\begin{code}
module SimplUtils (
- simplBinder, simplBinders, simplRecBndrs,
- simplLetBndr, simplLamBndrs,
- newId, mkLam, prepareAlts, mkCase,
+ mkLam, prepareAlts, mkCase,
+
+ -- Inlining,
+ preInlineUnconditionally, postInlineUnconditionally, activeInline, activeRule,
+ inlineMode,
-- The continuation type
SimplCont(..), DupFlag(..), LetRhsFlag(..),
contIsDupable, contResultType,
countValArgs, countArgs, pushContArgs,
- mkBoringStop, mkStop, contIsRhs, contIsRhsOrArg,
+ mkBoringStop, mkRhsStop, contIsRhs, contIsRhsOrArg,
getContArgs, interestingCallContext, interestingArg, isStrictType
) where
#include "HsVersions.h"
-import CmdLineOpts ( SimplifierSwitch(..),
- opt_SimplDoLambdaEtaExpansion, opt_SimplDoEtaReduction,
- opt_SimplCaseMerge, opt_UF_UpdateInPlace
- )
+import SimplEnv
+import DynFlags ( SimplifierSwitch(..), SimplifierMode(..),
+ DynFlag(..), dopt )
+import StaticFlags ( opt_UF_UpdateInPlace, opt_SimplNoPreInlining,
+ opt_RulesOff )
import CoreSyn
-import CoreUtils ( cheapEqExpr, exprType,
- etaExpand, exprEtaExpandArity, bindNonRec, mkCoerce,
- findDefault, exprOkForSpeculation, exprIsValue
+import CoreFVs ( exprFreeVars )
+import CoreUtils ( cheapEqExpr, exprType, exprIsTrivial, exprIsCheap,
+ etaExpand, exprEtaExpandArity, bindNonRec, mkCoerce2,
+ findDefault, exprOkForSpeculation, exprIsHNF
)
-import qualified Subst ( simplBndrs, simplBndr, simplLetId, simplLamBndr )
-import Id ( Id, idType, idInfo,
- mkSysLocal, isDeadBinder, idNewDemandInfo,
- idUnfolding, idNewStrictness
+import Literal ( mkStringLit )
+import CoreUnfold ( smallEnoughToInline )
+import MkId ( eRROR_ID )
+import Id ( idType, isDataConWorkId, idOccInfo, isDictId,
+ mkSysLocal, isDeadBinder, idNewDemandInfo, isExportedId,
+ idUnfolding, idNewStrictness, idInlinePragma,
)
import NewDemand ( isStrictDmd, isBotRes, splitStrictSig )
import SimplMonad
-import Type ( Type, seqType, splitFunTys, dropForAlls, isStrictType,
+import Type ( Type, splitFunTys, dropForAlls, isStrictType,
splitTyConApp_maybe, tyConAppArgs, mkTyVarTys
)
-import TcType ( isDictTy )
-import OccName ( EncodedFS )
+import Name ( mkSysTvName )
import TyCon ( tyConDataCons_maybe, isAlgTyCon, isNewTyCon )
-import DataCon ( dataConRepArity, dataConExistentialTyVars, dataConArgTys )
-import Var ( mkSysTyVar, tyVarKind )
-import Util ( lengthExceeds, mapAccumL )
+import DataCon ( dataConRepArity, dataConTyVars, dataConInstArgTys, isVanillaDataCon )
+import Var ( tyVarKind, mkTyVar )
+import VarSet
+import BasicTypes ( TopLevelFlag(..), isNotTopLevel, OccInfo(..), isLoopBreaker, isOneOcc,
+ Activation, isAlwaysActive, isActive )
+import Util ( lengthExceeds )
import Outputable
\end{code}
ppr AnRhs = ptext SLIT("rhs")
instance Outputable SimplCont where
- ppr (Stop _ is_rhs _) = ptext SLIT("Stop") <> brackets (ppr is_rhs)
+ 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 <+> ppr arg) $$ ppr cont
ppr (ArgOf _ _ _ _) = ptext SLIT("ArgOf...")
