JIT: SVE2 non-temporal scatter store tests are failing

[jakobbotsch]

Example pipeline run: https://dev.azure.com/dnceng-public/public/_build/results?buildId=1305236&view=results
Example console log: https://helixr18s23ayyeko0k025g8.blob.core.windows.net/dotnet-runtime-refs-heads-main-4424d7e9872d488fa0/HardwareIntrinsics_Arm_ro/1/console.2d74b0ab.log

11:04:47.043 Running test: _Sve2_ro::JIT.HardwareIntrinsics.Arm._Sve2._Sve.Program.Sve2_Scatter16BitNarrowingNonTemporal_Indices_long_long()
Beginning scenario: RunBasicScenario_UnsafeRead
Beginning scenario: RunBasicScenario_Load
Beginning scenario: RunBasicScenario_FalseMask
Beginning scenario: RunBasicScenario_NonFaulting
Beginning scenario: RunReflectionScenario_UnsafeRead
Beginning scenario: RunLclVarScenario_UnsafeRead
Beginning scenario: RunClassFldScenario
Beginning scenario: RunStructLclFldScenario
Sve2.Scatter16BitNarrowingNonTemporal(Int64, Int16*, Int64, Int64): RunStructLclFldScenario failed:
   mask: (1, 0)
  input: (598790890201539011, 197271212887199194)
indices: (1074, 1108)
 result: (0, 0)

These tests seem to have been added last week by #123892. cc @dotnet/arm64-contrib @ylpoonlg, can you please take a look with high priority?

Known Issue Error Message

Fill the error message using step by step known issues guidance.

{
  "ErrorMessage": "Failed test: _Sve2_ro::JIT.HardwareIntrinsics.Arm._Sve2._Sve.Program.Sve2_Scatter16BitNarrowingNonTemporal_Indices_long_long",
  "ErrorPattern": "",
  "BuildRetry": false,
  "ExcludeConsoleLog": false
}

Known issue validation

Build: 🔎 https://dev.azure.com/dnceng-public/public/_build/results?buildId=1305236
Error message validated: [Failed test: _Sve2_ro::JIT.HardwareIntrinsics.Arm._Sve2._Sve.Program.Sve2_Scatter16BitNarrowingNonTemporal_Indices_long_long]
Result validation: ✅ Known issue matched with the provided build.
Validation performed at: 2/23/2026 12:07:31 PM UTC

Report

Build	Definition	Test	Pull Request
1310810	dotnet/runtime	_Sve2_ro::JIT.HardwareIntrinsics.Arm._Sve2._Sve.Program.Sve2_Scatter16BitNarrowingNonTemporal_Indices_long_long()
1310556	dotnet/runtime	_Sve2_ro::JIT.HardwareIntrinsics.Arm._Sve2._Sve.Program.Sve2_Scatter16BitNarrowingNonTemporal_Indices_long_long()	#124883
1310413	dotnet/runtime	_Sve2_ro::JIT.HardwareIntrinsics.Arm._Sve2._Sve.Program.Sve2_Scatter16BitNarrowingNonTemporal_Indices_long_long()
1309823	dotnet/runtime	_Sve2_ro::JIT.HardwareIntrinsics.Arm._Sve2._Sve.Program.Sve2_Scatter16BitNarrowingNonTemporal_Indices_long_long()
1309055	dotnet/runtime	_Sve2_ro::JIT.HardwareIntrinsics.Arm._Sve2._Sve.Program.Sve2_Scatter16BitNarrowingNonTemporal_Indices_long_long()
2912133	dotnet-runtime	_Sve2_ro::JIT.HardwareIntrinsics.Arm._Sve2._Sve.Program.Sve2_Scatter16BitNarrowingNonTemporal_Indices_long_long()
1308591	dotnet/runtime	_Sve2_ro::JIT.HardwareIntrinsics.Arm._Sve2._Sve.Program.Sve2_Scatter16BitNarrowingNonTemporal_Indices_long_long()
1307889	dotnet/runtime	_Sve2_ro::JIT.HardwareIntrinsics.Arm._Sve2._Sve.Program.Sve2_Scatter16BitNarrowingNonTemporal_Indices_long_long()
1307223	dotnet/runtime	_Sve2_ro::JIT.HardwareIntrinsics.Arm._Sve2._Sve.Program.Sve2_Scatter16BitNarrowingNonTemporal_Indices_long_long()
1306995	dotnet/runtime	_Sve2_ro::JIT.HardwareIntrinsics.Arm._Sve2._Sve.Program.Sve2_Scatter16BitNarrowingNonTemporal_Indices_long_long()	#124684
1306746	dotnet/runtime	_Sve2_ro::JIT.HardwareIntrinsics.Arm._Sve2._Sve.Program.Sve2_Scatter16BitNarrowingNonTemporal_Indices_long_long()
1305950	dotnet/runtime	_Sve2_ro::JIT.HardwareIntrinsics.Arm._Sve2._Sve.Program.Sve2_Scatter16BitNarrowingNonTemporal_Indices_long_long()
1305236	dotnet/runtime	_Sve2_ro::JIT.HardwareIntrinsics.Arm._Sve2._Sve.Program.Sve2_Scatter16BitNarrowingNonTemporal_Indices_long_long()

Summary

24-Hour Hit Count	7-Day Hit Count	1-Month Count
4	13	13

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[a74nh]

@ylpoonlg is away. I'll take a look

[a74nh]

Not been able to get this to fail after many tries - probably another low frequency failure

[jakobbotsch]

The failures look quite consistent in outerloop/jitstress so I wonder what's different.