-> [Int]
-> ArgInfo
ArgInfo { ai_fun :: InId
ai_fun = InId
fun, ai_args :: [ArgSpec]
ai_args = [], ai_type :: OutType
ai_type = OutType
fun_ty
            , ai_rules :: FunRules
ai_rules = FunRules
fun_rules
            , ai_encl :: Bool
ai_encl = Bool
False
            , ai_strs :: [Bool]
ai_strs = [Bool]
vanilla_stricts
            , ai_discs :: [Int]
ai_discs = [Int]
vanilla_discounts }
  | Bool
otherwise
  = ArgInfo :: InId
-> [ArgSpec]
-> OutType
-> FunRules
-> Bool
-> [Bool]
-> [Int]
-> ArgInfo
ArgInfo { ai_fun :: InId
ai_fun = InId
fun, ai_args :: [ArgSpec]
ai_args = [], ai_type :: OutType
ai_type = OutType
fun_ty
            , ai_rules :: FunRules
ai_rules = FunRules
fun_rules
            , ai_encl :: Bool
ai_encl  = [CoreRule] -> SimplCont -> Bool
interestingArgContext [CoreRule]
rules SimplCont
call_cont
            , ai_strs :: [Bool]
ai_strs  = [Bool]
arg_stricts
            , ai_discs :: [Int]
ai_discs = [Int]
arg_discounts }
  where
    fun_ty :: OutType
fun_ty = InId -> OutType
idType InId
fun

    fun_rules :: FunRules
fun_rules = [CoreRule] -> FunRules
mkFunRules [CoreRule]
rules

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

    vanilla_stricts, arg_stricts :: [Bool]
    vanilla_stricts :: [Bool]
vanilla_stricts  = Bool -> [Bool]
forall a. a -> [a]
repeat Bool
False

    arg_stricts :: [Bool]
arg_stricts
      | Bool -> Bool
not (SimplMode -> Bool
sm_inline (StaticEnv -> SimplMode
seMode StaticEnv
env))
      = [Bool]
vanilla_stricts -- See Note [Do not expose strictness if sm_inline=False]
      | Bool
otherwise
      = OutType -> [Bool] -> [Bool]
add_type_str OutType
fun_ty ([Bool] -> [Bool]) -> [Bool] -> [Bool]
forall a b. (a -> b) -> a -> b
$
        case StrictSig -> ([Demand], DmdResult)
splitStrictSig (InId -> StrictSig
idStrictness InId
fun) of
          ([Demand]
demands, DmdResult
result_info)
                | Bool -> Bool
not ([Demand]
demands [Demand] -> Int -> Bool
forall a. [a] -> Int -> Bool
`lengthExceeds` Int
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 SimplUtils.analyseCont)
                   if DmdResult -> Bool
isBotRes DmdResult
result_info then
                        (Demand -> Bool) -> [Demand] -> [Bool]
forall a b. (a -> b) -> [a] -> [b]
map Demand -> Bool
forall s u. JointDmd (Str s) (Use u) -> Bool
isStrictDmd [Demand]
demands         -- Finite => result is bottom
                   else
                        (Demand -> Bool) -> [Demand] -> [Bool]
forall a b. (a -> b) -> [a] -> [b]
map Demand -> Bool
forall s u. JointDmd (Str s) (Use u) -> Bool
isStrictDmd [Demand]
demands [Bool] -> [Bool] -> [Bool]
forall a. [a] -> [a] -> [a]
++ [Bool]
vanilla_stricts
               | Bool
otherwise
               -> WARN( True, text "More demands than arity" <+> ppr fun <+> ppr (idArity fun)
                                <+> ppr n_val_args <+> ppr demands )
                   [Bool]
vanilla_stricts      -- Not enough args, or no strictness

    add_type_str :: Type -> [Bool] -> [Bool]
    -- 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_str is done repeatedly (for each call);
    --   might be better once-for-all in the function
    -- But beware primops/datacons with no strictness

    add_type_str :: OutType -> [Bool] -> [Bool]
add_type_str OutType
_ [] = []
    add_type_str OutType
fun_ty all_strs :: [Bool]
all_strs@(Bool
str:[Bool]
strs)
      | Just (OutType
arg_ty, OutType
fun_ty') <- OutType -> Maybe (OutType, OutType)
splitFunTy_maybe OutType
fun_ty        -- Add strict-type info
      = (Bool
str Bool -> Bool -> Bool
|| Bool -> Maybe Bool
forall a. a -> Maybe a
Just Bool
False Maybe Bool -> Maybe Bool -> Bool
forall a. Eq a => a -> a -> Bool
== HasDebugCallStack => OutType -> Maybe Bool
OutType -> Maybe Bool
isLiftedType_maybe OutType
arg_ty)
        Bool -> [Bool] -> [Bool]
forall a. a -> [a] -> [a]
: OutType -> [Bool] -> [Bool]
add_type_str OutType
fun_ty' [Bool]
strs
          -- If the type is levity-polymorphic, we can't know whether it's
          -- strict. isLiftedType_maybe will return Just False only when
          -- we're sure the type is unlifted.

