[Bug middle-end/47298] -O3 destroys beautifully vectorized code obtained at -O2

[ebotcazou at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47298

Eric Botcazou <ebotcazou at gcc dot gnu.org> changed:

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--- 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.