This is the mail archive of the
gcc@gcc.gnu.org
mailing list for the GCC project.
Re: Why is x86_sahf_1 pattern disabled in x86_64?
- From: Jan Hubicka <jh at suse dot cz>
- To: Michel Lespinasse <walken at zoy dot org>
- Cc: Uros Bizjak <uros at kss-loka dot si>, gcc at gcc dot gnu dot org,Jan Hubicka <jh at suse dot cz>
- Date: Fri, 7 May 2004 21:28:14 +0200
- Subject: Re: Why is x86_sahf_1 pattern disabled in x86_64?
- References: <409B6EFA.9020201@kss-loka.si> <20040507120401.GA18973@zoy.org>
> On Fri, May 07, 2004 at 01:11:54PM +0200, Uros Bizjak wrote:
> > According too ChangeLog, x86_sahf_1 pattern is disabled in x86_64 mode:
> >
> > Mon Mar 12 15:41:08 CET 2001 Jan Hubicka <jh@suse.cz>
> > * i386.md (all XFmode patterns except swapxf): Disable for 64bit.
> > * i386.md (x86_sahf_1): Disable for 64bit.
> > (popsi*, pophi*): Likewise.
> > ...
> >
> > However, AMD64 software optimization guide shows sahf instruction as
> > DirectPath, latency 1 instruction. This instruction is needed in
> > modf()/drem() patterns to perform conditional jump on P flag set
> > [ix86_emit_fp_unordered_jump()) function in config/i386/i386.c].
>
> I think SAHF/LAHF were not present in the original amd64 specification;
> they got added back later on as a correction.
Assuming that sahf/lahf is in the amd64 specification now, it would be
OK to just revert the patch.
Honza
>
> I'm not sure if the intel chips include that correction,
> someone who has access to such chips should double check this.
>
> --
> Michel "Walken" Lespinasse
> "In this time of war against Osama bin Laden and the oppressive
> Taliban regime, we are thankful that OUR leader isn't the spoiled son
> of a powerful politician from a wealthy oil family who is supported by
> religious fundamentalists, operates through clandestine organizations,
> has no respect for the democratic electoral process, bombs innocents,
> and uses war to deny people their civil liberties." --The Boondocks