JIT: Treat the indicator variable as transition-preserved

[jakobbotsch]

In OSR functions we recomputed this from the async continuation argument (which itself is transition-preserved). That approach is not sufficient for EnC. Instead just preserve the state across EnC/OSR transitions in the same way as other state.

To simplify the remapping/local allocation logic this also changes the indicator to consistently be a TYP_I_IMPL local, with all definitions of it writing that size. The arguments passed to the helper calls remain TYP_INT since they are bools in the managed signatures. We use TYP_INT typed local nodes for the indicator variable for these (allowed in JIT IR and used by optNarrowTree/IV widening also).

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[Copilot]

Pull request overview

This PR updates async OSR/EnC handling so the async “resumed?” indicator local is treated like other transition-preserved state: it gets a stable stack slot in the preserved area and its tier0-frame offset is communicated via PatchpointInfo for OSR compilations.

Changes:

• Adds PatchpointInfo support for a resumed-indicator stack offset and plumbs it through OSR patchpoint generation and OSR local offset resolution.
• Allocates lvaResumedIndicator as part of the async preserved-area locals and includes it in EnC preserved-area size verification across xarch/arm.
• Simplifies OSR async context setup by removing the OSR-specific recomputation of the indicator from the continuation argument.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/coreclr/jit/lclvars.cpp	Ensures the resumed-indicator local is stack-allocated as part of async preserved-area locals and excluded from later offset assignment passes.
src/coreclr/jit/compiler.h	Moves lvaResumedIndicator alongside other async preserved locals in the Compiler state.
src/coreclr/jit/compiler.cpp	Records and consumes the resumed-indicator tier0-frame offset via PatchpointInfo for OSR local remapping.
src/coreclr/jit/codegenxarch.cpp	Accounts for resumed-indicator in EnC preserved-area sizing assertions on x64.
src/coreclr/jit/codegenarmarch.cpp	Accounts for resumed-indicator in EnC preserved-area sizing assertions on arm64 (GC info encoder path).
src/coreclr/jit/codegenarm64.cpp	Includes resumed-indicator stack home in funclet prolog/epilog size accounting (non-OSR).
src/coreclr/jit/codegenarm.cpp	Includes resumed-indicator in funclet prolog/epilog size accounting (arm32).
src/coreclr/jit/async.cpp	Creates the resumed-indicator local as pointer-sized and removes OSR-only recomputation from continuation arg.
src/coreclr/inc/patchpointinfo.h	Adds a new resumed-indicator offset field + accessors to the shared OSR patchpoint info.

Suppressed comments (1)

src/coreclr/jit/async.cpp:380

• Same issue as in SaveAsyncContexts: lvaResumedIndicator has lvType = TYP_I_IMPL, so using gtNewLclVarNode(lvaResumedIndicator, TYP_INT) will trip the gtNewLclvNode type assert in DEBUG builds. Load as TYP_I_IMPL and cast to TYP_INT for the restoreContexts call argument.

    restoreCall->gtArgs.PushFront(this, NewCallArg::Primitive(gtNewLclVarNode(lvaResumedIndicator, TYP_INT)));

[Copilot]

Pull request overview

Copilot reviewed 10 out of 10 changed files in this pull request and generated no new comments.

Suppressed comments (1)

src/coreclr/jit/async.cpp:78

• lvaResumedIndicator is now declared as TYP_I_IMPL, but several downstream parts of the async transformation still treat it as a byte/boolean flag. In particular, AsyncTransformation::StoreResumedDef only does a full-width store when the local is TYP_UBYTE; with TYP_I_IMPL it falls back to a TYP_UBYTE field store (byte write) into a pointer-sized local. That leaves the upper bytes undefined and makes the value representation dependent on prior zero-init, which is brittle for OSR/EnC transitions and any future TYP_I_IMPL uses.

