[Llvm-bgq-discuss] QPX clang BGQ

[Hal Finkel]

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
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