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Re: PATCH: Allow cs/ds in 64bit for branch hints
- From: "H. J. Lu" <hjl at lucon dot org>
- To: Jakub Jelinek <jakub at redhat dot com>
- Cc: binutils at sources dot redhat dot com, gcc at gcc dot gnu dot org
- Date: Thu, 22 Jul 2004 12:45:04 -0700
- Subject: Re: PATCH: Allow cs/ds in 64bit for branch hints
- References: <20040722190656.GA14338@lucon.org> <20040722191251.GA14442@lucon.org> <20040722172244.GT30497@sunsite.ms.mff.cuni.cz>
On Thu, Jul 22, 2004 at 07:22:44PM +0200, Jakub Jelinek wrote:
> On Thu, Jul 22, 2004 at 12:12:51PM -0700, H. J. Lu wrote:
> > On Thu, Jul 22, 2004 at 12:06:56PM -0700, H. J. Lu wrote:
> > > cs/ds can be used as branch hints in 64bit. I will check this in
> > > shortly.
> >
> > This is the actual patch I checked in.
>
> Why? IMHO nobody should be using cs; je 1f instead of je,pn 1f
> which already works in 64bit (as well as je,pt 1f).
>
Gcc 3.3, 3.4 are 3.5 are still doing "cs ; jxx yyy" for EM64T.
Assembler should support it.
FYI, I was told by our compiler people that branch hints didn't provide
any performance benefit and it would hurt performance on P4/EM64T due
to the code size increase. I am trying to verify that.
H.J.