[PATCH] D75501: [DAGCombine] Check the uses of negated floating constant and remove the hack

[qshanz via Phabricator via llvm-commits]

steven.zhang created this revision.
steven.zhang added reviewers: spatel, lebedev.ri, craig.topper, arsenm, RKSimon, rampitec, nemanjai, jsji, PowerPC.
Herald added subscribers: kerbowa, wuzish, hiraditya, nhaehnle, wdng, jvesely.
Herald added a project: LLVM.

This patch is motivated by the case I added in PowerPC/fma-combine.ll, and we hit an assertion here due to somewhat the same reason as https://reviews.llvm.org/D70975 . The case is narrowed down from spec and it is important to us. Though we have some hack, it still failed with my case, as the operand 0 now is NOT a const fp, it is another fma that with const fp. And that const fp is negated which result in multi-uses.

So, I think a better fix is to check the uses of the negated const fp. If there are already use of its negated value, we will have benefit as no extra Node is added.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D75501

Files:
  llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
  llvm/test/CodeGen/AMDGPU/fdiv32-to-rcp-folding.ll
  llvm/test/CodeGen/PowerPC/fma-combine.ll
  llvm/test/CodeGen/X86/sse3-avx-addsub-2.ll

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