JIT: Use a "resumed?" indicator variable in runtime async instead of lvaAsyncContinuationArg != nullptr

[jakobbotsch]

We will need this to enable inlining, since lvaAsyncContinuationArg != nullptr is not a correct way to compute this value for inlinees.

Diffs are pretty mixed and not generally improvements since we have to generate stores to this local now. One possibility is that we use lvaAsyncContinuationArg != null for the root function and only use indicator locals in inlinees instead. This would also make things simpler for OSR.

[jakobbotsch]

cc @AndyAyersMS, this is the PR with the indicator variables we discussed

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[Copilot]

Pull request overview

Replaces the implicit "have we resumed?" check (lvaAsyncContinuationArg != nullptr) with an explicit boolean indicator local (lvaResumedIndicator). The root motivation is to enable async inlining, where the existing check is not valid for inlinees. Two new pseudo-args (AsyncResumedUse / AsyncResumedDef) are threaded through every async call so each callsite can read the indicator and the resumption path can write 1 back into it; the JIT machinery (lcl morph, address-of escape analysis, fgInline, local def visitors, diagnostic checks) is updated to recognize the new defined-via-address local.

Changes:

• Introduce lvaResumedIndicator (TYP_UBYTE) and initialize it in the prolog / OSR entry / loops, replacing the inline-special-cased continuation != null recipe at all uses.
• Add WellKnownArg::AsyncResumedUse / AsyncResumedDef plus gtCallGetDefinedAsyncResumedLclAddr, and propagate them through arg setup, IR sequencing, escape analysis, local-def visiting, and diagnostic checks.
• In AsyncTransformation, store 1 to the indicator on the resumption path, add common-def head-merging into the resumption switch, and add a shared "resumed" temp for shared finish-context handling.

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/coreclr/jit/async.h	Declares new shared resumed var, helper signatures, and updated parameter lists for finish-context BB construction.
src/coreclr/jit/async.cpp	Core change: introduces indicator local, initializes it, threads new well-known args through calls, writes 1 on resumption, and implements common-def head merging.
src/coreclr/jit/compiler.h / compiler.cpp	Adds lvaResumedIndicator field and includes it in the OSR-local sanity check.
src/coreclr/jit/compiler.hpp	Extends VisitLocalDefs / VisitLocalDefNodes to also visit the async-resumed def on calls.
src/coreclr/jit/gentree.h / gentree.cpp	Adds the two new WellKnownArg values, their names, and gtCallGetDefinedAsyncResumedLclAddr.
src/coreclr/jit/morph.cpp	Wires the new well-known arg names into getWellKnownArgName.
src/coreclr/jit/importer.cpp / fginline.cpp	Skips the new pseudo-args in inline arg-info construction and prepend-statements.
src/coreclr/jit/lclmorph.cpp	Generalizes the callsite address-escape logic to recognize the resumed def (size 1) alongside retbuf, and sequences the def address.
src/coreclr/jit/lclvars.cpp	Minor cleanup: uses INDEBUG(...) macro for SetDefinedViaAddress.
src/coreclr/jit/fgdiagnostic.cpp	Extends linked-locals debug check to also push/expect the async-resumed def.

[Copilot]

Pull request overview

Copilot reviewed 13 out of 13 changed files in this pull request and generated 2 comments.