Test Failure: Microsoft.Extensions.Logging.Generators.Roslyn3.11.Tests

[JulieLeeMSFT]

Summary:
JIT assertion failure varDsc->lvIsMultiRegRet in Lowering::ContainCheckRet at lower.cpp:9928 under JitStress=2f4 on arm64. Affects Microsoft.Extensions.Logging.Generators.Roslyn3.11.Tests in libraries-jitstress-random.

Failed in (1):

• runtime-coreclr libraries-jitstress-random 20260228.1

Failed tests:

- net11.0-linux-Release-arm64-jitstress_random_2-AzureLinux.3.Arm64.Open
  - Microsoft.Extensions.Logging.Generators.Roslyn3.11.Tests

Error Message:

[Assertion 'varDsc->lvIsMultiRegRet' failed in Lowering::ContainCheckRet at lower.cpp:9928](dotnet: /__w/1/s/src/coreclr/jit/lower.cpp:9928: void Lowering::ContainCheckRet(GenTreeUnOp *): Assertion `varDsc->lvIsMultiRegRet' failed.)

exit code 134 means SIGABRT Abort. Managed or native assert, or runtime check such as heap corruption, caused call to abort(). Core dumped.

Analysis:
JIT assertion failure in ContainCheckRet at lower.cpp:9928 under JitStress=2f4 on arm64. The assertion varDsc->lvIsMultiRegRet indicates the JIT expected a local variable to be marked as a multi-register return value but it was not. This is related to but distinct from closed #74774 (different assert expression at different line/function).

Failing since 2026-02-28 (build 1314581). Only observed on arm64 linux under jitstress_random_2 configuration.

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[JulieLeeMSFT]

@dhartglassMSFT, PTAL.
CC @dotnet/arm64-contrib