[wasm] Use GetDelegateCtor for CoreCLR R2R delegate construction by lewing · Pull Request #134611 · dotnet/runtime

lewing · 2026-09-24T19:00:51Z

Summary

Browser-Wasm CoreCLR ReadyToRun skipped delegate-constructor lowering. Wasm can't use the dynamically composed READYTORUN_DELEGATE_CTOR helpers, and because ReadyToRun is IsAot(), it also skipped the GetDelegateCtor path the JIT uses. As a result, every new D(target, ftn) called the original runtime-implemented .ctor(object, native int) through the interpreter.

With this change, Wasm ReadyToRun uses the same GetDelegateCtor transformation as the JIT. Crossgen2 selects the CoreLib constructor:

Selected constructor	Used for
`Delegate.CtorClosed`	Closed instance targets on reference types, with the same explicit arity as `Invoke` (including virtual and generic targets)
`Delegate.DelegateConstruct`	Every other shape

DelegateConstruct is the managed method the runtime already maps every delegate constructor to (ecall.cpp), so the fallback matches today's behavior for all shapes.
The CtorClosed shapes match those for which COMDelegate::GetDelegateCtor picks CtorClosed. The caller has already resolved the method pointer (ldftn/ldvirtftn, including instantiating stubs), so CtorClosed only stores the target and the pointer.
Generated code references the two CoreLib methods by name, the same way runtime async references AsyncHelpers methods such as RestoreInlinedFrameContexts. The JIT synthesizes these calls, so the caller's IL has no token for them. Crossgen2 therefore pre-seeds their manifest tokens, mirroring AddNecessaryAsyncReferences.

Changes

flowgraph.cpp:
- On TARGET_WASM, the ReadyToRun branch of fgOptimizeDelegateConstructor is taken only for NativeAOT, so Wasm ReadyToRun falls through to GetDelegateCtor.
- After retargeting the call, the AOT entry point is recomputed with getFunctionEntryPoint, because the importer cached the original constructor's entry point.
- Non-Wasm targets and NativeAOT are unchanged.
Crossgen2:
- GetDelegateCtor is implemented in the ReadyToRun partial; the RyuJit partial throws NotImplementedException, as before.
- Manifest tokens for CtorClosed and DelegateConstruct are seeded lazily on Wasm.
No R2R format, JIT-EE interface, or VM changes. The image version stays 30.0.

Validation

Local runs on macOS arm64, branch merged with current main:

Builds: Crossgen2, the cross-targeting Wasm JIT, the osx JIT and SuperPMI; browser-Wasm clr+libs+host+packs Release.
Image tests: ILCompiler.ReadyToRun.Tests with the Wasm target: 123 passed, 0 failed. WasmDelegateConstructors asserts that no DelegateCtor fixups remain and that both CoreLib constructors are imported.

Runtime test: readytorun/wasm/WasmInterpreterTransitions passes in these configurations:

Configuration	Result
Composite (harness default; CoreLib outside the bubble)	Pass; also passes with `DOTNET_GCStress=0xC`
Per-assembly, no cross-module inlining	Pass; also passes with `DOTNET_GCStress=0xC`
Per-assembly with `--opt-cross-module:*`	Pass; `CtorClosed` is inlined under a `CHECK_IL_BODY`/`VERIFY_IL_BODY` fixup, and the inlined null-receiver throw calls the private CoreLib helper through a manifest reference
Composite with `--inputbubble`	Pass

It covers the open static, open instance (via an IL helper), closed instance, closed static, virtual (including a derived override), generic owner, shared and unshared generic method, and null-receiver shapes, plus open- and closed-static retbuf shapes. Each is value-checked, with Target/Method identity and repeated construction.

Image dumps:
- The composite and per-assembly images call both constructors through METHOD_ENTRY_REF_TOKEN manifest references.
- CoreLib still contains compiled bodies for both constructors without any extra rooting.
Other: jitformat and git diff --check; independent code review with no findings.

