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

[Cameron McInally via llvm-commits]

Oh, that won't work since BinaryOperator::CreateFSub*(...) returns a
BinaryOperator. We'd need a UnaryOperator.

On Tue, May 7, 2019 at 3:41 PM Cameron McInally via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

> Ah, yeah. That was wrong. I should have said
> BinaryOperator::CreateFSub*(...).
>
>
>
> On Tue, May 7, 2019 at 3:07 PM Sanjay Patel <spatel at rotateright.com>
> wrote:
>
>> If we change the IRBuilder, that's not going to catch cases where a
>> regression test already has the 'fsub -0.0', is it? I'd think that only
>> comes into play if the regression test creates that op as part of its
>> transformations.
>>
>> On Tue, May 7, 2019 at 12:20 PM Cameron McInally <
>> cameron.mcinally at nyu.edu> wrote:
>>
>>> 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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