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[Bug middle-end/47298] -O3 destroys beautifully vectorized code obtained at -O2
- From: "ebotcazou at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Thu, 05 Jul 2012 07:36:15 +0000
- Subject: [Bug middle-end/47298] -O3 destroys beautifully vectorized code obtained at -O2
- Auto-submitted: auto-generated
- References: <bug-47298-4@http.gcc.gnu.org/bugzilla/>
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47298
Eric Botcazou <ebotcazou at gcc dot gnu.org> changed:
What |Removed |Added
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CC| |ebotcazou at gcc dot
| |gnu.org
--- Comment #6 from Eric Botcazou <ebotcazou at gcc dot gnu.org> 2012-07-05 07:36:15 UTC ---
> The issue is we completely unroll the innermost loop at -O3 -funroll-loops.
> We then vectorize the outer loop but have to peel for alignment (and are not
> good at seeing we run at most once there).
It's not cunroll (-funroll-loops), it's cunrolli which can have adverse effects
on vectorization and cannot be disabled. We run into this in Ada as well.