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Massive performance regression from switching to gcc 4.5
- From: Taras Glek <tglek at mozilla dot com>
- To: gcc at gcc dot gnu dot org
- Date: Thu, 24 Jun 2010 11:50:52 -0700
- Subject: Massive performance regression from switching to gcc 4.5
Just wanted to give a heads up on what might be the biggest
compiler-upgrade-related performance difference we've seen at Mozilla.
We switched gcc4.3 for gcc4.5 and our automated benchmarking
infrastructure reported 4-19% slowdown on most of our performance
metrics on 32 and 64bit Linux.
Here are some of the slowdowns reported:
Most of the code is compiled with -fPIC -fno-rtti -fno-exceptions -Os
-freorder-blocks -fomit-frame-pointer. The only difference in 4.5 is
that we link with -static-libstdc++ and compile libstdc++ with -fPIC.
However we barely make use of libstdc++, so I doubt that's the problem.
We needed to link statically because of 4.5 uses a handful of newer
We were upgrading to gcc 4.5.0 because of plugins and the fact that it
can compile Firefox with PGO on(above builds were not built with PGO).
Now we have to reconsider a complete switchover to 4.5.
I'm not sure how to proceed from here,