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[Bug target/52572] suboptimal assignment to avx element
- From: "marc.glisse at normalesup dot org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Tue, 13 Mar 2012 08:16:58 +0000
- Subject: [Bug target/52572] suboptimal assignment to avx element
- Auto-submitted: auto-generated
- References: <bug-52572-4@http.gcc.gnu.org/bugzilla/>
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52572
--- Comment #2 from Marc Glisse <marc.glisse at normalesup dot org> 2012-03-13 08:16:58 UTC ---
(In reply to comment #1)
> Have you actually tried that?
Ah, no, sorry, I only have occasional access to such a machine to benchmark the
code. From a -Os perspective it is still shorter (but indeed that matters less
to me than -O3 performance).
> Mixing VEX encoded insns with legacy encoded
> SSE* insns is very costly, for good performance there needs to be a vzeroupper
> in between (but then you lose the upper bits). See e.g. 2.8 in the AVX
> Programming Reference.
Thanks, I'd missed that.
The vblendpd solution should still apply (from the initial 'v' it sounds safe),
no?