[DirectX] Use an allowlist for DXIL-compatible module metadata

[inbelic]

At the moment there is no filter to remove any module metadata that is unrecognized by the LLVM 3.7 DXIL validator.

This results in clang producing invalid DXIL whenever a new type of module metadata is generated. To prevent this proactively we should create an allowlist that will filter out any unrecognized metadata during the DXILTranslateMetadata pass.

Please see #164472 for additional context.

From comments:

It appears the only known llvm metadata is llvm.ident and llvm.module.flags (debug is separate). All others would cause a validation error.

This is from here and here/here.

AC:

• Investigate and find all the module metadata that the DXIL validator is expecting to deal with (2 from above)
• Create the allowlist from this and add it to the DXILTranslateMetadata
• Ensure that there is sufficient testing of all metadata on the allowlist so that any upstream updates to produce invalid DXIL is detected

[tex3d]

Note: We need allowlists for both global named metadata and instruction metadata.

[inbelic]

Note: We need allowlists for both global named metadata and instruction metadata.

Yes, the allow list for instruction metadata was added here #134575 and edits to it are tracked here; llvm/wg-hlsl#263

[inbelic]

It appears the only known llvm metadata is llvm.ident and llvm.module.flags (debug is separate). All others would cause a validation error.

This is from here and here/here.

From checking both the Verifier.cpp file in DXC and upstream, all valid metadata from upstream will be valid now. We will require add tests to ensure that if this changes we will detect it.

As a separate issue, we should add the currently unused dx. named metadata options, here, that aren't generated in clang