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Re: RFC: Turn on -fomit-frame-pointer and -fasynchronous-unwind-tables for Linux/i386
- From: "H.J. Lu" <hjl dot tools at gmail dot com>
- To: Roland McGrath <roland at redhat dot com>
- Cc: Chris Lattner <clattner at apple dot com>, GNU C Library <libc-alpha at sourceware dot org>, gcc-patches at gcc dot gnu dot org, Uros Bizjak <ubizjak at gmail dot com>
- Date: Thu, 15 Jul 2010 13:46:46 -0700
- Subject: Re: RFC: Turn on -fomit-frame-pointer and -fasynchronous-unwind-tables for Linux/i386
- References: <20100715174246.GA20583@intel.com><B1EFE802-2B3F-4B20-B313-19C49C4D496D@apple.com><AANLkTilEiJ2MAAol3msSlbut6TjyvXwa34weDf2Aa0xe@mail.gmail.com><AANLkTikksmlRoxdB9HT69Dw5T1gP1xHyG_ycSzge9eJE@mail.gmail.com><20100715194939.280034A96D@magilla.sf.frob.com>
On Thu, Jul 15, 2010 at 12:49 PM, Roland McGrath <roland@redhat.com> wrote:
>> I updated the spread sheet with glibc 12.0 DSO sizes
>> I think -fomit-frame-pointer and -fasynchronous-unwind-tables
>> will increase size of DSO written in C by about 10%.
>
> Are you talking about code size or text size? ?Of course
> -fasynchronous-unwind-tables increases the size of .eh_frame,
> but that is not usually a performance issue. ?The actual code
> size increase is what affects hot path cache load and so forth.
-fomit-frame-pointer increases libc.so code size by 1%. We
have to save/restore EBP when using it GPR. But for some reason,
gcc will choose EBP even when ECX/EDX are available:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44958
--
H.J.