Either keep the local as TYP_UBYTE and explicitly force a pointer-sized stack home for the transition-preserved slot, or update the async transformation (and related address-def sizing logic) to store/load the indicator consistently as native-int (e.g., store 1 as TYP_I_IMPL when the local is TYP_I_IMPL).

    lvaGetDesc(lvaResumedIndicator)->lvType               = TYP_I_IMPL;
    lvaGetDesc(lvaAsyncThreadObjectVar)->lvType           = TYP_REF;
    lvaGetDesc(lvaAsyncExecutionContextVar)->lvType       = TYP_REF;
    lvaGetDesc(lvaAsyncSynchronizationContextVar)->lvType = TYP_REF;

[Copilot]

Pull request overview

Copilot reviewed 10 out of 10 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 10 out of 10 changed files in this pull request and generated 1 comment.

Suppressed comments (1)

src/coreclr/jit/lclvars.cpp:5864

• This comment says we "allocate 8 bytes" for the resumed indicator, but the actual allocation uses TARGET_POINTER_SIZE (4 bytes on x86, 8 bytes on 64-bit). The comment should describe the pointer-sized intent to avoid confusion when reading x86 EnC frame layout changes.

        // The indicator is actually a bool, but we allocate 8 bytes for it to
        // simplify EnC remapping.
        stkOffs = lvaAllocLocalAndSetVirtualOffset(lvaResumedIndicator, TARGET_POINTER_SIZE, stkOffs);

[Copilot]

Pull request overview

Copilot reviewed 14 out of 14 changed files in this pull request and generated no new comments.

Suppressed comments (4)

src/coreclr/inc/readytoruninstructionset.h:106

• This introduces an otherwise unrelated whitespace-only change (extra blank line) in the enum; please remove it to keep the PR focused and avoid diff noise.

    READYTORUN_INSTRUCTION_Zicond=94,

};

src/coreclr/jit/lclvars.cpp:5863

• The lvaAllocAsyncContexts header comment is now stale: the routine also allocates the resumed-indicator slot. Please update the comment so it matches the current behavior.

    if (lvaResumedIndicator != BAD_VAR_NUM)
    {
        stkOffs = lvaAllocLocalAndSetVirtualOffset(lvaResumedIndicator, lvaLclStackHomeSize(lvaResumedIndicator), stkOffs);
    }

src/coreclr/jit/codegenxarch.cpp:8382

• The EnC preserved-area comment immediately above is now incomplete: the code also preserves the async resumed-indicator slot. Please update the comment to match the frame header layout.

        if (m_compiler->lvaResumedIndicator != BAD_VAR_NUM)
        {
            preservedAreaSize += TARGET_POINTER_SIZE;

            assert(m_compiler->lvaGetCallerSPRelativeOffset(m_compiler->lvaResumedIndicator) == -preservedAreaSize);
        }

src/coreclr/jit/codegenarmarch.cpp:3936

• The EnC preserved-area comment immediately above is now incomplete: the code also preserves the async resumed-indicator slot. Please update the comment to match the frame header layout.

        if (m_compiler->lvaResumedIndicator != BAD_VAR_NUM)
        {
            preservedAreaSize += TARGET_POINTER_SIZE;

            assert(m_compiler->lvaGetCallerSPRelativeOffset(m_compiler->lvaResumedIndicator) == -preservedAreaSize);
        }

[Copilot]

Pull request overview

Copilot reviewed 14 out of 14 changed files in this pull request and generated no new comments.

Suppressed comments (2)

src/coreclr/inc/readytoruninstructionset.h:106

• Remove the extra blank line at the end of the enum; it looks like accidental whitespace-only churn unrelated to the JIT/async change and can cause avoidable merge conflicts.

    READYTORUN_INSTRUCTION_Cssc=93,
    READYTORUN_INSTRUCTION_Zicond=94,

};

src/coreclr/jit/lclvars.cpp:5864

• The header comment for lvaAllocAsyncContexts is now out of sync with the implementation: it also allocates the resumed indicator slot. Updating the comment will help keep the frame-layout invariants clear (especially around EnC).

    if (lvaResumedIndicator != BAD_VAR_NUM)
    {
        stkOffs =
            lvaAllocLocalAndSetVirtualOffset(lvaResumedIndicator, lvaLclStackHomeSize(lvaResumedIndicator), stkOffs);
    }

[jakobbotsch]

cc @dotnet/jit-contrib PTAL @AndyAyersMS

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