      | Just (InId
_, OutType
fun_ty') <- OutType -> Maybe (InId, OutType)
splitForAllTy_maybe OutType
fun_ty
      = OutType -> [Bool] -> [Bool]
add_type_str OutType
fun_ty' [Bool]
all_strs     -- Look through foralls

      | Bool
otherwise
      = [Bool]
all_strs

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


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

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

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

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

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

Another example:

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

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

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

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

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

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

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

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

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

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

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

    go :: SimplCont -> Bool
go (Select {})                  = Bool
False
    go (ApplyToVal {})              = Bool
False  -- Shouldn't really happen
    go (ApplyToTy  {})              = Bool
False  -- Ditto
    go (StrictArg { sc_cci :: SimplCont -> CallCtxt
sc_cci = CallCtxt
cci }) = CallCtxt -> Bool
interesting CallCtxt
cci
    go (StrictBind {})              = Bool
False      -- ??
    go (CastIt OutCoercion
_ SimplCont
c)                 = SimplCont -> Bool
go SimplCont
c
    go (Stop OutType
_ CallCtxt
cci)                 = CallCtxt -> Bool
interesting CallCtxt
cci
    go (TickIt Tickish InId
_ SimplCont
c)                 = SimplCont -> Bool
go SimplCont
c

    interesting :: CallCtxt -> Bool
interesting CallCtxt
RuleArgCtxt = Bool
True
    interesting CallCtxt
_           = 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 -> InExpr -> ArgSummary
interestingArg StaticEnv
env InExpr
e = StaticEnv -> Int -> InExpr -> ArgSummary
go StaticEnv
env Int
0 InExpr
e
  where
    -- n is # value args to which the expression is applied
    go :: StaticEnv -> Int -> InExpr -> ArgSummary
go StaticEnv
env Int
n (Var InId
v)
       = case StaticEnv -> InId -> SimplSR
substId StaticEnv
env InId
v of
           DoneId InId
v'            -> Int -> InId -> ArgSummary
go_var Int
n InId
v'
           DoneEx InExpr
e Maybe Int
_           -> StaticEnv -> Int -> InExpr -> ArgSummary
go (StaticEnv -> StaticEnv
zapSubstEnv StaticEnv
env)             Int
n InExpr
e
           ContEx TvSubstEnv
tvs CvSubstEnv
cvs SimplIdSubst
ids InExpr
e -> StaticEnv -> Int -> InExpr -> ArgSummary
go (StaticEnv -> TvSubstEnv -> CvSubstEnv -> SimplIdSubst -> StaticEnv
setSubstEnv StaticEnv
env TvSubstEnv
tvs CvSubstEnv
cvs SimplIdSubst
ids) Int
n InExpr
e

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

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

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

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

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

updModeForStableUnfoldings :: Activation -> SimplMode -> SimplMode
-- See Note [Simplifying inside stable unfoldings]
updModeForStableUnfoldings :: Activation -> SimplMode -> SimplMode
updModeForStableUnfoldings Activation
inline_rule_act SimplMode
current_mode
  = SimplMode
current_mode { sm_phase :: CompilerPhase
sm_phase      = Activation -> CompilerPhase
phaseFromActivation Activation
inline_rule_act
                 , sm_inline :: Bool
sm_inline     = Bool
True
                 , sm_eta_expand :: Bool
sm_eta_expand = Bool
False }
                     -- sm_eta_expand: see Note [No eta expansion in stable unfoldings]
       -- For sm_rules, just inherit; sm_rules might be "off"
       -- because of -fno-enable-rewrite-rules
  where
    phaseFromActivation :: Activation -> CompilerPhase
phaseFromActivation (ActiveAfter SourceText
_ Int
n) = Int -> CompilerPhase
Phase Int
n
    phaseFromActivation Activation
_                 = CompilerPhase
InitialPhase

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

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

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

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

Note [No eta expansion in stable unfoldings]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
If we have a stable unfolding

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

we 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 not specialisation of the overloading doesn't work properly
(see Note [Specialisation shape] in Specialise), #9509.

So we disable eta-expansion in stable unfoldings.

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

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

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

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

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

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

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

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

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

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

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

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

That ensures that

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

THE MAIN INVARIANT is this:

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

For example, it's tempting to look at trivial binding like
        x = y
and inline it unconditionally.  But suppose x is used many times,
but this is the unique occurrence of y.  Then inlining x would change
y's occurrence info, which breaks the invariant.  It matters: y
might have a BIG rhs, which will now be dup'd at every occurrenc 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 Phase 0 (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: if the pragma is INLINEABLE, then we don't want to behave in
this special way -- an INLINEABLE pragma just says to GHC "inline this
if you like".  But if there is a unique occurrence, we want to inline
the stable unfolding, not the RHS.

