[cfe-dev] [LLVMdev] [3.6 Release] RC3 has been tagged

[Jack Howarth]

On Tue, Feb 17, 2015 at 2:12 PM, Hans Wennborg <hans at chromium.org> wrote:
> Hi Jack,
>
> On Sun, Feb 15, 2015 at 6:05 AM, Jack Howarth
> <howarth.mailing.lists at gmail.com> wrote:
>>    What are the acceptable performance regressions in the generated
>> code for a llvm release? We seem to be badly regressed in some
>> benchmarks (which I first noticed from the review of 3.6-rc1 at
>> http://www.phoronix.com/scan.php?page=article&item=llvm-clang-3.5-3.6-rc1).
>> This same issue has also been reported in
>> http://llvm.org/bugs/show_bug.cgi?id=22058. In the case of the 22%
>> performance degradation in SciMark2's Sparse matmult benchmark, I have
>> identified both commits that contribute equally to this regression in
>> http://llvm.org/bugs/show_bug.cgi?id=22589...
>
> Thank you very much for trying out the release candidate.
>
> I asked a few of the other developers, and the consensus was that
> while unfortunate, we won't block the release on a perf regression
> like this, at least not at this stage in the release process.
>
> Having said that, we will be doing an rc4, and Hal said that he or
> Sanjoy might be able to squeeze in a patch for the issue you pointed
> out before that. Otherwise, it will have to wait to 3.6.1 or 3.7.
>
> Thanks,
> Hans

Hans,
    We probably ought to open a meta-bug for all of these new
performance regressions introduced in 3.6. The 20% performance
regression observed in the "8 queens puzzle" solver example
(http://llvm.org/bugs/show_bug.cgi?id=22058) doesn't seem to be
introduced by either the r217953 or r222451 commits. I'll try to do a
regression hunt later this week to pin down the offending commit for
that regression. Likewise, the reported regression in the -m32
performance of the sudoku solver example (reported in
http://llvm.org/bugs/show_bug.cgi?id=22589) doesn't match up to those
two commits either (but I suspect a register pressure issue since it
only shows up at 32-bit).
     Jack
ps Do we have a complete set of benchmark results for current 3.6svn
vs 3.5.1 posted anywhere? Hopefully some these are showing up the SPEC
benchmarks and should be added to the meta-bug by someone who has
access to the sources for those benchmarks.