This is the mail archive of the
gcc-help@gcc.gnu.org
mailing list for the GCC project.
Re: -O* Gives Different Results than Individual Optimizations?
Mike Sullivan wrote:
>> There was another interesting question in that mail: is "-O1" flag
>> something different from just combination of "-fsomething" flags?
>
> This really is the question I'm interested in. The problem itself was
> fixed, I just don't understand why applying the same optimizations
> (and more) which make up -O1 don't elicit the same behavior.
This is frequently asked on this list, and the answer is always the
same: yes, the -O<N> flag does more than just enable a series of -f<foo>
flags. Said another way, there are optimizations that do *not* have
-f<foo> flags that control them, they are enabled by directly checking
the value supplied to the -O flag, and they cannot be directly controlled.
--
Kevin P. Fleming
Digium, Inc. | Director of Software Technologies
445 Jan Davis Drive NW - Huntsville, AL 35806 - USA
skype: kpfleming | jabber: kpfleming@digium.com
Check us out at www.digium.com & www.asterisk.org