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

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

preInlineUnconditionally
    :: SimplEnv -> TopLevelFlag -> InId
    -> InExpr -> StaticEnv  -- These two go together
    -> Maybe SimplEnv       -- Returned env has extended substitution
-- Precondition: rhs satisfies the let/app invariant
-- See Note [CoreSyn let/app invariant] in CoreSyn
-- Reason: we don't want to inline single uses, or discard dead bindings,
--         for unlifted, side-effect-ful bindings
preInlineUnconditionally :: StaticEnv
-> TopLevelFlag -> InId -> InExpr -> StaticEnv -> Maybe StaticEnv
preInlineUnconditionally StaticEnv
env TopLevelFlag
top_lvl InId
bndr InExpr
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
&& InId -> Bool
isBottomingId InId
bndr = Maybe StaticEnv
forall a. Maybe a
Nothing -- Note [Top-level bottoming Ids]
  | InId -> Bool
isCoVar InId
bndr                             = Maybe StaticEnv
forall a. Maybe a
Nothing -- Note [Do not inline CoVars unconditionally]
  | InId -> Bool
isExitJoinId InId
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 (InId -> OccInfo
idOccInfo InId
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 (InExpr -> StaticEnv
extend_subst_with InExpr
rhs)

  -- Note [Stable unfoldings and preInlineUnconditionally]
  | InlinePragma -> Bool
isInlinablePragma InlinePragma
inline_prag
  , Just InExpr
inl <- Unfolding -> Maybe InExpr
maybeUnfoldingTemplate Unfolding
unf   = StaticEnv -> Maybe StaticEnv
forall a. a -> Maybe a
Just (InExpr -> StaticEnv
extend_subst_with InExpr
inl)
  | Bool
otherwise                                = Maybe StaticEnv
forall a. Maybe a
Nothing
  where
    unf :: Unfolding
unf = InId -> Unfolding
idUnfolding InId
bndr
    extend_subst_with :: InExpr -> StaticEnv
extend_subst_with InExpr
inl_rhs = StaticEnv -> InId -> SimplSR -> StaticEnv
extendIdSubst StaticEnv
env InId
bndr (StaticEnv -> InExpr -> SimplSR
mkContEx StaticEnv
rhs_env InExpr
inl_rhs)

    one_occ :: OccInfo -> Bool
one_occ OccInfo
IAmDead = Bool
True -- Happens in ((\x.1) v)
    one_occ (OneOcc { occ_one_br :: OccInfo -> Bool
occ_one_br = Bool
True      -- One textual occurrence
                    , occ_in_lam :: OccInfo -> Bool
occ_in_lam = Bool
in_lam
                    , occ_int_cxt :: OccInfo -> Bool
occ_int_cxt = Bool
int_cxt })
        | Bool -> Bool
not Bool
in_lam = TopLevelFlag -> Bool
isNotTopLevel TopLevelFlag
top_lvl Bool -> Bool -> Bool
|| Bool
early_phase
        | Bool
otherwise  = Bool
int_cxt Bool -> Bool -> Bool
&& InExpr -> Bool
canInlineInLam InExpr
rhs
    one_occ OccInfo
_        = Bool
False

    pre_inline_unconditionally :: Bool
pre_inline_unconditionally = GeneralFlag -> DynFlags -> Bool
gopt GeneralFlag
Opt_SimplPreInlining (StaticEnv -> DynFlags
seDynFlags StaticEnv
env)
    mode :: SimplMode
mode   = StaticEnv -> SimplMode
getMode StaticEnv
env
    active :: Bool
active = CompilerPhase -> Activation -> Bool
isActive (SimplMode -> CompilerPhase
sm_phase SimplMode
mode) (InlinePragma -> Activation
inlinePragmaActivation InlinePragma
inline_prag)
             -- See Note [pre/postInlineUnconditionally in gentle mode]
    inline_prag :: InlinePragma
inline_prag = InId -> InlinePragma
idInlinePragma InId
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 :: InExpr -> Bool
canInlineInLam (Lit Literal
_)    = Bool
True
    canInlineInLam (Lam InId
b InExpr
e)  = InId -> Bool
isRuntimeVar InId
b Bool -> Bool -> Bool
|| InExpr -> Bool
canInlineInLam InExpr
e
    canInlineInLam (Tick Tickish InId
t InExpr
e) = Bool -> Bool
not (Tickish InId -> Bool
forall id. Tickish id -> Bool
tickishIsCode Tickish InId
t) Bool -> Bool -> Bool
&& InExpr -> Bool
canInlineInLam InExpr
e
    canInlineInLam InExpr
_          = Bool
False
      -- not ticks.  Counting ticks cannot be duplicated, and non-counting
      -- ticks around a Lam will disappear anyway.

