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[Bug target/36992] Very stange code for _mm_move_epi64
- From: "hjl dot tools at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 1 Aug 2008 13:25:42 -0000
- Subject: [Bug target/36992] Very stange code for _mm_move_epi64
- References: <bug-36992-682@http.gcc.gnu.org/bugzilla/>
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
------- Comment #7 from hjl dot tools at gmail dot com 2008-08-01 13:25 -------
(In reply to comment #6)
> with -march=core2 it uses
>
> movd %xmm0, %rax
> movq %rax, %xmm0
>
Even this isn't necessary. We should just use
movq %xmm0,%xmm0
> with -march=opteron (and -march=generic) it uses
>
> movhps .LC0(%rip), %xmm0
>
> ISTR there is some penalty for using movq on opteron?
Opteron doesn't like inter-unit move, like
movd %xmm0, %rax
But it isn't necessary at all. We should use
movq %xmm0,%xmm0
anyway.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36992