ppr (Select dup bndr alts se cont) = (ptext SLIT("Select") <+> ppr dup <+> ppr bndr) $$
-------------------
-mkBoringStop :: OutType -> SimplCont
+mkBoringStop, mkRhsStop :: OutType -> SimplCont
mkBoringStop ty = Stop ty AnArg (canUpdateInPlace ty)
-
-mkStop :: OutType -> LetRhsFlag -> SimplCont
-mkStop ty is_rhs = Stop ty is_rhs (canUpdateInPlace ty)
+mkRhsStop ty = Stop ty AnRhs (canUpdateInPlace ty)
contIsRhs :: SimplCont -> Bool
contIsRhs (Stop _ AnRhs _) = True
contIsDupable (ApplyTo OkToDup _ _ _) = True
contIsDupable (Select OkToDup _ _ _ _) = True
contIsDupable (CoerceIt _ cont) = contIsDupable cont
-contIsDupable (InlinePlease cont) = contIsDupable cont
-contIsDupable other = False
+contIsDupable (InlinePlease cont) = contIsDupable cont
+contIsDupable other = False
-------------------
discardableCont :: SimplCont -> Bool
-- * (error "Hello") arg
-- * f (error "Hello") where f is strict
-- etc
+ -- Then, especially in the first of these cases, we'd like to discard
+ -- the continuation, leaving just the bottoming expression. But the
+ -- type might not be right, so we may have to add a coerce.
go acc ss inl cont
| null ss && discardableCont cont = (reverse acc, discardCont cont, inl)
| otherwise = (reverse acc, cont, inl)
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
interestingCallContext some_args some_val_args cont
= interesting cont
where
- interesting (InlinePlease _) = True
- interesting (Select _ _ _ _ _) = some_args
- interesting (ApplyTo _ _ _ _) = True -- Can happen if we have (coerce t (f x)) y
+ interesting (InlinePlease _) = True
+ 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
%************************************************************************
%* *
-\section{Dealing with a single binder}
+\subsection{Decisions about inlining}
%* *
%************************************************************************
-These functions are in the monad only so that they can be made strict via seq.
+Inlining is controlled partly by the SimplifierMode switch. This has two
+settings:
+
+ SimplGently (a) Simplifying before specialiser/full laziness
+ (b) Simplifiying inside INLINE pragma
+ (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.
+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-inling 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.
+
+INLINE pragmas
+~~~~~~~~~~~~~~
+SimplGently is also used as the mode to simplify inside an InlineMe note.
\begin{code}
-simplBinders :: SimplEnv -> [InBinder] -> SimplM (SimplEnv, [OutBinder])
-simplBinders env bndrs
- = let
- (subst', bndrs') = Subst.simplBndrs (getSubst env) bndrs
- in
- seqBndrs bndrs' `seq`
- returnSmpl (setSubst env subst', bndrs')
+inlineMode :: SimplifierMode
+inlineMode = SimplGently
+\end{code}
-simplBinder :: SimplEnv -> InBinder -> SimplM (SimplEnv, OutBinder)
-simplBinder env bndr
- = let
- (subst', bndr') = Subst.simplBndr (getSubst env) bndr
- in
- seqBndr bndr' `seq`
- returnSmpl (setSubst env subst', bndr')
+It really is important to switch off inlinings inside such
+expressions. 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 will be inlined inside g,
+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.
+
+E.g. {-# INLINE f #-}
+ 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
+of g when f is inlined at some call site (perhaps in some other
+module).
+
+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. That's why the keep_inline predicate returns True for
+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.
+
+ 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!
+
+
+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:
-simplLetBndr :: SimplEnv -> InBinder -> SimplM (SimplEnv, OutBinder)
-simplLetBndr env id
- = let
- (subst', id') = Subst.simplLetId (getSubst env) id
- in
- seqBndr id' `seq`
- returnSmpl (setSubst env subst', id')
+ f1 = \x1.e1
+ f2 = \xs.e2[f1]
+ f3 = \xs.e3[f3]
+ ...etc...
-simplLamBndrs, simplRecBndrs
- :: SimplEnv -> [InBinder] -> SimplM (SimplEnv, [OutBinder])
-simplRecBndrs = simplBndrs Subst.simplLetId
-simplLamBndrs = simplBndrs Subst.simplLamBndr
+THE MAIN INVARIANT is this:
-simplBndrs simpl_bndr env bndrs
- = let
- (subst', bndrs') = mapAccumL simpl_bndr (getSubst env) bndrs
- in
- seqBndrs bndrs' `seq`
- returnSmpl (setSubst env subst', bndrs')
+ ---- 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>
+ ----------------------------------------------
-seqBndrs [] = ()
-seqBndrs (b:bs) = seqBndr b `seq` seqBndrs bs
+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.
