\section[SimplUtils]{The simplifier utilities}
\begin{code}
-{-# OPTIONS -w #-}
--- The above warning supression flag is a temporary kludge.
--- While working on this module you are encouraged to remove it and fix
--- any warnings in the module. See
--- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
--- for details
-
module SimplUtils (
-- Rebuilding
mkLam, mkCase, prepareAlts, bindCaseBndr,
-- Inlining,
preInlineUnconditionally, postInlineUnconditionally,
- activeInline, activeRule, inlineMode,
+ activeInline, activeRule,
+ simplEnvForGHCi, simplEnvForRules, updModeForInlineRules,
-- The continuation type
- SimplCont(..), DupFlag(..), LetRhsFlag(..),
+ SimplCont(..), DupFlag(..), ArgInfo(..),
contIsDupable, contResultType, contIsTrivial, contArgs, dropArgs,
- countValArgs, countArgs, splitInlineCont,
- mkBoringStop, mkLazyArgStop, mkRhsStop, contIsRhsOrArg,
- interestingCallContext, interestingArgContext,
+ countValArgs, countArgs,
+ mkBoringStop, mkRhsStop, mkLazyArgStop, contIsRhsOrArg,
+ interestingCallContext,
interestingArg, mkArgInfo,
import PprCore
import CoreFVs
import CoreUtils
-import Literal
+import CoreArity ( etaExpand, exprEtaExpandArity )
import CoreUnfold
-import MkId
import Name
import Id
import Var ( isCoVar )
import NewDemand
import SimplMonad
-import Type ( Type, funArgTy, mkForAllTys, mkTyVarTys,
- splitTyConApp_maybe, tyConAppArgs )
+import Type hiding( substTy )
+import Coercion ( coercionKind )
import TyCon
-import DataCon
import Unify ( dataConCannotMatch )
import VarSet
import BasicTypes
import Util
+import MonadUtils
import Outputable
-import List( nub )
+import FastString
+
+import Data.List
\end{code}
\begin{code}
data SimplCont
= Stop -- An empty context, or hole, []
- OutType -- Type of the result
- LetRhsFlag
- Bool -- True <=> There is something interesting about
+ CallCtxt -- True <=> There is something interesting about
-- the context, and hence the inliner
-- should be a bit keener (see interestingCallContext)
- -- Two cases:
- -- (a) This is the RHS of a thunk whose type suggests
- -- that update-in-place would be possible
- -- (b) This is an argument of a function that has RULES
+ -- Specifically:
+ -- This is an argument of a function that has RULES
-- Inlining the call might allow the rule to fire
| CoerceIt -- C `cast` co
SimplCont
| StrictArg -- e C
- OutExpr OutType -- e and its type
- (Bool,[Bool]) -- Whether the function at the head of e has rules,
- SimplCont -- plus strictness flags for further args
-
-data LetRhsFlag = AnArg -- It's just an argument not a let RHS
- | AnRhs -- It's the RHS of a let (so please float lets out of big lambdas)
-
-instance Outputable LetRhsFlag where
- ppr AnArg = ptext SLIT("arg")
- ppr AnRhs = ptext SLIT("rhs")
+ OutExpr -- e; *always* of form (Var v `App1` e1 .. `App` en)
+ CallCtxt -- Whether *this* argument position is interesting
+ ArgInfo -- Whether the function at the head of e has rules, etc
+ SimplCont -- plus strictness flags for *further* args
+
+data ArgInfo
+ = ArgInfo {
+ ai_rules :: Bool, -- Function has rules (recursively)
+ -- => be keener to inline in all args
+ ai_strs :: [Bool], -- Strictness of arguments
+ -- Usually infinite, but if it is finite it guarantees
+ -- that the function diverges after being given
+ -- that number of args
+ ai_discs :: [Int] -- Discounts for arguments; non-zero => be keener to inline
+ -- Always infinite
+ }
instance Outputable SimplCont where
- ppr (Stop ty is_rhs _) = ptext SLIT("Stop") <> brackets (ppr is_rhs) <+> ppr ty
- ppr (ApplyTo dup arg se cont) = ((ptext SLIT("ApplyTo") <+> ppr dup <+> pprParendExpr arg)
+ ppr (Stop interesting) = ptext (sLit "Stop") <> brackets (ppr interesting)
+ ppr (ApplyTo dup arg _ cont) = ((ptext (sLit "ApplyTo") <+> ppr dup <+> pprParendExpr arg)
{- $$ nest 2 (pprSimplEnv se) -}) $$ ppr cont
- ppr (StrictBind b _ _ _ cont) = (ptext SLIT("StrictBind") <+> ppr b) $$ ppr cont
- ppr (StrictArg f _ _ cont) = (ptext SLIT("StrictArg") <+> ppr f) $$ ppr cont
- ppr (Select dup bndr alts se cont) = (ptext SLIT("Select") <+> ppr dup <+> ppr bndr) $$
+ ppr (StrictBind b _ _ _ cont) = (ptext (sLit "StrictBind") <+> ppr b) $$ ppr cont
+ ppr (StrictArg f _ _ cont) = (ptext (sLit "StrictArg") <+> ppr f) $$ ppr cont
+ ppr (Select dup bndr alts _ cont) = (ptext (sLit "Select") <+> ppr dup <+> ppr bndr) $$
(nest 4 (ppr alts)) $$ ppr cont
- ppr (CoerceIt co cont) = (ptext SLIT("CoerceIt") <+> ppr co) $$ ppr cont
+ ppr (CoerceIt co cont) = (ptext (sLit "CoerceIt") <+> ppr co) $$ ppr cont
data DupFlag = OkToDup | NoDup
instance Outputable DupFlag where
- ppr OkToDup = ptext SLIT("ok")
- ppr NoDup = ptext SLIT("nodup")
+ ppr OkToDup = ptext (sLit "ok")
+ ppr NoDup = ptext (sLit "nodup")
-------------------
-mkBoringStop :: OutType -> SimplCont
-mkBoringStop ty = Stop ty AnArg False
+mkBoringStop :: SimplCont
+mkBoringStop = Stop BoringCtxt
-mkLazyArgStop :: OutType -> Bool -> SimplCont
-mkLazyArgStop ty has_rules = Stop ty AnArg (canUpdateInPlace ty || has_rules)
+mkRhsStop :: SimplCont -- See Note [RHS of lets] in CoreUnfold
