#include "HsVersions.h"
-import DynFlags ( DynFlags, DynFlag(..) )
import CoreSyn
import CoreUtils ( exprIsHNF, exprIsDupable )
-import CoreLint ( showPass, endPass )
-import CoreFVs ( CoreExprWithFVs, freeVars, freeVarsOf )
-import Id ( isOneShotBndr )
-import Var ( Id, idType )
+import CoreFVs ( CoreExprWithFVs, freeVars, freeVarsOf, idRuleAndUnfoldingVars )
+import Id ( isOneShotBndr, idType )
+import Var
import Type ( isUnLiftedType )
import VarSet
import Util ( zipEqual, zipWithEqual, count )
+import UniqFM
import Outputable
\end{code}
actually float any bindings downwards from the top-level.
\begin{code}
-floatInwards :: DynFlags -> [CoreBind] -> IO [CoreBind]
-
-floatInwards dflags binds
- = do {
- showPass dflags "Float inwards";
- let { binds' = map fi_top_bind binds };
- endPass dflags "Float inwards" Opt_D_verbose_core2core binds'
- {- no specific flag for dumping float-in -}
- }
-
+floatInwards :: [CoreBind] -> [CoreBind]
+floatInwards = map fi_top_bind
where
fi_top_bind (NonRec binder rhs)
= NonRec binder (fiExpr [] (freeVars rhs))
type FreeVarsSet = IdSet
type FloatingBinds = [(CoreBind, FreeVarsSet)]
- -- In reverse dependency order (innermost bindiner first)
+ -- In reverse dependency order (innermost binder first)
-- The FreeVarsSet is the free variables of the binding. In the case
-- of recursive bindings, the set doesn't include the bound
fiExpr to_drop (_, AnnType ty) = ASSERT( null to_drop )
Type ty
+fiExpr to_drop (_, AnnCast expr co)
+ = Cast (fiExpr to_drop expr) co -- Just float in past coercion
-fiExpr to_drop (_, AnnLit lit) = Lit lit
+fiExpr _ (_, AnnLit lit) = Lit lit
\end{code}
Applications: we do float inside applications, mainly because we
[drop_here, fun_drop, arg_drop] = sepBindsByDropPoint False [freeVarsOf fun, freeVarsOf arg] to_drop
\end{code}
-We are careful about lambdas:
-
+Note [Floating in past a lambda group]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
* We must be careful about floating inside inside a value lambda.
That risks losing laziness.
The float-out pass might rescue us, but then again it might not.
This is bad as now f is an updatable closure (update PAP)
and has arity 0.
+* Hack alert! We only float in through one-shot lambdas,
+ not (as you might guess) through lone big lambdas.
+ Reason: we float *out* past big lambdas (see the test in the Lam
+ case of FloatOut.floatExpr) and we don't want to float straight
+ back in again.
+
+ It *is* important to float into one-shot lambdas, however;
+ see the remarks with noFloatIntoRhs.
+
So we treat lambda in groups, using the following rule:
- Float inside a group of lambdas only if
- they are all either type lambdas or one-shot lambdas.
+ Float in if (a) there is at least one Id,
+ and (b) there are no non-one-shot Ids
+
+ Otherwise drop all the bindings outside the group.
+
+This is what the 'go' function in the AnnLam case is doing.
- Otherwise drop all the bindings outside the group.
+Urk! if all are tyvars, and we don't float in, we may miss an
+ opportunity to float inside a nested case branch
\begin{code}
- -- Hack alert! We only float in through one-shot lambdas,
- -- not (as you might guess) through big lambdas.
- -- Reason: we float *out* past big lambdas (see the test in the Lam
- -- case of FloatOut.floatExpr) and we don't want to float straight
- -- back in again.
- --
- -- It *is* important to float into one-shot lambdas, however;
- -- see the remarks with noFloatIntoRhs.
fiExpr to_drop lam@(_, AnnLam _ _)
- | all is_one_shot bndrs -- Float in
+ | go False bndrs -- Float in
= mkLams bndrs (fiExpr to_drop body)
| otherwise -- Dump it all here
where
(bndrs, body) = collectAnnBndrs lam
+
+ go seen_one_shot_id [] = seen_one_shot_id
+ go seen_one_shot_id (b:bs)
+ | isTyCoVar b = go seen_one_shot_id bs
+ | isOneShotBndr b = go True bs
+ | otherwise = False -- Give up at a non-one-shot Id
\end{code}
We don't float lets inwards past an SCC.
cc, change current cc to the new one and float binds into expr.
