[PATCH] D69563: [LV] Strip wrap flags from vectorized reductions

[Ayal Zaks via Phabricator via llvm-commits]

Ayal added a comment.

Good catch, binary operations that perform reduction must indeed be vectorized w/o wrap flags.

But this should apply to all such operations that participate in the vectorized part of the loop. Note that (1) there may be several such add/sub instructions, as in llvm/test/Transforms/LoopVectorize/reduction.ll tests, and (2) the last instruction in the loop along a reduction chain may not be one of these binary wrapping ops, but may instead be e.g. a select or phi as in llvm/test/Transforms/LoopVectorize/if-reduction.ll tests. All these instructions should be identified either late as done here in fixReduction(), or early e.g. when they receive a (new) VPWidenRecipe with a additional indicator that they must not wrap.

Patch should be accompanied by test(s), e.g., derived from pr43828, and the fixing of existing tests.

Folding the partial sums in the middle block is already done w/o wrap flags, and the scalar loop used for leftover iterations and/or runtime guard default can continue to retain wrap flags.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D69563/new/

https://reviews.llvm.org/D69563