-seqBndr b | isTyVar b = b `seq` ()
- | otherwise = seqType (idType b) `seq`
- idInfo b `seq`
- ()
-\end{code}
+Evne 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.
\begin{code}
-newId :: EncodedFS -> Type -> SimplM Id
-newId fs ty = getUniqueSmpl `thenSmpl` \ uniq ->
- returnSmpl (mkSysLocal fs uniq ty)
+preInlineUnconditionally :: SimplEnv -> TopLevelFlag -> InId -> InExpr -> Bool
+preInlineUnconditionally env top_lvl bndr rhs
+ | not active = False
+ | opt_SimplNoPreInlining = False
+ | 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
+ where
+ phase = getMode env
+ active = case phase of
+ SimplGently -> isAlwaysActive prag
+ SimplPhase n -> isActive n prag
+ prag = idInlinePragma bndr
+
+ try_once in_lam int_cxt -- There's one textual occurrence
+ | not in_lam = isNotTopLevel top_lvl || early_phase
+ | otherwise = int_cxt && canInlineInLam rhs
+
+-- Be very careful before inlining inside a lambda, becuase (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 (Lit l) = 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
+-- 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.
+
\end{code}
+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
+ocurrence(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.
+
+\begin{code}
+postInlineUnconditionally :: SimplEnv -> TopLevelFlag -> OutId -> OccInfo -> OutExpr -> Unfolding -> Bool
+postInlineUnconditionally env top_lvl bndr occ_info rhs unfolding
+ | not active = False
+ | isLoopBreaker occ_info = False
+ | isExportedId bndr = False
+ | exprIsTrivial rhs = True
+ | otherwise
+ = case occ_info of
+ OneOcc in_lam one_br int_cxt
+ -> (one_br || smallEnoughToInline unfolding) -- Small enough to dup
+ -- ToDo: consider discount on smallEnoughToInline if int_cxt is true
+ --
+ -- NB: Do we want to inline arbitrarily big things becuase
+ -- one_br is True? that can lead to inline cascades. But
+ -- preInlineUnconditionlly has dealt with all the common cases
+ -- so perhaps it's worth the risk. Here's an example
+ -- let f = if b then Left (\x.BIG) else Right (\y.BIG)
+ -- in \y. ....f....
+ -- We can't preInlineUnconditionally because that woud invalidate
+ -- the occ info for b. Yet f is used just once, and duplicating
+ -- the case work is fine (exprIsCheap).
+
+ && ((isNotTopLevel top_lvl && not in_lam) ||
+ -- But 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'
+
+ (isCheapUnfolding unfolding && 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
+
+ other -> False
+ -- The point here is that for *non-values* that occur
+ -- outside a lambda, the call-site inliner won't have
+ -- a chance (becuase 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 ...
+ -- I'm not sure how important this is in practice
+ where
+ active = case getMode env of
+ SimplGently -> isAlwaysActive prag
+ SimplPhase n -> isActive n prag
+ prag = idInlinePragma bndr
+
+activeInline :: SimplEnv -> OutId -> OccInfo -> Bool
+activeInline env id occ
+ = case getMode env of
+ SimplGently -> isOneOcc occ && isAlwaysActive prag
+ -- 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
+
+ -- NB: we used to have a second exception, for data con wrappers.
+ -- On the grounds that we use gentle mode for rule LHSs, and
+ -- they match better when data con wrappers are inlined.
+ -- But that only really applies to the trivial wrappers (like (:)),
+ -- and they are now constructed as Compulsory unfoldings (in MkId)
+ -- so they'll happen anyway.
