[PATCH] D111846: [LV] Drop NUW/NSW flags from instructions that need predication

[Diego Caballero via Phabricator via llvm-commits]

dcaballe added inline comments.


================
Comment at: llvm/lib/Transforms/Vectorize/LoopVectorize.cpp:3045
+// linearizing the control flow as a result of vectorization.
+static void clearUnsafeFlagsAfterLinearizingCF(Instruction *NewInst) {
+  if (isa<OverflowingBinaryOperator>(NewInst)) {
----------------
spatel wrote:
> This could be Instruction::dropPoisonGeneratingFlags() instead of new code? That also handles GEP's `inbounds` flag. If `inbounds` is also a concern with this transform, can we add a test for it?
> 
> Note that `dropPoisonGeneratingFlags` has a TODO comment for FMF.
> That also handles GEP's inbounds flag. If inbounds is also a concern with this transform, can we add a test for it?

Thanks! That makes sense, I think. The load/store will be inbounds because we are masking out out-of-bounds elements but the GEP could be out-of-bounds.

> This could be Instruction::dropPoisonGeneratingFlags() instead of new code? 

Sure. The only problem I see is extending this utility to FMF. The utility is broadly used in LLVM (ValueTracking, LoopUtils, SimplifyIndVar, InstCombine*, BDCE, etc.). It might be hard to add FMF if that breaks all these passes, but we can try.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D111846/new/

https://reviews.llvm.org/D111846