JIT: stop treating ManagedThreadId helper as constant/pure

[Copilot]

This PR removes JIT assumptions that can treat CORINFO_HELP_GETCURRENTMANAGEDTHREADID as stable across async suspension, where execution may resume on a different thread.

• Description

  • Removed CORINFO_HELP_GETCURRENTMANAGEDTHREADID -> VNF_ManagedThreadId from fgValueNumberJitHelperMethodVNFunc in src/coreclr/jit/valuenum.cpp.
  • Removed the now-unused ValueNumFuncDef(ManagedThreadId, 0, false, false) from src/coreclr/jit/valuenumfuncs.h.
  • Kept a narrow fallback in fgValueNumberHelperCall to treat CORINFO_HELP_GETCURRENTMANAGEDTHREADID as non-pure for VN purposes if it survives as a helper call, so it goes through opaque VN handling instead of function-mapped VN.
  • Updated HelperCallProperties::init() in src/coreclr/jit/utils.cpp so CORINFO_HELP_GETCURRENTMANAGEDTHREADID is no longer marked pure, while still marked no-throw.

• What stays unchanged

  • Helper identity and JIT/EE interface are unchanged (CORINFO_HELP_GETCURRENTMANAGEDTHREADID remains).
  • Inline-candidate conversion path (impConvertToUserCallAndMarkForInlining) is unchanged.
  • The helper remains no-throw.

// Removed from fgValueNumberJitHelperMethodVNFunc:caseCORINFO_HELP_GETCURRENTMANAGEDTHREADID:
vnf = VNF_ManagedThreadId;
break;

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[VSadov]

@copilot we should also not mark the helper as "pure" in general, so that it cannot be moved and cross async suspend points. It is still valid to treat it as no-throw.

[Copilot]

@copilot we should also not mark the helper as "pure" in general, so that it cannot be moved and cross async suspend points. It is still valid to treat it as no-throw.

Updated in da58ef9: CORINFO_HELP_GETCURRENTMANAGEDTHREADID is no longer marked pure in HelperCallProperties::init(), and it remains marked no-throw (exceptions = ExceptionSetFlags::None).

[Copilot]

Pull request overview

This change updates CoreCLR JIT value numbering and helper metadata so CORINFO_HELP_GETCURRENTMANAGEDTHREADID is no longer modeled as a pure / method-constant operation, preventing VN from treating repeated uses as equivalent across the method.

Changes:

• Removed the VN function (VNF_ManagedThreadId) plumbing for CORINFO_HELP_GETCURRENTMANAGEDTHREADID.
• Updated helper call properties so CORINFO_HELP_GETCURRENTMANAGEDTHREADID is no longer marked pure (while remaining no-throw).
• Added a VN-path guard to ensure the helper is treated as non-pure during helper-call VN handling.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/coreclr/jit/valuenumfuncs.h	Removes the VNFunc definition previously used for ManagedThreadId.
src/coreclr/jit/valuenum.cpp	Stops mapping the helper to a VNFunc and adjusts helper-call VN handling accordingly.
src/coreclr/jit/utils.cpp	Updates helper metadata so GETCURRENTMANAGEDTHREADID is no longer classified as pure.

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

[Copilot]

@copilot we should also not mark the helper as "pure" in general, so that it cannot be moved and cross async suspend points. It is still valid to treat it as no-throw.

Added in the latest commit (src/tests/async/regression/managed-thread-id.cs):

1. TestThreadIdMatchesCurrentThread — verifies Environment.CurrentManagedThreadId == Thread.CurrentThread.ManagedThreadId both before and after await Task.Delay(1).

2. TestThreadIdReflectsResumptionThread — uses a custom awaiter (SwitchToNewThread) that guarantees the continuation runs on a brand-new dedicated thread, then asserts the thread ID reflects the resumption thread and differs from the pre-await thread ID.

The custom awaiter pattern matches the existing YieldToThreadWithCustomSyncContext approach in synchronization-context.cs, ensuring the thread switch is deterministic rather than relying on TCS inline-completion behavior.

[VSadov]

Thanks!