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

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

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

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

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

Note that we do this unconditional inlining only for trival 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.
-}

postInlineUnconditionally
    :: SimplEnv -> TopLevelFlag
    -> OutId            -- The binder (*not* a CoVar), including its unfolding
    -> OccInfo          -- From the InId
    -> OutExpr
    -> Bool
-- Precondition: rhs satisfies the let/app invariant
-- See Note [CoreSyn let/app invariant] in CoreSyn
-- Reason: we don't want to inline single uses, or discard dead bindings,
--         for unlifted, side-effect-ful bindings
postInlineUnconditionally :: StaticEnv -> TopLevelFlag -> InId -> OccInfo -> InExpr -> Bool
postInlineUnconditionally StaticEnv
env TopLevelFlag
top_lvl InId
bndr OccInfo
occ_info InExpr
rhs
  | Bool -> Bool
not Bool
active                  = Bool
False
  | OccInfo -> Bool
isWeakLoopBreaker OccInfo
occ_info  = Bool
False -- If it's a loop-breaker of any kind, don't inline
                                        -- because it might be referred to "earlier"
  | Unfolding -> Bool
isStableUnfolding Unfolding
unfolding = Bool
False -- Note [Stable unfoldings and postInlineUnconditionally]
  | TopLevelFlag -> Bool
isTopLevel TopLevelFlag
top_lvl          = Bool
False -- Note [Top level and postInlineUnconditionally]
  | InExpr -> Bool
exprIsTrivial InExpr
rhs           = Bool
True
  | Bool
otherwise
  = case OccInfo
occ_info of
        -- 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
      OneOcc { occ_in_lam :: OccInfo -> Bool
occ_in_lam = Bool
in_lam, occ_int_cxt :: OccInfo -> Bool
occ_int_cxt = Bool
int_cxt }
               -- OneOcc => no code-duplication issue
        ->     DynFlags -> Unfolding -> Bool
smallEnoughToInline DynFlags
dflags Unfolding
unfolding     -- Small enough to dup
                        -- ToDo: consider discount on smallEnoughToInline if int_cxt is true
                        --
                        -- NB: Do NOT inline arbitrarily big things, even if one_br is True
                        -- Reason: doing so risks exponential behaviour.  We simplify a big
                        --         expression, inline it, and simplify it again.  But if the
                        --         very same thing happens in the big expression, we get
                        --         exponential cost!
                        -- PRINCIPLE: when we've already simplified an expression once,
                        -- make sure that we only inline it if it's reasonably small.

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

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

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

      OccInfo
_ -> Bool
False

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

  where
    unfolding :: Unfolding
unfolding = InId -> Unfolding
idUnfolding InId
bndr
    dflags :: DynFlags
dflags    = StaticEnv -> DynFlags
seDynFlags StaticEnv
env
    active :: Bool
active    = CompilerPhase -> Activation -> Bool
isActive (SimplMode -> CompilerPhase
sm_phase (StaticEnv -> SimplMode
getMode StaticEnv
env)) (InId -> Activation
idInlineActivation InId
bndr)
        -- See Note [pre/postInlineUnconditionally in gentle mode]

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

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

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

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

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

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

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

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

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

Then there's a danger we'll optimise to

     f' = e
     f = f' |> co

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

    c.f. Note [Stable unfoldings and preInlineUnconditionally]


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

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

mkLam :: StaticEnv -> [InId] -> InExpr -> SimplCont -> SimplM InExpr
mkLam StaticEnv
_env [] InExpr
body SimplCont
_cont
  = InExpr -> SimplM InExpr
forall (m :: * -> *) a. Monad m => a -> m a
return InExpr
body
mkLam StaticEnv
env [InId]
bndrs InExpr
body SimplCont
cont
  = do { DynFlags
dflags <- SimplM DynFlags
forall (m :: * -> *). HasDynFlags m => m DynFlags
getDynFlags
       ; DynFlags -> [InId] -> InExpr -> SimplM InExpr
mkLam' DynFlags
dflags [InId]
bndrs InExpr
body }
  where
    mkLam' :: DynFlags -> [OutBndr] -> OutExpr -> SimplM OutExpr
    mkLam' :: DynFlags -> [InId] -> InExpr -> SimplM InExpr
mkLam' DynFlags
dflags [InId]
bndrs (Cast InExpr
body OutCoercion
co)
      | Bool -> Bool
not ((InId -> Bool) -> [InId] -> Bool
forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
any InId -> Bool
bad [InId]
bndrs)
        -- Note [Casts and lambdas]
      = do { InExpr
lam <- DynFlags -> [InId] -> InExpr -> SimplM InExpr
mkLam' DynFlags
dflags [InId]
bndrs InExpr
body
           ; InExpr -> SimplM InExpr
forall (m :: * -> *) a. Monad m => a -> m a
return (InExpr -> OutCoercion -> InExpr
mkCast InExpr
lam (Role -> [InId] -> OutCoercion -> OutCoercion
mkPiCos Role
Representational [InId]
bndrs OutCoercion
co)) }
      where
        co_vars :: TyCoVarSet
co_vars  = OutCoercion -> TyCoVarSet
tyCoVarsOfCo OutCoercion
co
        bad :: InId -> Bool
bad InId
bndr = InId -> Bool
isCoVar InId
bndr Bool -> Bool -> Bool
&& InId
bndr InId -> TyCoVarSet -> Bool
`elemVarSet` TyCoVarSet
co_vars