+mkRhsStop = Stop (ArgCtxt False)
-mkRhsStop :: OutType -> SimplCont
-mkRhsStop ty = Stop ty AnRhs (canUpdateInPlace ty)
+mkLazyArgStop :: CallCtxt -> SimplCont
+mkLazyArgStop cci = Stop cci
-------------------
-contIsRhsOrArg (Stop {}) = True
-contIsRhsOrArg (StrictBind {}) = True
-contIsRhsOrArg (StrictArg {}) = True
-contIsRhsOrArg other = False
+contIsRhsOrArg :: SimplCont -> Bool
+contIsRhsOrArg (Stop {}) = True
+contIsRhsOrArg (StrictBind {}) = True
+contIsRhsOrArg (StrictArg {}) = True
+contIsRhsOrArg _ = False
-------------------
contIsDupable :: SimplCont -> Bool
-contIsDupable (Stop {}) = True
+contIsDupable (Stop {}) = True
contIsDupable (ApplyTo OkToDup _ _ _) = True
contIsDupable (Select OkToDup _ _ _ _) = True
contIsDupable (CoerceIt _ cont) = contIsDupable cont
-contIsDupable other = False
+contIsDupable _ = False
-------------------
contIsTrivial :: SimplCont -> Bool
-contIsTrivial (Stop {}) = True
+contIsTrivial (Stop {}) = True
contIsTrivial (ApplyTo _ (Type _) _ cont) = contIsTrivial cont
-contIsTrivial (CoerceIt _ cont) = contIsTrivial cont
-contIsTrivial other = False
+contIsTrivial (CoerceIt _ cont) = contIsTrivial cont
+contIsTrivial _ = False
-------------------
-contResultType :: SimplCont -> OutType
-contResultType (Stop to_ty _ _) = to_ty
-contResultType (StrictArg _ _ _ cont) = contResultType cont
-contResultType (StrictBind _ _ _ _ cont) = contResultType cont
-contResultType (ApplyTo _ _ _ cont) = contResultType cont
-contResultType (CoerceIt _ cont) = contResultType cont
-contResultType (Select _ _ _ _ cont) = contResultType cont
+contResultType :: SimplEnv -> OutType -> SimplCont -> OutType
+contResultType env ty cont
+ = go cont ty
+ where
+ subst_ty se ty = substTy (se `setInScope` env) ty
+
+ go (Stop {}) ty = ty
+ go (CoerceIt co cont) _ = go cont (snd (coercionKind co))
+ go (StrictBind _ bs body se cont) _ = go cont (subst_ty se (exprType (mkLams bs body)))
+ go (StrictArg fn _ _ cont) _ = go cont (funResultTy (exprType fn))
+ go (Select _ _ alts se cont) _ = go cont (subst_ty se (coreAltsType alts))
+ go (ApplyTo _ arg se cont) ty = go cont (apply_to_arg ty arg se)
+
+ apply_to_arg ty (Type ty_arg) se = applyTy ty (subst_ty se ty_arg)
+ apply_to_arg ty _ _ = funResultTy ty
-------------------
countValArgs :: SimplCont -> Int
-countValArgs (ApplyTo _ (Type ty) se cont) = countValArgs cont
-countValArgs (ApplyTo _ val_arg se cont) = 1 + countValArgs cont
-countValArgs other = 0
+countValArgs (ApplyTo _ (Type _) _ cont) = countValArgs cont
+countValArgs (ApplyTo _ _ _ cont) = 1 + countValArgs cont
+countValArgs _ = 0
countArgs :: SimplCont -> Int
-countArgs (ApplyTo _ arg se cont) = 1 + countArgs cont
-countArgs other = 0
+countArgs (ApplyTo _ _ _ cont) = 1 + countArgs cont
+countArgs _ = 0
contArgs :: SimplCont -> ([OutExpr], SimplCont)
-- Uses substitution to turn each arg into an OutExpr
dropArgs 0 cont = cont
dropArgs n (ApplyTo _ _ _ cont) = dropArgs (n-1) cont
dropArgs n other = pprPanic "dropArgs" (ppr n <+> ppr other)
-
---------------------
-splitInlineCont :: SimplCont -> Maybe (SimplCont, SimplCont)
--- Returns Nothing if the continuation should dissolve an InlineMe Note
--- Return Just (c1,c2) otherwise,
--- where c1 is the continuation to put inside the InlineMe
--- and c2 outside
-
--- Example: (__inline_me__ (/\a. e)) ty
--- Here we want to do the beta-redex without dissolving the InlineMe
--- See test simpl017 (and Trac #1627) for a good example of why this is important
-
-splitInlineCont (ApplyTo dup (Type ty) se c)
- | Just (c1, c2) <- splitInlineCont c = Just (ApplyTo dup (Type ty) se c1, c2)
-splitInlineCont cont@(Stop ty _ _) = Just (mkBoringStop ty, cont)
-splitInlineCont cont@(StrictBind bndr _ _ se _) = Just (mkBoringStop (substTy se (idType bndr)), cont)
-splitInlineCont cont@(StrictArg _ fun_ty _ _) = Just (mkBoringStop (funArgTy fun_ty), cont)
-splitInlineCont other = Nothing
- -- NB: the calculation of the type for mkBoringStop is an annoying
- -- duplication of the same calucation in mkDupableCont
\end{code}
-\begin{code}
-interestingArg :: OutExpr -> Bool
- -- An argument is interesting if it has *some* structure
- -- We are here trying 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.
-interestingArg (Var v) = hasSomeUnfolding (idUnfolding v)
- -- Was: isValueUnfolding (idUnfolding v')
- -- But that seems over-pessimistic
- || isDataConWorkId v
- -- This accounts for an argument like
- -- () or [], which is definitely interesting
-interestingArg (Type _) = False
-interestingArg (App fn (Type _)) = interestingArg fn
-interestingArg (Note _ a) = interestingArg a
-
--- Idea (from Sam B); I'm not sure if it's a good idea, so commented out for now
--- interestingArg expr | isUnLiftedType (exprType expr)
--- -- Unlifted args are only ever interesting if we know what they are
--- = case expr of
--- Lit lit -> True
--- _ -> False
-
-interestingArg other = True
- -- Consider let x = 3 in f x
- -- The substitution will contain (x -> ContEx 3), and we want to
- -- to say that x is an interesting argument.
