[llvm] r225786 - SLPVectorizer: Cache results from memory alias checking.

[Chandler Carruth]

On Tue, Jan 13, 2015 at 3:37 AM, Erik Eckstein <eeckstein at apple.com> wrote:

> Author: eeckstein
> Date: Tue Jan 13 05:37:51 2015
> New Revision: 225786
>
> URL: http://llvm.org/viewvc/llvm-project?rev=225786&view=rev
> Log:
> SLPVectorizer: Cache results from memory alias checking.
>
> This speeds up the dependency calculations for blocks with many
> load/store/call instructions.
> Beside the improved runtime, there is no functional change.
>

Why should we do caching at this layer rather than in the AA layer itself?

And what invalidates this cache? As far as I can tell the vectorizer can
both delete and create new instructions, which should put this cache at
risk of getting incorrect collisions.

I feel like this patch probably should have gone through pre-commit review.
Neither this design nor why it is correct is obvious.
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