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

    mkLam' DynFlags
dflags [InId]
bndrs (Tick Tickish InId
t InExpr
expr)
      | Tickish InId -> Bool
forall id. Tickish id -> Bool
tickishFloatable Tickish InId
t
      = Tickish InId -> InExpr -> InExpr
mkTick Tickish InId
t (InExpr -> InExpr) -> SimplM InExpr -> SimplM InExpr
forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
<$> DynFlags -> [InId] -> InExpr -> SimplM InExpr
mkLam' DynFlags
dflags [InId]
bndrs InExpr
expr

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

      | Bool -> Bool
not (SimplCont -> Bool
contIsRhs SimplCont
cont)   -- See Note [Eta-expanding lambdas]
      , SimplMode -> Bool
sm_eta_expand (StaticEnv -> SimplMode
getMode StaticEnv
env)
      , (InId -> Bool) -> [InId] -> Bool
forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
any InId -> Bool
isRuntimeVar [InId]
bndrs
      , let body_arity :: Int
body_arity = DynFlags -> InExpr -> Int
exprEtaExpandArity DynFlags
dflags InExpr
body
      , Int
body_arity Int -> Int -> Bool
forall a. Ord a => a -> a -> Bool
> Int
0
      = do { Tick -> SimplM ()
tick (InId -> Tick
EtaExpansion ([InId] -> InId
forall a. [a] -> a
head [InId]
bndrs))
           ; let res :: InExpr
res = [InId] -> InExpr -> InExpr
forall b. [b] -> Expr b -> Expr b
mkLams [InId]
bndrs (Int -> InExpr -> InExpr
etaExpand Int
body_arity InExpr
body)
           ; String -> SDoc -> SimplM ()
traceSmpl String
"eta expand" ([SDoc] -> SDoc
vcat [String -> SDoc
text String
"before" SDoc -> SDoc -> SDoc
<+> InExpr -> SDoc
forall a. Outputable a => a -> SDoc
ppr ([InId] -> InExpr -> InExpr
forall b. [b] -> Expr b -> Expr b
mkLams [InId]
bndrs InExpr
body)
                                          , String -> SDoc
text String
"after" SDoc -> SDoc -> SDoc
<+> InExpr -> SDoc
forall a. Outputable a => a -> SDoc
ppr InExpr
res])
           ; InExpr -> SimplM InExpr
forall (m :: * -> *) a. Monad m => a -> m a
return InExpr
res }

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

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

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

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

NB: We check the SimplEnv (sm_eta_expand), not DynFlags.
    See Note [No eta expansion in stable unfoldings]

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

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

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

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.
It does not make sense to transform
        /\g. e `cast` g  ==>  (/\g.e) `cast` (/\g.g)
because the latter is not well-kinded.

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

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

  | Bool
otherwise
  = do { (Int
new_arity, Bool
is_bot, InExpr
new_rhs) <- SimplM (Int, Bool, InExpr)
try_expand

       ; WARN( new_arity < old_id_arity,
               (text "Arity decrease:" <+> (ppr bndr <+> ppr old_id_arity
                <+> ppr old_arity <+> ppr new_arity) $$ ppr new_rhs) )
                        -- Note [Arity decrease] in Simplify
         (Int, Bool, InExpr) -> SimplM (Int, Bool, InExpr)
forall (m :: * -> *) a. Monad m => a -> m a
return (Int
new_arity, Bool
is_bot, InExpr
new_rhs) }
  where
    try_expand :: SimplM (Int, Bool, InExpr)
try_expand
      | InExpr -> Bool
exprIsTrivial InExpr
rhs
      = (Int, Bool, InExpr) -> SimplM (Int, Bool, InExpr)
forall (m :: * -> *) a. Monad m => a -> m a
return (InExpr -> Int
exprArity InExpr
rhs, Bool
False, InExpr
rhs)

