[all-commits] [llvm/llvm-project] 955f12: [instcombine] Fold overflow check using overflow i...

[Philip Reames via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 955f12589940634acc6c9901e8b25534808f691c
      https://github.com/llvm/llvm-project/commit/955f12589940634acc6c9901e8b25534808f691c
  Author: Philip Reames <listmail at philipreames.com>
  Date:   2021-07-01 (Thu, 01 Jul 2021)

  Changed paths:
    M llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
    M llvm/test/Transforms/InstCombine/saddo.ll
    M llvm/test/Transforms/InstCombine/smulo.ll
    M llvm/test/Transforms/InstCombine/ssubo.ll
    M llvm/test/Transforms/InstCombine/usubo.ll

  Log Message:
  -----------
  [instcombine] Fold overflow check using overflow intrinsic to comparison

This follows up to D104665 (which added umulo handling alongside the existing uaddo case), and generalizes for the remaining overflow intrinsics.

I went to add analogous handling to LVI, and discovered that LVI already had a more general implementation. Instead, we can port was LVI does to instcombine. (For context, LVI uses makeExactNoWrapRegion to constrain the value 'x' in blocks reached after a branch on the condition `op.with.overflow(x, C).overflow`.)

Differential Revision: https://reviews.llvm.org/D104932