\begin{code}
-fiExpr to_drop (_, AnnNote note@(SCC cc) expr)
+fiExpr to_drop (_, AnnNote note@(SCC _) expr)
= -- Wimp out for now
mkCoLets' to_drop (Note note (fiExpr [] expr))
-fiExpr to_drop (_, AnnNote InlineMe expr)
- = -- Ditto... don't float anything into an INLINE expression
- mkCoLets' to_drop (Note InlineMe (fiExpr [] expr))
-
-fiExpr to_drop (_, AnnNote note@(Coerce _ _) expr)
- = -- Just float in past coercion
- Note note (fiExpr to_drop expr)
-
fiExpr to_drop (_, AnnNote note@(CoreNote _) expr)
= Note note (fiExpr to_drop expr)
\end{code}
things to drop in the outer let's body, and let nature take its
course.
+Note [extra_fvs (1): avoid floating into RHS]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Consdider let x=\y....t... in body. We do not necessarily want to float
+a binding for t into the RHS, because it'll immediately be floated out
+again. (It won't go inside the lambda else we risk losing work.)
+In letrec, we need to be more careful still. We don't want to transform
+ let x# = y# +# 1#
+ in
+ letrec f = \z. ...x#...f...
+ in ...
+into
+ letrec f = let x# = y# +# 1# in \z. ...x#...f... in ...
+because now we can't float the let out again, because a letrec
+can't have unboxed bindings.
+
+So we make "extra_fvs" which is the rhs_fvs of such bindings, and
+arrange to dump bindings that bind extra_fvs before the entire let.
+
+Note [extra_fvs (s): free variables of rules]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Consider
+ let x{rule mentioning y} = rhs in body
+Here y is not free in rhs or body; but we still want to dump bindings
+that bind y outside the let. So we augment extra_fvs with the
+idRuleAndUnfoldingVars of x. No need for type variables, hence not using
+idFreeVars.
+
+
\begin{code}
fiExpr to_drop (_,AnnLet (AnnNonRec id rhs@(rhs_fvs, ann_rhs)) body)
= fiExpr new_to_drop body
where
body_fvs = freeVarsOf body
- final_body_fvs | noFloatIntoRhs ann_rhs
- || isUnLiftedType (idType id) = body_fvs `unionVarSet` rhs_fvs
- | otherwise = body_fvs
- -- See commments with letrec below
+ rule_fvs = idRuleAndUnfoldingVars id -- See Note [extra_fvs (2): free variables of rules]
+ extra_fvs | noFloatIntoRhs ann_rhs
+ || isUnLiftedType (idType id) = rule_fvs `unionVarSet` rhs_fvs
+ | otherwise = rule_fvs
+ -- See Note [extra_fvs (2): avoid floating into RHS]
-- No point in floating in only to float straight out again
-- Ditto ok-for-speculation unlifted RHSs
- [shared_binds, rhs_binds, body_binds] = sepBindsByDropPoint False [rhs_fvs, final_body_fvs] to_drop
+ [shared_binds, extra_binds, rhs_binds, body_binds]
+ = sepBindsByDropPoint False [extra_fvs, rhs_fvs, body_fvs] to_drop
new_to_drop = body_binds ++ -- the bindings used only in the body
[(NonRec id rhs', rhs_fvs')] ++ -- the new binding itself
+ extra_binds ++ -- bindings from extra_fvs
shared_binds -- the bindings used both in rhs and body
-- Push rhs_binds into the right hand side of the binding
rhs' = fiExpr rhs_binds rhs
- rhs_fvs' = rhs_fvs `unionVarSet` floatedBindsFVs rhs_binds
+ rhs_fvs' = rhs_fvs `unionVarSet` floatedBindsFVs rhs_binds `unionVarSet` rule_fvs
+ -- Don't forget the rule_fvs; the binding mentions them!
fiExpr to_drop (_,AnnLet (AnnRec bindings) body)
= fiExpr new_to_drop body
where
- rhss = map snd bindings
-
+ (ids, rhss) = unzip bindings
rhss_fvs = map freeVarsOf rhss
body_fvs = freeVarsOf body
- -- Add to body_fvs the free vars of any RHS that has
- -- a lambda at the top. This has the effect of making it seem
- -- that such things are used in the body as well, and hence prevents
- -- them getting floated in. The big idea is to avoid turning:
- -- let x# = y# +# 1#
- -- in
- -- letrec f = \z. ...x#...f...
- -- in ...
- -- into
- -- letrec f = let x# = y# +# 1# in \z. ...x#...f... in ...
- --
- -- Because now we can't float the let out again, because a letrec
- -- can't have unboxed bindings.
