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

[Qing Shan Zhang via Phabricator via llvm-commits]

steven.zhang added a comment.

In D76585#2009908 <https://reviews.llvm.org/D76585#2009908>, @spatel wrote:

> 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).


Thank you for the information. Maybe,we can add fmsub(A*B-C), fnmsub(-A*B-C), fnmadd(-A*B+C). But yes, we need to see if other targets can benefit from this.


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