[Docs][TypeMetadata] Type metadata is generated for targets other than x86-64 so remove the stale comments.

[mingmingl]

Hi, I modified triples to aarch64 ones in https://github.com/llvm/llvm-project/blob/main/clang/test/CodeGenCXX/type-metadata.cpp, and was able to get type metadata on the generated IR.

So send out this patch which seems outdated.

[pcc]

This should probably be replaced with a list of supported architectures instead.

[mingmingl]

In D149614#4310751, @pcc wrote:

This should probably be replaced with a list of supported architectures instead.

The code where vtable type metadata is annotated (https://github.com/llvm/llvm-project/blob/c9d14b23292979a9b3846cd55e2fc4d96b20f33f/clang/lib/CodeGen/CGVTables.cpp#L1328) doesn't seem to rely on target-specific information. May I get some input on where the x86_64 limitation is initially added (even if it's just an implementation artifact)?

A best-effort exhaustive test would tell the list of supported architectures currently but could become stale; so if there is no target-specific dependency, i wonder if 'the type metadata is generated on arch1, arch2.. and could be extended at <pointer> for other archs' (which I would need input with).

[pcc]

This is function type metadata, which uses a separate implementation to vtable type metadata that is platform-dependent. See LowerTypeTestsModule::createJumpTableEntry for the list of supported architectures.

[mingmingl]

In D149614#4310989, @pcc wrote:

This is function type metadata, which uses a separate implementation to vtable type metadata that is platform-dependent. See LowerTypeTestsModule::createJumpTableEntry for the list of supported architectures.

thanks! Just to make sure my understanding is correct,

• LowerTypeTests.cpp makes use of function type metadata to emit jump tables, and the support for jump table is platform-dependent (which makes sense).
• Assuming that function type metadata is generated in Clang (at this place https://github.com/llvm/llvm-project/blob/7dc5635d71ea919c933a6dc7c204d7bcfb8711b8/clang/lib/CodeGen/CodeGenModule.cpp#L2177), the generation of function type metadata doesn't seem to be platform dependent.

The reason to update this part is that type metadata exist in non x86-64 IR, and used in places more than creating jump-table entries. So I thought the update would be useful for availability of the metadata (more than the platform-dependent use of it).

[pcc]

What are we using function type metadata for besides CFI? I couldn't find any evidence of it being used for anything else.

llvm/docs/TypeMetadata.rst

 2. a metadata object representing an identifier for the type
 
 These metadata nodes are associated with globals by using global object
 metadata attachments with the ``!type`` metadata kind.
 
 Each type identifier must exclusively identify either global variables
 or functions.
 
-.. admonition:: Limitation
-
-  The current implementation only supports attaching metadata to functions on
-  the x86-32 and x86-64 architectures.
-
 An intrinsic, :ref:`llvm.type.test <type.test>`, is used to test whether a
 given pointer is associated with a type identifier.
 
 .. _control flow integrity: https://clang.llvm.org/docs/ControlFlowIntegrity.html
 
 Representing Type Information using Type Metadata
 =================================================