- -- But consider also (\x. f x y) y
- -- The substitution will contain (x -> ContEx y), and we want to say
- -- that x is not interesting (assuming y has no unfolding)
-\end{code}
-
-
-Comment about interestingCallContext
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+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
contIsInteresting looks for case expressions with just a single
default case.
+
\begin{code}
-interestingCallContext :: Bool -- False <=> no args at all
- -> Bool -- False <=> no value args
- -> SimplCont -> Bool
- -- The "lone-variable" case is important. I spent ages
- -- messing about with unsatisfactory varaints, but this is nice.
- -- The idea is that if a variable appear all alone
- -- as an arg of lazy fn, or rhs Stop
- -- as scrutinee of a case Select
- -- as arg of a strict fn ArgOf
- -- then we should not inline it (unless there is some other reason,
- -- e.g. is is the sole occurrence). We achieve this by making
- -- interestingCallContext return False for a lone variable.
- --
- -- Why? At least in the case-scrutinee situation, turning
- -- let x = (a,b) in case x of y -> ...
- -- into
- -- let x = (a,b) in case (a,b) of y -> ...
- -- and thence to
- -- let x = (a,b) in let y = (a,b) in ...
- -- is bad if the binding for x will remain.
- --
- -- Another example: I discovered that strings
- -- were getting inlined straight back into applications of 'error'
- -- because the latter is strict.
- -- s = "foo"
- -- f = \x -> ...(error s)...
-
- -- Fundamentally such contexts should not ecourage inlining because
- -- the context can ``see'' the unfolding of the variable (e.g. case or a RULE)
- -- so there's no gain.
- --
- -- However, even a type application or coercion isn't a lone variable.
- -- Consider
- -- case $fMonadST @ RealWorld of { :DMonad a b c -> c }
- -- We had better inline that sucker! The case won't see through it.
- --
- -- For now, I'm treating treating a variable applied to types
- -- in a *lazy* context "lone". The motivating example was
- -- f = /\a. \x. BIG
- -- g = /\a. \y. h (f a)
- -- There's no advantage in inlining f here, and perhaps
- -- a significant disadvantage. Hence some_val_args in the Stop case
-
-interestingCallContext some_args some_val_args cont
+interestingCallContext :: SimplCont -> CallCtxt
+-- See Note [Interesting call context]
+interestingCallContext cont
= interesting cont
where
- interesting (Select {}) = some_args
- interesting (ApplyTo {}) = True -- Can happen if we have (coerce t (f x)) y
- -- Perhaps True is a bit over-keen, but I've
- -- seen (coerce f) x, where f has an INLINE prag,
- -- So we have to give some motivaiton for inlining it
- interesting (StrictArg {}) = some_val_args
- interesting (StrictBind {}) = some_val_args -- ??
- interesting (Stop ty _ interesting) = some_val_args && interesting
- interesting (CoerceIt _ cont) = interesting cont
+ interesting (Select _ bndr _ _ _)
+ | isDeadBinder bndr = CaseCtxt
+ | otherwise = ArgCtxt False -- If the binder is used, this
+ -- is like a strict let
+ -- See Note [RHS of lets] in CoreUnfold
+
+ interesting (ApplyTo _ arg _ cont)
+ | isTypeArg arg = interesting cont
+ | otherwise = 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 _ cci _ _) = cci
+ interesting (StrictBind {}) = BoringCtxt
+ interesting (Stop cci) = cci
+ interesting (CoerceIt _ cont) = interesting cont
-- 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.
-------------------
mkArgInfo :: Id
+ -> [CoreRule] -- Rules for function
-> Int -- Number of value args
- -> SimplCont -- Context of the cal
- -> (Bool, [Bool]) -- Arg info
--- The arg info consists of
--- * A Bool indicating if the function has rules (recursively)
--- * A [Bool] indicating strictness for each arg
--- The [Bool] is usually infinite, but if it is finite it
--- guarantees that the function diverges after being given
--- that number of args
-
-mkArgInfo fun n_val_args call_cont
- = (interestingArgContext fun call_cont, fun_stricts)
+ -> SimplCont -- Context of the call
+ -> ArgInfo
+
+mkArgInfo fun rules n_val_args call_cont
+ | n_val_args < idArity fun -- Note [Unsaturated functions]
+ = ArgInfo { ai_rules = False
+ , ai_strs = vanilla_stricts
+ , ai_discs = vanilla_discounts }
+ | otherwise
+ = ArgInfo { ai_rules = interestingArgContext rules call_cont
+ , ai_strs = add_type_str (idType fun) arg_stricts
+ , ai_discs = arg_discounts }
where
- vanilla_stricts, fun_stricts :: [Bool]
+ vanilla_discounts, arg_discounts :: [Int]
+ vanilla_discounts = repeat 0
+ arg_discounts = case idUnfolding fun of
+ CoreUnfolding {uf_guidance = UnfoldIfGoodArgs {ug_args = discounts}}
+ -> discounts ++ vanilla_discounts
+ _ -> vanilla_discounts
+
+ vanilla_stricts, arg_stricts :: [Bool]
vanilla_stricts = repeat False
- fun_stricts
+ arg_stricts
= case splitStrictSig (idNewStrictness fun) of
(demands, result_info)
| not (demands `lengthExceeds` n_val_args)
map isStrictDmd demands -- Finite => result is bottom
else
map isStrictDmd demands ++ vanilla_stricts
+ | otherwise
+ -> WARN( True, text "More demands than arity" <+> ppr fun <+> ppr (idArity fun)
+ <+> ppr n_val_args <+> ppr demands )
+ 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 _ [] = []
+ add_type_str fun_ty strs -- Look through foralls
+ | Just (_, fun_ty') <- splitForAllTy_maybe fun_ty -- Includes coercions
+ = add_type_str fun_ty' strs
+ add_type_str fun_ty (str:strs) -- Add strict-type info
+ | Just (arg_ty, fun_ty') <- splitFunTy_maybe fun_ty
+ = (str || isStrictType arg_ty) : add_type_str fun_ty' strs
+ add_type_str _ strs
+ = 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
+-}
- other -> vanilla_stricts -- Not enough args, or no strictness
-
-interestingArgContext :: Id -> SimplCont -> Bool
+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
-- 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.
