RecFlag(..), isNonRuleLoopBreaker )
import Maybes ( orElse )
import Data.List ( mapAccumL )
+import MonadUtils ( foldlM )
+import StaticFlags ( opt_PassCaseBndrToJoinPoints )
import Outputable
import FastString
\end{code}
-- case e of t { (a,b) -> ...(case t of (p,q) -> p)... }
-- ==> case e of t { (a,b) -> ...(a)... }
-- Look, Ma, a is alive now.
- zap_occ_info | isDeadBinder case_bndr' = \ident -> ident
- | otherwise = zapIdOccInfo
+ zap_occ_info = zapCasePatIdOcc case_bndr'
addBinderUnfolding :: SimplEnv -> Id -> CoreExpr -> SimplEnv
addBinderUnfolding env bndr rhs
addBinderOtherCon :: SimplEnv -> Id -> [AltCon] -> SimplEnv
addBinderOtherCon env bndr cons
= modifyInScope env (bndr `setIdUnfolding` mkOtherCon cons)
+
+zapCasePatIdOcc :: Id -> Id -> Id
+-- Consider case e of b { (a,b) -> ... }
+-- Then if we bind b to (a,b) in "...", and b is not dead,
+-- then we must zap the deadness info on a,b
+zapCasePatIdOcc case_bndr
+ | isDeadBinder case_bndr = \ pat_id -> pat_id
+ | otherwise = \ pat_id -> zapIdOccInfo pat_id
\end{code}
; simplExprF env' rhs cont }
knownAlt env scrut the_args bndr (DataAlt dc, bs, rhs) cont
- = do { let dead_bndr = isDeadBinder bndr -- bndr is an InId
- n_drop_tys = length (dataConUnivTyVars dc)
- ; env' <- bind_args env dead_bndr bs (drop n_drop_tys the_args)
+ = do { let n_drop_tys = length (dataConUnivTyVars dc)
+ ; env' <- bind_args env bs (drop n_drop_tys the_args)
; let
-- It's useful to bind bndr to scrut, rather than to a fresh
-- binding x = Con arg1 .. argn
; env'' <- simplNonRecX env' bndr bndr_rhs
; simplExprF env'' rhs cont }
where
- -- Ugh!
- bind_args env' _ [] _ = return env'
+ zap_occ = zapCasePatIdOcc bndr -- bndr is an InId
+
+ -- Ugh!
+ bind_args env' [] _ = return env'
- bind_args env' dead_bndr (b:bs') (Type ty : args)
+ bind_args env' (b:bs') (Type ty : args)
= ASSERT( isTyVar b )
- bind_args (extendTvSubst env' b ty) dead_bndr bs' args
+ bind_args (extendTvSubst env' b ty) bs' args
- bind_args env' dead_bndr (b:bs') (arg : args)
+ bind_args env' (b:bs') (arg : args)
= ASSERT( isId b )
- do { let b' = if dead_bndr then b else zapIdOccInfo b
+ do { let b' = zap_occ b
-- Note that the binder might be "dead", because it doesn't
-- occur in the RHS; and simplNonRecX may therefore discard
-- it via postInlineUnconditionally.
-- Nevertheless we must keep it if the case-binder is alive,
-- because it may be used in the con_app. See Note [zapOccInfo]
; env'' <- simplNonRecX env' b' arg
- ; bind_args env'' dead_bndr bs' args }
+ ; bind_args env'' bs' args }
- bind_args _ _ _ _ =
+ bind_args _ _ _ =
pprPanic "bind_args" $ ppr dc $$ ppr bs $$ ppr the_args $$
text "scrut:" <+> ppr scrut
\end{code}
mkDupableAlt :: SimplEnv -> OutId -> (AltCon, [CoreBndr], CoreExpr)
-> SimplM (SimplEnv, (AltCon, [CoreBndr], CoreExpr))
-mkDupableAlt env case_bndr' (con, bndrs', rhs')
- | exprIsDupable rhs' -- Note [Small alternative rhs]
- = return (env, (con, bndrs', rhs'))
+mkDupableAlt env case_bndr1 (con, bndrs1, rhs1)
+ | exprIsDupable rhs1 -- Note [Small alternative rhs]
+ = return (env, (con, bndrs1, rhs1))
| otherwise
- = do { let rhs_ty' = exprType rhs'
- used_bndrs' = filter abstract_over (case_bndr' : bndrs')
- abstract_over bndr
+ = do { let 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
- ; (final_bndrs', final_args) -- Note [Join point abstraction]
- <- if (any isId used_bndrs')
- then return (used_bndrs', varsToCoreExprs used_bndrs')
+ 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)
else do { rw_id <- newId (fsLit "w") realWorldStatePrimTy
- ; return ([rw_id], [Var realWorldPrimId]) }
+ ; return (rw_id : final_bndrs,
+ Var realWorldPrimId : varsToCoreExprs final_bndrs) }
- ; join_bndr <- newId (fsLit "$j") (mkPiTypes final_bndrs' rhs_ty')
+ ; let rhs_ty1 = exprType rhs1
+ ; join_bndr <- newId (fsLit "$j") (mkPiTypes final_bndrs1 rhs_ty1)
-- 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_bndrs'
+ really_final_bndrs = map one_shot final_bndrs1
one_shot v | isId v = setOneShotLambda v
| otherwise = v
- join_rhs = mkLams really_final_bndrs rhs'
+ join_rhs = mkLams really_final_bndrs rhs2
join_call = mkApps (Var join_bndr) final_args
- ; return (addPolyBind NotTopLevel env (NonRec join_bndr join_rhs), (con, bndrs', join_call)) }
+ ; env1 <- addPolyBind NotTopLevel env (NonRec join_bndr join_rhs)
+ ; return (env1, (con, bndrs1, 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
projects / ghc-hetmet.git / blobdiff