llvm dev - May 2021 - LLVM LNT floating point performance tests on X86 - using the llvm-test-suite benchmarks

Hello.
I have a patch to commit to community https://reviews.llvm.org/D74436?id=282577
that changes command line settings for floating point.  When I committed it
previously, it was ultimately rolled back due to bot failures with LNT.

Looking for suggestions on how to use the llvm-test-suite benchmarks to analyze
this issue so I can commit this change.

We think the key difference in the tests that regressed when I tried to commit
the change was caused by differences in unrolling decisions when the fmuladd
intrinsic was present.

As far as I can tell, the LNT bots aren't currently running on any x86
systems, so I have no idea what settings the bots used when they were running.
I'm really not sure how to proceed.

It seems to me that FMA should give better performance on systems that support
it on any non-trivial benchmark.

Thanks!

You can run the LNT tests locally and I would assume the tests to be 
impacted (on X86).

The Polybench benchmarks, probably some others, have hased result files. 
Thus, any change
to the output is flagged regardless how minor. I'd run it without and 
with this patch and
compare the results. If they are in the expected tolerance I'd recreate 
the hash files for
them and create a dependent commit for the LLVM test suite.

Does that make sense?

~ Johannes


On 5/18/21 3:32 PM, Blower, Melanie I wrote:
> Hello.
> I have a patch to commit to community
https://reviews.llvm.org/D74436?id=282577 that changes command line settings for
floating point.  When I committed it previously, it was ultimately rolled back
due to bot failures with LNT.
>
> Looking for suggestions on how to use the llvm-test-suite benchmarks to
analyze this issue so I can commit this change.
>
> We think the key difference in the tests that regressed when I tried to
commit the change was caused by differences in unrolling decisions when the
fmuladd intrinsic was present.
>
> As far as I can tell, the LNT bots aren't currently running on any x86
systems, so I have no idea what settings the bots used when they were running.
I'm really not sure how to proceed.
>
> It seems to me that FMA should give better performance on systems that
support it on any non-trivial benchmark.
>
> Thanks!