[PATCH] D149423: [ValueTracking] Use knownbits interface for determining if `div`/`rem` are safe to speculate

[Nikita Popov via Phabricator via llvm-commits]

nikic added a comment.

In D149423#4309375 <https://reviews.llvm.org/D149423#4309375>, @nikic wrote:

> Ooops, I missed an important pre-condition here: You also need to check that the value isGuaranteedNotToBePoison. All the "known" APIs have an implicit "OrPoison" at the end, and this is one of the case where it makes a difference, as division by poison is UB as well. See for example https://alive2.llvm.org/ce/z/WAFYny.

Unfortunately alive2 doesn't detect this in the LICM tests. It looks like we should be able to test this in a way that alive2 understands using SimplifyCFG block speculation: https://llvm.godbolt.org/z/ehbMKqqxz Apparently this transform is willing to always speculate one instruction even if it's expensive, so it should work well for this purpose and be understood by alive.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D149423/new/

https://reviews.llvm.org/D149423