--- The interesting_arg_ctxt flag makes this happen; if it's
+-- 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
-interestingArgContext fn cont
- = idHasRules fn || go cont
+interestingArgContext rules call_cont
+ = notNull rules || enclosing_fn_has_rules
where
- go (Select {}) = False
- go (ApplyTo {}) = False
- go (StrictArg {}) = True
- go (StrictBind {}) = False -- ??
- go (CoerceIt _ c) = go c
- go (Stop _ _ interesting) = interesting
+ enclosing_fn_has_rules = go call_cont
--------------------
-canUpdateInPlace :: Type -> Bool
--- Consider let x = <wurble> in ...
--- If <wurble> returns an explicit constructor, we might be able
--- to do update in place. So we treat even a thunk RHS context
--- as interesting if update in place is possible. We approximate
--- this by seeing if the type has a single constructor with a
--- small arity. But arity zero isn't good -- we share the single copy
--- for that case, so no point in sharing.
-
-canUpdateInPlace ty
- | not opt_UF_UpdateInPlace = False
- | otherwise
- = case splitTyConApp_maybe ty of
- Nothing -> False
- Just (tycon, _) -> case tyConDataCons_maybe tycon of
- Just [dc] -> arity == 1 || arity == 2
- where
- arity = dataConRepArity dc
- other -> False
+ go (Select {}) = False
+ go (ApplyTo {}) = False
+ go (StrictArg _ cci _ _) = interesting cci
+ go (StrictBind {}) = False -- ??
+ go (CoerceIt _ c) = go c
+ go (Stop cci) = interesting cci
+
+ interesting (ArgCtxt rules) = rules
+ interesting _ = False
\end{code}
%* *
%************************************************************************
-Inlining is controlled partly by the SimplifierMode switch. This has two
-settings:
+\begin{code}
+simplEnvForGHCi :: SimplEnv
+simplEnvForGHCi = mkSimplEnv allOffSwitchChecker $
+ SimplGently { sm_rules = False, sm_inline = False }
+ -- Do not do any inlining, in case we expose some unboxed
+ -- tuple stuff that confuses the bytecode interpreter
+
+simplEnvForRules :: SimplEnv
+simplEnvForRules = mkSimplEnv allOffSwitchChecker $
+ SimplGently { sm_rules = True, sm_inline = False }
+
+updModeForInlineRules :: SimplifierMode -> SimplifierMode
+updModeForInlineRules mode
+ = case mode of
+ SimplGently {} -> mode -- Don't modify mode if we already gentle
+ SimplPhase {} -> SimplGently { sm_rules = True, sm_inline = True }
+ -- Simplify as much as possible, subject to the usual "gentle" rules
+\end{code}
+Inlining is controlled partly by the SimplifierMode switch. This has two
+settings
+
SimplGently (a) Simplifying before specialiser/full laziness
- (b) Simplifiying inside INLINE pragma
+ (b) Simplifiying inside InlineRules
(c) Simplifying the LHS of a rule
(d) Simplifying a GHCi expression or Template
Haskell splice
- SimplPhase n Used at all other times
-
-The key thing about SimplGently is that it does no call-site inlining.
+ SimplPhase n _ Used at all other times
+
+Note [Gentle mode]
+~~~~~~~~~~~~~~~~~~
+Gentle mode has a separate boolean flag to control
+ a) inlining (sm_inline flag)
+ b) rules (sm_rules flag)
+A key invariant about Gentle mode is that it is treated as the EARLIEST
+phase. Something is inlined if the sm_inline flag is on AND the thing
+is inlinable in the earliest phase. This is important. Example
+
+ {-# 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 InlineRule for f has had g inlined into it.
+
+On the other hand, it is bad not to do ANY inlining into an
+InlineRule, because then recursive knots in instance declarations
+don't get unravelled.
+
+However, *sometimes* SimplGently must do no call-site inlining at all.
Before full laziness we must be careful not to inline wrappers,
because doing so inhibits floating
e.g. ...(case f x of ...)...
anything, because the byte-code interpreter might get confused about
unboxed tuples and suchlike.
-INLINE pragmas
-~~~~~~~~~~~~~~
-SimplGently is also used as the mode to simplify inside an InlineMe note.
+Note [RULEs enabled in SimplGently]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+RULES are enabled when doing "gentle" simplification. Two reasons:
-\begin{code}
-inlineMode :: SimplifierMode
-inlineMode = SimplGently
-\end{code}
+ * We really want the class-op cancellation to happen:
+ op (df d1 d2) --> $cop3 d1 d2
+ because this breaks the mutual recursion between 'op' and 'df'
-It really is important to switch off inlinings inside such
-expressions. Consider the following example
+ * I wanted the RULE
+ lift String ===> ...
+ to work in Template Haskell when simplifying
+ splices, so we get simpler code for literal strings
+
+Note [Simplifying gently inside InlineRules]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+We don't do much simplification inside InlineRules (which come from
+INLINE pragmas). It really is important to switch off inlinings
+inside such expressions. Consider the following example
let f = \pq -> BIG
in
in ...g...g...g...g...g...
Now, if that's the ONLY occurrence of f, it will be inlined inside g,
-and thence copied multiple times when g is inlined.
-
+and thence copied multiple times when g is inlined.
-This function may be inlinined in other modules, so we
-don't want to remove (by inlining) calls to functions that have
-specialisations, or that may have transformation rules in an importing
-scope.
+This function may be inlinined in other modules, so we don't want to
+remove (by inlining) calls to functions that have specialisations, or
+that may have transformation rules in an importing scope.
E.g. {-# INLINE f #-}
- f x = ...g...
+ f x = ...g...
and suppose that g is strict *and* has specialisations. If we inline
g's wrapper, we deny f the chance of getting the specialised version
ArgOf continuations. It shouldn't do any harm not to dissolve the
inline-me note under these circumstances.
