[PATCH] D73978: [WIP][FPEnv] Don't transform FSUB(-0.0,X)->FNEG(X) when flushing denormals

[Cameron McInally via Phabricator via llvm-commits]

cameron.mcinally added a comment.

Thanks, Matt. It looks like preventing the FSUB->FNEG transform is still causing trouble with folding the negate into instructions. E.g.

  <scrubbed>/clang/llvm-project/llvm/test/CodeGen/AMDGPU/v_mac_f16.ll:125:7: error: SI: expected string not found in input
  ; SI: v_mad_f32 v{{[0-9]+}}, v{{[0-9]+}}, v{{[0-9]+}}, -v{{[0-9]+}}

It seems that there are a handful of new test failures too.

Any suggestions on how to proceed?

Should we not expect the explicit FSUB(-0,X) to fold under denormal flushing modes? (Too big a hammer, but correct)

Or maybe fold the FSUB(-0,X) into the instruction in the backend where possible? (Might cause some slightly wrong answers, unless we're careful)


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https://reviews.llvm.org/D73978