[all-commits] [llvm/llvm-project] 5bd38a: [DAG] ComputeNumSignBits - subo_carry(x, x, c) -> bi...

[Simon Pilgrim via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 5bd38a98d7585841c1688f6b9eee8ce150dc429c
      https://github.com/llvm/llvm-project/commit/5bd38a98d7585841c1688f6b9eee8ce150dc429c
  Author: Simon Pilgrim <llvm-dev at redking.me.uk>
  Date:   2024-07-23 (Tue, 23 Jul 2024)

  Changed paths:
    M llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
    M llvm/test/CodeGen/AArch64/neon-abd.ll
    M llvm/test/CodeGen/ARM/neon_vabd.ll
    M llvm/test/CodeGen/X86/abdu.ll

  Log Message:
  -----------
  [DAG] ComputeNumSignBits - subo_carry(x,x,c) -> bitwidth 'allsignbits' (#99935)

Handle cases where the subo_carry is subtracting the same operand (=zero) - so only the subtraction of the 0/1 carry bit is affecting the result, giving a 0/-1 allsignbits value.

Noticed while improving ABDS/ABDU expansion.



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