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Re: Apple's -fast option for gcc
- From: Mike Stump <mrs at apple dot com>
- To: Jim Wilson <wilson at specifixinc dot com>
- Cc: Bradley Lucier <lucier at math dot purdue dot edu>, gcc at gcc dot gnu dot org
- Date: Wed, 17 Sep 2003 16:22:34 -0700
- Subject: Re: Apple's -fast option for gcc
On Wednesday, September 17, 2003, at 11:32 AM, Jim Wilson wrote:
Mike Stump wrote:
-fast is very, very small. It just turns on 5-25 other, existing
flags. There isn't a reason why it could not be contributed. Do
others want it? It is _good_ for SPEC.
The set of options that gives best performance on SPEC for a PPC970 is
unlikely to be right for other targets or for other programs. So what
exactly does -fast mean when that is considered?
It means give the best numbers that are real and possible for SPEC.
This is target and host and build independent. The details of what
exactly is done to achieve this on any particular target is, uhm,
target specific, however, some things, like turning on all the flags
implied by -O2 or unsigned characters and turning off pic, need not be
target specific. This doesn't mean this would be the end-all-be-all
for setting the flags, as later, the target config can inspect and set
or reset flags, as it sees fit.
How do we choose which options to include?
Uhm, those that give lower overall spec score. If you mean for the mi
part, oh, any half way reasonable set, tending to fewer, than to many.
Maybe just -O2, for example.
Apple probably doesn't want to sacrifice SPEC performance to make the
option useful to others, so perhaps it makes more sense to rename it
to something like -mfast-spec to make it clear that it is target
dependent, and is the set of options that is known to give best SPEC
performance.
The exact spelling doesn't really matter too much to anyone.
Trivially, we can make any spelling work. Internally, we use -fast
currently. -mfast isn't out of the question.
However, if the mi parts of the compiler inspect a flag, necessarily,
that flag has to be mi, hence, easier if the flag is mi, though,
obviously, a hook would work.
The question of spelling can be deferred until such time as someone
submits a patch. With luck, we can avoid the -mcpu, -mtune, -march,
-m386 fun...