Re: [PATCH, i386]: Implement -mcmpxchg16b and -msahf options

["Uros Bizjak" <ubizjak at gmail dot com>]

On 3/14/07, Jan Hubicka <jh@suse.cz> wrote:
> > Jan Hubicka wrote:
> > >>+@item -mcmpxchg16b
> > >>+@opindex -mcmpxchg16b
> > >>+This option will enable GCC to use CMPXCHG16B instruction in generated
> > >>code.

> If the patch is not commited yet, perhaps
> > +This option will enable GCC to use SAHF instruction in generated code.  Early
> > +Intel CPUs with Intel 64 lacked LAHF and SAHF instructions supported by AMD64
> > +until introduction of Pentium 4 G1 step in December 2005.  LAHF and SAHF are
> > +load and store instructions, respectively, for certain status flags.  These
> > +instructions are used for virtualization and floating-point condition handling.
>
> I would leave out the virtualization - GCC won't use it in this context
> so it is a bit misleading. It might be nice to make clear that sahf use
> is very limited, since fcomi can be used in wast majority cases. But
> this is all just nitpicking.

I hope that attached patch clarifies -msahf description.

Thanks,
Uros.

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