[LLVMdev] Recent compile time performance regressions

[Chandler Carruth]

Note that I've fixed one bad compile time regression quite recently, and
we're bisecting to another one. We benchmarked the multithreading stuff
pretty carefully, so I doubt its that. Have you tried reverting locally and
reproducing?


On Fri, Aug 1, 2014 at 1:05 PM, Tobias Grosser <tobias at grosser.es> wrote:

> Hi,
>
> I was just browsing my LNT performance builder and it seems within the
> last month we managed to increase compile time from 37 to 47 seconds for
> the bullet benchmark:
>
> http://llvm.org/perf/db_default/v4/nts/graph?plot.0=
> 34.274.3&highlight_run=29054
>
> A similar pattern can be seen for MallocBench/gs/gs where we go from 5.3
> to 7.4 seconds.
>
> http://llvm.org/perf/db_default/v4/nts/graph?plot.0=
> 34.301.3&highlight_run=29054
>
> One contributing patch seems to be the following one (surprisingly):
>
> Author: Chandler Carruth <chandlerc at gmail.com>
> Date:   Fri Jun 27 15:13:01 2014 +0000
>
>     Re-apply r211287: Remove support for LLVM runtime multi-threading.
>
>     I'll fix the problems in libclang and other projects in ways that
>     don't require <mutex> until we sort out the cygwin situation.
>
>     git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211900
>
> I also looked at the earlier performance regressions, but could not find
> any obvious commits that could have caused these regressions.
>
> This is mostly a drive by observation, but maybe someone is motivated to
> investigate this further.
>
> Cheers,
> Tobias
>
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