Performance

100,000 constructions per sample; median of 3 runs × 4 samples, from the same build:

Shape	Interpreter only	R2R	R2R + `--opt-cross-module:*`
Open static	9.83 ms	6.61 ms	6.55 ms
Closed instance	6.15 ms	2.50 ms	2.22 ms

Before this change, R2R construction took ~44–46 ms for both shapes in an earlier build (directional only). Open static might get faster later from a dedicated CtorOpen path, which would need the shuffle thunk and collectible data; that would be a follow-up.

Related work

[wasm][R2R] Fix closed static delegate struct returns #134108 (merged): the closed-static struct-return invocation adapter, now exercised by the runtime test.
[wasm][R2R] Root interpreter thunks for closed static delegate targets #134497 (merged): complementary coverage of closed-static target interpreter thunks.

Resolves #134564

Note

This pull request description was generated with GitHub Copilot.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: 4dd9dfb0-13d5-4a8c-9419-3f808cbd9b8b

…asm-r2r-delegate-lowering

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…asm-r2r-delegate-lowering

azure-pipelines · 2026-09-24T19:01:48Z

Azure Pipelines: Successfully started running 5 pipeline(s). 11 pipeline(s) were filtered out due to trigger conditions. There may be pipelines that require an authorized user to comment /azp run to run.

dotnet-policy-service · 2026-09-24T19:02:10Z

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dotnet-policy-service · 2026-09-24T20:15:34Z

Tagging subscribers to 'arch-wasm': @lewing, @pavelsavara
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Copilot

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🟡 Changes recommended

Three moderate review issues remain unresolved.

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Review effort: Lite
Findings: 1

Open (1)

Invoke closed-static return-buffer delegate in the regression test · New

What changed in this PR

Enables browser-Wasm ReadyToRun delegate-constructor lowering with shared DC0/DC1 thunks and portable fixup metadata.

Changes:

Adds Wasm fixup handling, constructor rooting, and interpreter-transition dependencies.
Emits shared delegate-constructor thunks with GC argument tracking.
Adds runtime, IL, and ReadyToRun image coverage.

Review findings:

Moderate: Image tests do not verify the matching interpreter-thunk keys.
Moderate: The fallback condition excludes open-static delegates with hidden return buffers.
Moderate: The closed-static return-buffer test does not invoke the delegate.

File	Description
`src/tests/readytorun/wasm/WasmInterpreterTransitions/WasmInterpreterTransitions.csproj`	Adds the IL helper project reference.
`src/tests/readytorun/wasm/WasmInterpreterTransitions/WasmInterpreterTransitions.cs`	Adds delegate runtime coverage.
`src/tests/readytorun/wasm/WasmInterpreterTransitions/OpenInstanceDelegateHelper.ilproj`	Defines the helper IL project.
`src/tests/readytorun/wasm/WasmInterpreterTransitions/OpenInstanceDelegateHelper.il`	Provides the open-instance delegate fixture.
`src/coreclr/vm/wasm/helpers.hpp`	Declares return-buffer classification.
`src/coreclr/vm/wasm/helpers.cpp`	Implements Wasm return-buffer classification.
`src/coreclr/vm/wasm/dynamichelpers.cpp`	Adds the Wasm delay-load bridge.
`src/coreclr/vm/prestub.cpp`	Resolves delegate-constructor fixups.
`src/coreclr/vm/precode_portable.hpp`	Defines portable constructor entry-point data.
`src/coreclr/vm/method.hpp`	Declares the constructor R2R publication helper.
`src/coreclr/vm/frames.cpp`	Tracks Wasm object argument roots.
`src/coreclr/vm/cgensys.h`	Declares the typed Wasm helper entry point.
`src/coreclr/tools/aot/ILCompiler.ReadyToRun/ILCompiler.ReadyToRun.csproj`	Includes the new compiler components.
`src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/ReadyToRunDelegateCtorRootProvider.cs`	Roots delegate constructors.
`src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/ReadyToRunCodegenCompilationBuilder.cs`	Registers Wasm constructor roots.
`src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRunCodegenNodeFactory.cs`	Caches constructor thunk nodes.
`src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/WasmImportThunkPortableEntrypoint.cs`	Connects delegate fixups to shared thunks.
`src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/WasmDelegateCtorThunkNode.cs`	Emits `DC0` and `DC1` Wasm thunks.
`src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCases/Webcil/WasmDelegateConstructors.cs`	Adds ReadyToRun image fixtures.
`src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCases/R2RTestSuites.cs`	Validates delegate fixups and thunks.
`src/coreclr/jit/flowgraph.cpp`	Enables the Wasm R2R optimization.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: 4dd9dfb0-13d5-4a8c-9419-3f808cbd9b8b

Copilot

Copilot review overview

🔵 Needs a closer look

The cross-layer Wasm, JIT, and ReadyToRun changes warrant final human review; one documentation nit also remains.

