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

[Denis Antrushin via Phabricator via llvm-commits]

dantrushin added a comment.

In D69563#1763159 <https://reviews.llvm.org/D69563#1763159>, @Ayal wrote:

> 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


Is there some existing API to find them all? Or I need to invite my own?
Would not it be easier just to not copy wrap flags in widenInstruction() for all instructions [which I was shy to do initially :) ]  or it is too aggressive?

> (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.

But as far as I understand, neither select nor phi carry no wrap flags? Or you're saying I need to look through them?

> 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.

Doing this early would make me build reduction's instruction list in buildVPlanWithVPRecipies and for each instruction in list pass new flag to VPWidenRecipe and then (during execute()) to widenInstruction()
Again, adding this new flag to it.
Is it correct?

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

Oops, I had them initially, but lost during review update. I'll add them back.


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https://reviews.llvm.org/D69563