Who contributed to .NET on May 24, 2026?

3 developers shipped this update, including AndyAyersMS, EgorBo, and dotnet-maestro[bot].

What were the notable .NET updates?

JIT: don't stress-tailcall named intrinsics (#122479), JIT: don't stress-tailcall named intrinsics (#122479) (#128336), and Restore E_NOTIMPL fallback in DacDbiInterfaceImpl::GetContext (#128499).

May 24, 2026

$ the-wire · showcase

JIT INTRINSICS BUG FIX UNBLOCKS STRESS TESTING, DEBUGGER FALLBACK RESTORED FOR NON-WINDOWS

By RepoJournal · Filed 06:03 UTC on May 24, 2026 · About .NET · Composed from the cited sources · methodology

3 people shipped this

dotnet-maestro[bot] @dotnet-maestro[bot] 2 cited

AndyAyersMS @AndyAyersMS 1 cited

EgorBo @EgorBo 1 cited

The runtime team patched a critical JIT assertion that was breaking stress-tailcall testing on methods with SuppressGCTransition calls, while simultaneously restoring managed debugging on non-Windows platforms.

The JIT compiler was incorrectly marking call+ret patterns for tail-call optimization before determining whether the callee was a named intrinsic [1]. When intrinsics like GC.KeepAlive get imported as non-CALL IR nodes, this left malformed return blocks that triggered assertions during GC poll insertion on methods containing SuppressGCTransition calls. That fix is now landed [2]. In parallel, the runtime team restored a critical fallback in the debugging layer that reconstructs register context from thread frame chains on platforms where ICorDebugDataTarget::GetThreadContext returns E_NOTIMPL [3]. This was removed in a previous commit and broke managed debugging stack walks on non-Windows platforms. The team caught it through internal Visual Studio testing. On the optimization side, the JIT now folds always-true isinst checks using PHI node analysis and improved type comparison logic [4], extending the reach of assertion-based optimizations. WinForms continues pulling codeflow updates from the main VMR [5] [6].

Action items

→ Test JIT stress modes on next runtime build to confirm intrinsic assertion fix dotnet/runtime [plan]
→ Verify managed debugging on non-Windows platforms with latest runtime changes dotnet/runtime [plan]
→ Monitor WinForms codeflow PR merges for any integration issues dotnet/winforms [monitor]

References

[1] JIT: don't stress-tailcall named intrinsics (#122479) ↗ dotnet/runtime
[2] JIT: don't stress-tailcall named intrinsics (#122479) (#128336) ↗ dotnet/runtime
[3] Restore E_NOTIMPL fallback in DacDbiInterfaceImpl::GetContext (#128499) ↗ dotnet/runtime
[4] JIT: fold isinst using reaching VNs and compareTypesForCast ↗ dotnet/runtime
[5] [main] Source code updates from dotnet/dotnet ↗ dotnet/winforms
[6] [main] Source code updates from dotnet/dotnet ↗ dotnet/winforms