[Llvm-bgq-discuss] QPX clang BGQ

[Hal Finkel]

And I should add, please *always* check the results of your codes (fast-math or not); this compiler is still under active development, and the standard test suite is large, but not anywhere near large enough to be exhaustive. Of course, the same is true with any compiler.

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
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