import Type hiding ( substTy, extendTvSubst )
import SimplEnv
import SimplUtils
-import MkId ( rUNTIME_ERROR_ID )
import FamInstEnv ( FamInstEnv )
import Id
+import MkId ( mkImpossibleExpr )
import Var
import IdInfo
import Coercion
import PprCore ( pprParendExpr, pprCoreExpr )
import CoreUnfold ( mkUnfolding, callSiteInline, CallCtxt(..) )
import CoreUtils
+import CoreArity ( exprArity )
import Rules ( lookupRule, getRules )
import BasicTypes ( isMarkedStrict )
import CostCentre ( currentCCS )
RecFlag(..), isNonRuleLoopBreaker )
import Maybes ( orElse )
import Data.List ( mapAccumL )
-import MonadUtils ( foldlM )
-import StaticFlags ( opt_PassCaseBndrToJoinPoints )
import Outputable
import FastString
\end{code}
; (env', rhs')
<- if not (doFloatFromRhs top_lvl is_rec False body2 body_env2)
then -- No floating, just wrap up!
- do { rhs' <- mkLam tvs' (wrapFloats body_env2 body2)
+ do { rhs' <- mkLam env tvs' (wrapFloats body_env2 body2)
; return (env, rhs') }
else if null tvs then -- Simple floating
else -- Do type-abstraction first
do { tick LetFloatFromLet
; (poly_binds, body3) <- abstractFloats tvs' body_env2 body2
- ; rhs' <- mkLam tvs' body3
+ ; rhs' <- mkLam env tvs' body3
; let env' = foldl (addPolyBind top_lvl) env poly_binds
; return (env', rhs') }
where
is_val = n_val_args > 0 -- There is at least one arg
-- ...and the fun a constructor or PAP
- && (isDataConWorkId fun || n_val_args < idArity fun)
+ && (isConLikeId fun || n_val_args < idArity fun)
go _ env other
= return (False, env, other)
\end{code}
= return (addNonRecWithUnf env new_bndr new_rhs unfolding wkr)
where
unfolding | omit_unfolding = NoUnfolding
- | otherwise = mkUnfolding (isTopLevel top_lvl) new_rhs
+ | otherwise = mkUnfolding (isTopLevel top_lvl) new_rhs
old_info = idInfo old_bndr
occ_info = occInfo old_info
wkr = substWorker env (workerInfo old_info)
addNonRecWithUnf env new_bndr rhs unfolding wkr
= ASSERT( isId new_bndr )
WARN( new_arity < old_arity || new_arity < dmd_arity,
- (ppr final_id <+> ppr old_arity <+> ppr new_arity <+> ppr dmd_arity) $$ ppr rhs )
+ (ptext (sLit "Arity decrease:") <+> ppr final_id <+> ppr old_arity
+ <+> ppr new_arity <+> ppr dmd_arity) $$ ppr rhs )
+ -- Note [Arity decrease]
final_id `seq` -- This seq forces the Id, and hence its IdInfo,
-- and hence any inner substitutions
addNonRec env final_id rhs
final_id = new_bndr `setIdInfo` final_info
\end{code}
+Note [Arity decrease]
+~~~~~~~~~~~~~~~~~~~~~
+Generally speaking the arity of a binding should not decrease. But it *can*
+legitimately happen becuase of RULES. Eg
+ f = g Int
+where g has arity 2, will have arity 2. But if there's a rewrite rule
+ g Int --> h
+where h has arity 1, then f's arity will decrease. Here's a real-life example,
+which is in the output of Specialise:
+
+ Rec {
+ $dm {Arity 2} = \d.\x. op d
+ {-# RULES forall d. $dm Int d = $s$dm #-}
+
+ dInt = MkD .... opInt ...
+ opInt {Arity 1} = $dm dInt
+
+ $s$dm {Arity 0} = \x. op dInt }
+
+Here opInt has arity 1; but when we apply the rule its arity drops to 0.
+That's why Specialise goes to a little trouble to pin the right arity
+on specialised functions too.