-Note that the result is that we do very little simplification
-inside an InlineMe.
+Although we do very little simplification inside an InlineRule,
+the RHS is simplified as normal. For example:
all xs = foldr (&&) True xs
any p = all . map p {-# INLINE any #-}
-Problem: any won't get deforested, and so if it's exported and the
-importer doesn't use the inlining, (eg passes it as an arg) then we
-won't get deforestation at all. We havn't solved this problem yet!
+The RHS of 'any' will get optimised and deforested; but the InlineRule
+will still mention the original RHS.
preInlineUnconditionally
might have a BIG rhs, which will now be dup'd at every occurrenc of x.
-Evne RHSs labelled InlineMe aren't caught here, because there might be
+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
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 intial stages. See Note [Gentle mode].
+
\begin{code}
preInlineUnconditionally :: SimplEnv -> TopLevelFlag -> InId -> InExpr -> Bool
preInlineUnconditionally env top_lvl bndr rhs
| otherwise = case idOccInfo bndr of
IAmDead -> True -- Happens in ((\x.1) v)
OneOcc in_lam True int_cxt -> try_once in_lam int_cxt
- other -> False
+ _ -> False
where
phase = getMode env
active = case phase of
- SimplGently -> isAlwaysActive prag
- SimplPhase n -> isActive n prag
- prag = idInlinePragma bndr
+ SimplGently {} -> isEarlyActive act
+ -- See Note [pre/postInlineUnconditionally in gentle mode]
+ SimplPhase n _ -> isActive n act
+ act = idInlineActivation bndr
try_once in_lam int_cxt -- There's one textual occurrence
| not in_lam = isNotTopLevel top_lvl || early_phase
-- 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 (Lit l) = True
+ canInlineInLam (Lit _) = True
canInlineInLam (Lam b e) = isRuntimeVar b || canInlineInLam e
canInlineInLam (Note _ e) = canInlineInLam e
canInlineInLam _ = False
early_phase = case phase of
- SimplPhase 0 -> False
- other -> True
+ SimplPhase 0 _ -> False
+ _ -> 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
\begin{code}
postInlineUnconditionally
:: SimplEnv -> TopLevelFlag
- -> InId -- The binder (an OutId would be fine too)
+ -> OutId -- The binder (an InId would be fine too)
-> OccInfo -- From the InId
-> OutExpr
-> Unfolding
-> Bool
postInlineUnconditionally env top_lvl bndr occ_info rhs unfolding
| not active = False
- | isLoopBreaker occ_info = False -- If it's a loop-breaker of any kind, dont' inline
+ | isLoopBreaker occ_info = False -- If it's a loop-breaker of any kind, don't inline
-- because it might be referred to "earlier"
| isExportedId bndr = False
+ | isInlineRule unfolding = False -- Note [InlineRule and postInlineUnconditionally]
| exprIsTrivial rhs = True
| otherwise
= case occ_info of
-- True -> case x of ...
-- False -> case x of ...
-- I'm not sure how important this is in practice
- OneOcc in_lam one_br int_cxt -- OneOcc => no code-duplication issue
+ OneOcc in_lam _one_br int_cxt -- OneOcc => no code-duplication issue
-> smallEnoughToInline unfolding -- Small enough to dup
-- ToDo: consider discount on smallEnoughToInline if int_cxt is true
--
-- Here x isn't mentioned in the RHS, so we don't want to
-- create the (dead) let-binding let x = (a,b) in ...
- other -> False
+ _ -> 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
+-- - 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
active = case getMode env of
- SimplGently -> isAlwaysActive prag
- SimplPhase n -> isActive n prag
- prag = idInlinePragma bndr
+ SimplGently {} -> isEarlyActive act
+ -- See Note [pre/postInlineUnconditionally in gentle mode]
+ SimplPhase n _ -> isActive n act
+ act = idInlineActivation bndr
activeInline :: SimplEnv -> OutId -> Bool
activeInline env id
+ | isNonRuleLoopBreaker (idOccInfo id) -- Things with an INLINE pragma may have
+ -- an unfolding *and* be a loop breaker
+ = False -- (maybe the knot is not yet untied)
+ | otherwise
= case getMode env of
- SimplGently -> False
- -- No inlining at all when doing gentle stuff,
- -- except for local things that occur once
- -- 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
+ SimplGently { sm_inline = inlining_on }
+ -> inlining_on && isEarlyActive act
+ -- See Note [Gentle mode]
-- NB: we used to have a second exception, for data con wrappers.
-- On the grounds that we use gentle mode for rule LHSs, and
-- and they are now constructed as Compulsory unfoldings (in MkId)
-- so they'll happen anyway.
- SimplPhase n -> isActive n prag
+ SimplPhase n _ -> isActive n act
where
- prag = idInlinePragma id
+ act = idInlineActivation id
activeRule :: DynFlags -> SimplEnv -> Maybe (Activation -> Bool)
-- Nothing => No rules at all
activeRule dflags env
- | not (dopt Opt_RewriteRules dflags)
+ | not (dopt Opt_EnableRewriteRules dflags)
= Nothing -- Rewriting is off
| otherwise
= case getMode env of
- SimplGently -> Just isAlwaysActive
- -- Used to be Nothing (no rules in gentle mode)
- -- Main motivation for changing is that I wanted
- -- lift String ===> ...
- -- to work in Template Haskell when simplifying
- -- splices, so we get simpler code for literal strings
- SimplPhase n -> Just (isActive n)
+ SimplGently { sm_rules = rules_on }
+ | rules_on -> Just isEarlyActive -- Note [RULEs enabled in SimplGently]
+ | otherwise -> Nothing
+ SimplPhase n _ -> Just (isActive n)
\end{code}
+Note [InlineRule and postInlineUnconditionally]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Do not do postInlineUnconditionally if the Id has an InlineRule, otherwise
+we lose the unfolding. Example
+
+ -- f has InlineRule 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 InlineRule on f. Now f'
+won't inline because 'e' is too big.
