#4914: FPU initialization required again
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Reporter: aruiz | Owner: simonmar
Type: bug | Status: new
Priority: high | Milestone: 7.2.1
Component: Compiler (NCG) | Version: 7.0.1
Keywords: | Testcase:
Blockedby: | Difficulty:
Os: Unknown/Multiple | Blocking:
Architecture: x86 | Failure: Incorrect result at runtime
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Comment(by simonmar):
I think I've found it, Thanks for all your help in tracking this one down,
it was a very tricky one to find!
{{{
Fri Mar 25 16:12:34 GMT 2011 Simon Marlow <[email protected]>
* Fix #4914 (I hope)
Here's a bit of erroneous code:
00000c5c <s1ad_info>:
c5c: 8b 45 08 mov 0x8(%ebp),%eax
c5f: d9 46 03 flds 0x3(%esi)
c62: dd d9 fstp %st(1)
c64: d9 55 08 fsts 0x8(%ebp)
c67: 89 c6 mov %eax,%esi
c69: c7 45 00 24 0c 00 00 movl $0xc24,0x0(%ebp)
c70: f7 c6 03 00 00 00 test $0x3,%esi
c76: 75 ac jne c24 <s1ac_info>
So we should be doing some ffrees before the jne. The code that
inserts the ffrees wasn't expecting to do it for a conditional jump,
because they are usually local, but we have a late optimisation that
shortcuts jumps-to-jumps, and that can result in a non-local
conditional jump.
This at least fixes an instance of the bug that I was able to
reproduce, let's hope there aren't any more.
}}}
I'll leave the bug open until you can confirm that the bug is fixed.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4914#comment:18>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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