Hi,
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.
A lone 8% speedup was measured on the Sunspider javascript benchmark on
64bit linux.
Here are some of the slowdowns reported:
http://groups.google.com/group/mozilla.dev.tree-management/browse_thread/thread/77951ccb76b5e630#
http://groups.google.com/group/mozilla.dev.tree-management/browse_thread/thread/624246d7d900ed41#
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
libstdc++ symbols.
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,
Taras
