Add CORINFO_HELP_TYPEHANDLE_TO_RUNTIMETYPE_MAYBENULL to ReadyToRun

[adamperlin]

Fixes #132185.
CORINFO_HELP_TYPEHANDLE_TO_RUNTIMETYPE_MAYBENULL does not exist on ReadyToRun and crossgen will throw a RequiresRuntimeJit exception if the helper is requested. CORINFO_HELP_TYPEHANDLE_TO_RUNTIMETYPE (non-null handling variant) exists already though, so this PR adds a fixup kind to expose the MAYBENULL variant for R2R for platforms like Wasm which don't have a runtime JIT.

Validation

refanytype1.il has been updated to:

1. Ensure non-null TypedReference still works as expected
2. Ensure CORINFO_HELP_TYPEHANDLE_TO_RUNTIMETYPEHANDLE_MAYBENULL(default(TypedReference)) = default(TypedReference)
3. Ensure CORINFO_HELP_TYPEHANDLE_TO_RUNTIMETYPE_MAYBENULL(default(TypedReference))) = null

Use __reftype(TypedReference) to trigger the use of CORINFO_HELP_TYPEHANDLE_TO_RUNTIMETYPE_MAYBENULL and assert that the containing method exists in the Wasm R2R image.

Note

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Pull request overview

Adds a ReadyToRun (R2R) helper/fixup kind for the CORINFO_HELP_TYPEHANDLE_TO_RUNTIMETYPE_MAYBENULL family so Crossgen2 can emit/resolve it during R2R compilation (notably for Wasm targets without a runtime JIT), avoiding RequiresRuntimeJit failures when importing patterns like refanytype + Type.GetTypeFromHandle.

Changes:

• Introduces ReadyToRunHelper.GetRuntimeTypeHandleMaybeNull (0x57) across CoreCLR headers and tooling, and bumps the R2R minor version to 26.2.
• Updates the R2R JIT-EE (CorInfoImpl.ReadyToRun) to map *_MAYBENULL TypeHandle→RuntimeType helpers to the new R2R helper cell instead of throwing RequiresRuntimeJitException.
• Extends test coverage: updates the importer IL test and adds a Wasm Webcil R2R test that ensures a __reftype(TypedReference) path compiles into the Wasm R2R image.

Reviewed changes

Copilot reviewed 9 out of 10 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/tests/JIT/Directed/coverage/importer/refanytype1.il	Extends IL test to exercise non-null and default TypedReference paths and trigger the MAYBENULL helper.
src/coreclr/tools/Common/Internal/Runtime/ReadyToRunConstants.cs	Adds the new ReadyToRunHelper enum value used by tooling.
src/coreclr/tools/Common/Internal/Runtime/ModuleHeaders.cs	Bumps R2R header minor version to 26.2 for managed tooling.
src/coreclr/tools/aot/ILCompiler.Reflection.ReadyToRun/ReadyToRunSignature.cs	Teaches signature pretty-printer to decode/display the new helper.
src/coreclr/tools/aot/ILCompiler.ReadyToRun/JitInterface/CorInfoImpl.ReadyToRun.cs	Maps the MAYBENULL helpers to the new R2R helper cell and removes the runtime-JIT-only classification.
src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCases/Webcil/WasmWebcilModule.cs	Adds a method using __reftype to ensure the helper is requested during Wasm R2R compilation.
src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCases/R2RTestSuites.cs	Validates the new Webcil method is compiled into the Wasm R2R image.
src/coreclr/nativeaot/Runtime/inc/ModuleHeaders.h	Bumps R2R header minor version to 26.2 for NativeAOT runtime.
src/coreclr/inc/readytorunhelpers.h	Adds the new helper mapping in the CoreCLR R2R helper table.
src/coreclr/inc/readytorun.h	Bumps R2R minor version constant and adds the new helper enum value in native headers.

[EgorBo]

Not for this PR, but I think all _MAYBENULL variants should be removed. JIT should just emit a quick nullcheck itself (we would be able to constant fold it then). e.g.

CORINFO_HELP_TYPEHANDLE_TO_RUNTIMETYPE_MAYBENULL(handle)

to

handle == 0 ? null : CORINFO_HELP_TYPEHANDLE_TO_RUNTIMETYPE(handle)

[adamperlin]

Not for this PR, but I think all _MAYBENULL variants should be removed. JIT should just emit a quick nullcheck itself (we would be able to constant fold it then). e.g.

That seems like a good idea. I opened a tracking issue!

EDIT: Closed, I see you already did!

[jkotas]

all _MAYBENULL variants should be removed. JIT should just emit a quick nullcheck itself

Can we do this instead? Once we add the helper for R2R, it is going to be around forever.

[adamperlin]

all _MAYBENULL variants should be removed. JIT should just emit a quick nullcheck itself

Can we do this instead? Once we add the helper for R2R, it is going to be around forever.

Yeah, that is a good point. It seems reasonable to do now instead of adding the helper. I'll close this and instead prioritize removing the MAYBENULL variants.