Review effort: Lite
Findings: 1

Open (1)

Update comment to describe the current managed-helper path · New

Resolved since last review (1)

Invoke closed-static return-buffer delegate in the regression test

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: 4dd9dfb0-13d5-4a8c-9419-3f808cbd9b8b

Copilot

Copilot review overview

🟡 Changes recommended

Virtual targets may be incorrectly routed to CtorClosed, and coverage for excluded generic/value-type shapes is incomplete.

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Review effort: Lite
Findings: 1 · 1

Open (2)

Exclude virtual methods from CtorClosed delegate selection · New
Add coverage for generic delegate fallback construction · New

Resolved since last review (1)

Update comment to describe the current managed-helper path

davidwrighton

Lets use an R2R helper for this case. We'll need to modify the jit interface, but that's ok.

…ate-lowering # Conflicts: # src/tests/readytorun/wasm/WasmInterpreterTransitions/WasmInterpreterTransitions.cs

Replace the Crossgen GetDelegateCtor override (which returned CoreLib MethodDescs across module boundaries) with a new JIT-EE callback, getDelegateCtorHelper, that selects a fixed managed helper: - CORINFO_HELP_DELEGATE_CTOR_CLOSED (Delegate.CtorClosed) for closed non-virtual, non-generic reference-type instance targets. - CORINFO_HELP_DELEGATE_CONSTRUCT (Delegate.DelegateConstruct) for all other shapes; this is the managed implementation of every delegate ctor. The helpers are exposed as READYTORUN_HELPER_DelegateConstruct/ DelegateCtorClosed (R2R 30.1), so images stay valid across split composite and non-cross-module-inlining builds. Removes the dedicated root provider and manifest token pre-creation. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: 4dd9dfb0-13d5-4a8c-9419-3f808cbd9b8b

…ate-lowering

Revert the R2R-helper lowering (b970b2f) and go back to having Wasm ReadyToRun use the same GetDelegateCtor transformation as the JIT, with Crossgen2 selecting Delegate.CtorClosed or Delegate.DelegateConstruct. The CoreLib method references are pre-seeded in the manifest the same way as the runtime-async helpers the JIT synthesizes calls to. Compared to the earlier version of this approach: - Keep main's structure in fgOptimizeDelegateConstructor; Wasm only skips the dynamically composed ReadyToRun helper branch. - Implement GetDelegateCtor in the ReadyToRun/RyuJit partial files. - Exclude virtual targets from CtorClosed. - Seed the manifest tokens lazily, alongside the async references. - Drop the dedicated root provider; CoreLib compiles these bodies anyway. - Assert the selected constructor per method in the image test. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: 4dd9dfb0-13d5-4a8c-9419-3f808cbd9b8b

…ate-lowering # Conflicts: # src/tests/readytorun/wasm/WasmInterpreterTransitions/WasmInterpreterTransitions.cs # src/tests/readytorun/wasm/WasmInterpreterTransitions/WasmInterpreterTransitions.csproj

Delegate constructor calls use lazily bound delay-load call cells, which are not part of a method's eager fixup list, so the constructor selected for a given method cannot be attributed from the image. Check the image's import signatures instead; the runtime test covers per-shape behavior. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: 4dd9dfb0-13d5-4a8c-9419-3f808cbd9b8b

Match COMDelegate::GetDelegateCtor: closed delegates over instance methods on reference types use CtorClosed regardless of whether the target is virtual or generic. The method pointer has already been resolved by the caller (ldftn/ldvirtftn, including instantiating stubs), so CtorClosed only stores the target and pointer. Add runtime test coverage for a virtual target bound through an override and for shared and unshared generic method targets. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: 4dd9dfb0-13d5-4a8c-9419-3f808cbd9b8b

lewing added 8 commits September 24, 2026 00:01

Enable Wasm R2R delegate constructor lowering

b01d8ae

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: 4dd9dfb0-13d5-4a8c-9419-3f808cbd9b8b

