From: DJ Delorie <dj@redhat.com>
To: gcc@gcc.gnu.org
Subject: -Os is weak...
Date: Thu, 09 Sep 2010 16:43:00 -0000 [thread overview]
Message-ID: <201009091643.o89Gh16l009805@greed.delorie.com> (raw)
The docs say...
@item -Os
@opindex Os
Optimize for size. @option{-Os} enables all @option{-O2} optimizations that
do not typically increase code size. It also performs further
optimizations designed to reduce code size.
@option{-Os} disables the following optimization flags:
@gccoptlist{-falign-functions -falign-jumps -falign-loops @gol
-falign-labels -freorder-blocks -freorder-blocks-and-partition @gol
-fprefetch-loop-arrays -ftree-vect-loop-version}
But in reality, the only thing -Os does beyond -O2, aside from a few
niche special cases, is enable inlining, and maybe scheduling, which
for some cases may be the wrong thing to do.
Is this what we want?
flag_schedule_insns = opt2 && ! optimize_size;
if (optimize_size)
{
/* Inlining of functions reducing size is a good idea regardless of them
being declared inline. */
flag_inline_functions = 1;
/* Basic optimization options. */
optimize_size = 1;
if (optimize > 2)
optimize = 2;
/* We want to crossjump as much as possible. */
set_param_value ("min-crossjump-insns", 1);
}
else
set_param_value ("min-crossjump-insns", initial_min_crossjump_insns);
$ grep optimize_size *.c
genconditions.c: { "! optimize_size && ! TARGET_READ_MODIFY_WRITE",
genconditions.c: __builtin_constant_p (! optimize_size && ! TARGET_READ_MODIFY_WRITE)
genconditions.c: ? (int) (! optimize_size && ! TARGET_READ_MODIFY_WRITE)
opts.c: optimize_size = 0;
opts.c: optimize_size = 0;
opts.c: optimize_size = 1;
opts.c: optimize_size = 0;
opts.c: flag_schedule_insns = opt2 && ! optimize_size;
opts.c: if (optimize_size)
opts.c: optimize_size = 1;
opts.c: OPTIMIZATION_OPTIONS (optimize, optimize_size);
predict.c: if (optimize_size)
predict.c: return (optimize_size
toplev.c: The only valid values are zero and nonzero. When optimize_size is
toplev.c:int optimize_size = 0;
toplev.c: if (flag_prefetch_loop_arrays > 0 && optimize_size)
tree-inline.c: if (size < 0 || size > MOVE_MAX_PIECES * MOVE_RATIO (!optimize_size))
tree-inline.c: || (caller_opt->optimize_size != callee_opt->optimize_size))
next reply other threads:[~2010-09-09 16:43 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-09-09 16:43 DJ Delorie [this message]
2010-09-09 17:16 ` Ian Lance Taylor
2010-09-09 17:20 ` Andrew Pinski
2010-09-09 17:38 ` DJ Delorie
2010-09-09 19:42 ` Steven Bosscher
2010-09-09 20:00 ` Steven Bosscher
2010-09-10 8:44 ` Steven Bosscher
2010-09-10 16:49 ` DJ Delorie
2010-09-16 17:13 ` Yao Qi
2010-09-16 22:06 ` Andi Kleen
2010-09-18 13:31 ` Jakub Jelinek
2010-09-16 22:15 ` Steven Bosscher
2010-09-27 3:50 ` Gerald Pfeifer
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