[wasm][R2R] crossgen2 NotImplementedException in ModuleTokenResolver with --embed-pgo-data + --opt-cross-module #132825

Summary

crossgen2 aborts with an unhandled NotImplementedException when compiling browser-wasm ReadyToRun images that combine embedded PGO instrumentation data (--embed-pgo-data) with cross-module optimization (--opt-cross-module:*).

This blocks per-app R2R publish on any build leg where EnableNgenOptimization=true (e.g. the checked CI legs), because eng/codeOptimization.targets then sets IncludeMibcFilesInReadyToRun=true, feeds StandardOptimizationData.mibc, and appends --embed-pgo-data to the crossgen2 command line.

Repro

1. Build CoreCLR + libraries for browser-wasm with EnableNgenOptimization=true (the checked libraries legs qualify).
2. Publish a browser-wasm app with PublishReadyToRun=true so the crossgen2 command line includes both --embed-pgo-data and --opt-cross-module:*.
   • In CI this is the browser-wasm linux checked CoreCLR_ReleaseLibraries and browser-wasm windows checked CoreCLR_ReleaseLibraries legs.
3. crossgen2 crashes:

artifacts/bin/Crossgen2Tasks/Release/Microsoft.NET.CrossGen.targets(497,5): error MSB6006:
  ".../crossgen2" exited with code 134   (linux)   /   57005 (windows)
Microsoft.NET.CrossGen.targets(377,5): error NETSDK1096: Optimizing assemblies for performance failed.

Underlying exception (captured from a checked crossgen2 run):

System.NotImplementedException: [System.Text.Json]System.Text.Json.JsonDocument+<ReadToEndAsync>d__85
   at ...DependencyAnalysis.ReadyToRun.ModuleTokenResolver.GetModuleTokenForType(TypeDesc, bool, bool)
        in ModuleTokenResolver.cs:line 92
   at ...SignatureBuilder.EmitMethodSignature(...)
   at ...InstanceEntryPointTableNode.BuildSignatureForMethodDefinedInModule(MethodDesc, NodeFactory)
   at ...InstrumentationDataTableNode.GetData(NodeFactory, bool) in InstrumentationDataTableNode.cs:line 274
   at ...ReadyToRunObjectWriter.EmitReadyToRunObjects(...)

Root cause

InstrumentationDataTableNode.GetData emits a method signature for every method carrying PGO data via InstanceEntryPointTableNode.BuildSignatureForMethodDefinedInModule (InstrumentationDataTableNode.cs#L274). Building that signature resolves module tokens for the types referenced in the method's signature through ModuleTokenResolver.GetModuleTokenForType(type, allowDynamicallyCreatedReference, throwIfNotFound: true).

For a cross-module method whose signature references a type that has no token in any module of the cross-module compile group (here the async state machine System.Text.Json...JsonDocument+<ReadToEndAsync>d__85), every reverse-lookup branch fails and the resolver throws NotImplementedException (ModuleTokenResolver.cs#L90-L92).

Notes:

• Specific to the --embed-pgo-data + --opt-cross-module combination. The Release legs don't set EnableNgenOptimization, so they don't embed PGO and don't crash.
• Not a wasm-JIT NYI, so JitWasm{,Simd}NyiToR2RUnsupported does not help.
• There is no wasm-specific PGO profile — eng/codeOptimization.targets feeds the generic StandardOptimizationData.mibc for all targets, so the mibc contents are not the trigger; the emission path is.

Fix proposal

Make the instrumentation-data signature emitter tolerate a method whose signature can't be tokenized in the current cross-module group instead of hard-crashing:

• In the InstrumentationDataTableNode path, resolve tokens with throwIfNotFound: false and skip (drop the PGO entry for) any method whose signature can't be fully resolved; or
• Ensure the referenced types are added to the manifest / version-bubble module so a token exists; or
• Exclude such cross-module methods from the embedded PGO set up front.

Temporary workaround (applied on the wasm R2R branch)

Disable --embed-pgo-data / IncludeMibcFilesInReadyToRun for browser/wasi per-app R2R in eng/codeOptimization.targets (there is no wasm PGO profile to gain from), with a TODO linking to this issue. To be reverted once the crossgen2 fix above lands.