[LoopVectorizer] NFC: Return ElementCount from compute[Feasible]MaxVF

[sdesmalen]

Summary

Interfaces changed to return ElementCount:

• LoopVectorizationCostModel::computeMaxVF
• LoopVectorizationCostModel::computeFeasibleMaxVF

This is NFC for fixed-width vectors.

[ctetreau]

looks good to me

[dmgreen]

Is expected to make anything work yet for scalable vectors, or is it just updating interfaces? (i.e. will the code be checked somehow to make sure it will work for scalable vectors).

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

5283

Would this TC mod check still be valid for scalable vectors? If not does it need an assert?

[sdesmalen]

Added assert

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

5283

Good spot, you're right that this shouldn't work yet for scalable vectors. I've added an assert here.

[sdesmalen]

Is expected to make anything work yet for scalable vectors, or is it just updating interfaces? (i.e. will the code be checked somehow to make sure it will work for scalable vectors).

For this patch, it is just a matter of updating the interfaces. It will be up to follow-up patches to make the code actually work for scalable vectors (such as D91077).
That's why adding the assert on line 5271 that scalable vectors are not yet supported is good enough for this patch.

[dmgreen]

Makes sense, thanks

[sdesmalen]

Thanks @ctetreau and @dmgreen!