[Natalie Chouinard (sudonatalie)]

This backports llvm/llvm-project@56df0ec (rL264996) which fixes PR27137. It corrects SPF_SMIN matching in matchSelectPattern where the previous code blindly assumed the predicate was ICMP_SGT, leading to incorrect MIN/MAX matching for other predicates.

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[Copilot]

🟡 Changes recommended

The regression test is excluded from normal test discovery, so an active DXC test is needed to ensure CI catches a reversion of the matcher fix.

1 open issue

• Add active CI regression test for instruction-combining matcher · New

What changed in this PR

Backports LLVM’s PR27137 fix to DXC’s value-tracking analysis, correcting min/max recognition for selects involving bitwise-not comparisons.

Changes:

• Restricts the affected pattern to signed comparisons and selects the correct minimum or maximum flavor.
• Adds an LLVM IR regression case for the incorrect folding.

File	Description
test/​Transforms/​InstCombine/​select.ll	Adds the PR27137 regression case and expected optimized output.
lib/​Analysis/​ValueTracking.cpp	Checks the comparison predicate before classifying the select as signed min/max.

_{Review effort: Balanced}

[Copilot]

🔵 Needs a closer look

The new regression test is in a disabled suite, leaving the miscompile fix without automated regression coverage in CI.

1 open issue

• Add active CI regression test for instruction-combining matcher

1 previously missed issue

In code that hasn't changed since last review

Document optimizer correctness fix in release notes

lib/​Analysis/​ValueTracking.cpp:3395

Please add a one-sentence bug-fix entry under ### Upcoming Release in docs/ReleaseNotes.md. This changes user-visible optimizer correctness by preventing incorrect min/max folding, and CONTRIBUTING.md calls for release notes for important compiler bug fixes; the current notes do not cover this change.

_{Review effort: Balanced}

[Copilot]

🔵 Needs a closer look

The regression test is in a disabled suite, leaving the miscompile fix without automated regression coverage until an equivalent test is added to the enabled DXC suite.

1 open issue

• Add active CI regression test for instruction-combining matcher

_{Review effort: Balanced}

[Copilot]

🟢 Approval recommended

No active review issues are reported for the signed min/max recognition fix.

No open issues 🎉

1 resolved since last review

• Add active CI regression test for instruction-combining matcher

_{Review effort: Balanced}

[Copilot]

🔵 Needs a closer look

Human assessment is needed because the signed-only regression leaves the unsigned-predicate guard untested despite its role in preventing incorrect folds.

No open issues 🎉

_{Review effort: Balanced}

[Damyan Pepper (damyanp)]

/azp run

[azure-pipelines]

Azure Pipelines:
Successfully started running 1 pipeline(s).

[Copilot]

🟢 Approval recommended

No active review issues are reported for the targeted signed-minimum pattern fix and its regression coverage.

No open issues 🎉

_{Review effort: Balanced}