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[Bug lto/45375] [meta-bug] Issues with building Mozilla with LTO
- From: "hubicka at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Sat, 15 Jan 2011 16:42:19 +0000
- Subject: [Bug lto/45375] [meta-bug] Issues with building Mozilla with LTO
- Auto-submitted: auto-generated
- References: <bug-45375-4@http.gcc.gnu.org/bugzilla/>
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45375
--- Comment #35 from Jan Hubicka <hubicka at gcc dot gnu.org> 2011-01-15 16:42:06 UTC ---
I looked briefly into effectivity of the devirtualization bits and they don't
seem to work terribly well.
In GCC 4.3 -O3 copmiled libxul there are 82155 indirect calls.
In mainline -O3 libxul there are 83023 and with LTO there are 87763.
The ipa-prop bits at LTO devirtualize 1 call that is consequently optimized
away (since -fno-devirtualize seems same to -fdevirtualize).
I will give a try http://gcc.gnu.org/ml/gcc-patches/2010-12/msg01214.html
However we _really_ need testcases from Mozilla where devirtualization is valid
and we don't do it.