[LLVMdev] RFC: Should we have (something like) -extra-vectorizer-passes in -O2?

[Chandler Carruth]

On Tue, Oct 14, 2014 at 10:28 AM, Hal Finkel <hfinkel at anl.gov> wrote:

> > I think it’s generally useful to have an “extreme” level of
> > optimization without much regard for compile time, and in that
> > scenario this pipeline makes sense. But this is hardly something
> > that should happen at -O2/-Os, unless real data shows otherwise.
>
> Doing all this only at >= -O3 does not seem unreasonable to me.


FWIW, I think we're being overly conservative if we're relegating these to
-O3 when the total cost is 2%. That doesn't seem like the right tradeoff.

I actually agree that the set I proposed is on the aggressive end -- that
was the point -- but we have more than 2% fluctuations in the optimizers'
runtime from month to month. If we want to rip stuff out it should be
because of a principled reason that it isn't going to help the code in that
phase.
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