[PATCH] D88086: [ARM][MVE] tail-predication: checks for the elementcount, cont'd

[Sjoerd Meijer via Phabricator via llvm-commits]

SjoerdMeijer added a comment.

In D88086#2291810 <https://reviews.llvm.org/D88086#2291810>, @samparker wrote:

>> Actually, I guess if you could prove that the tripcount is precisely equal to (ElementCount + VectorWidth - 1)/VectorWidth, you could also use that to prove the subtraction doesn't overflow.
>
> This sounds like the same suggestion that I made many moons ago... I suggested taking these values and substituting them into the expected SCEV expression, and then perform some SCEV algebra on it and the vector TC expression, until hopefully they both just equal ElementCount == ElementCount. My quick prototype 'worked', but I don't know if that says much.

Sorry about that. I don't know if I missed that, or forgot about it.... but we have tried many things, and learned a few things. :-) But I am very happy with this as the way forward.


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