+
%************************************************************************
%* *
%************************************************************************
\begin{code}
-mkLam :: [OutBndr] -> OutExpr -> SimplM OutExpr
+mkLam :: SimplEnv -> [OutBndr] -> OutExpr -> 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 [] body
+mkLam _b [] body
= return body
-mkLam bndrs body
+mkLam env bndrs body
= do { dflags <- getDOptsSmpl
; mkLam' dflags bndrs body }
where
mkLam' :: DynFlags -> [OutBndr] -> OutExpr -> SimplM OutExpr
- mkLam' dflags bndrs (Cast body@(Lam _ _) co)
+ mkLam' dflags bndrs (Cast body co)
+ | not (any bad bndrs)
-- Note [Casts and lambdas]
- = do { lam <- mkLam' dflags (bndrs ++ bndrs') body'
+ = do { lam <- mkLam' dflags bndrs body
; return (mkCoerce (mkPiTypes bndrs co) lam) }
- where
- (bndrs',body') = collectBinders body
+ where
+ co_vars = tyVarsOfType co
+ bad bndr = isCoVar bndr && bndr `elemVarSet` co_vars
mkLam' dflags bndrs body
| dopt Opt_DoEtaReduction dflags,
; return etad_lam }
| dopt Opt_DoLambdaEtaExpansion dflags,
- any isRuntimeVar bndrs
- = do { body' <- tryEtaExpansion dflags body
+ not (inGentleMode env), -- In gentle mode don't eta-expansion
+ any isRuntimeVar bndrs -- because it can clutter up the code
+ -- with casts etc that may not be removed
+ = do { let body' = tryEtaExpansion dflags body
; return (mkLams bndrs body') }
| otherwise
- = returnSmpl (mkLams bndrs body)
+ = return (mkLams bndrs body)
\end{code}
Note [Casts and lambdas]
(\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.
-
+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.
-- c) floating lets out through big lambdas
-- [only if all tyvar lambdas, and only if this lambda
-- if this is indeed a right-hand side; otherwise
-- we end up floating the thing out, only for float-in
-- to float it right back in again!
- = tryRhsTyLam env bndrs body `thenSmpl` \ (floats, body') ->
- returnSmpl (floats, mkLams bndrs body')
+ = do (floats, body') <- tryRhsTyLam env bndrs body
+ return (floats, mkLams bndrs body')
-}
%************************************************************************
%* *
-\subsection{Eta expansion and reduction}
+ Eta reduction
%* *
%************************************************************************
-We try for eta reduction here, but *only* if we get all the
-way to an exprIsTrivial expression.
-We don't want to remove extra lambdas unless we are going
-to avoid allocating this thing altogether
+Note [Eta reduction conditions]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+We try for eta reduction here, but *only* if we get all the way to an
+trivial expression. We don't want to remove extra lambdas unless we
+are going to avoid allocating this thing altogether.
+
+There are some particularly delicate points here:
+
+* Eta reduction is not valid in general:
+ \x. bot /= bot
+ This matters, partly for old-fashioned correctness reasons but,
+ worse, getting it wrong can yield a seg fault. Consider
+ f = \x.f x
+ h y = case (case y of { True -> f `seq` True; False -> False }) of
+ True -> ...; False -> ...
+
+ If we (unsoundly) eta-reduce f to get f=f, the strictness analyser
+ says f=bottom, and replaces the (f `seq` True) with just
+ (f `cast` unsafe-co). BUT, as thing stand, 'f' got arity 1, and it
+ *keeps* arity 1 (perhaps also wrongly). So CorePrep eta-expands
+ the definition again, so that it does not termninate after all.
+ Result: seg-fault because the boolean case actually gets a function value.
+ See Trac #1947.
+
+ So it's important to to the right thing.
+
+* Note [Arity care]: we need to be careful if we just look at f's
+ arity. Currently (Dec07), f's arity is visible in its own RHS (see
+ Note [Arity robustness] in SimplEnv) so we must *not* trust the
+ arity when checking that 'f' is a value. Otherwise we will
+ eta-reduce
+ f = \x. f x
+ to
+ f = f
+ Which might change a terminiating program (think (f `seq` e)) to a
+ non-terminating one. So we check for being a loop breaker first.
+
+ However for GlobalIds we can look at the arity; and for primops we
+ must, since they have no unfolding.
+
+* Regardless of whether 'f' is a value, we always want to
+ reduce (/\a -> f a) to f
+ This came up in a RULE: foldr (build (/\a -> g a))
+ did not match foldr (build (/\b -> ...something complex...))
+ The type checker can insert these eta-expanded versions,
+ with both type and dictionary lambdas; hence the slightly
+ ad-hoc isDictId
+
+* Never *reduce* arity. For example
+ f = \xy. g x y
+ Then if h has arity 1 we don't want to eta-reduce because then
+ f's arity would decrease, and that is bad
+
+These delicacies are why we don't use exprIsTrivial and exprIsHNF here.
+Alas.
\begin{code}
tryEtaReduce :: [OutBndr] -> OutExpr -> Maybe OutExpr
tryEtaReduce bndrs body
- -- We don't use CoreUtils.etaReduce, because we can be more
- -- efficient here:
- -- (a) we already have the binders
- -- (b) we can do the triviality test before computing the free vars
= go (reverse bndrs) body
where
+ incoming_arity = count isId bndrs
+
go (b : bs) (App fun arg) | ok_arg b arg = go bs fun -- Loop round
go [] fun | ok_fun fun = Just fun -- Success!
go _ _ = Nothing -- Failure!
- ok_fun fun = exprIsTrivial fun
- && not (any (`elemVarSet` (exprFreeVars fun)) bndrs)
- && (exprIsHNF fun || all ok_lam bndrs)
+ -- Note [Eta reduction conditions]
+ ok_fun (App fun (Type ty))
+ | not (any (`elemVarSet` tyVarsOfType ty) bndrs)
+ = ok_fun fun
+ ok_fun (Var fun_id)
+ = not (fun_id `elem` bndrs)
+ && (ok_fun_id fun_id || all ok_lam bndrs)
+ ok_fun _fun = False
+
+ ok_fun_id fun = fun_arity fun >= incoming_arity
+
+ fun_arity fun -- See Note [Arity care]
+ | isLocalId fun && isLoopBreaker (idOccInfo fun) = 0
+ | otherwise = idArity fun
+
ok_lam v = isTyVar v || isDictId v
- -- The exprIsHNF is because eta reduction is not
- -- valid in general: \x. bot /= bot
- -- So we need to be sure that the "fun" is a value.
