activeInline, activeRule, inlineMode,
-- The continuation type
- SimplCont(..), DupFlag(..), LetRhsFlag(..),
+ SimplCont(..), DupFlag(..), ArgInfo(..),
contIsDupable, contResultType, contIsTrivial, contArgs, dropArgs,
countValArgs, countArgs, splitInlineCont,
mkBoringStop, mkLazyArgStop, mkRhsStop, contIsRhsOrArg,
import Var ( isCoVar )
import NewDemand
import SimplMonad
-import Type ( Type, funArgTy, mkForAllTys, mkTyVarTys,
- splitTyConApp_maybe, tyConAppArgs )
+import Type hiding( substTy )
import TyCon
import DataCon
import Unify ( dataConCannotMatch )
import VarSet
import BasicTypes
import Util
+import MonadUtils
import Outputable
+import FastString
+
import List( nub )
\end{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
| 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")
+ 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 (Stop ty _) = ptext SLIT("Stop") <+> ppr ty
ppr (ApplyTo dup arg se 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 (StrictArg f _ _ _ cont) = (ptext SLIT("StrictArg") <+> ppr f) $$ ppr cont
ppr (Select dup bndr alts se cont) = (ptext SLIT("Select") <+> ppr dup <+> ppr bndr) $$
(nest 4 (ppr alts)) $$ ppr cont
ppr (CoerceIt co cont) = (ptext SLIT("CoerceIt") <+> ppr co) $$ ppr cont
-------------------
mkBoringStop :: OutType -> SimplCont
-mkBoringStop ty = Stop ty AnArg False
+mkBoringStop ty = Stop ty BoringCtxt
-mkLazyArgStop :: OutType -> Bool -> SimplCont
-mkLazyArgStop ty has_rules = Stop ty AnArg (canUpdateInPlace ty || has_rules)
+mkLazyArgStop :: OutType -> CallCtxt -> SimplCont
+mkLazyArgStop ty cci = Stop ty cci
mkRhsStop :: OutType -> SimplCont
-mkRhsStop ty = Stop ty AnRhs (canUpdateInPlace ty)
+mkRhsStop ty = Stop ty BoringCtxt
-------------------
contIsRhsOrArg (Stop {}) = True
-------------------
contResultType :: SimplCont -> OutType
-contResultType (Stop to_ty _ _) = to_ty
-contResultType (StrictArg _ _ _ cont) = contResultType cont
+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
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@(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 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
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
+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
+ interestingCtxt = ArgCtxt False 2 -- Give *some* incentive!
+
+ interesting (Select _ bndr _ _ _)
+ | isDeadBinder bndr = CaseCtxt
+ | otherwise = interestingCtxt
+
+ interesting (ApplyTo {}) = interestingCtxt
+ -- Can happen if we have (coerce t (f x)) y
+ -- Perhaps interestingCtxt is a bit over-keen, but I've
+ -- seen (coerce f) x, where f has an INLINE prag,
+ -- So we have to give some motivation for inlining it
+
+ interesting (StrictArg _ _ cci _ _) = cci
+ interesting (StrictBind {}) = BoringCtxt
+ interesting (Stop ty 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
-> 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
+ -> ArgInfo
mkArgInfo fun n_val_args call_cont
- = (interestingArgContext fun call_cont, fun_stricts)
+ = ArgInfo { ai_rules = interestingArgContext fun call_cont
+ , ai_strs = 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 _ _ _ _ (UnfoldIfGoodArgs _ discounts _ _)
+ -> discounts ++ vanilla_discounts
+ other -> 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)
-- 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.
+-- where h has rules, then we do want to inline f; hence the
+-- call_cont argument to interestingArgContext
+--
-- The interesting_arg_ctxt 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 fn call_cont
+ = idHasRules fn || go call_cont
where
- go (Select {}) = False
- go (ApplyTo {}) = False
- go (StrictArg {}) = True
- go (StrictBind {}) = False -- ??
- go (CoerceIt _ c) = go c
- go (Stop _ _ interesting) = interesting
-
--------------------
-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 other = False
\end{code}
(d) Simplifying a GHCi expression or Template
Haskell splice
- SimplPhase n Used at all other times
+ SimplPhase n _ Used at all other times
The key thing about SimplGently is that it does no call-site inlining.
Before full laziness we must be careful not to inline wrappers,
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
where
phase = getMode env
active = case phase of
- SimplGently -> isAlwaysActive prag
- SimplPhase n -> isActive n prag
+ SimplGently -> isAlwaysActive prag
+ SimplPhase n _ -> isActive n prag
prag = idInlinePragma bndr
try_once in_lam int_cxt -- There's one textual occurrence
canInlineInLam _ = False
early_phase = case phase of
- SimplPhase 0 -> False
- other -> True
+ SimplPhase 0 _ -> False
+ other -> 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
where
active = case getMode env of
- SimplGently -> isAlwaysActive prag
- SimplPhase n -> isActive n prag
+ SimplGently -> isAlwaysActive prag
+ SimplPhase n _ -> isActive n prag
prag = idInlinePragma bndr
activeInline :: SimplEnv -> OutId -> Bool
-- and they are now constructed as Compulsory unfoldings (in MkId)
-- so they'll happen anyway.
- SimplPhase n -> isActive n prag
+ SimplPhase n _ -> isActive n prag
where
prag = idInlinePragma id
= Nothing -- Rewriting is off
| otherwise
= case getMode env of
- SimplGently -> Just isAlwaysActive
+ 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)
+ SimplPhase n _ -> Just (isActive n)
\end{code}
; 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 (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.
+
+* 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. Instead, look at the unfolding.
+
+ 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 vlaue, 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
+
+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
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
+ | isLocalId fun = isEvaldUnfolding (idUnfolding fun)
+ | isDataConWorkId fun = True
+ | isGlobalId fun = idArity fun > 0
+
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
\begin{code}
tryEtaExpansion :: DynFlags -> OutExpr -> SimplM 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))
+tryEtaExpansion dflags body = do
+ us <- getUniquesM
+ return (etaExpand fun_arity us body (exprType body))
where
fun_arity = exprEtaExpandArity dflags body
\end{code}
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
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
-- 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 dflags env 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)]
--------- 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}
mkCase scrut case_bndr ty 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)
--------------------------------------------------
-- Catch-all
--------------------------------------------------
-mkCase scrut bndr ty alts = returnSmpl (Case scrut bndr ty alts)
+mkCase scrut bndr ty alts = return (Case scrut bndr ty alts)
\end{code}
projects / ghc-hetmet.git / blobdiff