Harden Wasm delegate constructor fallback

fab21ab

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Merge commit '6a48f796d5110849e860bfb3cc67af254c242557' into lewing-w…

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…asm-r2r-delegate-lowering

Merge commit '6c08d3879bd26bad726940cda89248ee4d9b6aa4' into lewing-w…

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Merge commit '99f3a6778c67851f3db251bb544718ec9dd09b3e' into lewing-w…

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…asm-r2r-delegate-lowering

Merge commit 'f3fc53da21dd6108174678a7cd778fb7fef313c7' into lewing-w…

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…asm-r2r-delegate-lowering

Support interpreted Wasm delegate constructors

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2e9feba

…asm-r2r-delegate-lowering

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[wasm][coreclr][R2R] Delegate construction skips alternate-constructor lowering and remains interpreted #134564

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lewing requested review from AndyAyersMS, davidwrighton and pavelsavara September 24, 2026 20:10

lewing added the arch-wasm WebAssembly architecture label Sep 24, 2026

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build-analysis Bot mentioned this pull request Sep 25, 2026

Async2TaskAdapters.TestValueTaskOfTaskValueVersusAsync fails with SanityCheck() in Wasm R2R test #133953

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Comment thread ...ot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/WasmDelegateCtorThunkNode.cs Outdated

Use direct Wasm delegate helpers

057a66f

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lewing requested a review from MichalStrehovsky as a code owner September 25, 2026 16:16

lewing changed the title ~~[wasm][R2R] Enable delegate constructor lowering~~ [wasm][R2R] Call delegate construction helpers directly Sep 25, 2026

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Comment thread src/tests/readytorun/wasm/WasmInterpreterTransitions/WasmInterpreterTransitions.cs Outdated

Update Wasm delegate test comment

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Comment thread src/coreclr/tools/aot/ILCompiler.ReadyToRun/JitInterface/CorInfoImpl.ReadyToRun.cs

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Comment thread src/coreclr/tools/Common/JitInterface/CorInfoImpl.cs Outdated

lewing marked this pull request as draft September 26, 2026 00:04

lewing and others added 3 commits September 27, 2026 12:10

Merge remote-tracking branch 'origin/main' into lewing-wasm-r2r-deleg…

197dc72

…ate-lowering # Conflicts: # src/tests/readytorun/wasm/WasmInterpreterTransitions/WasmInterpreterTransitions.cs

Merge remote-tracking branch 'origin/main' into lewing-wasm-r2r-deleg…

f8f6058

…ate-lowering

lewing changed the title ~~[wasm][R2R] Call delegate construction helpers directly~~ [wasm] Lower CoreCLR R2R delegate constructors to R2R helpers Sep 27, 2026

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Merge remote-tracking branch 'origin/main' into lewing-wasm-r2r-deleg…

698954b

…ate-lowering # Conflicts: # src/tests/readytorun/wasm/WasmInterpreterTransitions/WasmInterpreterTransitions.cs # src/tests/readytorun/wasm/WasmInterpreterTransitions/WasmInterpreterTransitions.csproj

lewing changed the title ~~[wasm] Lower CoreCLR R2R delegate constructors to R2R helpers~~ [wasm] Use GetDelegateCtor for CoreCLR R2R delegate construction Sep 30, 2026

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lewing enabled auto-merge (squash) October 1, 2026 00:55

lewing merged commit 1863c9f into main Oct 1, 2026
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[linux-bionic] TimeZoneInfoTests.IsIanaIdTest fails - GMT has wrong IANA Id indicator #133999

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[main] Source code updates from dotnet/runtime dotnet/dotnet#9905

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[wasm] Use GetDelegateCtor for CoreCLR R2R delegate construction - #134611

[wasm] Use GetDelegateCtor for CoreCLR R2R delegate construction#134611
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lewing commented Sep 24, 2026 •

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