[PATCH] D111077: [LV] Support converting FP add to integer reductions.

[Florian Hahn via Phabricator via llvm-commits]

fhahn added a comment.

In D111077#3040417 <https://reviews.llvm.org/D111077#3040417>, @dmgreen wrote:

> Interesting idea. Are these two bits of code always the same?
> https://godbolt.org/z/EfPKPTMdf

I think both cases above should be the same. But I think we can construct slight variations where is they would not be. E.g. consider a loop where the induction variable starts at 0 and is incremented and overflow is allowed. If `n` would be negative, the result of removing the loop and converting `n` to a float would yield a negative number , but the loop version would always return a positive number. I might be missing some subtleties when it comes to sign handling, perhaps @scanon as further thoughts.

> Should we be doing this more generally, outside the vectorizing reductions?

I think it might be worthwhile to convert such reductions outside the vectorizer in some cases. My motivation for starting in LV is that it should be clearly profitable if it allows vectorization. For general loops without vectorization, it might not be profitable I think, e.g. for loops that only execute once, due to the conversion overhead.


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