%************************************************************************
simplLam env bndrs body cont
= do { (env', bndrs') <- simplLamBndrs env bndrs
; body' <- simplExpr env' body
- ; new_lam <- mkLam bndrs' body'
+ ; new_lam <- mkLam env' bndrs' body'
; rebuild env' new_lam cont }
------------------
Just unfolding -- There is an inlining!
-> do { tick (UnfoldingDone var)
; (if dopt Opt_D_dump_inlinings dflags then
- pprTrace ("Inlining done" ++ showSDoc (ppr var)) (vcat [
+ pprTrace ("Inlining done: " ++ showSDoc (ppr var)) (vcat [
text "Before:" <+> ppr var <+> sep (map pprParendExpr args),
text "Inlined fn: " <+> nest 2 (ppr unfolding),
text "Cont: " <+> ppr call_cont])
; (scrut', case_bndr', alts') <- simplAlts env' scrut case_bndr alts dup_cont
-- Check for empty alternatives
- ; if null alts' then
- -- This isn't strictly an error, although it is unusual.
- -- 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 instead.
- pprTrace "mkCase: null alts" (ppr case_bndr <+> ppr scrut) $
- let res_ty' = contResultType env' (substTy env' (coreAltsType alts)) dup_cont
- lit = mkStringLit "Impossible alternative"
- in return (env', mkApps (Var rUNTIME_ERROR_ID) [Type res_ty', lit])
-
+ ; if null alts' then missingAlt env case_bndr alts cont
else do
{ case_expr <- mkCase scrut' case_bndr' alts'
LiberateCase gets to see it.)
-Historical note [no-case-of-case]
-~~~~~~~~~~~~~~~~~~~~~~
-We *used* to suppress the binder-swap in case expressoins when
--fno-case-of-case is on. Old remarks:
- "This happens in the first simplifier pass,
- and enhances full laziness. Here's the bad case:
- f = \ y -> ...(case x of I# v -> ...(case x of ...) ... )
- If we eliminate the inner case, we trap it inside the I# v -> arm,
- which might prevent some full laziness happening. I've seen this
- in action in spectral/cichelli/Prog.hs:
- [(m,n) | m <- [1..max], n <- [1..max]]
- Hence the check for NoCaseOfCase."
-However, now the full-laziness pass itself reverses the binder-swap, so this
-check is no longer necessary.
-
-Historical note [Suppressing the case binder-swap]
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-There is another situation when it might make sense to suppress the
-case-expression binde-swap. If we have
-
- case x of w1 { DEFAULT -> case x of w2 { A -> e1; B -> e2 }
- ...other cases .... }
-
-We'll perform the binder-swap for the outer case, giving
-
- case x of w1 { DEFAULT -> case w1 of w2 { A -> e1; B -> e2 }
- ...other cases .... }
-
-But there is no point in doing it for the inner case, because w1 can't
-be inlined anyway. Furthermore, doing the case-swapping involves
-zapping w2's occurrence info (see paragraphs that follow), and that
-forces us to bind w2 when doing case merging. So we get
-
- case x of w1 { A -> let w2 = w1 in e1
- B -> let w2 = w1 in e2
- ...other cases .... }
-
-This is plain silly in the common case where w2 is dead.
-
-Even so, I can't see a good way to implement this idea. I tried
-not doing the binder-swap if the scrutinee was already evaluated
-but that failed big-time:
-
- data T = MkT !Int
-
- case v of w { MkT x ->
- case x of x1 { I# y1 ->
- case x of x2 { I# y2 -> ...
