JIT assert in ILC in test runs: ILC: Assertion failed 'operand->isUsedFromReg()' during 'Generate code'

[jkoritzinsky]

Build Information

Build: https://dev.azure.com/dnceng-public/public/_build/results?buildId=1098314&view=logs&jobId=a9eab304-9375-5df6-9f7c-f505bd759fef&j=ea7d6d51-d18d-5306-47bd-e3b7db04467e&t=6f613bc6-161e-53a2-c035-24718f3c6909
Build error leg or test failing: windows-x64 Checked NativeAOT

Error Message

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

{
  "ErrorPattern": "ILC: Assertion failed 'operand->isUsedFromReg\\(\\)' in '.+' during 'Generate code'",
  "BuildRetry": false,
  "ExcludeConsoleLog": false
}

Known issue validation

Build: 🔎 https://dev.azure.com/dnceng-public/public/_build/results?buildId=1098314
Error message validated: [ILC: Assertion failed 'operand->isUsedFromReg\(\)' in '.+' during 'Generate code']
Result validation: ✅ Known issue matched with the provided build.
Validation performed at: 7/17/2025 11:27:26 PM UTC

Report

Build	Definition	Step Name	Console log	Pull Request
1098562	dotnet/runtime	Build Tests	Log	#117258
1098544	dotnet/runtime	Build Tests	Log	#117799
1098488	dotnet/runtime	Build Tests	Log	#117797
1098458	dotnet/runtime	Build Tests	Log	#117796
1098452	dotnet/runtime	Build Tests	Log	#117684
1098432	dotnet/runtime	Build Tests	Log	#117635
1098425	dotnet/runtime	Build Tests	Log	#117793
1098385	dotnet/runtime	Build Tests	Log	#117583
1098379	dotnet/runtime	Build Tests	Log	#117784
1098369	dotnet/runtime	Build Tests	Log	#117792
1098365	dotnet/runtime	Build Tests	Log	#117791
1098359	dotnet/runtime	Build Tests	Log	#117790
1098349	dotnet/runtime	Build Tests	Log	#117258
1098342	dotnet/runtime	Build Tests	Log	#117700
1098314	dotnet/runtime	Build Tests	Log	#117635
1098284	dotnet/runtime	Build Tests	Log	#117686
1098280	dotnet/runtime	Build Tests	Log	#117690
1098270	dotnet/runtime	Build Tests	Log	#117738
1098263	dotnet/runtime	Build Tests	Log
1098209	dotnet/runtime	Build Tests	Log
1098201	dotnet/runtime	Build Tests	Log	#117725
1098172	dotnet/runtime	Build Tests	Log	#117779

Summary

24-Hour Hit Count	7-Day Hit Count	1-Month Count
22	22	22

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[AndyAyersMS]

Looks like #117783 is the same issue.

[AndyAyersMS]

fyi @dotnet/jit-contrib

[tannergooding]

Looks like the assert is in genCodeForNegNot because we're expecting a GT_NOT node to never have its operand contained.

We don't actually support marking such nodes as contained on xarch (the path for GT_NOT just no-ops), so something is likely doing a lowering transform without calling ClearContained

There's only been 4 lowering changes in the past few days:

• allow containment of CnsVec under GetElement node with non-const index (https://github.com/dotnet/runtime/pull/117562[)](https://github.com/dotnet/runtime/commit/ede442a9233fb67b2af40709a7d23418e0e491e5)
• Remove BBF_HAS_NULLCHECK, BBF_HAS_IDX_LEN, BBF_HAS_MD_IDX_LEN (https://github.com/dotnet/runtime/pull/117603[)](https://github.com/dotnet/runtime/commit/cbdc0eff824c5b8a646dee9cbaa91ec1b47c36de)
• JIT: Store unique switch successors in BBswtDesc (https://github.com/dotnet/runtime/pull/117423[)](https://github.com/dotnet/runtime/commit/3d689551bc6b5f6d50258ba2030f5203461dc899)
• JIT: Preparatory refactoring to support multiple defs per single node (https://github.com/dotnet/runtime/pull/117662[)](https://github.com/dotnet/runtime/commit/23323e91728ba356ea8ed029631a63a55d90907a)

[EgorBo]

Filed #117795 to fix it

[tannergooding]

👍, thanks!

Looks like that one stuck around silently for a few months!