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Re: [PATCH i386] Enable -freorder-blocks-and-partition
- From: Andi Kleen <andi at firstfloor dot org>
- To: Teresa Johnson <tejohnson at google dot com>
- Cc: "gcc-patches\ at gcc dot gnu dot org" <gcc-patches at gcc dot gnu dot org>, David Li <davidxl at google dot com>, Jan Hubicka <hubicka at ucw dot cz>, Steven Bosscher <stevenb dot gcc at gmail dot com>
- Date: Tue, 19 Nov 2013 13:00:15 -0800
- Subject: Re: [PATCH i386] Enable -freorder-blocks-and-partition
- Authentication-results: sourceware.org; auth=none
- References: <CAAe5K+XeggoZGd8OgdGhh49RF-=5JbBdOEg+j2ZyYBCno0GfdA at mail dot gmail dot com>
Teresa Johnson <tejohnson@google.com> writes:
> This patch enables -freorder-blocks-and-partition by default for x86
> at -O2 and up. It is showing some modest gains in cpu2006 performance
> with profile feedback and -O2 on an Intel Westmere system. Specifically,
> I am seeing consistent improvements in 401.bzip2 (1.5-3%), 483.xalancbmk
> (1.5-3%), and 453.povray (2.5-3%), and no apparent regressions.
One thing that worries me is what this will do to profilers.
I had to hack some assembler code using out of line sections
to able to handle the libunwind based perf dwarf unwinder.
My understanding is that these out of line sections can be
only described properly in dwarf3, and there's still some
dwarf2 based unwinder code around.
So this may cause problems with profiling and debugging.
It's probably still a good idea, just may need some extra
care.
-Andi
--
ak@linux.intel.com -- Speaking for myself only