[llvm-dev] [FPEnv] FNEG instruction

[Cameron McInally via llvm-dev]

>
> On Wed, Sep 26, 2018 at 1:24 PM Sanjay Patel <spatel at rotateright.com>
> wrote:
> ...
>
>> To bring it back to the question of fneg, let me know if this is an
>> accurate summary:
>> 1. fneg would be nice to have for clarity, but it doesn't make
>> optimization in the default LLVM FP environment any easier/better.
>> 2. We will have to do some preliminary work in the IR optimizer to avoid
>> regressions if we add fneg to the IR.
>> 3. We want fneg as a 1st class instruction even though the related
>> fabs/copysign bitstring ops are intrinsics (because fneg is more common
>> than the others?).
>> 4. Adding fneg to IR means we do not need to add a constrained intrinsic
>> for fneg (likewise, there's no need for constrained fabs/copysign because
>> those intrinsics already exist).
>>
>>
>
For simplicity's sake, I agree with all this. I could nit-pick a bit, but
it's not productive to the FNEG conversation.

Thanks for summarizing, Sanjay.
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