JIT: Fix promoted liveness in forward substitution - #133703
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AndyAyersMS merged 4 commits intoSep 18, 2026
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@jakobbotsch ptal No diffs expected |
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🔵 Needs a closer look
The JIT liveness change is correctness-sensitive and warrants final human review.
Pull request overview
Fixes a CoreCLR JIT forward-substitution liveness bug involving promoted structs.
Changes:
- Adds promotion-aware last-use invalidation for substitution.
- Adds and registers regression coverage for issue #133641.
File summaries
| File | Changes |
|---|---|
src/tests/JIT/Regression/Regression_ro_2.csproj |
Registers the regression test. |
src/tests/JIT/Regression/JitBlue/Runtime_133641/Runtime_133641.cs |
Adds regression coverage. |
src/coreclr/jit/forwardsub.cpp |
Updates liveness invalidation logic. |
src/coreclr/jit/compiler.h |
Declares the shared helper. |
Review details
- Files reviewed: 3/3 changed files
- Comments generated: 0
- Review effort level: Lite
jakobbotsch
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Sep 14, 2026
jakobbotsch
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Sep 14, 2026
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Somehow this agent was able to auto-post. Still working on this, more changes to come. |
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
jakobbotsch
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Sep 18, 2026
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a few diffs |
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/backport to release/11.0 |
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Started backporting to |
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Sep 21, 2026
…34349) Backport of #133703 to release/11.0 /cc @AndyAyersMS ## Customer Impact - [ ] Customer reported - [x] Found internally Forward substitution can leave stale last-use flags on promoted struct parents and remove a live struct copy. The reported case returns `6` instead of the correct value `8`. This reproduces on .NET 11 RC2; .NET 8, 9, and 10 are correct. See #133641. ## Regression - [x] Yes - [ ] No Introduced during the .NET 11 cycle by #129312. ## Testing Added a focused regression test that exercises multi-use forward substitution of a promoted struct and verifies that the defining copy remains live. The source PR was validated through JIT CI and SuperPMI analysis; only a small number of expected code-generation differences were observed. ## Risk Low. The fix makes last-use invalidation promotion-aware and reuses the same logic for single- and multi-use substitution. It preserves liveness conservatively rather than enabling a new optimization. Co-authored-by: Andy Ayers <andya@microsoft.com> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Multi-use forward substitution could leave stale last-use flags on promoted struct parents, allowing a live struct copy to be removed.
Make last-use invalidation promotion-aware and reuse the same logic for single- and multi-use substitution. Add a regression test.
Fixes #133641
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