Re: -mtune=generic for i386 backend

[Jan Hubicka <jh at suse dot cz>]

> Jan Hubicka wrote:
> 
> > I wanted to express this by "is supposed to envolve in future versions
> > of GCC as new CPU models are introduced and other become obsolette.".
> > Since my english is poor, perhaps you can suggest better wording?
> 
> Actually, your English is very good, and a heck of a lot better than my
> Czech!  Your spelling needs a little work though; you might try M-x
> ispell-region in your friendly local emacs. :-) :-)
> 
> I've taken the liberty of reworking your paragraph.
> 
> "Produce code optimized for the most common IA32/AMD64/EM64T processors.
>    If you know the CPU on which your code will run, then you should use
> the corresponding @option{-mtune} option instead of
> @option{-mtune=generic}.  But, if you do not know exactly what CPU users
> of your application will have, then you should use this option.
> 
> As new processors are deployed in the marketplace, the behavior of this
> option will change.  Therefore, if you upgrade to a newer version of
> GCC, the code generated option will change to reflect the processors
> that were most common when that version of GCC was released.
> 
> There is no @option{-march=generic} option because @option{-march}
> indicates the instruction set the compiler can use, and there is no
> generic instruction set applicable to all processors.  In contrast,
> @option{-mtune} indicates the processor (or, in this case, collection of
> processors) for which the code is optimized."
> 
> Your patch is OK with that change, if you like the paragraphs I wrote. :-)

Thanks, I like your paragraphs ;)
Perhaps we can explicitely mention the set of CPUs we are tuning generic
for in current version of GCC, so people can answer the question whether
their CPU is included in our definition of "most common" and we also
fail to document "virtual" -march=x86-64 target, but this can be done as
followup.  I am going to finally test the patch with your paragraph and
H. J.'s fix to default CPU and commit it.

Honza
> 
> -- 
> Mark Mitchell
> CodeSourcery
> mark@codesourcery.com
> (650) 331-3385 x713