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

Sun May 10 10:40:01 CDT 2015

Hi Hal,

See attachment!

From: Hal Finkel <hfinkel at anl.gov>
Reply: Hal Finkel <hfinkel at anl.gov>>
Date: 10 May 2015 at 17:22:52
To: Erik Lindahl <erik.lindahl at gmail.com>>
Cc: llvm-bgq-discuss at lists.alcf.anl.gov <llvm-bgq-discuss at lists.alcf.anl.gov>>, Mark Abraham <mark.j.abraham at gmail.com>>
Subject:  Re: [Llvm-bgq-discuss] New bgclang nighty builds (and other updates)  

Hi Erik,  

If you could send this trivial piece of code, that would be greatly appreciated.  

Thanks again,  
Hal  

----- Original Message -----  
> From: "Erik Lindahl" <erik.lindahl at gmail.com>  
> To: "Hal Finkel" <hfinkel at anl.gov>, "Mark Abraham" <mark.j.abraham at gmail.com>  
> Cc: llvm-bgq-discuss at lists.alcf.anl.gov  
> Sent: Sunday, May 10, 2015 9:25:34 AM  
> Subject: Re: [Llvm-bgq-discuss] New bgclang nighty builds (and other updates)  
>  
>  
> Hi,  
>  
>  
> Super-brief summary:  
>  
>  
> The bug occurs at high optimization (-O3) with the vec_ld() or  
> vec_st() functions when calling the (overloaded) version with  
> single-precision arguments (i.e., float pointers).  
>  
>  
> This is reproducible even with a trivial piece of code that tries to  
> load from single precision memory and then write out the contents of  
> the (double precision) vector4doubles by storing to a double  
> variable.  
>  
>  
> - Everything works fine with the double-precision functions,  
> regardless of optimization  
> - It works fine with clang in single precision without optimization  
> - It works fine with xlc.  
>  
>  
> Cheers,  
>  
>  
> Erik  
>  
>  
>  
>  
> From: Mark Abraham <mark.j.abraham at gmail.com>  
> Reply: Mark Abraham <mark.j.abraham at gmail.com>>  
> Date: 10 May 2015 at 16:04:51  
> To: Hal Finkel <hfinkel at anl.gov>>  
> Cc: llvm-bgq-discuss at lists.alcf.anl.gov  
> <llvm-bgq-discuss at lists.alcf.anl.gov>> , Erik Lindahl  
> <erik.lindahl at gmail.com>>  
> Subject: Re: [Llvm-bgq-discuss] New bgclang nighty builds (and other  
> updates)  
>  
>  
>  
>  
>  
>  
>  
> Hi,  
>  
> Bump. Erik Lindahl has also observed this on bgclang on JUQUEEN. Is  
> it helpful if I produce a small piece of code that reproduces some  
> of the issues on bgclang 3.6?  
>  
>  
>  
> Mark  
>  
> On Wed, Mar 25, 2015 at 4:16 PM Mark Abraham <  
> mark.j.abraham at gmail.com > wrote:  
>  
>  
>  
>  
>  
> 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  
>  
>  
> --  
> Erik Lindahl < erik.lindahl at gmail.com >  
> Professor of Biophysics, Dept. Biochemistry & Biophysics, Stockholm  
> University  
> Professor of Theoretical biophysics, Dept. Theoretical Physics, Royal  
> Inst. Technology  
> Science for Life Laboratory, Box 1031, 17121 Solna, Sweden  

--  
Hal Finkel  
Assistant Computational Scientist  
Leadership Computing Facility  
Argonne National Laboratory  
-- 
Erik Lindahl <erik.lindahl at gmail.com> 
Professor of Biophysics, Dept. Biochemistry & Biophysics, Stockholm University 
Professor of Theoretical biophysics, Dept. Theoretical Physics, Royal Inst. Technology 
Science for Life Laboratory, Box 1031, 17121 Solna, Sweden
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