[PATCH] D122933: [RISCV][AMDGPU][TargetLowering] Special case overflow expansion for (uaddo X, 1).

[Craig Topper via Phabricator via llvm-commits]

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If we expand (uaddo X, 1) we previously expanded the overflow calculation
as (X + 1) <u X. This potentially increases the live range of X and
can prevent X+1 from reusing the register that previously held X.

Since we're adding 1, overflow only occurs if X was UINT_MAX in which
case (X+1) would be 0. So this patch adds a special case to expand
the overflow calculation to (X+1) == 0.

This seems to help with uaddo intrinsics that get introduced by
CodeGenPrepare after LSR. Alternatively, we could block the uaddo
transform in CodeGenPrepare for this case.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D122933

Files:
  llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
  llvm/lib/Target/RISCV/RISCVISelLowering.cpp
  llvm/test/CodeGen/AMDGPU/sdiv64.ll
  llvm/test/CodeGen/AMDGPU/srem64.ll
  llvm/test/CodeGen/AMDGPU/udiv64.ll
  llvm/test/CodeGen/AMDGPU/urem64.ll
  llvm/test/CodeGen/RISCV/rvv/sink-splat-operands.ll
  llvm/test/CodeGen/RISCV/xaluo.ll

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