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Re: [tree-ssa] Miscompilation (SIGSEGV) with -ffast-math (!?),huge compile time regression
- From: Diego Novillo <dnovillo at redhat dot com>
- To: Richard Guenther <rguenth at tat dot physik dot uni-tuebingen dot de>
- Cc: "gcc at gcc dot gnu dot org" <gcc at gcc dot gnu dot org>
- Date: Mon, 23 Feb 2004 10:21:27 -0500
- Subject: Re: [tree-ssa] Miscompilation (SIGSEGV) with -ffast-math (!?),huge compile time regression
- Organization: Red Hat Canada
- References: <403A0162.2070207@tat.physik.uni-tuebingen.de> <403A07CB.2080306@tat.physik.uni-tuebingen.de>
On Mon, 2004-02-23 at 09:01, Richard Guenther wrote:
> g++ (GCC) 3.5-tree-ssa 20040217 (merged 20040211) endlessly loops,
> g++ (GCC) 3.5-tree-ssa 20040209 (merged 20040126) is fine. Note that
> between these two a huge compile time regression occoured, 20040209
> takes 6m36s, 20040217 over 12m!
>
Yeah, it certainly takes a while to build (roughly 4m30s on a 2.2Ghz P4
w/ 1Gb of RAM). It also makes cc1plus to grow quite big (about 480Mb).
The biggest time consumers according to -ftime-report are
dominator optimization: 47.83 (20%) usr 0.27 ( 4%) sys 48.29 (20%) wall
expand : 46.79 (20%) usr 0.08 ( 1%) sys 46.95 (19%) wall
tree DSE : 23.53 (10%) usr 0.01 ( 0%) sys 23.55 (10%) wall
tree SSA rewrite : 16.31 ( 7%) usr 0.00 ( 0%) sys 16.31 ( 7%) wall
integration : 13.86 ( 6%) usr 0.07 ( 1%) sys 13.93 ( 6%) wall
> So maybe its the merge from mainline that brought all these problems?
> Though enough, I never checked mainline, but stayed with the 3.4 branch
> which is fine in both regards.
>
The compile time regression you experienced is probably not all because
of the merge. We are spending a significant chunk of time in the tree
optimizers.
Diego.