[LLVMdev] Performance regression on ARM

Hal Finkel hfinkel at anl.gov
Thu Oct 16 01:34:00 PDT 2014

----- Original Message -----
> From: "Renato Golin" <renato.golin at linaro.org>
> To: "LLVM Dev" <llvmdev at cs.uiuc.edu>
> Sent: Thursday, October 16, 2014 2:47:11 AM
> Subject: [LLVMdev] Performance regression on ARM
> Folks,
> First win of the benchmark buildbot!
> http://llvm.org/perf/db_default/v4/nts/graph?plot.0=49.128.2&highlight_run=31861
> It seems mandel-2 had a huge regression a few commits ago, and based
> on a quick look, it may have to do with the inst combine changes. I
> haven't investigated yet, but this is the first time I spot
> regressions on test-suite, so I'd like to first congratulate the
> people that worked on making that a reality!

Interesting. Looks like the problem is in (219545, 219569].

Based on the commit logs, it does seem like the best candidates are:
  r219566, r219567, r219568 - InstCombine bug fixes re: no-wrap flags
  r219550, r219562 - Fixes to trip-count computations in the vectorizer/unroller

and given the magnitude of the change, I think that the trip-count changes are more likely. Of course, all of these things are bug fixes :( -- So how do we follow-up on this?


> Now, I'd like to have been warned of that automatically, by email,
> based on some simple heuristics... But that's a topic for the
> Performance/Benchmarking BoF in a few weeks... :)
> cheers,
> --renato
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Hal Finkel
Assistant Computational Scientist
Leadership Computing Facility
Argonne National Laboratory

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