[PATCH] D61604: [InstCombine] sink FP negation of operands through select

[Cameron McInally via llvm-commits]

On Tue, May 7, 2019 at 11:44 AM Sanjay Patel <spatel at rotateright.com> wrote:

>
> On Tue, May 7, 2019 at 7:16 AM Kevin Neal <Kevin.Neal at sas.com> wrote:
>
>>
>> How should we handle regressions in code quality that are exposed by
>> tests?
>>
>
> One idea I had (or I may be remembering someone else's suggestion) was to
> grep the existing IR regression tests for 'fsub -0.0', then create a
> sibling test using fneg. If that doesn't result in the same output, then we
> need to do some pattern matching enhancement.
>

I'm not opposed to this, but it does sound like a ton of work.

What if we checked for a -0.0 constant in IRBuilder::FSub*(...) and created
an FNeg instead? Then we should only see test changes with `fsub -0.0`->
`fneg`. If we find anything else, it would need a closer look. Does that
miss anything?
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