Why is x86_sahf_1 pattern disabled in x86_64?

[Lu, Hongjiu]

Please make sure TARGET_USE_SAHF is only enabled for specific CPUs.

H.J. Lu
Intel Corporation


> -----Original Message-----
> From: Uros Bizjak [ mailto:uros@kss-loka.si ]
> Sent: Tuesday, May 18, 2004 1:37 AM
> To: Lu, Hongjiu
> Cc: Jan Hubicka; Michel Lespinasse; gcc@gcc.gnu.org
> Subject: Re: Why is x86_sahf_1 pattern disabled in x86_64?
> 
> H. J. Lu wrote:
> 
> >>This is the current Intel's position:
> >>
> >>Intel has no plans to support SAHF/LAHF on current processors or
> >>future processors that include EM64T.  Intel advises against using
> >>those instructions.  If those instructions are to be generated, they
> >>should be under an architecture specific flag and not be included
> when the
> >>compiler is expected to be generating portable code.
> >>
> >>
> >>
> I guess that "x86_sahf_1" instruction should stay disabled for
> TARGET_64BIT. The same functionality is now implemented with test
> instruction if !TARGET_USE_SAHF.
> 
> Thanks,
> Uros.