[ci-scan] Test failure: ElidedBoundsChecks Assert.Throws mismatch under R2R_CG2

[github-actions]

Build Information

Build: https://dev.azure.com/dnceng-public/public/_build/results?buildId=1451092
Build error leg or test failing: coreclr Pri1 Runtime Tests Run R2R_CG2 linux x64 checked - JIT.opt (JIT/opt/RangeChecks/ElidedBoundsChecks/ElidedBoundsChecks.cmd)

Error Details

Xunit.Sdk.ThrowsException: Assert.Throws() Failure: Exception type was not an exact match
Expected: typeof(System.ArgumentOutOfRangeException)
Actual:   typeof(System.IndexOutOfRangeException)
   at Xunit.Assert.ThrowsImpl(Type exceptionType, Exception exception, Func`2 inspector)
   at Xunit.Assert.Throws[T](Func`1 testCode)
   at ElidedBoundsChecks.TestEntryPoint()
   at __GeneratedMainWrapper.Main()
Expected: 100
Actual: 101
END EXECUTION - FAILED

The test ElidedBoundsChecks expects an ArgumentOutOfRangeException from a bounds check on a ReadOnlySpan<char>, but under R2R/CrossGen2 compilation (R2R_CG2 mode) the JIT emits a raw IndexOutOfRangeException instead. The elided bounds check optimization is not preserving the correct exception type. This failure is distinct from the previous KBE #124322 (which was a FileCheck ARM64-NOT assertion failure, now closed).

Error Message

{
  "ErrorMessage": ["ElidedBoundsChecks", "Exception type was not an exact match"],
  "ErrorPattern": "",
  "BuildRetry": false,
  "ExcludeConsoleLog": false
}

Impact on platforms

• runtime-coreclr outerloop (def 108), linux x64, linux arm64, linux_musl x64, linux_musl arm64, windows x64, windows x86, osx x64, osx arm64 — all R2R_CG2 checked legs

First build it occurred

• Build: https://dev.azure.com/dnceng-public/public/_build/results?buildId=1439560
• Finished: 2026-05-29T00:51:06Z
• Persistent across the entire scanned window (25+ builds); true origin may predate 2026-05-29.
• Occurrences in window: 25+ (100% failure rate across all sampled builds)

---

Filed by ci-failure-scan, which scans dnceng-public outer-loop pipelines on main and converts stable failures into KBEs and test-disable PRs.

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Generated by CI Outer-Loop Failure Scanner · ● 43.4M · ◷

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Summary

24-Hour Hit Count	7-Day Hit Count	1-Month Count
0	0	0

[AndyAyersMS]

This was fixed by #129044