X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2FsimplCore%2FFloatIn.lhs;h=b6cd86a75ed7c8e05877babc461fae8a394e3f1e;hp=b80a8e0b2a7081158bce453ba3b08ec6ad64508f;hb=7fc749a43b4b6b85d234fa95d4928648259584f4;hpb=d5934bbb856aa0aa620c9b2e0fa51c90a1a5a048 diff --git a/compiler/simplCore/FloatIn.lhs b/compiler/simplCore/FloatIn.lhs index b80a8e0..b6cd86a 100644 --- a/compiler/simplCore/FloatIn.lhs +++ b/compiler/simplCore/FloatIn.lhs @@ -12,6 +12,13 @@ case, so that we don't allocate things, save them on the stack, and then discover that they aren't needed in the chosen branch. \begin{code} +{-# OPTIONS -w #-} +-- The above warning supression flag is a temporary kludge. +-- While working on this module you are encouraged to remove it and fix +-- any warnings in the module. See +-- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings +-- for details + module FloatIn ( floatInwards ) where #include "HsVersions.h" @@ -20,7 +27,7 @@ import DynFlags ( DynFlags, DynFlag(..) ) import CoreSyn import CoreUtils ( exprIsHNF, exprIsDupable ) import CoreLint ( showPass, endPass ) -import CoreFVs ( CoreExprWithFVs, freeVars, freeVarsOf ) +import CoreFVs ( CoreExprWithFVs, freeVars, freeVarsOf, idRuleVars ) import Id ( isOneShotBndr ) import Var ( Id, idType ) import Type ( isUnLiftedType ) @@ -124,7 +131,7 @@ the closure for a is not built. 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 @@ -214,13 +221,6 @@ 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@(TickBox {}) expr) - = -- Wimp out for now - mkCoLets' to_drop (Note note (fiExpr [] expr)) -fiExpr to_drop (_, AnnNote note@(BinaryTickBox {}) expr) - = -- Wimp out for now - mkCoLets' to_drop (Note note (fiExpr [] expr)) - fiExpr to_drop (_, AnnNote note@(CoreNote _) expr) = Note note (fiExpr to_drop expr) \end{code} @@ -247,23 +247,52 @@ So: rather than drop \tr{w}'s binding here, we add it onto the list of 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 +idRuleVars of x. + + \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 = idRuleVars 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 @@ -278,32 +307,20 @@ fiExpr to_drop (_,AnnLet (AnnRec bindings) body) 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)] + extra_fvs = foldr (unionVarSet . get_extras) emptyVarSet bindings + get_extras (id, (rhs_fvs, rhs)) + | noFloatIntoRhs rhs = idRuleVars id `unionVarSet` rhs_fvs + | otherwise = idRuleVars id + + (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))