[PATCH] D60395: [InstCombine] Canonicalize (-X s/ Y) to -(X s/ Y)

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri added a comment.

In D60395#1458889 <https://reviews.llvm.org/D60395#1458889>, @spatel wrote:

> In D60395#1458421 <https://reviews.llvm.org/D60395#1458421>, @lebedev.ri wrote:
>
> > Given that this doesn't fall into endless loop, i guess we don't do reverse transform.
> >  I'm just wondering, this is the direction we should be doing it? @spatel
>
>
> We already have these for mul:
>
>   // -X * Y --> -(X * Y)
>   // X * -Y --> -(X * Y)
>
> ...so that provides some precedent for the direction to move the negation.


Okay, that confirmed my suspicions.

> Is there a sibling fold for srem?

Yep!

  ----------------------------------------
  Optimization: nsw preserved
  Precondition: true
    %o0 = sub nsw i8 0, %x
    %r = srem i8 %o0, %y
  =>
    %n0 = srem i8 %x, %y
    %r = sub nsw i8 0, %n0
  
  Done: 1
  Optimization is correct!


Repository:
  rL LLVM

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https://reviews.llvm.org/D60395