[PATCH] D80542: [DAGCombiner] Require ninf for division estimation

[Qiu Chaofan via Phabricator via llvm-commits]

qiucf created this revision.
qiucf added reviewers: nemanjai, spatel, hfinkel, craig.topper, arsenm, PowerPC.
Herald added subscribers: llvm-commits, ecnelises, kerbowa, hiraditya, nhaehnle, wdng, jvesely.
Herald added a project: LLVM.

This is similar to D76853 <https://reviews.llvm.org/D76853>. Current implementation of division estimation isn't correct for `1.0/0.0` (result is `nan`, not expected `inf`).

And this change exposes a potential infinite loop: in `combineRepeatedFPDivisors`, we use `isConstOrConstSplatFP` to look up if the divisor is some constant. But it doesn't work after legalized on some platforms. This patch restricts the method to act before `LegalDAG`.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D80542

Files:
  llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  llvm/test/CodeGen/AMDGPU/fdiv.ll
  llvm/test/CodeGen/PowerPC/combine-fneg.ll
  llvm/test/CodeGen/PowerPC/fdiv.ll
  llvm/test/CodeGen/PowerPC/qpx-recipest.ll
  llvm/test/CodeGen/PowerPC/recipest.ll
  llvm/test/CodeGen/PowerPC/repeated-fp-divisors.ll
  llvm/test/CodeGen/PowerPC/vsx-recip-est.ll
  llvm/test/CodeGen/X86/fdiv-combine-vec.ll

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