Commit 6f547477 authored by's avatar
Browse files

Add static flag -fsimple-list-literals

The new static flag -fsimple-list-literals makes ExplicitList literals
be desugared in the straightforward way, rather than using 'build' as
now.  See SLPJ comments with Note [Desugaring explicit lists].

I don't expect this flag to be used by users (hence no docs). It's just
there to let me try the performance effects of switching on and off.
parent d56631cb
......@@ -47,6 +47,7 @@ import CoreUtils
import MkCore
import DynFlags
import StaticFlags
import CostCentre
import Id
import PrelInfo
......@@ -609,6 +610,23 @@ allocation in some nofib programs. Specifically
Of course, if rules aren't turned on then there is pretty much no
point doing this fancy stuff, and it may even be harmful.
=======> Note by SLPJ Dec 08.
I'm unconvinced that we should *ever* generate a build for an explicit
list. See the comments in GHC.Base about the foldr/cons rule, which
points out that (foldr k z [a,b,c]) may generate *much* less code than
(a `k` b `k` c `k` z).
Furthermore generating builds messes up the LHS of RULES.
Example: the foldr/single rule in GHC.Base
foldr k z [x] = ...
We do not want to generate a build invocation on the LHS of this RULE!
To test this I've added a (static) flag -fsimple-list-literals, which
makes all list literals be generated via the simple route.
dsExplicitList :: PostTcType -> [LHsExpr Id] -> DsM CoreExpr
......@@ -616,7 +634,7 @@ dsExplicitList :: PostTcType -> [LHsExpr Id] -> DsM CoreExpr
dsExplicitList elt_ty xs = do
dflags <- getDOptsDs
xs' <- mapM dsLExpr xs
if not (dopt Opt_EnableRewriteRules dflags)
if opt_SimpleListLiterals || not (dopt Opt_EnableRewriteRules dflags)
then return $ mkListExpr elt_ty xs'
else mkBuildExpr elt_ty (mkSplitExplicitList (thisPackage dflags) xs')
......@@ -159,8 +159,7 @@ static_flags = [
-- Pass all remaining "-f<blah>" options to hsc
, Flag "f" (AnySuffixPred (isStaticFlag) addOpt)
, Flag "f" (AnySuffixPred isStaticFlag addOpt) Supported
isStaticFlag :: String -> Bool
......@@ -178,6 +177,7 @@ isStaticFlag f =
......@@ -43,6 +43,7 @@ module StaticFlags (
-- optimisation opts
......@@ -227,8 +228,12 @@ opt_DsMultiTyVar = not (lookUp (fsLit "-fno-ds-multi-tyvar"))
opt_SpecInlineJoinPoints :: Bool
opt_SpecInlineJoinPoints = lookUp (fsLit "-fspec-inline-join-points")
opt_SimpleListLiterals :: Bool
opt_SimpleListLiterals = lookUp (fsLit "-fsimple-list-literals")
opt_NoStateHack :: Bool
opt_NoStateHack = lookUp (fsLit "-fno-state-hack")
opt_CprOff :: Bool
opt_CprOff = lookUp (fsLit "-fcpr-off")
-- Switch off CPR analysis in the new demand analyser
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