[LLVMdev] Enabling the vectorizer for -Os

[JF Bastien]

>
> Will knowing the exact number help us in making a better decision ? I
> don’t think so. On modern processors when running vectorizable loops, the
> code size of the vector instructions is almost never the bottleneck.
>

I'd make a slightly different point: being able to estimate the number of
UOPs will make a big difference if it allows you to fit your loop in the
loop stream detector.

So I'd agree that estimating x86 encoded code size doesn't matter that much
for performance (though I$ pressure is a big issue for may codebases, but I
assume you're talking about tight vectorizable kernels), but estimating
UOPs does matter a great deal.
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