[PATCH] D76585: [PowerPC] Require NSZ flag for c-a*b to FNMSUB

[Sanjay Patel via Phabricator via llvm-commits]

spatel added a comment.

In D76585#2009259 <https://reviews.llvm.org/D76585#2009259>, @steven.zhang wrote:

> @spatel @RKSimon Do you know that why we didn't have the generic node for FNMSUB/FMSUB as I see the duplicate logic between X86 and PowerPC ?


I can't say for sure, but my guess is that target-specific logic could be added without incurring the overhead of general discussion/approval:
rG3cb3b0045c62bc6cc <https://reviews.llvm.org/rG3cb3b0045c62bc6cc3ef377144c433a796d48405>

There's also a question of deciding what name corresponds to each math operation. The x86 instructions don't match PPC. For example:
[PPC] fnmsub = -(A * B - C)
[x86] vfnmsub132sd = -(A * B) - C

It would be nice to have common nodes/optimizations if we can find enough code to share. If we do that, we also need to see if other targets can benefit (AArch64 has fnmsub machine IR).


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