Re: -mtune=generic for i386 backend

["H. J. Lu" <hjl at lucon dot org>]

On Thu, Jan 19, 2006 at 12:15:47PM +0100, Jan Hubicka wrote:
> > 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.
> 

Jan, your last patch has some unrelated changes. Would you mind to
post your final version before committing it?

Thanks.


H.J.