[GHC] #1052: NCG doesn't realise shift instructions trash shifted input?

[GHC]

#1052: NCG doesn't realise shift instructions trash shifted input?
----------------------------+-----------------------------------------------
 Reporter:  igloo           |          Owner:                
     Type:  bug             |         Status:  new           
 Priority:  normal          |      Milestone:  6.8           
Component:  Compiler (NCG)  |        Version:  6.6           
 Severity:  normal          |     Resolution:                
 Keywords:                  |     Difficulty:  Unknown       
 Testcase:  arith011        |   Architecture:  x86_64 (amd64)
       Os:  Linux           |  
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Comment (by simonmar):

 I think I see the bug:
 {{{
     shift_code rep instr x y{-amount-} = do
         (x_reg, x_code) <- getNonClobberedReg x
         y_code <- getAnyReg y
         let
            code = x_code `appOL`
                   y_code ecx `snocOL`
                   instr (OpReg ecx) (OpReg x_reg)
         -- in
         return (Fixed rep x_reg code)
 }}}

 If getNonClobberedReg returns a Fixed reg, this code generates a shift
 instruction that modifies the Fixed reg, which is wrong.

 However, I can't reproduce the bug locally, arith011 isn't failing in our
 nightly builds.  Any idea why that might be?

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1052>
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