[PATCH] D97160: [DAGCombiner] Optimize SMULO/UMULO if we can prove that overflow is impossible.

[Craig Topper via Phabricator via llvm-commits]

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Using ComputeNumSignBits or computeKnownBits we might be able
to determine that overflow is impossible.

This especially helps after type legalization if the type was
promoted from a type with half the bits or more. Type legalization
conservatively creates a promoted smulo/umulo and an overflow
check for the promoted bits. The overflow from the promoted
smulo/umulo is ORed with the result of the promoted bits
overflow check. Proving that the promoted smulo/umulo can never
overflow will leave us with just the promoted bits overflow check.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D97160

Files:
  llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  llvm/test/CodeGen/AArch64/vec_umulo.ll
  llvm/test/CodeGen/RISCV/xaluo.ll
  llvm/test/CodeGen/X86/vec_smulo.ll
  llvm/test/CodeGen/X86/vec_umulo.ll
  llvm/test/CodeGen/X86/xmulo.ll

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