#5152: GHC generates poor code for large 64-bit literals
---------------------------------+------------------------------------------
Reporter: bos | Owner: igloo
Type: bug | Status: new
Priority: normal | Milestone: 7.4.1
Component: Compiler | Version: 7.0.3
Keywords: | Testcase:
Blockedby: | Difficulty:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: Runtime performance bug
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Comment(by thoughtpolice):
I've fixed this in the `Word64` case at least. My branch with the fix is
here:
https://github.com/thoughtpolice/ghc/tree/trac-5152
Relevant commit:
https://github.com/thoughtpolice/ghc/commit/18cf5ba840a7ecdf1860e54b8a6c8f3fcdf0441d
With GHC 7.0.4, here are my results:
{{{
$ cat ghc_5152.hs
module Main where
import Data.Word (Word64)
{-# NOINLINE a #-}
a :: Word64
a = 0x9ddfea08eb382d69
main = print a
}}}
I get:
{{{
ghc -ddump-simpl -fforce-recomp ghc_5152.hs
[1 of 1] Compiling Main ( ghc_5152.hs, ghc_5152.o )
==================== Tidy Core ====================
Main.a [InlPrag=NOINLINE] :: GHC.Word.Word64
[GblId]
Main.a =
GHC.Num.fromInteger
@ GHC.Word.Word64
GHC.Word.$fNumWord64
(GHC.Integer.plusInteger
(GHC.Integer.smallInteger 2152696470933351786)
(GHC.Integer.smallInteger 9223372036854775807))
Main.main :: GHC.Types.IO ()
[GblId]
Main.main =
System.IO.print @ GHC.Word.Word64 GHC.Word.$fShowWord64 Main.a
:Main.main :: GHC.Types.IO ()
[GblId]
:Main.main = GHC.TopHandler.runMainIO @ () Main.main
}}}
With my patch, I get:
{{{
~/code/ghc/inplace/bin/ghc-stage2 -ddump-simpl -fforce-recomp ghc_5152.hs
[1 of 1] Compiling Main ( ghc_5152.hs, ghc_5152.o )
==================== Tidy Core ====================
Result size = 12
Main.a [InlPrag=NOINLINE] :: GHC.Word.Word64
[GblId, Caf=NoCafRefs]
Main.a = GHC.Word.W# __word 11376068507788127593
Main.main :: GHC.Types.IO ()
[GblId]
Main.main =
System.IO.print @ GHC.Word.Word64 GHC.Word.$fShowWord64 Main.a
:Main.main :: GHC.Types.IO ()
[GblId]
:Main.main = GHC.TopHandler.runMainIO @ () Main.main
}}}
Which should be exactly what you want, Bryan.
I'm willing to extend this patch to handle other fixed-width types - I
assume `Int64` probably needs handling among other things. If this is what
should be done, I'm willing to assign this ticket to myself and add those
cases.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5152#comment:3>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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