[Llvm-bgq-discuss] New bgclang nighty builds (and other updates)

[Mark Abraham]

On Tue, Mar 24, 2015 at 7:29 PM, Hal Finkel <hfinkel at anl.gov> wrote:

> ----- Original Message -----
> > From: "Mark Abraham" <mark.j.abraham at gmail.com>
> > To: "Hal Finkel" <hfinkel at anl.gov>
> > Cc: llvm-bgq-discuss at lists.alcf.anl.gov
> > Sent: Tuesday, March 24, 2015 12:35:20 PM
> > Subject: Re: [Llvm-bgq-discuss] New bgclang nighty builds (and other
> updates)
> >
> >
> > Hi Hal,
> >
> >
> > Thanks very much for the update & effort.
> >
>
> You're very welcome.
>
> >
> > I tried out the default bgclang 3.6.0 on vesta, but found a bunch of
> > the GROMACS SIMD-layer unit tests failing. These need correct QPX
> > vector intrinsics available. From memory, things worked fine with
> > bgclang in ~August last year, but I no longer have those results. Is
> > there a simple way I can compile on vesta with older bgclang to see
> > where a problem might lie? Otherwise / depending what I learn, I'll
> > break out a debugger.
>
> The old builds are still all installed. Just use the MPI wrappers from:
>
> /home/projects/llvm/<whatever>/mpi/bgclang/bin -- I don't know exactly
> which build you were using in August of last year, r209570-20140527 maybe?
>

Yes, that was it, looking at some cruft in my former build script. In any
case, the latest GROMACS SIMD single-precision unit tests pass on that old
compiler version (3.5.0), and many of them fail in a release build on the
default 3.6.0 bgclang on vesta. For some of the cases, it looks like some
junk memory gets loaded, somehow. A few tests pass, but no theme for
passing or failing tests leaps out at me. Double precision unit tests are
OK, though.

Naturally, in debug mode most of the tests pass. However, the two I looked
at in ddt were fine up until they called vec_extract(x, 0) e.g. on lines
https://github.com/gromacs/gromacs/blob/master/src/gromacs/simd/impl_ibm_qpx/impl_ibm_qpx.h#L315
(where  a SIMD vector of 1 2 3 1 was summed to 3, rather than 7) and
https://github.com/gromacs/gromacs/blob/master/src/gromacs/simd/impl_ibm_qpx/impl_ibm_qpx.h#L462
(where a SIMD vector dot product of the first 3 lanes returns a garbage
answer). So maybe that is a productive lead?

I couldn't inspect the disassembly in ddt, so I'm not sure where we can
take this from here, Hal. Tarball of test results attached.

Thanks,

Mark


>  -Hal
>
> >
> >
> > Thanks,
> >
> >
> > Mark
> >
> >
> >
> >
> > On Fri, Mar 20, 2015 at 12:15 AM, Hal Finkel < hfinkel at anl.gov >
> > wrote:
> >
> >
> > Hello everyone,
> >
> > First, let me apologize to everyone, this is a few months late...
> > but, hopefully, this will never be a problem again...
> >
> > I now have a system setup which automatically pulls in upstream
> > changes and tries to merge those with the bgclang-specific patches,
> > and then builds the resulting suite of bgclang RPMs. When this
> > succeeds, the RPMs should be posted automatically to:
> >
> > http://www.mcs.anl.gov/~hfinkel/bgclang/
> > (note that installing a build from here now also requires both the
> > 'stage1' and 'stage2' RPMs as well)
> >
> > The first such nightly build, r232720-20150319, has been posted to
> > that page.
> >
> > And, for the curious, the local repositories used for version control
> > are now mirrored to github:
> >
> > https://github.com/hfinkel/clang-bgq
> > https://github.com/hfinkel/llvm-bgq
> > https://github.com/hfinkel/bgclang-aux
> > https://github.com/hfinkel/compiler-rt-bgq
> > https://github.com/hfinkel/libcxx-bgq
> > https://github.com/hfinkel/openmp-bgq
> > https://github.com/hfinkel/sleef-bgq
> >
> > Compared to the latest "released" version (r220548-20141024), the
> > most-recent nightly build does show some performance regressions,
> > and there are a few things I've not even tested yet (LTO, ASan,
> > etc.), but it also contains a number of bug fixes and improvements,
> > so feel free to test on your applications.
> >
> > One particular noteworthy improvement is that our OpenMP runtime
> > library now has affinity support enabled. This means that all of the
> > OpenMP 4 affinity features should work, and also that the default
> > thread<->core bindings are now sensible.
> >
> > The bgclang wrapper script no longer disables 'fast-isel' instruction
> > selection at -O0, so your debug builds should now be faster too.
> > Also, the automated vectorization of math functions using our SLEEF
> > library adaptation is controlled using the new -fveclib flag (so the
> > wrapper script contains -fveclib=SLEEF, and you can add
> > -fveclib=none to turn it off if desired for whatever reason).
> >
> > Also, the core QPX support has been contributed upstream (although
> > not yet the Clang-level intrinsics support); so if you're using LLVM
> > as a library, and want to just build from upstream sources instead
> > of depending on the bgclang builds, that is now possible.
> >
> > Thanks again everyone, and please let me know if you experience any
> > difficulties,
> > Hal
> >
> > --
> > Hal Finkel
> > Assistant Computational Scientist
> > Leadership Computing Facility
> > Argonne National Laboratory
> > _______________________________________________
> > llvm-bgq-discuss mailing list
> > llvm-bgq-discuss at lists.alcf.anl.gov
> > https://lists.alcf.anl.gov/mailman/listinfo/llvm-bgq-discuss
> >
> >
>
> --
> Hal Finkel
> Assistant Computational Scientist
> Leadership Computing Facility
> Argonne National Laboratory
>
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