- --
- -- However, we always want to reduce (/\a -> f a) to f
- -- This came up in a RULE: foldr (build (/\a -> g a))
- -- did not match foldr (build (/\b -> ...something complex...))
- -- The type checker can insert these eta-expanded versions,
- -- with both type and dictionary lambdas; hence the slightly
- -- ad-hoc isDictTy
ok_arg b arg = varToCoreExpr b `cheapEqExpr` arg
\end{code}
- Try eta expansion for RHSs
+%************************************************************************
+%* *
+ Eta expansion
+%* *
+%************************************************************************
+
We go for:
f = \x1..xn -> N ==> f = \x1..xn y1..ym -> N y1..ym
* N is a NORMAL FORM (i.e. no redexes anywhere)
wanting a suitable number of extra args.
+The biggest reason for doing this is for cases like
+
+ f = \x -> case x of
+ True -> \y -> e1
+ False -> \y -> e2
+
+Here we want to get the lambdas together. A good exmaple is the nofib
+program fibheaps, which gets 25% more allocation if you don't do this
+eta-expansion.
+
We may have to sandwich some coerces between the lambdas
to make the types work. exprEtaExpandArity looks through coerces
when computing arity; and etaExpand adds the coerces as necessary when
actually computing the expansion.
\begin{code}
-tryEtaExpansion :: DynFlags -> OutExpr -> SimplM OutExpr
+tryEtaExpansion :: DynFlags -> OutExpr -> OutExpr
-- There is at least one runtime binder in the binders
tryEtaExpansion dflags body
- = getUniquesSmpl `thenSmpl` \ us ->
- returnSmpl (etaExpand fun_arity us body (exprType body))
+ = etaExpand fun_arity body
where
fun_arity = exprEtaExpandArity dflags body
\end{code}
We'd like to float this to
y1 = /\a. e1
y2 = /\a. e2
- x = /\a. C (y1 a) (y2 a)
+ 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
abstractFloats :: [OutTyVar] -> SimplEnv -> OutExpr -> SimplM ([OutBind], OutExpr)
abstractFloats main_tvs body_env body
= ASSERT( notNull body_floats )
- do { (subst, float_binds) <- mapAccumLSmpl abstract empty_subst body_floats
+ do { (subst, float_binds) <- mapAccumLM abstract empty_subst body_floats
; return (float_binds, CoreSubst.substExpr subst body) }
where
main_tv_set = mkVarSet main_tvs
-- gives rise to problems. SLPJ June 98
abstract subst (Rec prs)
- = do { (poly_ids, poly_apps) <- mapAndUnzipSmpl (mk_poly tvs_here) ids
+ = do { (poly_ids, poly_apps) <- mapAndUnzipM (mk_poly tvs_here) ids
; let subst' = CoreSubst.extendSubstList subst (ids `zip` poly_apps)
poly_rhss = [mkLams tvs_here (CoreSubst.substExpr subst' rhs) | rhs <- rhss]
; return (subst', Rec (poly_ids `zip` poly_rhss)) }
tvs_here = main_tvs
mk_poly tvs_here var
- = do { uniq <- getUniqueSmpl
+ = do { uniq <- getUniqueM
; let poly_name = setNameUnique (idName var) uniq -- Keep same name
poly_ty = mkForAllTys tvs_here (idType var) -- But new type of course
- poly_id = mkLocalId poly_name poly_ty
+ poly_id = transferPolyIdInfo var tvs_here $ -- Note [transferPolyIdInfo] in Id.lhs
+ mkLocalId poly_name poly_ty
; return (poly_id, mkTyApps (Var poly_id) (mkTyVarTys tvs_here)) }
-- In the olden days, it was crucial to copy the occInfo of the original var,
-- because we were looking at occurrence-analysed but as yet unsimplified code!
pattern in each alternative, so the binder-info is rather useful.
\begin{code}
-prepareAlts :: OutExpr -> OutId -> [InAlt] -> SimplM ([AltCon], [InAlt])
-prepareAlts scrut case_bndr' alts
+prepareAlts :: SimplEnv -> OutExpr -> OutId -> [InAlt] -> SimplM ([AltCon], [InAlt])
+prepareAlts env scrut case_bndr' alts
= do { dflags <- getDOptsSmpl
; alts <- combineIdenticalAlts case_bndr' alts
-- EITHER by the context,
-- OR by a non-DEFAULT branch in this case expression.
- ; default_alts <- prepareDefault dflags scrut case_bndr' mb_tc_app
+ ; default_alts <- prepareDefault dflags env case_bndr' mb_tc_app
imposs_deflt_cons maybe_deflt
; let trimmed_alts = filterOut impossible_alt alts_wo_default
imposs_cons = case scrut of
Var v -> otherCons (idUnfolding v)
- other -> []
+ _ -> []
impossible_alt :: CoreAlt -> Bool
impossible_alt (con, _, _) | con `elem` imposs_cons = True
impossible_alt (DataAlt con, _, _) = dataConCannotMatch inst_tys con
- impossible_alt alt = False
+ impossible_alt _ = False
--------------------------------------------------
--------------------------------------------------
combineIdenticalAlts :: OutId -> [InAlt] -> SimplM [InAlt]
-combineIdenticalAlts case_bndr alts@((con1,bndrs1,rhs1) : con_alts)
+combineIdenticalAlts case_bndr ((_con1,bndrs1,rhs1) : con_alts)
| all isDeadBinder bndrs1, -- Remember the default
length filtered_alts < length con_alts -- alternative comes first
-- Also Note [Dead binders]
; return ((DEFAULT, [], rhs1) : filtered_alts) }
where
filtered_alts = filter keep con_alts
- keep (con,bndrs,rhs) = not (all isDeadBinder bndrs && rhs `cheapEqExpr` rhs1)
+ keep (_con,bndrs,rhs) = not (all isDeadBinder bndrs && rhs `cheapEqExpr` rhs1)
-combineIdenticalAlts case_bndr alts = return alts
+combineIdenticalAlts _ alts = return alts
-------------------------------------------------------------------------
-- Prepare the default alternative
-------------------------------------------------------------------------
prepareDefault :: DynFlags
- -> OutExpr -- Scrutinee
+ -> SimplEnv
-> OutId -- Case binder; need just for its type. Note that as an
-- OutId, it has maximum information; this is important.
