Implement TentativeMethodNode for WASM by Copilot · Pull Request #132814 · dotnet/runtime

Copilot · 2026-08-27T01:54:29Z

NativeAOT’s WASM backend could not emit tentative method stubs.

Stub emission
- Forward managed ABI parameters to the selected target.
- Emit call plus unreachable for throw helpers.
- Emit return_call when forwarding to the real body.
Compiler integration
- Register tentative method signatures with the WASM object writer.
- Add function-index relocations and NativeAOT emitter support.

Fixes Implement TentativeMethodNode for WASM #132813

azure-pipelines · 2026-08-27T01:54:44Z

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Co-authored-by: jtschuster <36744439+jtschuster@users.noreply.github.com>

dotnet-policy-service · 2026-08-27T02:37:07Z

Tagging subscribers to this area: @agocke, @dotnet/ilc-contrib
See info in area-owners.md if you want to be subscribed.

Co-authored-by: jtschuster <36744439+jtschuster@users.noreply.github.com>

azure-pipelines · 2026-08-27T16:53:26Z

Azure Pipelines: Successfully started running 3 pipeline(s). 13 pipeline(s) were filtered out due to trigger conditions. There may be pipelines that require an authorized user to comment /azp run to run.

Copilot

Pull request overview

This PR implements WebAssembly (Wasm) codegen support for TentativeMethodNode in the NativeAOT compiler pipeline, enabling emission of tentative method stubs and ensuring the Wasm object writer can register the correct function signatures and relocations.

Changes:

Add Wasm instruction support for unreachable, call, and return_call, plus helpers to emit them with function-index relocations.
Enable Wasm emission in WasmEmitter outside #if READYTORUN, and implement Wasm stub emission for TentativeMethodNode.
Update TentativeMethodNode to provide a type signature to the Wasm object writer, and add a unit test that validates emitted bytes + relocation behavior.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/coreclr/tools/Common/Compiler/ObjectWriter/WasmInstructions.cs	Adds Wasm expr kinds and helpers to emit `unreachable`, `call`, and `return_call` with function-index relocations.
src/coreclr/tools/Common/Compiler/DependencyAnalysis/Target_Wasm/WasmEmitter.cs	Removes `#if READYTORUN` gating so Wasm function bodies/relocs can be emitted in this compilation path.
src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/TentativeMethodNode.cs	Makes `TentativeMethodNode` provide a type signature (via `IMethodCodeNodeWithTypeSignature`) for Wasm signature registration.
src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/Target_Wasm/WasmTentativeMethodNode.cs	Implements Wasm stub emission: forward args to real body (`return_call`) or call throw-helper then `unreachable`.
src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/NodeFactory.cs	Implements `WasmTypeNode(MethodDesc)` using `WasmLowering.GetSignature(...).FuncType` so Wasm signatures can be registered.
src/coreclr/tools/aot/ILCompiler.Compiler.Tests/DependencyGraphTests.cs	Adds a focused unit test asserting Wasm encoding + relocation for tentative stubs.

Copilot · 2026-08-28T16:46:25Z

    {
-#if READYTORUN
        public WasmFunctionBody FunctionBody = null;
-#endif



Updated FunctionBody to initialize with null! in ae1d521.

Co-authored-by: jtschuster <36744439+jtschuster@users.noreply.github.com>

MichalStrehovsky · 2026-08-28T00:29:41Z

+            if (ReferenceEquals(target, RealBody))
+            {
+                // No throw helper is available, so forward all parameters and tail-call the real body.
+                int parameterCount = signature.Params.Types.Length;
+                expressions = new WasmExpr[parameterCount + 1];
+                for (int i = 0; i < parameterCount; i++)
+                {
+                    expressions[i] = Local.Get(i);
+                }
+                expressions[parameterCount] = ControlFlow.ReturnCall(target);
+            }


Whatever is generated in this codepath is never actually written into the output object file (we're generating a reloc to RealBody; doing that marks it and makes object emission of this node skipped):

runtime/src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/TentativeMethodNode.cs

Lines 46 to 50 in d9a6b9e

public override bool ShouldSkipEmittingObjectNode(NodeFactory factory)

{

// If the real body was marked, don't emit this assembly stub.

return _methodNode.Marked;

}

I think it would be completely fine to always do the else branch, the WASM doesn't need to be valid here.

Simplified WASM emission to always generate the minimal call relocation path in ae1d521.

MichalStrehovsky · 2026-08-28T00:37:00Z

+        [Theory]
+        [InlineData(false)]
+        [InlineData(true)]
+        public void TentativeMethodNodeEmitsWasmCall(bool useRealBody)


This test is quite some slop forcing invariants that are not useful, I'd delete it.

Deleted this test and its supporting test-only node in ae1d521.

