[Llvm-bgq-discuss] QPX clang BGQ

[Hal Finkel]

Rich,

I've just finished updating your installation with a new version (r181589-20130510). The qvfnmsub bug (which I suppose was your fast-math bug) should be fixed, as well as a few others. Please run your tests again.

Thanks again,
Hal

----- Original Message -----
> 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
> >> > >>
> >> > >>
> >> > >> 
> >> > 
> >>>>-----------------------------------------------------------------------
> >>>>--
> >> > >>-----------------------
> >> > >> 
> >> > 
> >>>>-----------------------------------------------------------------------
> >>>>--
> >> > >>-----------------------
> >> > >> Forschungszentrum Juelich GmbH
> >> > >> 52425 Juelich
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> >> > >> Bolt,
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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
> >> > >ALCF docs: http://www.alcf.anl.gov/user-guides
> >> > >_______________________________________________
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> >> > 
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