GC.GetGeneration test fails under R2R with JitStressRegs=2

[dhartglassMSFT]

(from copilot):

GC.GetGeneration test fails under R2R with JitStressRegs=2

Build information

• Pipeline: runtime-coreclr r2r-extra
• Build: 20260809.1 (1546038)
• Test result: GC/API/GC/GetGeneration/GetGeneration.dll
• Helix console log: https://helix.dot.net/api/2019-06-17/jobs/9113bb5d-b1e4-4117-98bc-2a7821ca1231/workitems/GC/console

Configuration

• OS: Azure Linux 3
• Architecture: x64
• Runtime configuration: Checked
• ReadyToRun: Crossgen2 (RunCrossGen2=1)
• JIT stress mode: DOTNET_JitStressRegs=2
• Test run: R2R-CG2 linux x64 Checked jitstressregs2 @ AzureLinux.3.Amd64.Open

Failure

GC/API/GC/GetGeneration/GetGeneration.dll fails when run from the R2R-CG2 test suite with register stress enabled. The object test passes, but the array test observes generation 0 both before and after a full collection. The test expects the array's generation to increase.

Relevant Helix log:

+ export RunCrossGen2=1
+ RunCrossGen2=1

export DOTNET_JitStressRegs=2

03:34:03.426 Running test: GC/API/GC/GetGeneration/GetGeneration.dll
ObjectTest Passed!
0 0
arrayTest Failed!
failTest Passed!

Test for GetGeneration() FAILED!
Xunit.Sdk.EqualException: Assert.Equal() Failure: Values differ
Expected: 100
Actual:   1
   at Xunit.Assert.Equal[T](T expected, T actual, IEqualityComparer`1 comparer) in /_/src/arcade/src/Microsoft.DotNet.XUnitAssert/src/EqualityAsserts.cs:line 102
   at Program.<<Main>$>g__TestExecutor26|0_27(StreamWriter tempLogSw, StreamWriter statsCsvSw, StreamWriter outOfProcessPlanWriter, <>c__DisplayClass0_0&)
03:34:03.645 Failed test: GC/API/GC/GetGeneration/GetGeneration.dll

[dhartglassMSFT]

@janvorli I'm assuming that this issue is totally distinct from #131542 , since this run used jit stress modes and not the interpreter. Let me know if this is not the case.

[janvorli]

@dhartglassMSFT you are right. The most likely reason for the failure is the same as for the GC.Collect and GC.Collect0 tests and the fix would be the same as #132076

[dhartglassMSFT]

Thanks Jan
@kkokosa sending this your way then for an initial look, per Jan's pointer.

Though I saw this did not fail on the latest pipeline run from this weekend.

[VincentBu]

Failed in: runtime-coreclr jitstress 20260816.1

Failed tests:

coreclr linux arm64 Checked jitstress1 @ AzureLinux.3.Arm64.Open
- GC/API/GC/GetGeneration/GetGeneration.dll

Error message:

Assert.Equal() Failure: Values differ
Expected: 100
Actual:   1

Stack trace:

   at Xunit.Assert.Equal[T](T expected, T actual, IEqualityComparer`1 comparer) in /_/src/arcade/src/Microsoft.DotNet.XUnitAssert/src/EqualityAsserts.cs:line 102
   at Program.<<Main>$>g__TestExecutor23|0_24(StreamWriter tempLogSw, StreamWriter statsCsvSw, StreamWriter outOfProcessPlanWriter, <>c__DisplayClass0_0&)

[VincentBu]

This run doesn't set JitStressRegs. Please let me know if I need to create another issue for this.

Failed in: runtime-coreclr jitstress 20260902.1

Failed tests:

coreclr linux arm64 Checked jitstress1_tiered @ AzureLinux.3.Arm64.Open
- GC/API/GC/GetGeneration/GetGeneration.dll

Error message:

Assert.Equal() Failure: Values differ
Expected: 100
Actual:   1

Stack trace:

   at Xunit.Assert.Equal[T](T expected, T actual, IEqualityComparer`1 comparer) in /_/src/arcade/src/Microsoft.DotNet.XUnitAssert/src/EqualityAsserts.cs:line 102
   at Program.<<Main>$>g__TestExecutor23|0_24(StreamWriter tempLogSw, StreamWriter statsCsvSw, StreamWriter outOfProcessPlanWriter, <>c__DisplayClass0_0&)