[LLVMdev] Recent compile time performance regressions

[Tobias Grosser]

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