[GHC] #7976: Failure building master (perf) on i686-pc-linux-gnu

[GHC]

#7976: Failure building master (perf) on i686-pc-linux-gnu
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Reporter:  nickie               |          Owner:          
    Type:  bug                  |         Status:  new     
Priority:  normal               |      Component:  Compiler
 Version:  7.7                  |       Keywords:          
      Os:  Linux                |   Architecture:  x86     
 Failure:  Building GHC failed  |      Blockedby:          
Blocking:                       |        Related:          
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Comment(by int-e):

 We have discussed the following patch briefly on #ghc:
 {{{
 diff --git a/compiler/nativeGen/X86/CodeGen.hs
 b/compiler/nativeGen/X86/CodeGen.hs
 index 7c58114..84f19b7 100644
 --- a/compiler/nativeGen/X86/CodeGen.hs
 +++ b/compiler/nativeGen/X86/CodeGen.hs
 @@ -1658,6 +1658,20 @@ genCCall _ (PrimTarget MO_Touch) _ _ = return nilOL

  genCCall _ (PrimTarget MO_Prefetch_Data) _ _ = return nilOL

 +genCCall is32Bit (PrimTarget (MO_BSwap W64)) [dst] [src] | is32Bit = do
 +    dflags <- getDynFlags
 +    let platform = targetPlatform dflags
 +    let dst_rlo = getRegisterReg platform False (CmmLocal dst)
 +        dst_rhi = getHiVRegFromLo dst_rlo
 +    ChildCode64 vcode rlo <- iselExpr64 src
 +    let rhi = getHiVRegFromLo rlo
 +    -- XXX: can we be sure that the registers rlo/rhi and dst_rlo/dst_rhi
 don't overlap?
 +    return $ vcode `appOL`
 +             toOL [ MOV II32 (OpReg rlo) (OpReg dst_rhi),
 +                    MOV II32 (OpReg rhi) (OpReg dst_rlo),
 +                    BSWAP II32 dst_rhi,
 +                    BSWAP II32 dst_rlo ]
 +
  genCCall _ (PrimTarget (MO_BSwap width)) [dst] [src] = do
      dflags <- getDynFlags
      let platform = targetPlatform dflags
 }}}
 With it, building on x86 works, and the bswap test (cgrun072) passes. But
 the patch needs somebody who knows the code generator better than I to
 figure out whether the registers {{{rlo,rhi}}} may clash with
 {{{dst_rlo,dst_rhi}}}, in which case the resulting code would be
 incorrect.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7976#comment:1>
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