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

[Qiu Chaofan via Phabricator via llvm-commits]

qiucf created this revision.
qiucf added reviewers: PowerPC, spatel, RKSimon, lebedev.ri.
Herald added subscribers: llvm-commits, steven.zhang, shchenz, kbarton, hiraditya, nemanjai.
Herald added a project: LLVM.

On PowerPC, FNMSUB (including VSX and non-VSX version) means `-(a*b-c)`. But the backend now generates these instructions regardless whether `nsz` flag exists or not.

If `a*b-c==0`, such transformation changes sign of zero. This patch fixes this issue.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D76585

Files:
  llvm/lib/Target/PowerPC/PPCISelLowering.cpp
  llvm/lib/Target/PowerPC/PPCISelLowering.h
  llvm/lib/Target/PowerPC/PPCInstrInfo.td
  llvm/lib/Target/PowerPC/PPCInstrVSX.td
  llvm/test/CodeGen/PowerPC/combine-fneg.ll
  llvm/test/CodeGen/PowerPC/fma-assoc.ll
  llvm/test/CodeGen/PowerPC/fma-ext.ll
  llvm/test/CodeGen/PowerPC/fma-negate.ll
  llvm/test/CodeGen/PowerPC/fma.ll
  llvm/test/CodeGen/PowerPC/repeated-fp-divisors.ll

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