[Haskell-cafe] Possible floating point bug in GHC?

Peter Verswyvelen bugfact at gmail.com
Fri Apr 3 17:04:10 EDT 2009

Okay, I can confirm the bug is fixed.
It's insane this bug did not cause any more problems. Every call into every
C function that uses floating point could have been affected (OpenGL, BLAS,

On Fri, Apr 3, 2009 at 10:47 PM, Peter Verswyvelen <bugfact at gmail.com>wrote:

> Ouch, what a waste of time on my side :-(
> This bugfix is not mentioned in the "notable bug fixes" here<http://haskell.org/ghc/docs/6.10.2/html/users_guide/release-6-10-2.html>
> Since this is such a severe bug, I would recommend listing it :)
> Anyway, I have a very small repro test case now. Will certainly test this
> with GHC 6.10.2.
> On Fri, Apr 3, 2009 at 10:35 PM, Ian Lynagh <igloo at earth.li> wrote:
>> On Fri, Apr 03, 2009 at 10:10:17PM +0200, Peter Verswyvelen wrote:
>> > I tried both precise and fast, but that did not help. Compiling to SSE2
>> > fixed it, since that does not use a floating point stack I guess.
>> You didn't say what version of GHC you are using, but it sounds like
>> this might already be fixed in 6.10.2 by:
>> Tue Nov 11 12:56:19 GMT 2008  Simon Marlow <marlowsd at gmail.com>
>>  * Fix to i386_insert_ffrees (#2724, #1944)
>>  The i386 native code generator has to arrange that the FPU stack is
>>  clear on exit from any function that uses the FPU.  Unfortunately it
>>  was getting this wrong (and has been ever since this code was written,
>>  I think): it was looking for basic blocks that used the FPU and adding
>>  the code to clear the FPU stack on any non-local exit from the block.
>>  In fact it should be doing this on a whole-function basis, rather than
>>  individual basic blocks.
>> Thanks
>> Ian
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