X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2FsimplCore%2FFloatOut.lhs;h=2af48bde13c172814d0cba2abcb65d47857a61a5;hp=988bd53015d53474cc51ccb94b8ddf35e5657b55;hb=7fc749a43b4b6b85d234fa95d4928648259584f4;hpb=0065d5ab628975892cea1ec7303f968c3338cbe1 diff --git a/compiler/simplCore/FloatOut.lhs b/compiler/simplCore/FloatOut.lhs index 988bd53..2af48bd 100644 --- a/compiler/simplCore/FloatOut.lhs +++ b/compiler/simplCore/FloatOut.lhs @@ -6,12 +6,19 @@ ``Long-distance'' floating of bindings towards the top level. \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 FloatOut ( floatOutwards ) where #include "HsVersions.h" import CoreSyn -import CoreUtils ( mkSCC, exprIsHNF, exprIsTrivial ) +import CoreUtils import DynFlags ( DynFlags, DynFlag(..), FloatOutSwitches(..) ) import ErrUtils ( dumpIfSet_dyn ) @@ -24,7 +31,6 @@ import SetLevels ( Level(..), LevelledExpr, LevelledBind, import UniqSupply ( UniqSupply ) import List ( partition ) import Outputable -import Util ( notNull ) \end{code} ----------------- @@ -144,15 +150,10 @@ floatOutwards float_sws dflags us pgm pp_not True = empty pp_not False = text "not" -floatTopBind bind@(NonRec _ _) - = case (floatBind bind) of { (fs, floats, bind') -> - (fs, floatsToBinds floats ++ [bind']) +floatTopBind bind + = case (floatBind bind) of { (fs, floats) -> + (fs, floatsToBinds floats) } - -floatTopBind bind@(Rec _) - = case (floatBind bind) of { (fs, floats, Rec pairs') -> - WARN( notNull floats, ppr bind $$ ppr floats ) - (fs, [Rec (floatsToBindPairs floats ++ pairs')]) } \end{code} %************************************************************************ @@ -163,21 +164,25 @@ floatTopBind bind@(Rec _) \begin{code} -floatBind :: LevelledBind - -> (FloatStats, FloatBinds, CoreBind) +floatBind :: LevelledBind -> (FloatStats, FloatBinds) floatBind (NonRec (TB name level) rhs) - = case (floatNonRecRhs level rhs) of { (fs, rhs_floats, rhs') -> - (fs, rhs_floats, NonRec name rhs') } + = case (floatRhs level rhs) of { (fs, rhs_floats, rhs') -> + (fs, rhs_floats ++ [(level, NonRec name rhs')]) } floatBind bind@(Rec pairs) = case (unzip3 (map do_pair pairs)) of { (fss, rhss_floats, new_pairs) -> - - if not (isTopLvl bind_dest_level) then - -- Standard case; the floated bindings can't mention the - -- binders, because they couldn't be escaping a major level - -- if so. - (sum_stats fss, concat rhss_floats, Rec new_pairs) + let rhs_floats = concat rhss_floats in + + if not (isTopLvl bind_dest_lvl) then + -- Find which bindings float out at least one lambda beyond this one + -- These ones can't mention the binders, because they couldn't + -- be escaping a major level if so. + -- The ones that are not going further can join the letrec; + -- they may not be mutually recursive but the occurrence analyser will + -- find that out. + case (partitionByMajorLevel bind_dest_lvl rhs_floats) of { (floats', heres) -> + (sum_stats fss, floats' ++ [(bind_dest_lvl, Rec (floatsToBindPairs heres ++ new_pairs))]) } else -- In a recursive binding, *destined for* the top level -- (only), the rhs floats may contain references to the @@ -192,11 +197,10 @@ floatBind bind@(Rec pairs) -- This can only happen for bindings destined for the top level, -- because only then will partitionByMajorLevel allow through a binding -- that only differs in its minor level - (sum_stats fss, [], - Rec (new_pairs ++ floatsToBindPairs (concat rhss_floats))) + (sum_stats fss, [(bind_dest_lvl, Rec (new_pairs ++ floatsToBindPairs rhs_floats))]) } where - bind_dest_level = getBindLevel bind + bind_dest_lvl = getBindLevel bind do_pair (TB name level, rhs) = case (floatRhs level rhs) of { (fs, rhs_floats, rhs') -> @@ -211,12 +215,12 @@ floatBind bind@(Rec pairs) %************************************************************************ \begin{code} -floatExpr, floatRhs, floatNonRecRhs +floatExpr, floatRhs, floatCaseAlt :: Level -> LevelledExpr -> (FloatStats, FloatBinds, CoreExpr) -floatRhs lvl arg -- Used rec rhss, and case-alternative rhss +floatCaseAlt lvl arg -- Used rec rhss, and case-alternative rhss = case (floatExpr lvl arg) of { (fsa, floats, arg') -> case (partitionByMajorLevel lvl floats) of { (floats', heres) -> -- Dump bindings that aren't going to escape from a lambda; @@ -224,38 +228,46 @@ floatRhs lvl arg -- Used rec rhss, and case-alternative rhss -- the rec or case alternative (fsa, floats', install heres arg') }} -floatNonRecRhs lvl arg -- Used for nested non-rec rhss, and fn args +floatRhs lvl arg -- Used for nested non-rec