[llvm-dev] [FPEnv] FNEG instruction

[Roman Lebedev via llvm-dev]

On Tue, Oct 2, 2018 at 10:06 PM Cameron McInally via llvm-dev
<llvm-dev at lists.llvm.org> 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.
Will this affect (regress, pessimize) the current optimizations for
non-strict cases?
What about -ffast-math?

Roman.
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