      | SimplMode -> Bool
sm_eta_expand SimplMode
mode      -- Provided eta-expansion is on
      , Int
new_arity Int -> Int -> Bool
forall a. Ord a => a -> a -> Bool
> Int
old_arity   -- And the current manifest arity isn't enough
      = do { Tick -> SimplM ()
tick (InId -> Tick
EtaExpansion InId
bndr)
           ; (Int, Bool, InExpr) -> SimplM (Int, Bool, InExpr)
forall (m :: * -> *) a. Monad m => a -> m a
return (Int
new_arity, Bool
is_bot, Int -> InExpr -> InExpr
etaExpand Int
new_arity InExpr
rhs) }

      | Bool
otherwise
      = (Int, Bool, InExpr) -> SimplM (Int, Bool, InExpr)
forall (m :: * -> *) a. Monad m => a -> m a
return (Int
old_arity, Bool
is_bot Bool -> Bool -> Bool
&& Int
new_arity Int -> Int -> Bool
forall a. Eq a => a -> a -> Bool
== Int
old_arity, InExpr
rhs)

    dflags :: DynFlags
dflags       = SimplMode -> DynFlags
sm_dflags SimplMode
mode
    old_arity :: Int
old_arity    = InExpr -> Int
exprArity InExpr
rhs -- See Note [Do not expand eta-expand PAPs]
    old_id_arity :: Int
old_id_arity = InId -> Int
idArity InId
bndr

    (Int
new_arity1, Bool
is_bot) = DynFlags -> InId -> InExpr -> Int -> (Int, Bool)
findRhsArity DynFlags
dflags InId
bndr InExpr
rhs Int
old_arity
    new_arity2 :: Int
new_arity2 = InId -> Int
idCallArity InId
bndr
    new_arity :: Int
new_arity  = Int -> Int -> Int
forall a. Ord a => a -> a -> a
max Int
new_arity1 Int
new_arity2

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

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

    =>

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

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

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

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

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

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 SimplUtils.abstractFloats,
but there is quite a bit of plumbing in simplLazyBind as well.

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

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

This is good because it can turn things like:

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

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

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

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

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

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

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

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

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

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

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

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

abstractFloats :: DynFlags -> TopLevelFlag -> [OutTyVar] -> SimplFloats
              -> OutExpr -> SimplM ([OutBind], OutExpr)
abstractFloats :: DynFlags
-> TopLevelFlag
-> [InId]
-> SimplFloats
-> InExpr
-> SimplM ([Bind InId], InExpr)
abstractFloats DynFlags
dflags TopLevelFlag
top_lvl [InId]
main_tvs SimplFloats
floats InExpr
body
  = ASSERT( notNull body_floats )
    ASSERT( isNilOL (sfJoinFloats floats) )
    do  { (Subst
subst, [Bind InId]
float_binds) <- (Subst -> Bind InId -> SimplM (Subst, Bind InId))
-> Subst -> [Bind InId] -> SimplM (Subst, [Bind InId])
forall (m :: * -> *) acc x y.
Monad m =>
(acc -> x -> m (acc, y)) -> acc -> [x] -> m (acc, [y])
mapAccumLM Subst -> Bind InId -> SimplM (Subst, Bind InId)
abstract Subst
empty_subst [Bind InId]
body_floats
        ; ([Bind InId], InExpr) -> SimplM ([Bind InId], InExpr)
forall (m :: * -> *) a. Monad m => a -> m a
return ([Bind InId]
float_binds, SDoc -> Subst -> InExpr -> InExpr
CoreSubst.substExpr (String -> SDoc
text String
"abstract_floats1") Subst
subst InExpr
body) }
  where
    is_top_lvl :: Bool
is_top_lvl  = TopLevelFlag -> Bool
isTopLevel TopLevelFlag
top_lvl
    main_tv_set :: TyCoVarSet
main_tv_set = [InId] -> TyCoVarSet
mkVarSet [InId]
main_tvs
    body_floats :: [Bind InId]
body_floats = LetFloats -> [Bind InId]
letFloatBinds (SimplFloats -> LetFloats
sfLetFloats SimplFloats
floats)
    empty_subst :: Subst
empty_subst = InScopeSet -> Subst
CoreSubst.mkEmptySubst (SimplFloats -> InScopeSet
sfInScope SimplFloats
floats)

    abstract :: CoreSubst.Subst -> OutBind -> SimplM (CoreSubst.Subst, OutBind)
    abstract :: Subst -> Bind InId -> SimplM (Subst, Bind InId)
abstract Subst
subst (NonRec InId
id InExpr
rhs)
      = do { (InId
poly_id1, InExpr
poly_app) <- [InId] -> InId -> SimplM (InId, InExpr)
mk_poly1 [InId]
tvs_here InId
id
           ; let (InId
poly_id2, InExpr
poly_rhs) = InId -> [InId] -> InExpr -> (InId, InExpr)
mk_poly2 InId
poly_id1 [InId]
tvs_here InExpr
rhs'
                 subst' :: Subst
subst' = Subst -> InId -> InExpr -> Subst
CoreSubst.extendIdSubst Subst
subst InId
id InExpr
poly_app
           ; (Subst, Bind InId) -> SimplM (Subst, Bind InId)
forall (m :: * -> *) a. Monad m => a -> m a
return (Subst
subst', InId -> InExpr -> Bind InId
forall b. b -> Expr b -> Bind b
NonRec InId
poly_id2 InExpr
poly_rhs) }
      where
        rhs' :: InExpr
rhs' = SDoc -> Subst -> InExpr -> InExpr
CoreSubst.substExpr (String -> SDoc
text String
"abstract_floats2") Subst
subst InExpr
rhs