-
- final_body_fvs = foldr (unionVarSet . get_extras) body_fvs rhss
- get_extras (rhs_fvs, rhs) | noFloatIntoRhs rhs = rhs_fvs
- | otherwise = emptyVarSet
-
- (shared_binds:body_binds:rhss_binds) = sepBindsByDropPoint False (final_body_fvs:rhss_fvs) to_drop
-
- new_to_drop = -- the bindings used only in the body
- body_binds ++
- -- the new binding itself
+ -- See Note [extra_fvs (1,2)]
+ rule_fvs = foldr (unionVarSet . idRuleAndUnfoldingVars) emptyVarSet ids
+ extra_fvs = rule_fvs `unionVarSet`
+ unionVarSets [ fvs | (fvs, rhs) <- rhss
+ , noFloatIntoRhs rhs ]
+
+ (shared_binds:extra_binds:body_binds:rhss_binds)
+ = sepBindsByDropPoint False (extra_fvs:body_fvs:rhss_fvs) to_drop
+
+ new_to_drop = body_binds ++ -- the bindings used only in the body
[(Rec (fi_bind rhss_binds bindings), rhs_fvs')] ++
- -- the bindings used both in rhs and body or in more than one rhs
- shared_binds
+ -- The new binding itself
+ extra_binds ++ -- Note [extra_fvs (1,2)]
+ shared_binds -- Used in more than one place
- rhs_fvs' = unionVarSet (unionVarSets rhss_fvs)
- (unionVarSets (map floatedBindsFVs rhss_binds))
+ rhs_fvs' = unionVarSets rhss_fvs `unionVarSet`
+ unionVarSets (map floatedBindsFVs rhss_binds) `unionVarSet`
+ rule_fvs -- Don't forget the rule variables!
-- Push rhs_binds into the right hand side of the binding
fi_bind :: [FloatingBinds] -- one per "drop pt" conjured w/ fvs_of_rhss
scrut_fvs = freeVarsOf scrut
alts_fvs = map alt_fvs alts
all_alts_fvs = unionVarSets alts_fvs
- alt_fvs (con, args, rhs) = foldl delVarSet (freeVarsOf rhs) (case_bndr:args)
+ alt_fvs (_con, args, rhs) = foldl delVarSet (freeVarsOf rhs) (case_bndr:args)
-- Delete case_bndr and args from free vars of rhs
-- to get free vars of alt
fi_alt to_drop (con, args, rhs) = (con, args, fiExpr to_drop rhs)
-noFloatIntoRhs (AnnNote InlineMe _) = True
-noFloatIntoRhs (AnnLam b _) = not (is_one_shot b)
+noFloatIntoRhs :: AnnExpr' Var (UniqFM Var) -> Bool
+noFloatIntoRhs (AnnLam b _) = not (is_one_shot b)
-- IMPORTANT: don't say 'True' for a RHS with a one-shot lambda at the top.
-- This makes a big difference for things like
-- f x# = let x = I# x#
noFloatIntoRhs rhs = exprIsHNF (deAnnotate' rhs) -- We'd just float right back out again...
+is_one_shot :: Var -> Bool
is_one_shot b = isId b && isOneShotBndr b
\end{code}
type DropBox = (FreeVarsSet, FloatingBinds)
-sepBindsByDropPoint is_case drop_pts []
- = [] : [[] | p <- drop_pts] -- cut to the chase scene; it happens
+sepBindsByDropPoint _is_case drop_pts []
+ = [] : [[] | _ <- drop_pts] -- cut to the chase scene; it happens
sepBindsByDropPoint is_case drop_pts floaters
= go floaters (map (\fvs -> (fvs, [])) (emptyVarSet : drop_pts))
-- "here" means the group of bindings dropped at the top of the fork
(used_here : used_in_flags) = [ any (`elemVarSet` fvs) (bindersOf bind)
- | (fvs, drops) <- drop_boxes]
+ | (fvs, _) <- drop_boxes]
drop_here = used_here || not can_push
insert_maybe box True = insert box
insert_maybe box False = box
+ go _ _ = panic "sepBindsByDropPoint/go"
+
floatedBindsFVs :: FloatingBinds -> FreeVarsSet
floatedBindsFVs binds = unionVarSets (map snd binds)
mkCoLets' to_drop e = foldl (flip (Let . fst)) e to_drop
-- Remember to_drop is in *reverse* dependency order
+bindIsDupable :: Bind CoreBndr -> Bool
bindIsDupable (Rec prs) = all (exprIsDupable . snd) prs
-bindIsDupable (NonRec b r) = exprIsDupable r
+bindIsDupable (NonRec _ r) = exprIsDupable r
\end{code}
projects / ghc-hetmet.git / blobdiff