[PATCH] D85446: [InstCombine] Add vector support to mul(add(x,c),negpow2) -> mul(sub(-c,x),pow2) folds

Wed Aug 12 08:18:08 PDT 2020

bjope added a comment.

In D85446#2212757 <https://reviews.llvm.org/D85446#2212757>, @bjope wrote:

> In D85446#2205778 <https://reviews.llvm.org/D85446#2205778>, @lebedev.ri wrote:
>
>> In D85446#2205616 <https://reviews.llvm.org/D85446#2205616>, @bjope wrote:
>>
>>> (Just some heads up, in case someone else got the same problem...)
>>>
>>> I've noticed some regressions downstream after this patch. Haven't debugged/reduced it completely yet, but at least in one case I suspect that the problem actually might be in load-store-vectorizer.
>>>
>>> Used to get something like this before load-store-vectorizer:
>>>
>>> <...>
>>>
>>> The old input to load-store-vectorizer resulted in two <8 x i16> loads, but the new input gives one <8 x i16 load, two <2 x i16> loads and one <4 x i16> load. So for some reason LSV fails to detect that the loads are consecutive given the new IR. At least that is my current theory.
>>
>> Please can you file a bug with reproducer?
>
> Yes, I'm working on that (although progress has been a bit slow at the moment).

Here is a PR: https://bugs.llvm.org/show_bug.cgi?id=47136

Repository:
  rG LLVM Github Monorepo

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https://reviews.llvm.org/D85446