[all-commits] [llvm/llvm-project] fa12df: [SCEV] Check correct value for UB (#124302)

[Nikita Popov via All-commits]

  Branch: refs/heads/release/20.x
  Home:   https://github.com/llvm/llvm-project
  Commit: fa12df5e22aa5ae6d3c0a5b261acd15bd49081e8
      https://github.com/llvm/llvm-project/commit/fa12df5e22aa5ae6d3c0a5b261acd15bd49081e8
  Author: Nikita Popov <npopov at redhat.com>
  Date:   2025-01-30 (Thu, 30 Jan 2025)

  Changed paths:
    M llvm/lib/Analysis/ScalarEvolution.cpp
    M llvm/test/Analysis/ScalarEvolution/pr123550.ll

  Log Message:
  -----------
  [SCEV] Check correct value for UB (#124302)

This is a followup to #117152. That patch introduced a check for
UB/poison on BEValue. However, the SCEV we're actually going to use is
Shifted. In some cases, it's possible for Shifted to contain UB, while
BEValue doesn't.

In the test case the values are:

BEValue: (-1 * (zext i8 (-83 + ((-83 /u {1,+,1}<%loop>) *
{-1,+,-1}<%loop>)) to i32))<nuw><nsw>
Shifted: (-173 + (-1 * (zext i8 ((-83 /u {0,+,1}<%loop>) *
{0,+,-1}<%loop>) to i32))<nuw><nsw>)<nuw><nsw>

Fixes https://github.com/llvm/llvm-project/issues/123550.

(cherry picked from commit 07efe2c18a63423943a4f9d9daeada23601f84c8)



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