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

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

    mk_poly1 :: [TyVar] -> Id -> SimplM (Id, CoreExpr)
    mk_poly1 :: [InId] -> InId -> SimplM (InId, InExpr)
mk_poly1 [InId]
tvs_here InId
var
      = do { Unique
uniq <- SimplM Unique
forall (m :: * -> *). MonadUnique m => m Unique
getUniqueM
           ; let  poly_name :: Name
poly_name = Name -> Unique -> Name
setNameUnique (InId -> Name
idName InId
var) Unique
uniq           -- Keep same name
                  poly_ty :: OutType
poly_ty   = [InId] -> OutType -> OutType
mkInvForAllTys [InId]
tvs_here (InId -> OutType
idType InId
var) -- But new type of course
                  poly_id :: InId
poly_id   = InId -> [InId] -> InId -> InId
transferPolyIdInfo InId
var [InId]
tvs_here (InId -> InId) -> InId -> InId
forall a b. (a -> b) -> a -> b
$ -- Note [transferPolyIdInfo] in Id.hs
                              Name -> OutType -> InId
mkLocalIdOrCoVar Name
poly_name OutType
poly_ty
           ; (InId, InExpr) -> SimplM (InId, InExpr)
forall (m :: * -> *) a. Monad m => a -> m a
return (InId
poly_id, InExpr -> [OutType] -> InExpr
forall b. Expr b -> [OutType] -> Expr b
mkTyApps (InId -> InExpr
forall b. InId -> Expr b
Var InId
poly_id) ([InId] -> [OutType]
mkTyVarTys [InId]
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 :: InId -> [InId] -> InExpr -> (InId, InExpr)
mk_poly2 InId
poly_id [InId]
tvs_here InExpr
rhs
      = (InId
poly_id InId -> Unfolding -> InId
`setIdUnfolding` Unfolding
unf, InExpr
poly_rhs)
      where
        poly_rhs :: InExpr
poly_rhs = [InId] -> InExpr -> InExpr
forall b. [b] -> Expr b -> Expr b
mkLams [InId]
tvs_here InExpr
rhs
        unf :: Unfolding
unf = DynFlags -> UnfoldingSource -> Bool -> Bool -> InExpr -> Unfolding
mkUnfolding DynFlags
dflags UnfoldingSource
InlineRhs Bool
is_top_lvl Bool
False InExpr
poly_rhs

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

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


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

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

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

prepareAlts tries these things:

1.  Eliminate alternatives that cannot match, including the
    DEFAULT alternative.

2.  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.

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

Here "cannot match" includes knowledge from GADTs

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

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

data Colour = Red | Green | Blue

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

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

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

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

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


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

mkCase tries these things

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

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

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

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

and similar friends.

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

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

And similarly for commuted arguments and for some unary operations.

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

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

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

  becomes:

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

There are some wrinkles

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

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

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

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

* In dataToTag we might need to make up some fake binders;
  see Note [caseRules for dataToTag] in PrelRules
-}

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

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

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

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

              wrapped_alts :: [InAlt]
wrapped_alts | InId -> Bool
isDeadBinder InId
inner_bndr = [InAlt]
inner_alts
                           | Bool
otherwise               = (InAlt -> InAlt) -> [InAlt] -> [InAlt]
forall a b. (a -> b) -> [a] -> [b]
map InAlt -> InAlt
forall (t :: * -> *) a.
Foldable t =>
(a, t InId, InExpr) -> (a, t InId, InExpr)
wrap_alt [InAlt]
inner_alts

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

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

mkCase DynFlags
dflags InExpr
scrut InId
bndr OutType
alts_ty [InAlt]
alts = DynFlags -> InExpr -> InId -> OutType -> [InAlt] -> SimplM InExpr
mkCase1 DynFlags
dflags InExpr
scrut InId
bndr OutType
alts_ty [InAlt]
alts

