[PATCH] D130164: [LV] Support predicated div/rem operations via safe-divisor select idiom

[Philip Reames via Phabricator via llvm-commits]

reames added a comment.

In D130164#3666181 <https://reviews.llvm.org/D130164#3666181>, @craig.topper wrote:

> What does SelectionDAG do with a scalable vector division if it isn't legal for the target?

Not sure, but this patch shouldn't result in that being created.  Such a target is responsible for setting a reasonable cost.  If that cost is invalid, existing logic should bailout of vectorization for scalable vector factors.

In D130164#3666157 <https://reviews.llvm.org/D130164#3666157>, @craig.topper wrote:

>>> Div/Rem by 1 is the same as using the undisturbed LHS.
>
> That's true for Div, but Rem by 1 would produce 0.

True, didn't think carefully enough.  If we end up trying to implement the undisturbed case, we can explore using an alternate value for the safe-divisor for rem.  Not thinking about it real hard, int_max/uint_max might be reasonable.


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https://reviews.llvm.org/D130164