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[Bug other/47167] Performance regression in numerical code
- From: "ubizjak at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Thu, 6 Jan 2011 07:38:14 +0000
- Subject: [Bug other/47167] Performance regression in numerical code
- Auto-submitted: auto-generated
- References: <bug-47167-4@http.gcc.gnu.org/bugzilla/>
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47167
--- Comment #6 from Uros Bizjak <ubizjak at gmail dot com> 2011-01-06 07:38:11 UTC ---
(In reply to comment #5)
> Some loop performance is very sensitive to code sizes. This change
>
> - mulpd %xmm10, %xmm2
> + mulpd %xmm0, %xmm2
>
> will impact loop size due to exta REX prefix.
Adding nop (or several of them, FWIW) around changed mulpd insn does not affect
the performance, so IMO it is not the loop layout that matters in this case.