Qiu Chaofan 7a001a2d92 [PowerPC] Require nsz flag for c-a*b to FNMSUB ...

On PowerPC, FNMSUB (both VSX and non-VSX version) means -(a*b-c). But
the backend used to generate these instructions regardless whether nsz
flag exists or not. If a*b-c==0, such transformation changes sign of
zero.

This patch introduces PPC specific FNMSUB ISD opcode, which may help
improving combined FMA code sequence.

Reviewed By: steven.zhang

Differential Revision: https://reviews.llvm.org/D76585

2020-06-04 16:41:27 +08:00

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