[release/10.0] JIT: Fix CEA cloning when enumerator local is reassigned from an untracked source - #128909
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…cognized source In the conditional escape analysis (CEA) pipeline for GDV-guarded enumerator allocations, CheckForGuardedAllocationOrCopy only recorded stores whose data was GT_ALLOCOBJ, GT_LCL_VAR, or GT_BOX. Stores whose data was something else (e.g. a non-devirtualized virtual call) were silently ignored, so a reassignment of the enumerator local in a second spread loop was never recorded as a def. CheckCanClone therefore saw the local as single-def and proceeded to clone, renaming all uses of the local in the cloned region to a new local that held the first allocation. The second loop's body ended up iterating over the first source array. Record such stores as appearances so the multiple-defs check fires and we bail out of unsafe cloning. Skip null/zero constant stores: the inliner emits these to clear dead inlinee gc-ref temps and treating them as real defs would pessimize unrelated methods. Fixes #127075
… source Direct I[] -> IReadOnlyCollection<I> assignment lets Tier1+PGO devirt the second GetEnumerator() into an inlined SZGenericArrayEnumerator allocation, so the buggy code path (where the second store is a non-devirt virtual call into the shared enumerator local) never executes and the test passes even against the broken JIT. Storing a collection literal directly to the interface type forces Roslyn's <>z__ReadOnlyArray<I> wrapper, whose GetEnumerator() remains a virtual call and exercises the fix.
AndyAyersMS
approved these changes
Jun 2, 2026
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@EgorBo Pull-request seems stuck: |
This was referenced Jun 9, 2026
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Backport of #127079 to release/10.0
/cc @EgorBo
Customer Impact
Customer-reported (#127075). Silent data loss: a C# collection expression spread with two sources,
[.. a, .. b], miscompiles under Tier1 + PGO. The result array has the correct length but the tail elements coming from the second source are left at their default value (nullfor reference types) because the second copy loop becomes dead code.A bug in JIT's escape analysis.
Regression
Introduced in .NET 10
Testing
Added a standalone JIT regression test (
src/tests/JIT/Regression/JitBlue/Runtime_127075) that reproduces the wrong codegen under Tier1 + PGO.Risk
Low