-
-Notice that because MkT is strict, x is marked "evaluated". But to
-eliminate the last case, we must either make sure that x (as well as
-x1) has unfolding MkT y1. THe straightforward thing to do is to do
-the binder-swap. So this whole note is a no-op.
\begin{code}
knownCon env scrut con args bndr alts cont
= do { tick (KnownBranch bndr)
- ; knownAlt env scrut args bndr (findAlt con alts) cont }
+ ; case findAlt con alts of
+ Nothing -> missingAlt env bndr alts cont
+ Just alt -> knownAlt env scrut args bndr alt cont
+ }
+-------------------
knownAlt :: SimplEnv -> OutExpr -> [OutExpr]
- -> InId -> (AltCon, [CoreBndr], InExpr) -> SimplCont
+ -> InId -> InAlt -> SimplCont
-> SimplM (SimplEnv, OutExpr)
-knownAlt env scrut _ bndr (DEFAULT, bs, rhs) cont
- = ASSERT( null bs )
- do { env' <- simplNonRecX env bndr scrut
- -- This might give rise to a binding with non-atomic args
- -- like x = Node (f x) (g x)
- -- but simplNonRecX will atomic-ify it
- ; simplExprF env' rhs cont }
-
-knownAlt env scrut _ bndr (LitAlt _, bs, rhs) cont
- = ASSERT( null bs )
- do { env' <- simplNonRecX env bndr scrut
- ; simplExprF env' rhs cont }
knownAlt env scrut the_args bndr (DataAlt dc, bs, rhs) cont
= do { let n_drop_tys = length (dataConUnivTyVars dc)
bind_args _ _ _ =
pprPanic "bind_args" $ ppr dc $$ ppr bs $$ ppr the_args $$
text "scrut:" <+> ppr scrut
+
+knownAlt env scrut _ bndr (_, bs, rhs) cont
+ = ASSERT( null bs ) -- Works for LitAlt and DEFAULT
+ do { env' <- simplNonRecX env bndr scrut
+ ; simplExprF env' rhs cont }
+
+
+-------------------
+missingAlt :: SimplEnv -> Id -> [InAlt] -> SimplCont -> SimplM (SimplEnv, OutExpr)
+ -- This isn't strictly an error, although it is unusual.
+ -- 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 instead.
+missingAlt env case_bndr alts cont
+ = WARN( True, ptext (sLit "missingAlt") <+> ppr case_bndr )
+ return (env, mkImpossibleExpr res_ty)
+ where
+ res_ty = contResultType env (substTy env (coreAltsType alts)) cont
\end{code}
mkDupableCont env cont@(StrictBind {})
= return (env, mkBoringStop, cont)
- -- See Note [Duplicating strict continuations]
+ -- See Note [Duplicating StrictBind]
-mkDupableCont env cont@(StrictArg {})
- = return (env, mkBoringStop, cont)
- -- See Note [Duplicating strict continuations]
+mkDupableCont env (StrictArg fun cci ai cont)
+ -- See Note [Duplicating StrictArg]
+ = do { (env', dup, nodup) <- mkDupableCont env cont
+ ; (env'', fun') <- mk_dupable_call env' fun
+ ; return (env'', StrictArg fun' cci ai dup, nodup) }
+ where
+ mk_dupable_call env (Var v) = return (env, Var v)
+ mk_dupable_call env (App fun arg) = do { (env', fun') <- mk_dupable_call env fun
+ ; (env'', arg') <- makeTrivial env' arg
+ ; return (env'', fun' `App` arg') }
+ mk_dupable_call _ other = pprPanic "mk_dupable_call" (ppr other)
+ -- The invariant of StrictArg is that the first arg is always an App chain
mkDupableCont env (ApplyTo _ arg se cont)
= -- e.g. [...hole...] (...arg...)
