[PATCH] D158673: [SDAG][RISCV] Avoid neg instructions when lowering atomic_load_sub with a constant rhs

Thu Aug 24 15:43:20 PDT 2023

jrtc27 added a comment.

In D158673#4615395 <https://reviews.llvm.org/D158673#4615395>, @jrtc27 wrote:

> In D158673#4615391 <https://reviews.llvm.org/D158673#4615391>, @craig.topper wrote:
>
>> In D158673#4615369 <https://reviews.llvm.org/D158673#4615369>, @jrtc27 wrote:
>>
>>> (But AArch64 does mark ATOMIC_LOAD_ADD as LibCall already)
>>
>> So AArch64 would fail your suggestion "just check if add is legal, use that if so, otherwise fall back on a libcall?" since add wouldn't be legal it would be libcall.
>
> I guess "not Expand" rather than "is Legal" then?

(or "is Legal or LibCall" depending on your view of Custom)

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https://reviews.llvm.org/D158673