+
+ SimplPhase n -> isActive n prag
+ where
+ prag = idInlinePragma id
+
+activeRule :: SimplEnv -> Maybe (Activation -> Bool)
+-- Nothing => No rules at all
+activeRule env
+ | opt_RulesOff = Nothing
+ | 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)
+\end{code}
+
%************************************************************************
%* *
\begin{code}
mkLam env bndrs body cont
- | opt_SimplDoEtaReduction,
- Just etad_lam <- tryEtaReduce bndrs body
- = tick (EtaReduction (head bndrs)) `thenSmpl_`
- returnSmpl (emptyFloats env, etad_lam)
-
- | opt_SimplDoLambdaEtaExpansion,
- any isRuntimeVar bndrs
- = tryEtaExpansion body `thenSmpl` \ body' ->
- returnSmpl (emptyFloats env, mkLams bndrs body')
+ = getDOptsSmpl `thenSmpl` \dflags ->
+ mkLam' dflags env bndrs body cont
+ where
+ mkLam' dflags env bndrs body cont
+ | dopt Opt_DoEtaReduction dflags,
+ Just etad_lam <- tryEtaReduce bndrs body
+ = tick (EtaReduction (head bndrs)) `thenSmpl_`
+ returnSmpl (emptyFloats env, etad_lam)
+
+ | dopt Opt_DoLambdaEtaExpansion dflags,
+ any isRuntimeVar bndrs
+ = tryEtaExpansion body `thenSmpl` \ body' ->
+ returnSmpl (emptyFloats env, mkLams bndrs body')
{- Sept 01: I'm experimenting with getting the
full laziness pass to float out past big lambdsa
returnSmpl (floats, mkLams bndrs body')
-}
- | otherwise
- = returnSmpl (emptyFloats env, mkLams bndrs body)
+ | otherwise
+ = returnSmpl (emptyFloats env, mkLams bndrs body)
\end{code}
-- efficient here:
-- (a) we already have the binders
-- (b) we can do the triviality test before computing the free vars
- -- [in fact I take the simple path and look for just a variable]
= go (reverse bndrs) body
where
go (b : bs) (App fun arg) | ok_arg b arg = go bs fun -- Loop round
- go [] (Var fun) | ok_fun fun = Just (Var fun) -- Success!
+ go [] fun | ok_fun fun = Just fun -- Success!
go _ _ = Nothing -- Failure!
- ok_fun fun = not (fun `elem` bndrs) &&
- (isEvaldUnfolding (idUnfolding fun) || all ok_lam bndrs)
- ok_lam v = isTyVar v || isDictTy (idType v)
- -- The isEvaldUnfolding is because eta reduction is not
+ ok_fun fun = exprIsTrivial fun
+ && not (any (`elemVarSet` (exprFreeVars fun)) bndrs)
+ && (exprIsHNF fun || all ok_lam bndrs)
+ 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.
--
\begin{code}
prepareAlts :: OutExpr -- Scrutinee
- -> InId -- Case binder
- -> [InAlt]
- -> SimplM ([InAlt], -- Better alternatives
+ -> InId -- Case binder (passed only to use in statistics)
+ -> [InAlt] -- Increasing order
+ -> SimplM ([InAlt], -- Better alternatives, still incresaing order
[AltCon]) -- These cases are handled
prepareAlts scrut case_bndr alts
-- Filter out the default, if it can't happen,
-- or replace it with "proper" alternative if there
-- is only one constructor left
- prepareDefault case_bndr handled_cons maybe_deflt `thenSmpl` \ deflt_alt ->
+ prepareDefault scrut case_bndr handled_cons maybe_deflt `thenSmpl` \ deflt_alt ->
- returnSmpl (deflt_alt ++ better_alts, handled_cons)
+ returnSmpl (mergeAlts better_alts deflt_alt, handled_cons)
+ -- We need the mergeAlts in case the new default_alt
+ -- has turned into a constructor alternative.
-prepareDefault case_bndr handled_cons (Just rhs)
- | Just (tycon, inst_tys) <- splitTyConApp_maybe (idType case_bndr),
+prepareDefault scrut case_bndr handled_cons (Just rhs)
+ | Just (tycon, inst_tys) <- splitTyConApp_maybe (exprType scrut),
+ -- Use exprType scrut here, rather than idType case_bndr, because
+ -- case_bndr is an InId, so exprType scrut may have more information
+ -- Test simpl013 is an example
isAlgTyCon tycon, -- It's a data type, tuple, or unboxed tuples.
not (isNewTyCon tycon), -- We can have a newtype, if we are just doing an eval:
-- case x of { DEFAULT -> e }
-- and we don't want to fill in a default for them!