mkDupableAlt :: SimplEnv -> OutId -> (AltCon, [CoreBndr], CoreExpr)
-> SimplM (SimplEnv, (AltCon, [CoreBndr], CoreExpr))
-mkDupableAlt env case_bndr1 (con, bndrs1, rhs1)
- | exprIsDupable rhs1 -- Note [Small alternative rhs]
- = return (env, (con, bndrs1, rhs1))
+mkDupableAlt env case_bndr' (con, bndrs', rhs')
+ | exprIsDupable rhs' -- Note [Small alternative rhs]
+ = return (env, (con, bndrs', rhs'))
| otherwise
- = do { let abstract_over bndr
+ = do { let rhs_ty' = exprType rhs'
+ used_bndrs' = filter abstract_over (case_bndr' : bndrs')
+ abstract_over bndr
| isTyVar bndr = True -- Abstract over all type variables just in case
| otherwise = not (isDeadBinder bndr)
-- The deadness info on the new Ids is preserved by simplBinders
- inst_tys1 = tyConAppArgs (idType case_bndr1)
- con_app dc = mkConApp dc (map Type inst_tys1 ++ varsToCoreExprs bndrs1)
-
- (rhs2, final_bndrs) -- See Note [Passing the case binder to join points]
- | isDeadBinder case_bndr1
- = (rhs1, filter abstract_over bndrs1)
- | opt_PassCaseBndrToJoinPoints, not (null bndrs1)
- = (rhs1, (case_bndr1 : filter abstract_over bndrs1))
- | otherwise
- = case con of
- DataAlt dc -> (Let (NonRec case_bndr1 (con_app dc)) rhs1, bndrs1)
- LitAlt lit -> ASSERT( null bndrs1 ) (Let (NonRec case_bndr1 (Lit lit)) rhs1, [])
- DEFAULT -> ASSERT( null bndrs1 ) (rhs1, [case_bndr1])
-
- ; (final_bndrs1, final_args) -- Note [Join point abstraction]
- <- if (any isId final_bndrs)
- then return (final_bndrs, varsToCoreExprs final_bndrs)
+ ; (final_bndrs', final_args) -- Note [Join point abstraction]
+ <- if (any isId used_bndrs')
+ then return (used_bndrs', varsToCoreExprs used_bndrs')
else do { rw_id <- newId (fsLit "w") realWorldStatePrimTy
- ; return (rw_id : final_bndrs,
- Var realWorldPrimId : varsToCoreExprs final_bndrs) }
+ ; return ([rw_id], [Var realWorldPrimId]) }
- ; let rhs_ty1 = exprType rhs1
- ; join_bndr <- newId (fsLit "$j") (mkPiTypes final_bndrs1 rhs_ty1)
+ ; join_bndr <- newId (fsLit "$j") (mkPiTypes final_bndrs' rhs_ty')
-- Note [Funky mkPiTypes]
; let -- We make the lambdas into one-shot-lambdas. The
-- join point is sure to be applied at most once, and doing so
-- prevents the body of the join point being floated out by
-- the full laziness pass
- really_final_bndrs = map one_shot final_bndrs1
+ really_final_bndrs = map one_shot final_bndrs'
one_shot v | isId v = setOneShotLambda v
| otherwise = v
- join_rhs = mkLams really_final_bndrs rhs2
+ join_rhs = mkLams really_final_bndrs rhs'
join_call = mkApps (Var join_bndr) final_args
- ; env1 <- addPolyBind NotTopLevel env (NonRec join_bndr join_rhs)
- ; return (env1, (con, bndrs1, join_call)) }
+ ; return (addPolyBind NotTopLevel env (NonRec join_bndr join_rhs), (con, bndrs', join_call)) }
-- See Note [Duplicated env]
\end{code}
-Note [Passing the case binder to join points]
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-Suppose we have
- case e of cb { C1 -> r1[cb]; C2 x y z -> r2[cb,x] }
-and we want to make join points for the two alternatives,
-which mention the case binder 'cb'. Should we pass 'cb' to
-the join point, or reconstruct it? Here are the two alternatives
-for the C2 alternative:
-
- Plan A(pass cb): j2 cb x = r2[cb,x]
-
- Plan B(reconstruct cb): j2 x y z = let cb = C2 x y z in r2[cb,x]
-
-The advantge of Plan B is that we can "see" the definition of cb
-in r2, and that may be important when we inline stuff in r2. The
-disadvantage is that if this optimisation doesn't happen, we end up
-re-allocating C2, when it already exists. This does happen occasionally;
-an example is the function nofib/spectral/cichelli/Auxil.$whinsert.
-
-Plan B is always better if the constructor is nullary.
-
-In both cases we don't have liveness info for cb on a branch-by-branch
-basis, and it's possible that 'cb' is used in some branches but not
-others. Well, the absence analyser will find that out later, so it's
-not too bad.