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

mkCase1 :: DynFlags -> InExpr -> InId -> OutType -> [InAlt] -> SimplM InExpr
mkCase1 DynFlags
_dflags InExpr
scrut InId
case_bndr OutType
_ alts :: [InAlt]
alts@((AltCon
_,[InId]
_,InExpr
rhs1) : [InAlt]
_)      -- Identity case
  | (InAlt -> Bool) -> [InAlt] -> Bool
forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
all InAlt -> Bool
forall b. (AltCon, [InId], Expr b) -> Bool
identity_alt [InAlt]
alts
  = do { Tick -> SimplM ()
tick (InId -> Tick
CaseIdentity InId
case_bndr)
       ; InExpr -> SimplM InExpr
forall (m :: * -> *) a. Monad m => a -> m a
return ([Tickish InId] -> InExpr -> InExpr
mkTicks [Tickish InId]
ticks (InExpr -> InExpr) -> InExpr -> InExpr
forall a b. (a -> b) -> a -> b
$ InExpr -> InExpr -> InExpr
forall b b. Expr b -> Expr b -> Expr b
re_cast InExpr
scrut InExpr
rhs1) }
  where
    ticks :: [Tickish InId]
ticks = (InAlt -> [Tickish InId]) -> [InAlt] -> [Tickish InId]
forall (t :: * -> *) a b. Foldable t => (a -> [b]) -> t a -> [b]
concatMap ((Tickish InId -> Bool) -> InExpr -> [Tickish InId]
forall b. (Tickish InId -> Bool) -> Expr b -> [Tickish InId]
stripTicksT Tickish InId -> Bool
forall id. Tickish id -> Bool
tickishFloatable (InExpr -> [Tickish InId])
-> (InAlt -> InExpr) -> InAlt -> [Tickish InId]
forall b c a. (b -> c) -> (a -> b) -> a -> c
. InAlt -> InExpr
forall a b c. (a, b, c) -> c
thdOf3) ([InAlt] -> [InAlt]
forall a. [a] -> [a]
tail [InAlt]
alts)
    identity_alt :: (AltCon, [InId], Expr b) -> Bool
identity_alt (AltCon
con, [InId]
args, Expr b
rhs) = Expr b -> AltCon -> [InId] -> Bool
forall b. Expr b -> AltCon -> [InId] -> Bool
check_eq Expr b
rhs AltCon
con [InId]
args

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

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

    arg_tys :: [OutType]
arg_tys = OutType -> [OutType]
tyConAppArgs (InId -> OutType
idType InId
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 DynFlags
dflags InExpr
scrut InId
bndr OutType
alts_ty [InAlt]
alts = DynFlags -> InExpr -> InId -> OutType -> [InAlt] -> SimplM InExpr
mkCase2 DynFlags
dflags InExpr
scrut InId
bndr OutType
alts_ty [InAlt]
alts

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

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

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

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

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

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

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

    mk_new_bndrs :: InId -> AltCon -> m [InId]
mk_new_bndrs InId
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 PrelRules
        do { [Unique]
us <- m [Unique]
forall (m :: * -> *). MonadUnique m => m [Unique]
getUniquesM
           ; let ([InId]
ex_tvs, [InId]
arg_ids) = [Unique] -> DataCon -> [OutType] -> ([InId], [InId])
dataConRepInstPat [Unique]
us DataCon
dc
                                        (OutType -> [OutType]
tyConAppArgs (InId -> OutType
idType InId
new_bndr))
           ; [InId] -> m [InId]
forall (m :: * -> *) a. Monad m => a -> m a
return ([InId]
ex_tvs [InId] -> [InId] -> [InId]
forall a. [a] -> [a] -> [a]
++ [InId]
arg_ids) }
    mk_new_bndrs InId
_ AltCon
_ = [InId] -> m [InId]
forall (m :: * -> *) a. Monad m => a -> m a
return []

    re_sort :: [CoreAlt] -> [CoreAlt]
    -- Sort the alternatives to re-establish
    -- CoreSyn 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 b. (AltCon, a, b) -> (AltCon, a, b) -> Ordering
cmpAlt [InAlt]
alts

    add_default :: [CoreAlt] -> [CoreAlt]
    -- See Note [Literal cases]
    add_default :: [InAlt] -> [InAlt]
add_default ((LitAlt {}, [InId]
bs, InExpr
rhs) : [InAlt]
alts) = (AltCon
DEFAULT, [InId]
bs, InExpr
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 sligthtly better code (although it should not, since
all cases are exhaustive) and/or optimise better.  I'm not certain that
it's necessary, but currenty we do make this change.  We do it here,
NOT in the TagToEnum rules (see "Beware" in Note [caseRules for tagToEnum]
in PrelRules)
-}

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

-- See Note [Exitification] and Note [Do not inline exit join points] in Exitify.hs
-- 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 :: InId -> Bool
isExitJoinId InId
id = InId -> Bool
isJoinId InId
id Bool -> Bool -> Bool
&& OccInfo -> Bool
isOneOcc (InId -> OccInfo
idOccInfo InId
id) Bool -> Bool -> Bool
&& OccInfo -> Bool
occ_in_lam (InId -> OccInfo
idOccInfo InId
id)

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


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

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


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

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

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

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

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

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

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

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