Just all_cons <- tyConDataCons_maybe tycon,
+ not (null all_cons), -- This is a tricky corner case. If the data type has no constructors,
+ -- which GHC allows, then the case expression will have at most a default
+ -- alternative. We don't want to eliminate that alternative, because the
+ -- invariant is that there's always one alternative. It's more convenient
+ -- to leave
+ -- case x of { DEFAULT -> e }
+ -- as it is, rather than transform it to
+ -- error "case cant match"
+ -- which would be quite legitmate. But it's a really obscure corner, and
+ -- not worth wasting code on.
let handled_data_cons = [data_con | DataAlt data_con <- handled_cons],
let missing_cons = [con | con <- all_cons,
not (con `elem` handled_data_cons)]
| otherwise
= returnSmpl [(DEFAULT, [], rhs)]
-prepareDefault case_bndr handled_cons Nothing
+prepareDefault scrut case_bndr handled_cons Nothing
= returnSmpl []
mk_args missing_con inst_tys
- = getUniquesSmpl `thenSmpl` \ tv_uniqs ->
- getUniquesSmpl `thenSmpl` \ id_uniqs ->
- let
- ex_tyvars = dataConExistentialTyVars missing_con
- ex_tyvars' = zipWith mk tv_uniqs ex_tyvars
- mk uniq tv = mkSysTyVar uniq (tyVarKind tv)
- arg_tys = dataConArgTys missing_con (inst_tys ++ mkTyVarTys ex_tyvars')
- arg_ids = zipWith (mkSysLocal FSLIT("a")) id_uniqs arg_tys
- in
- returnSmpl (ex_tyvars' ++ arg_ids)
+ = mk_tv_bndrs missing_con inst_tys `thenSmpl` \ (tv_bndrs, inst_tys') ->
+ getUniquesSmpl `thenSmpl` \ id_uniqs ->
+ let arg_tys = dataConInstArgTys missing_con inst_tys'
+ arg_ids = zipWith (mkSysLocal FSLIT("a")) id_uniqs arg_tys
+ in
+ returnSmpl (tv_bndrs ++ arg_ids)
+
+mk_tv_bndrs missing_con inst_tys
+ | isVanillaDataCon missing_con
+ = returnSmpl ([], inst_tys)
+ | otherwise
+ = getUniquesSmpl `thenSmpl` \ tv_uniqs ->
+ let new_tvs = zipWith mk tv_uniqs (dataConTyVars missing_con)
+ mk uniq tv = mkTyVar (mkSysTvName uniq FSLIT("t")) (tyVarKind tv)
+ in
+ returnSmpl (new_tvs, mkTyVarTys new_tvs)
\end{code}
mkCase puts a case expression back together, trying various transformations first.
\begin{code}
-mkCase :: OutExpr -> OutId -> [OutAlt] -> SimplM OutExpr
-
-mkCase scrut case_bndr alts
- = mkAlts scrut case_bndr alts `thenSmpl` \ better_alts ->
- mkCase1 scrut case_bndr better_alts
+mkCase :: OutExpr -> OutId -> OutType
+ -> [OutAlt] -- Increasing order
+ -> SimplM OutExpr
+
+mkCase scrut case_bndr ty alts
+ = getDOptsSmpl `thenSmpl` \dflags ->
+ mkAlts dflags scrut case_bndr alts `thenSmpl` \ better_alts ->
+ mkCase1 scrut case_bndr ty better_alts
\end{code}
--------------------------------------------------
-- 1. Merge identical branches
--------------------------------------------------
-mkAlts scrut case_bndr alts@((con1,bndrs1,rhs1) : con_alts)
+mkAlts dflags scrut case_bndr alts@((con1,bndrs1,rhs1) : con_alts)
| all isDeadBinder bndrs1, -- Remember the default
length filtered_alts < length con_alts -- alternative comes first
= tick (AltMerge case_bndr) `thenSmpl_`
-- 2. Merge nested cases
--------------------------------------------------
-mkAlts scrut outer_bndr outer_alts
- | opt_SimplCaseMerge,
+mkAlts dflags scrut outer_bndr outer_alts
+ | dopt Opt_CaseMerge dflags,
(outer_alts_without_deflt, maybe_outer_deflt) <- findDefault outer_alts,
- Just (Case (Var scrut_var) inner_bndr inner_alts) <- maybe_outer_deflt,
+ Just (Case (Var scrut_var) inner_bndr _ inner_alts) <- maybe_outer_deflt,
scruting_same_var scrut_var
-
- = let -- Eliminate any inner alts which are shadowed by the outer ones
- outer_cons = [con | (con,_,_) <- outer_alts_without_deflt]
-
- munged_inner_alts = [ (con, args, munge_rhs rhs)
- | (con, args, rhs) <- inner_alts,
- not (con `elem` outer_cons) -- Eliminate shadowed inner alts
- ]
- munge_rhs rhs = bindCaseBndr inner_bndr (Var outer_bndr) rhs
-
- (inner_con_alts, maybe_inner_default) = findDefault munged_inner_alts
-
- new_alts = add_default maybe_inner_default
- (outer_alts_without_deflt ++ inner_con_alts)
+ = let
+ munged_inner_alts = [(con, args, munge_rhs rhs) | (con, args, rhs) <- inner_alts]
+ munge_rhs rhs = bindCaseBndr inner_bndr (Var outer_bndr) rhs
+
+ new_alts = mergeAlts outer_alts_without_deflt munged_inner_alts
+ -- The merge keeps the inner DEFAULT at the front, if there is one
+ -- and eliminates any inner_alts that are shadowed by the outer_alts
in
tick (CaseMerge outer_bndr) `thenSmpl_`
returnSmpl new_alts
- -- Warning: don't call mkAlts 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!
