[all-commits] [llvm/llvm-project] 418c21: Return "[Codegenprepare][X86] Use usub with overfl...

[max-azul via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 418c218efa950245ba075b9bb3a53505b807c5df
      https://github.com/llvm/llvm-project/commit/418c218efa950245ba075b9bb3a53505b807c5df
  Author: Max Kazantsev <mkazantsev at azul.com>
  Date:   2021-02-11 (Thu, 11 Feb 2021)

  Changed paths:
    M llvm/lib/CodeGen/CodeGenPrepare.cpp
    M llvm/test/CodeGen/X86/2020_12_02_decrementing_loop.ll
    M llvm/test/CodeGen/X86/lsr-loop-exit-cond.ll
    M llvm/test/CodeGen/X86/usub_inc_iv.ll

  Log Message:
  -----------
  Return "[Codegenprepare][X86] Use usub with overflow opt for IV increment"

The patch did not account for one corner case where cmp does not dominate
the loop latch. This patch adds this check, hopefully it's cheap because
the CFG does not change during the transform, so DT queries should be
executed quickly.

If you see compile time slowness from this, please revert.

Differential Revision: https://reviews.llvm.org/D96119