[all-commits] [llvm/llvm-project] 14ef87: [ValueTracking] usub(a, b) cannot overflow if a >= b.

[Florian Hahn via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: 14ef87bda67d53f351217c4522150e41fb5695e8
      https://github.com/llvm/llvm-project/commit/14ef87bda67d53f351217c4522150e41fb5695e8
  Author: Florian Hahn <flo at fhahn.com>
  Date:   2020-02-07 (Fri, 07 Feb 2020)

  Changed paths:
    M llvm/lib/Analysis/ValueTracking.cpp
    M llvm/test/Transforms/InstCombine/usub-overflow-known-by-implied-cond.ll

  Log Message:
  -----------
  [ValueTracking] usub(a, b) cannot overflow if a >= b.

If we know that a >= b (unsigned), usub.with.overflow(a, b) cannot
overflow. Similarly, if b > a, the same expression overflows.

Reviewers: nikic, RKSimon, lebedev.ri, spatel

Reviewed By: nikic, Gerolf

Differential Revision: https://reviews.llvm.org/D74066