-Os versus -O2
- From: Adrian Bunk <bunk@xxxxxxxxx>
- Date: Mon, 25 Jun 2007 02:41:06 +0200
On Sun, Jun 24, 2007 at 05:23:42PM -0700, Arjan van de Ven wrote:
On Sun, 2007-06-24 at 20:12 -0400, Benjamin LaHaise wrote:
On Sun, Jun 24, 2007 at 05:09:16PM -0700, Arjan van de Ven wrote:
if you care about the last cycle, don't specify -Os but -O2.
simple as that... you get what you tell the compiler you want.
Certain distros are shipping kernels compiled with -Os. And it's more
than just a couple of cycles.
so those distros pick space over some cycles. Who are you to then
override that choice ? ;-)
seriously, why are we even talking about overriding a choice the user
(or distro vendor as user) made here?
There is a real issue in the fact that compiling with -Os is available
through a kconfig option and AFAIR used by some distributions.
I doubt distros enable CONFIG_CC_OPTIMIZE_FOR_SIZE due to size
considerations, but due to speed considerations.
I wouldn't care if CONFIG_CC_OPTIMIZE_FOR_SIZE was hidden behind
CONFIG_EMBEDDED, but as long as it's available as a general purpose
option we have to consider it's performance.
The interesting questions are:
Does -Os still sometimes generate faster code with gcc 4.2?
If yes, why?
cu
Adrian
--
"Is there not promise of rain?" Ling Tan asked suddenly out
of the darkness. There had been need of rain for many days.
"Only a promise," Lao Er said.
Pearl S. Buck - Dragon Seed
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