[llvm-dev] [FPEnv] FNEG instruction

[Sanjay Patel via llvm-dev]

On Tue, Oct 2, 2018 at 1:06 PM Cameron McInally <cameron.mcinally at nyu.edu>
wrote:

> On Mon, Oct 1, 2018 at 5:41 PM Sanjay Patel <spatel at rotateright.com>
> wrote:
>
>> I don't see any controversy for the preliminary requirement of removing BinaryOperator::isFNeg()
>> and friends, so start with that?
>> That work may reveal other potential regressions that we can patch in
>> advance too.
>>
>
> This is true and I will agree to do this work...
>
>
>> Other than that, I think there's really only a question of do we want 1
>> or both of fneg and fneg_constrained (and if we choose both, then I assume
>> we'd also add fabs_constrained and copysign_constrained).
>>
>
> but this is the real goal. Doing the BinaryOperator::isFNeg() work is in
> vain if we don't have at least a conditional approval of an explicit FNEG
> IR instruction.
>
> Would it be possible to obtain that conditional approval before work
> begins? That seems most prudent.
>

I can't speak for anyone else, but I approve for the same reasons that were
mentioned early on: fneg makes the intended behavior and potential
transforms easier to discern.

I don't have much knowledge of the problems/requirements in the constrained
environment, so I'll leave the constrained counterpart decision to people
who are working on that.
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