Re: mutex in frame code

["Matthias Urlichs" <smurf at noris dot de>]

Hi,

David Edelsohn:
> 	The POWER and PowerPC architecture do not describe a nested set
> which is exactly what is assumed by this entire -march= discussion.  You
> and Richard and others are relying on the fact that -march=X is a complete
> subset of -march=X+1.  On POWER and PowerPC that is not the case.
> 
But there's an instruction set X such that all Xn with n>0 are superset of
that X, right? (X may not correspond to any existing piece of hardware, but
that's not the point.)

The real question is, though, whether there are scheduler or other
differences between different PowerPC CPUs such that optimizing for any of
them makes sense. (Like the difference between i586 and i686.)
If there are, an -mtune=FOO option makes sense; if not, it doesn't.

> architecture.  Using the option -march= but specifying CPU is confusing
> and incorrect.
> 
We need options for controlling (a) which instruction set to assume, and
(b) which particular CPU to optimize for. Calling (a) -march and (b) -mcpu
may not be 100% optimal or intuitive, but it's there. I'd name them
(a) -mbase and (b) -mtune if I felt the need to make the option tags more
unambiguous.

If the assumption above doesn't hold and there are incompatible sets X and
Y instead, they should have different targets.

-- 
Matthias Urlichs  |  noris network GmbH   |   smurf@noris.de  |  ICQ: 20193661
The quote was selected randomly. Really.    |      http://www.noris.de/~smurf/
-- 
National security is the chief cause of national insecurity.