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Re: S/390: -march= and -mcpu= options


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.


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