[mlir-translate] More specific error message for BlockAddress

[lafrance]

Summary

BlockAddress is currently unimplemented in the LLVM dialect of MLIR; when converting to LLVM dialect MLIR from LLVM IR, mlir-translate currently terminates with an "unhandled constant" error message. Instead, this message could be made more specific, to let the user know that the specific issue is that BlockAddress is unimplemented in the LLVM dialect.

First time contributor here so I'm happy to provide more detail or discussion if necessary -- wasn't sure how much to include for a change with such a simple implementation.

[ftynse]

Thank you for the patch! Please reupload with more context info (https://llvm.org/docs/Phabricator.html#requesting-a-review-via-the-web-interface) and address the review.

mlir/lib/Target/LLVMIR/ModuleImport.cpp

1066–1067

Please add a test for any user-visible error message.

1068

This should return failure() rather than null (which will be interpreted as success).

[lafrance]

@ftynse I saw that there was already a test that included blockaddress so I updated the error message there to provide coverage for the new message and changed my code to return a failure as it should; hopefully that should cover both comments in the review.

[lafrance]

Fixed formatting issues after changes introduced in the previous revision

mlir/lib/Target/LLVMIR/ModuleImport.cpp

     return root;
   }
 
+  if (isa<llvm::BlockAddress>(c)) {
+    emitError(unknownLoc)
+        << "blockaddress is not implemented in the LLVM dialect";
+    return nullptr;
+  }
+
   return emitError(loc) << "unhandled constant: " << diag(*constant);
 }