Re: [PATCH] PR 16373: -fomit-frame-pointer when optimizing on x86

[Roger Sayle <roger@eyesopen.com>]

On Sun, 11 Jul 2004, Joseph S. Myers wrote:
> Performance statistics (compile time, run time and code size)?  After all,
> the point of this change is presumably that it improves performance.

Do you have any doubt at all that this patch won't improve run-time,
reduce code size and speed up a bootstrapped compiler?  :>

The bugzilla PR reports performance increases of up to 40% on some
benchmarks, and indeed the Intel and Microsoft C/C++ compilers omit
frame pointers by default.  I'd hope that any gains will help redress
some of the tree-ssa related compile-time slow-down, but I haven't
done any timings.  The benefits of -fomit-frame-pointer are otherwise
well documented by Robert Scott Ladd and others.


But the real reason I submitted the patch was to decrease the maintenance
burden of the six additional lines in i386.c that provide target dependent
defaults for flag_omit_frame_pointer, but break the documented semantics
of the CAN_DEBUG_WITHOUT_FP target macro.  Any other side-effects of this
patch are unintentional and purely coincidental.  :>   The alternative
fix to PR middle-end/16373 is to change the documentation.

Roger
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