rhss, and fn args + -- See Note [Floating out of RHS] = case (floatExpr lvl arg) of { (fsa, floats, arg') -> - -- Dump bindings that aren't going to escape from a lambda - -- This isn't a scoping issue (the binder isn't in scope in the RHS of a non-rec binding) - -- Rather, it is to avoid floating the x binding out of - -- f (let x = e in b) - -- unnecessarily. But we first test for values or trival rhss, - -- because (in particular) we don't want to insert new bindings between - -- the "=" and the "\". E.g. - -- f = \x -> let in - -- We do not want - -- f = let in \x -> - -- (a) The simplifier will immediately float it further out, so we may - -- as well do so right now; in general, keeping rhss as manifest - -- values is good - -- (b) If a float-in pass follows immediately, it might add yet more - -- bindings just after the '='. And some of them might (correctly) - -- be strict even though the 'let f' is lazy, because f, being a value, - -- gets its demand-info zapped by the simplifier. - if exprIsHNF arg' || exprIsTrivial arg' then + if exprIsCheap arg' then (fsa, floats, arg') else case (partitionByMajorLevel lvl floats) of { (floats', heres) -> (fsa, floats', install heres arg') }} +-- Note [Floating out of RHSs] +-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~ +-- Dump bindings that aren't going to escape from a lambda +-- This isn't a scoping issue (the binder isn't in scope in the RHS +-- of a non-rec binding) +-- Rather, it is to avoid floating the x binding out of +-- f (let x = e in b) +-- unnecessarily. But we first test for values or trival rhss, +-- because (in particular) we don't want to insert new bindings between +-- the "=" and the "\". E.g. +-- f = \x -> let in +-- We do not want +-- f = let in \x -> +-- (a) The simplifier will immediately float it further out, so we may +-- as well do so right now; in general, keeping rhss as manifest +-- values is good +-- (b) If a float-in pass follows immediately, it might add yet more +-- bindings just after the '='. And some of them might (correctly) +-- be strict even though the 'let f' is lazy, because f, being a value, +-- gets its demand-info zapped by the simplifier. +-- +-- We use exprIsCheap because that is also what's used by the simplifier +-- to decide whether to float a let out of a let + floatExpr _ (Var v) = (zeroStats, [], Var v) floatExpr _ (Type ty) = (zeroStats, [], Type ty) floatExpr _ (Lit lit) = (zeroStats, [], Lit lit) floatExpr lvl (App e a) = case (floatExpr lvl e) of { (fse, floats_e, e') -> - case (floatNonRecRhs lvl a) of { (fsa, floats_a, a') -> + case (floatRhs lvl a) of { (fsa, floats_a, a') -> (fse `add_stats` fsa, floats_e ++ floats_a, App e' a') }} floatExpr lvl lam@(Lam _ _) @@ -315,20 +327,23 @@ floatExpr lvl (Note note expr) -- Other than SCCs = case (floatExpr lvl expr) of { (fs, floating_defns, expr') -> (fs, floating_defns, Note note expr') } +floatExpr lvl (Cast expr co) + = case (floatExpr lvl expr) of { (fs, floating_defns, expr') -> + (fs, floating_defns, Cast expr' co) } + floatExpr lvl (Let (NonRec (TB bndr bndr_lvl) rhs) body) | isUnLiftedType (idType bndr) -- Treat unlifted lets just like a case - = case floatExpr lvl rhs of { (fs, rhs_floats, rhs') -> - case floatRhs bndr_lvl body of { (fs, body_floats, body') -> + -- I.e. floatExpr for rhs, floatCaseAlt for body + = case floatExpr lvl rhs of { (fs, rhs_floats, rhs') -> + case floatCaseAlt bndr_lvl body of { (fs, body_floats, body') -> (fs, rhs_floats ++ body_floats, Let (NonRec bndr rhs') body') }} floatExpr lvl (Let bind body) - = case (floatBind bind) of { (fsb, rhs_floats, bind') -> + = case (floatBind bind) of { (fsb, bind_floats) -> case (floatExpr lvl body) of { (fse, body_floats, body') -> (add_stats fsb fse, - rhs_floats ++ [(bind_lvl, bind')] ++ body_floats, + bind_floats ++ body_floats, body') }} - where - bind_lvl = getBindLevel bind floatExpr lvl (Case scrut (TB case_bndr case_lvl) ty alts) = case floatExpr lvl scrut of { (fse, fde, scrut') -> @@ -336,10 +351,10 @@ floatExpr lvl (Case scrut (TB case_bndr case_lvl) ty alts) (add_stats fse fsa, fda ++ fde, Case scrut' case_bndr ty alts') }} where - -- Use floatRhs for the alternatives, so that we + -- Use floatCaseAlt for the alternatives, so that we -- don't gratuitiously float bindings out of the RHSs float_alt (con, bs, rhs) - = case (floatRhs case_lvl rhs) of { (fs, rhs_floats, rhs') -> + = case (floatCaseAlt case_lvl rhs) of { (fs, rhs_floats, rhs') -> (fs, rhs_floats, (con, [b | TB b _ <- bs], rhs')) }