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Re: S/390: -march= and -mcpu= options
- From: Fergus Henderson <fjh at cs dot mu dot OZ dot AU>
- To: Alexandre Oliva <aoliva at redhat dot com>
- Cc: Ulrich Weigand <weigand at immd1 dot informatik dot uni-erlangen dot de>, dje at watson dot ibm dot com, drow at mvista dot com, hpenner at de dot ibm dot com, gcc-patches at gcc dot gnu dot org
- Date: Fri, 27 Dec 2002 10:26:56 +1100
- Subject: Re: S/390: -march= and -mcpu= options
- References: <200212232242.XAA21354@faui11.informatik.uni-erlangen.de> <ord6nr2k67.fsf@free.redhat.lsd.ic.unicamp.br>
On 24-Dec-2002, Alexandre Oliva <aoliva@redhat.com> wrote:
> IMHO, any sane implementation of -march/-mtune should tune
> for the specified arch unless an -mtune argument is present, which
> renders -mcpu (which is an alias for -march -mtune) totally useless.
>
> The only exception I can think of is in case the default tuning is
> something actually more recent than the default arch, in which case
> someone might want to downgrade the arch without downgrading tuning.
Or they might want to upgrade the arch, but still to a point which
is lower than the default tuning.
> This probably happens seldom enough, if ever, that arranging for
> -march to be the -mtune default is perfectly reasonable.
For any long-lived architecture, it is likely that the default arch
will not match the default tuning.
Anyway, fewer options doesn't necessarily make it easier for users
to understand and use. I think it would be much cleaner to have
-march setting the arch (only), -mtune setting the tuning (only),
and another option for setting both at once. If there are historical
problems with using `-mcpu' for that, another name could be chosen,
e.g. `-mtarget'.
--
Fergus Henderson <fjh@cs.mu.oz.au> | "I have always known that the pursuit
The University of Melbourne | of excellence is a lethal habit"
WWW: <http://www.cs.mu.oz.au/~fjh> | -- the last words of T. S. Garp.