-
-Sadly, at the time of writing, neither choice seems an unequivocal
-win. Here are nofib results, for adding -fpass-case-bndr-to-join-points
-(all others are zero effect):
-
- Program Size Allocs Runtime Elapsed
---------------------------------------------------------------------------------
- cichelli +0.0% -4.4% 0.13 0.13
- pic +0.0% -0.7% 0.01 0.04
- transform -0.0% +2.8% -0.4% -9.1%
- wave4main +0.0% +10.5% +3.1% +3.4%
---------------------------------------------------------------------------------
- Min -0.0% -4.4% -7.0% -31.9%
- Max +0.1% +10.5% +3.1% +15.0%
- Geometric Mean +0.0% +0.1% -1.7% -6.1%
-
-
Note [Duplicated env]
~~~~~~~~~~~~~~~~~~~~~
Some of the alternatives are simplified, but have not been turned into a join point
but zapping it (as we do in mkDupableCont, the Select case) is safe, and
at worst delays the join-point inlining.
-Note [Small alterantive rhs]
+Note [Small alternative rhs]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
It is worth checking for a small RHS because otherwise we
get extra let bindings that may cause an extra iteration of the simplifier to
True -> $j s
(the \v alone is enough to make CPR happy) but I think it's rare
-Note [Duplicating strict continuations]
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-Do *not* duplicate StrictBind and StritArg continuations. We gain
-nothing by propagating them into the expressions, and we do lose a
-lot. Here's an example:
- && (case x of { T -> F; F -> T }) E
+Note [Duplicating StrictArg]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The original plan had (where E is a big argument)
+e.g. f E [..hole..]
+ ==> let $j = \a -> f E a
+ in $j [..hole..]
+
+But this is terrible! Here's an example:
+ && E (case x of { T -> F; F -> T })
Now, && is strict so we end up simplifying the case with
an ArgOf continuation. If we let-bind it, we get
-
- let $j = \v -> && v E
+ let $j = \v -> && E v
in simplExpr (case x of { T -> F; F -> T })
(ArgOf (\r -> $j r)
And after simplifying more we get
-
- let $j = \v -> && v E
+ let $j = \v -> && E v
in case x of { T -> $j F; F -> $j T }
Which is a Very Bad Thing
+What we do now is this
+ f E [..hole..]
+ ==> let a = E
+ in f a [..hole..]
+Now if the thing in the hole is a case expression (which is when
+we'll call mkDupableCont), we'll push the function call into the
+branches, which is what we want. Now RULES for f may fire, and
+call-pattern specialisation. Here's an example from Trac #3116
+ go (n+1) (case l of
+ 1 -> bs'
+ _ -> Chunk p fpc (o+1) (l-1) bs')
+If we can push the call for 'go' inside the case, we get
+call-pattern specialisation for 'go', which is *crucial* for
+this program.
+
+Here is the (&&) example:
+ && E (case x of { T -> F; F -> T })
+ ==> let a = E in
+ case x of { T -> && a F; F -> && a T }
+Much better!
+
+Notice that
+ * Arguments to f *after* the strict one are handled by
+ the ApplyTo case of mkDupableCont. Eg
+ f [..hole..] E
+
+ * We can only do the let-binding of E because the function
+ part of a StrictArg continuation is an explicit syntax
+ tree. In earlier versions we represented it as a function
+ (CoreExpr -> CoreEpxr) which we couldn't take apart.
+
+Do *not* duplicate StrictBind and StritArg continuations. We gain
+nothing by propagating them into the expressions, and we do lose a
+lot.
+
+The desire not to duplicate is the entire reason that
+mkDupableCont returns a pair of continuations.
+
+Note [Duplicating StrictBind]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Unlike StrictArg, there doesn't seem anything to gain from
+duplicating a StrictBind continuation, so we don't.
+
The desire not to duplicate is the entire reason that
mkDupableCont returns a pair of continuations.
-The original plan had:
-e.g. (...strict-fn...) [...hole...]
- ==>
- let $j = \a -> ...strict-fn...
- in $j [...hole...]
Note [Single-alternative cases]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
projects / ghc-hetmet.git / blobdiff