-- Test simpl013 is an example
-- And becuase case-merging can cause many to show up
------- Merge nested cases ----------
-prepareDefault dflags scrut outer_bndr bndr_ty imposs_cons (Just deflt_rhs)
+prepareDefault dflags env outer_bndr _bndr_ty imposs_cons (Just deflt_rhs)
| dopt Opt_CaseMerge dflags
- , Case (Var scrut_var) inner_bndr _ inner_alts <- deflt_rhs
- , scruting_same_var scrut_var
+ , Case (Var inner_scrut_var) inner_bndr _ inner_alts <- deflt_rhs
+ , DoneId inner_scrut_var' <- substId env inner_scrut_var
+ -- Remember, inner_scrut_var is an InId, but outer_bndr is an OutId
+ , inner_scrut_var' == outer_bndr
+ -- NB: the substId means that if the outer scrutinee was a
+ -- variable, and inner scrutinee is the same variable,
+ -- then inner_scrut_var' will be outer_bndr
+ -- via the magic of simplCaseBinder
= do { tick (CaseMerge outer_bndr)
; let munge_rhs rhs = bindCaseBndr inner_bndr (Var outer_bndr) rhs
-- 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!
- where
- -- We are scrutinising the same variable if it's
- -- the outer case-binder, or if the outer case scrutinises a variable
- -- (and it's the same). Testing both allows us not to replace the
- -- outer scrut-var with the outer case-binder (Simplify.simplCaseBinder).
- scruting_same_var = case scrut of
- Var outer_scrut -> \ v -> v == outer_bndr || v == outer_scrut
- other -> \ v -> v == outer_bndr
+
--------- Fill in known constructor -----------
-prepareDefault dflags scrut case_bndr (Just (tycon, inst_tys)) imposs_cons (Just deflt_rhs)
+prepareDefault _ _ case_bndr (Just (tycon, inst_tys)) imposs_cons (Just deflt_rhs)
| -- This branch handles the case where we are
-- scrutinisng an algebraic data type
isAlgTyCon tycon -- It's a data type, tuple, or unboxed tuples.
[con] -> -- It matches exactly one constructor, so fill it in
do { tick (FillInCaseDefault case_bndr)
- ; us <- getUniquesSmpl
+ ; us <- getUniquesM
; let (ex_tvs, co_tvs, arg_ids) =
dataConRepInstPat us con inst_tys
; return [(DataAlt con, ex_tvs ++ co_tvs ++ arg_ids, deflt_rhs)] }
- two_or_more -> return [(DEFAULT, [], deflt_rhs)]
+ _ -> return [(DEFAULT, [], deflt_rhs)]
+
+ | debugIsOn, isAlgTyCon tycon, not (isOpenTyCon tycon), null (tyConDataCons tycon)
+ -- This can legitimately happen for type families, so don't report that
+ = pprTrace "prepareDefault" (ppr case_bndr <+> ppr tycon)
+ $ return [(DEFAULT, [], deflt_rhs)]
--------- Catch-all cases -----------
-prepareDefault dflags scrut case_bndr bndr_ty imposs_cons (Just deflt_rhs)
+prepareDefault _dflags _env _case_bndr _bndr_ty _imposs_cons (Just deflt_rhs)
= return [(DEFAULT, [], deflt_rhs)]
-prepareDefault dflags scrut case_bndr bndr_ty imposs_cons Nothing
+prepareDefault _dflags _env _case_bndr _bndr_ty _imposs_cons Nothing
= return [] -- No default branch
\end{code}
\begin{code}
-mkCase :: OutExpr -> OutId -> OutType
- -> [OutAlt] -- Increasing order
+mkCase :: OutExpr -> OutId -> [OutAlt] -- Increasing order
-> SimplM OutExpr
--------------------------------------------------
--- 1. Check for empty alternatives
---------------------------------------------------
-
--- This isn't strictly an error. It's possible that the simplifer might "see"
--- that an inner case has no accessible alternatives before it "sees" that the
--- entire branch of an outer case is inaccessible. So we simply
--- put an error case here insteadd
-mkCase scrut case_bndr ty []
- = pprTrace "mkCase: null alts" (ppr case_bndr <+> ppr scrut) $
- return (mkApps (Var rUNTIME_ERROR_ID)
- [Type ty, Lit (mkStringLit "Impossible alternative")])
-
-
---------------------------------------------------
-- 2. Identity case
--------------------------------------------------
-mkCase scrut case_bndr ty alts -- Identity case
+mkCase scrut case_bndr alts -- Identity case
| all identity_alt alts
- = tick (CaseIdentity case_bndr) `thenSmpl_`
- returnSmpl (re_cast scrut)
+ = do tick (CaseIdentity case_bndr)
+ return (re_cast scrut)
where
identity_alt (con, args, rhs) = check_eq con args (de_cast rhs)
check_eq (LitAlt lit') _ (Lit lit) = lit == lit'
check_eq (DataAlt con) args rhs = rhs `cheapEqExpr` mkConApp con (arg_tys ++ varsToCoreExprs args)
|| rhs `cheapEqExpr` Var case_bndr
- check_eq con args rhs = False
+ check_eq _ _ _ = False
arg_tys = map Type (tyConAppArgs (idType case_bndr))
re_cast scrut = case head alts of
(_,_,Cast _ co) -> Cast scrut co
- other -> scrut
+ _ -> scrut
--------------------------------------------------
-- Catch-all
--------------------------------------------------
-mkCase scrut bndr ty alts = returnSmpl (Case scrut bndr ty alts)
+mkCase scrut bndr alts = return (Case scrut bndr (coreAltsType alts) alts)
\end{code}
cascade rather nicely.
\begin{code}
+bindCaseBndr :: Id -> CoreExpr -> CoreExpr -> CoreExpr
bindCaseBndr bndr rhs body
| isDeadBinder bndr = body
- | otherwise = bindNonRec bndr rhs body
+ | otherwise = bindNonRec bndr rhs body
\end{code}