MichalStrehovsky · 2026-08-28T00:46:03Z

+            else
+            {
+                // The real body was removed, so call the throw helper with the shadow stack pointer.
+                Debug.Assert(!Method.IsUnmanagedCallersOnly);


If we really want to assert this, it should be done in the constructor so we get a useful stack pointing to the blame place. But I don't find it likely we could accidentally use this with UnmanagedCallersOnly methods, I don't see a world where they could be tentative (i.e. reloc to them is reachable, but they could be effectively unexecutable).

Removed the unmanaged-caller assertion in ae1d521.

Co-authored-by: jtschuster <36744439+jtschuster@users.noreply.github.com>

MichalStrehovsky · 2026-08-31T00:47:12Z

        End = 0x0B,
+        Call = 0x10,
        CallIndirect = 0x11,
+        ReturnCall = 0x12,


This is dead code now. LGTM otherwise.

Initial plan

a1bdfd3

Copilot AI assigned Copilot and jtschuster Aug 27, 2026

github-project-automation Bot added this to AppModel Aug 27, 2026

Copilot AI linked an issue Aug 27, 2026 that may be closed by this pull request

Implement TentativeMethodNode for WASM #132813

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Copilot started work on behalf of jtschuster August 27, 2026 01:55 View session

github-actions Bot added the area-Infrastructure label Aug 27, 2026

github-project-automation Bot added this to Runtime Infra Aug 27, 2026

Implement WASM tentative method stubs

1a7e6a7

Co-authored-by: jtschuster <36744439+jtschuster@users.noreply.github.com>

jkotas added trimming-for-aot `EnableAggressiveTrimming=true` used for running tests with AOT area-NativeAOT-coreclr and removed trimming-for-aot `EnableAggressiveTrimming=true` used for running tests with AOT area-Infrastructure labels Aug 27, 2026

Copilot AI and others added 2 commits August 27, 2026 02:39

Complete WASM tentative method validation

24e9f8c

Co-authored-by: jtschuster <36744439+jtschuster@users.noreply.github.com>

Remove temporary review artifacts

f5d05f3

Co-authored-by: jtschuster <36744439+jtschuster@users.noreply.github.com>

Copilot AI changed the title ~~[WIP] Implement TentativeMethodNode for WASM~~ Implement TentativeMethodNode for WASM Aug 27, 2026

Copilot finished work on behalf of jtschuster August 27, 2026 02:48

Copilot AI requested a review from jtschuster August 27, 2026 02:48

This was referenced Aug 27, 2026

The Operation will be canceled. The next steps may not contain expected logs. dotnet/dnceng#3008

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[ci-scan] Build break: Windows Helix work items fail on unexpanded $HELIX_PYTHONPATH in gen-debug-dump-docs post-command #131382

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jtschuster marked this pull request as ready for review August 27, 2026 16:52

Copilot AI lite review requested due to automatic review settings August 27, 2026 16:52

jtschuster requested a review from MichalStrehovsky as a code owner August 27, 2026 16:52

Copilot started reviewing on behalf of jtschuster August 27, 2026 16:53 View session

jtschuster marked this pull request as draft August 27, 2026 16:54

Copilot started work on behalf of jtschuster August 27, 2026 17:03 View session

Copilot AI reviewed Aug 27, 2026

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Copilot finished work on behalf of jtschuster August 27, 2026 17:10

Copilot started work on behalf of jtschuster August 27, 2026 17:21 View session

Copilot AI and others added 2 commits August 27, 2026 17:46

Remove PEP from WASM throw helper call

3e8ce78

Co-authored-by: jtschuster <36744439+jtschuster@users.noreply.github.com>

Clarify WASM tentative stub paths

eae0c18

Co-authored-by: jtschuster <36744439+jtschuster@users.noreply.github.com>

Copilot finished work on behalf of jtschuster August 27, 2026 17:52

This was referenced Aug 27, 2026

Android WebSocket failure #121518

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System.Net.WebSockets.Client.Tests.CancelTest_HttpClient_Loopback.SendAsync_Cancel_Success failure: Actual Open when System.Threading.Tasks.TaskCanceledException #132031

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MichalStrehovsky reviewed Aug 28, 2026

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Copilot started work on behalf of jtschuster August 28, 2026 16:19 View session

Address WASM tentative node review feedback

ae1d521

Co-authored-by: jtschuster <36744439+jtschuster@users.noreply.github.com>

Copilot finished work on behalf of jtschuster August 28, 2026 16:50

build-analysis Bot mentioned this pull request Aug 28, 2026

slow macOS - "##[error]The job running on agent Azure Pipelines 9 ran longer than the maximum time of 60 minutes." dotnet/dnceng#1883

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MichalStrehovsky reviewed Aug 31, 2026

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Implement TentativeMethodNode for WASM - #132814

Implement TentativeMethodNode for WASM#132814
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	public override bool ShouldSkipEmittingObjectNode(NodeFactory factory)
	{
	// If the real body was marked, don't emit this assembly stub.
	return _methodNode.Marked;
	}

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