Add method-list MIBC writer to dotnet-pgo

[lewing]

Summary

• add dotnet-pgo create-mibc-from-method-list for constructing deterministic profile root sets from JSON
• resolve assembly-qualified declaring, parameter, and generic argument types through an Ecma-backed type-system context
• reject invalid JSON, missing references, unresolved or ambiguous methods, wrong generic arity, duplicate entries, open generic types, and non-.mibc output
• document the JSON format and add focused end-to-end tests, including MIBC dump round-tripping and input-order determinism

This is an exploratory, general-purpose profile-rooting tool motivated by the scenarios discussed in #132825. It does not claim to resolve that issue.

The tool supports controlled differential ReadyToRun investigations without collecting a trace or hand-authoring MIBC IL. It has already been used to:

• root MemoryExtensions.Contains<int> through PublishReadyToRunPgoFiles, proving the profile was accepted and the compiled body was emitted while live execution still entered WasmR2RToInterpreterThunk; this isolated the problem to closed-generic dispatch/adapter behavior rather than missing rooting
• root Delegate.CtorOpen and Delegate.CtorClosed, proving that adding the compiled bodies did not change delegate construction dispatch or timing and ruling out missing bodies as the cause of [wasm][coreclr][R2R] Delegate construction skips alternate-constructor lowering and remains interpreted #134564

This tool is not needed as a workaround for automatic hardware-intrinsic rooting in partial no-JIT compilations; #134030 fixed that behavior.

Validation

• ./dotnet.sh test src/coreclr/tools/dotnet-pgo/tests/dotnet-pgo.Tests.csproj -c Debug — 7 passed
• ./dotnet.sh test src/coreclr/tools/dotnet-pgo/tests/dotnet-pgo.Tests.csproj -c Release — 7 passed
• repeated default compressed generation after a delay produced identical SHA-256 hashes
• an assembly-qualified array signature continued to resolve successfully
• a constructed generic type with an unqualified generic argument was rejected

Note

This pull request description was generated with GitHub Copilot.

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[Copilot]

Copilot review overview

🟡 Changes recommended

Critical emission failures can be reported as success, and array and generic type handling remains incomplete.

Get a fresh assessment by requesting another Copilot review.

Review effort: Lite
Findings: 2

Open (2)

• Fail when requested methods are omitted during emission · New
• Keep emission validation enabled for complete method roots · New

What changed in this PR

Adds dotnet-pgo create-mibc-from-method-list for deterministic MIBC root generation from JSON.

Changes:

• Adds Ecma-backed type and method resolution.
• Adds deterministic MIBC emission and CLI integration.
• Adds documentation, end-to-end tests, and build integration.
• Review found unresolved critical validation and type-handling issues.

File	Summary
src/​coreclr/​tools/​dotnet-pgo/​tests/​MethodListMibcTests.cs	End-to-end method-list and round-trip tests.
src/​coreclr/​tools/​dotnet-pgo/​tests/​dotnet-pgo.Tests.csproj	Defines the test project.
src/​coreclr/​tools/​dotnet-pgo/​README.md	Documents the command and JSON format.
src/​coreclr/​tools/​dotnet-pgo/​Program.cs	Dispatches the new command.
src/​coreclr/​tools/​dotnet-pgo/​PgoRootCommand.cs	Registers command options and output handling.
src/​coreclr/​tools/​dotnet-pgo/​MibcEmitter.cs	Provides deterministic compressed output.
src/​coreclr/​tools/​dotnet-pgo/​MethodListTypeSystemContext.cs	Loads reference assemblies for resolution.
src/​coreclr/​tools/​dotnet-pgo/​MethodListMibcWriter.cs	Resolves methods and emits MIBC roots; requires fixes for emission failures, array methods, and generic constraints.
src/​coreclr/​tools/​dotnet-pgo/​dotnet-pgo.csproj	Excludes test sources from the tool.
src/​coreclr/​tools/​Common/​TypeSystem/​Common/​Utilities/​CustomAttributeTypeNameParser.cs	Parses assembly-qualified type names; array, pointer, and byref qualification handling requires correction.
eng/​Subsets.props	Registers the tests in the CLR tools subset.

[Copilot]

Copilot review overview

🔵 Needs a closer look

Address generic-constraint validation, synthetic declaring-type handling, culture-independent ordering, and the test pipe-read deadlock.

Review effort: Lite
Findings: None

Resolved since last review (2)

• Keep emission validation enabled for complete method roots
• Fail when requested methods are omitted during emission

Previously missed (1)

In code that hasn't changed since last review

Validate generic constraints on instantiated methods

src/​coreclr/​tools/​dotnet-pgo/​MethodListMibcWriter.cs:174

MakeInstantiatedMethod only creates an instantiated descriptor; it does not validate generic constraints (the type system explicitly calls CheckConstraints() after instantiation in src/coreclr/tools/Common/TypeSystem/IL/UnsafeAccessors.cs:407-414). As written, a method list can pass an invalid class/struct/new()/interface argument and this command will accept and emit an invalid MIBC root. Reject candidates whose instantiated method fails CheckConstraints() and add a regression case for an invalid method generic argument.

This issue also appears on line 226 of the same file.

[lewing]

/ba-g ssl errors are tracked