This is the mail archive of the gcc@gcc.gnu.org mailing list for the GCC project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: Why is x86_sahf_1 pattern disabled in x86_64?


On Fri, May 07, 2004 at 09:28:14PM +0200, Jan Hubicka wrote:
> > 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.
> 

I am trying to find out if it is supported on Intel EM64T. I will
let you know what I get.


H.J.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]