Re: [patches] powerpc 8xx dcbz problem

[Mark Mitchell <mark@xxxxxxxxxxxxxxxx>]

Steven Munroe wrote:

> -with-cpu= basically adds another level (to that selected for the
> platform/ABI) to the search order. For this case we might like a
> --with-fixes=cpu-type1,cpu-type2 where we could select overrides from a
> fixes add-on?

Yes, perhaps something like that would work.  For convenience, one would
want a "--with-fixes=all" that would pull in all applicable fixes, so
that you could really say "for 603 and all allegedly compatible chips
that we know about, working around bugs in those chips".

I'm not quite sure where the line between "fixes" and "optimizations"
lies; if you're really trying to build a "generic" GLIBC, you want to
work on all CPUs, and the costs of some level of dynamism might be worth
it, so as to get optimized versions of particular routines.

So, maybe what we really want is "--with-tune=generic --with-arch=XXX"
to mean "run on XXX and later CPUs, trying to get good performance
across all of them, including dynamism where necessary to work around
bugs or to go fast"?  And, maybe we could spell that "--with-cpu=603+"
to use the existing mechanism?  By default, the "+" variant is exactly
like the plain variant -- but now, if we populate the "power603+"
directory with additional files, those take precedence over plain
"power603", so we can include the necessary dynamism there?

-- 
Mark Mitchell
CodeSourcery
mark@xxxxxxxxxxxxxxxx
(650) 331-3385 x713