[Llvm-bgq-discuss] QPX clang BGQ

[Hornung, Rich]

Hal,

Sounds good. Please don't hesitate to ask if you would like me to help by
running loop suite tests, etc.

Thanks,

Rich





On 5/10/13 1:07 AM, "Hal Finkel" <hfinkel at anl.gov> wrote:

>Rich, et al.,
>
>I've found the fast-math bug (which actually was not fast-math specific*,
>but was almost always triggered by the Newton-iteration-based QPX
>division code that is now generated in fast-math mode). I've fixed this
>issue in my local repository, and also rebased to pick up some upstream
>bug fixes that could affect us. vesta has been updated with the new
>version. Unfortunately, my standard testing has revealed a new upstream
>bug. I've filed a bug report (PR15952), and as soon as that is fixed,
>I'll rebase again and make a new release.
>
>(*) The problem was specifically that there was an incorrect optimization
>pattern for qvfnmsub[s].
>
>Thanks again,
>Hal
>
>----- Original Message -----
>> Rich,
>> 
>> Thanks for sending this! I can confirm that there appears to be a
>> fast-math bug (enabled by passing -ffast-math or -Ofast), and I've
>> found some local codes that also display this anomalous behavior.
>> Tracking this down is next on my TODO list.
>> 
>>  -Hal
>> 
>> ----- Original Message -----
>> > Folks,
>> > 
>> > I have recently taken Hal's latest compiler updates (version
>> > r176829-20130309) out for a spin on a suite of loop kernels I have
>> > developed for checking compiler optimizations.  What I found is
>> > that
>> > when
>> > using the -ffast-math option, my result checksums are very
>> > different
>> > from
>> > when I do not use -ffast-math (for all 30 loops in the suite except
>> > one).
>> > An earlier version (r176751-20130307) does not show these
>> > differences.
>> > Also, I did not see any significant performance differences across
>> > the
>> > loop suite between these compiler versions.  For completeness, I
>> > also
>> > compared the checksums generated when the code was compiled with
>> > the
>> > xlc
>> > 12.1 compiler.  The checksums for -O0 vs. -O3 -qnostrict vs. -O3
>> > -qstrict
>> > are all essentially the same.  From this I concluded that something
>> > is
>> > broken in the latest version of the optimizer.
>> > 
>> > So, if you're going to use the latest compiler version, make sure
>> > you
>> > check your answers.
>> > 
>> > --Rich
>> > 
>> > 
>> > 
>> > 
>> > 
>> > On 5/8/13 9:42 AM, "Jeff Hammond" <jhammond at alcf.anl.gov> wrote:
>> > 
>> > >(copying LLVM discuss - you should sign up for this list)
>> > >
>> > >Hi Ivo,
>> > >
>> > >I don't know the answer, but if you're on BGQ, you should use
>> > >Hal's
>> > >version of LLVM anyways because I think it has other important
>> > >patches, not just QPX ones.
>> > >
>> > >Best,
>> > >
>> > >Jeff
>> > >
>> > >2013/5/8 Ivo Kabadshow <i.kabadshow at fz-juelich.de>:
>> > >> Jeff,
>> > >>
>> > >>  does clang work with QPX on BGQ or do I need Hals clang
>> > >>  version?
>> > >>
>> > >> Best
>> > >>  Ivo
>> > >>
>> > >>
>> > >> 
>> > 
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>> > >
>> > >
>> > >--
>> > >Jeff Hammond
>> > >Argonne Leadership Computing Facility
>> > >University of Chicago Computation Institute
>> > >jhammond at alcf.anl.gov / (630) 252-5381
>> > >http://www.linkedin.com/in/jeffhammond
>> > >https://wiki.alcf.anl.gov/parts/index.php/User:Jhammond
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