+ -- Warning: don't call mkAlts 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!
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).
+ -- 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
- add_default (Just rhs) alts = (DEFAULT,[],rhs) : alts
- add_default Nothing alts = alts
-
-
---------------------------------------------------
+------------------------------------------------
-- Catch-all
---------------------------------------------------
-
-mkAlts scrut case_bndr other_alts = returnSmpl other_alts
+------------------------------------------------
+
+mkAlts dflags scrut case_bndr other_alts = returnSmpl other_alts
+
+
+---------------------------------
+mergeAlts :: [OutAlt] -> [OutAlt] -> [OutAlt]
+-- Merge preserving order; alternatives in the first arg
+-- shadow ones in the second
+mergeAlts [] as2 = as2
+mergeAlts as1 [] = as1
+mergeAlts (a1:as1) (a2:as2)
+ = case a1 `cmpAlt` a2 of
+ LT -> a1 : mergeAlts as1 (a2:as2)
+ EQ -> a1 : mergeAlts as1 as2 -- Discard a2
+ GT -> a2 : mergeAlts (a1:as1) as2
\end{code}
\begin{code}
--------------------------------------------------
+-- 0. 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
+mkCase1 scrut case_bndr ty []
+ = pprTrace "mkCase1: null alts" (ppr case_bndr <+> ppr scrut) $
+ return (mkApps (Var eRROR_ID)
+ [Type ty, Lit (mkStringLit "Impossible alternative")])
+
+--------------------------------------------------
-- 1. Eliminate the case altogether if poss
--------------------------------------------------
-mkCase1 scrut case_bndr [(con,bndrs,rhs)]
+mkCase1 scrut case_bndr ty [(con,bndrs,rhs)]
-- See if we can get rid of the case altogether
-- See the extensive notes on case-elimination above
-- mkCase made sure that if all the alternatives are equal,
-- x
-- This particular example shows up in default methods for
-- comparision operations (e.g. in (>=) for Int.Int32)
- || exprIsValue scrut -- It's already evaluated
+ || exprIsHNF scrut -- It's already evaluated
|| var_demanded_later scrut -- It'll be demanded later
-- || not opt_SimplPedanticBottoms) -- Or we don't care!
-- 2. Identity case
--------------------------------------------------
-#ifdef DEBUG
-mkCase1 scrut case_bndr []
- = pprTrace "mkCase1: null alts" (ppr case_bndr <+> ppr scrut) $
- returnSmpl scrut
-#endif
-
-mkCase1 scrut case_bndr alts -- Identity case
+mkCase1 scrut case_bndr ty alts -- Identity case
| all identity_alt alts
= tick (CaseIdentity case_bndr) `thenSmpl_`
returnSmpl (re_note scrut)
-- re_note wraps a coerce if it might be necessary
re_note scrut = case head alts of
- (_,_,rhs1@(Note _ _)) -> mkCoerce (exprType rhs1) (idType case_bndr) scrut
+ (_,_,rhs1@(Note _ _)) -> mkCoerce2 (exprType rhs1) (idType case_bndr) scrut
other -> scrut
--------------------------------------------------
-- Catch-all
--------------------------------------------------
-mkCase1 scrut bndr alts = returnSmpl (Case scrut bndr alts)
+mkCase1 scrut bndr ty alts = returnSmpl (Case scrut bndr ty alts)
\end{code}
projects / ghc-hetmet.git / blobdiff