``Long-distance'' floating of bindings towards the top level.
\begin{code}
-module FloatOut ( floatOutwards ) where
+{-# 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
-#include "HsVersions.h"
+module FloatOut ( floatOutwards ) where
import CoreSyn
-import CoreUtils ( mkSCC, exprIsHNF, exprIsTrivial )
+import CoreUtils
import DynFlags ( DynFlags, DynFlag(..), FloatOutSwitches(..) )
import ErrUtils ( dumpIfSet_dyn )
import UniqSupply ( UniqSupply )
import List ( partition )
import Outputable
-import Util ( notNull )
+import FastString
\end{code}
-----------------
let { (tlets, ntlets, lams) = get_stats (sum_stats fss) };
dumpIfSet_dyn dflags Opt_D_dump_simpl_stats "FloatOut stats:"
- (hcat [ int tlets, ptext SLIT(" Lets floated to top level; "),
- int ntlets, ptext SLIT(" Lets floated elsewhere; from "),
- int lams, ptext SLIT(" Lambda groups")]);
+ (hcat [ int tlets, ptext (sLit " Lets floated to top level; "),
+ int ntlets, ptext (sLit " Lets floated elsewhere; from "),
+ int lams, ptext (sLit " Lambda groups")]);
endPass dflags float_msg Opt_D_verbose_core2core (concat binds_s')
{- no specific flag for dumping float-out -}
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}
%************************************************************************
\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
-- 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') ->
%************************************************************************
\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;
-- 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 <bind> in <body>
- -- We do not want
- -- f = let <bind> in \x -> <body>
- -- (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 <bind> in <body>
+-- We do not want
+-- f = let <bind> in \x -> <body>
+-- (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 _ _)
= Rec [(binder, mkSCC dupd_cc rhs) | (binder, rhs) <- pairs]
floatExpr lvl (Note InlineMe expr) -- Other than SCCs
- = case floatExpr InlineCtxt expr of { (fs, floating_defns, expr') ->
- -- There can be some floating_defns, arising from
- -- ordinary lets that were there all the time. It seems
- -- more efficient to test once here than to avoid putting
- -- them into floating_defns (which would mean testing for
- -- inlineCtxt at every let)
- (fs, [], Note InlineMe (install floating_defns expr')) } -- See notes in SetLevels
+ = (zeroStats, [], Note InlineMe (unTag expr))
+ -- Do no floating at all inside INLINE. [_$_]
+ -- The SetLevels pass did not clone the bindings, so it's
+ -- unsafe to do any floating, even if we dump the results
+ -- inside the Note (which is what we used to do).
floatExpr lvl (Note note expr) -- Other than SCCs
= case (floatExpr lvl expr) of { (fs, floating_defns, expr') ->
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') ->
(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')) }
floatList f (a:as) = case f a of { (fs_a, binds_a, b) ->
case floatList f as of { (fs_as, binds_as, bs) ->
(fs_a `add_stats` fs_as, binds_a ++ binds_as, b:bs) }}
+
+unTagBndr :: TaggedBndr tag -> CoreBndr
+unTagBndr (TB b _) = b
+
+unTag :: TaggedExpr tag -> CoreExpr
+unTag (Var v) = Var v
+unTag (Lit l) = Lit l
+unTag (Type ty) = Type ty
+unTag (Note n e) = Note n (unTag e)
+unTag (App e1 e2) = App (unTag e1) (unTag e2)
+unTag (Lam b e) = Lam (unTagBndr b) (unTag e)
+unTag (Cast e co) = Cast (unTag e) co
+unTag (Let (Rec prs) e) = Let (Rec [(unTagBndr b,unTag r) | (b, r) <- prs]) (unTag e)
+unTag (Let (NonRec b r) e) = Let (NonRec (unTagBndr b) (unTag r)) (unTag e)
+unTag (Case e b ty alts) = Case (unTag e) (unTagBndr b) ty
+ [(c, map unTagBndr bs, unTag r) | (c,bs,r) <- alts]
\end{code}
%************************************************************************