[MLIR][LLVM] Add function metadata to LLVMFuncOp

Add a generic LLVM dialect carrier for LLVM IR function metadata on LLVMFuncOp.
Represent attachments as an ordered list so repeated metadata kinds, such as
multiple type metadata attachments, can be preserved while keeping metadata names
language-agnostic.

mlir/include/mlir/Dialect/LLVMIR/LLVMAttrDefs.td

@@ -1810,6 +1810,28 @@ def LLVM_MDNodeArrayAttr
     : TypedArrayAttrBase<LLVM_MDNodeAttr,
                          "array of #llvm.md_node attributes">;
 
+def LLVM_FunctionMetadataAttr
+    : LLVM_Attr<"FunctionMetadata", "func_metadata"> {
+  let summary = "LLVM function metadata attachment";
+  let description = [{
+    Models one LLVM IR function metadata attachment. LLVM IR allows several
+    attachments with the same metadata kind, so function metadata is represented
+    as an ordered list of these entries instead of a dictionary.
+
+    Example:
+    ```mlir
+    #llvm.func_metadata<"type", <#llvm.md_string<"id">>>
+    ```
+  }];
+  let parameters = (ins "StringAttr":$metadataName, "MDNodeAttr":$node);
+  let assemblyFormat = "`<` $metadataName `,` $node `>`";
+  let genVerifyDecl = 1;
+}
+
+def LLVM_FunctionMetadataArrayAttr
+    : TypedArrayAttrBase<LLVM_FunctionMetadataAttr,
+                         "array of #llvm.func_metadata attributes">;
+
 def LLVM_AnyMDAttr : AnyAttrOf<[
     LLVM_MDStringAttr, LLVM_MDConstantAttr, LLVM_MDGlobalValueAttr,
     LLVM_MDNodeAttr],

mlir/include/mlir/Dialect/LLVMIR/LLVMOps.td

@@ -2077,6 +2077,7 @@ def LLVM_LLVMFuncOp : LLVM_Op<"func", [
     OptionalAttr<DenseI32ArrayAttr>:$work_group_size_hint,
     OptionalAttr<DenseI32ArrayAttr>:$reqd_work_group_size,
     OptionalAttr<I32Attr>:$intel_reqd_sub_group_size,
+    OptionalAttr<LLVM_FunctionMetadataArrayAttr>:$function_metadata,
     OptionalAttr<UWTableKindAttr>:$uwtable_kind,
     OptionalAttr<BoolAttr>:$use_sample_profile
   );

mlir/lib/Dialect/LLVMIR/IR/LLVMAttrs.cpp

@@ -135,6 +135,24 @@ bool AddressSpaceAttr::isValidPtrIntCast(
   return false;
 }
 
+//===----------------------------------------------------------------------===//
+// FunctionMetadataAttr
+//===----------------------------------------------------------------------===//
+
+LogicalResult
+FunctionMetadataAttr::verify(function_ref<InFlightDiagnostic()> emitError,
+                             StringAttr metadataName, MDNodeAttr node) {
+  (void)node;
+  StringRef name = metadataName.getValue();
+  if (name.empty())
+    return emitError() << "function_metadata entry name must not be empty";
+  if (name == "dbg" || name == "prof") {
+    return emitError() << "reserved function_metadata entry '" << name
+                       << "' must use a dedicated LLVM dialect representation";
+  }
+  return success();
+}
+
 //===----------------------------------------------------------------------===//
 // AliasScopeAttr
 //===----------------------------------------------------------------------===//

mlir/lib/Target/LLVMIR/ModuleTranslation.cpp

@@ -2063,6 +2063,9 @@ LogicalResult ModuleTranslation::convertFunctionSignatures() {
     llvmFunc->setLinkage(convertLinkageToLLVM(function.getLinkage()));
     llvmFunc->setCallingConv(convertCConvToLLVM(function.getCConv()));
     mapFunction(function.getName(), llvmFunc);
+    if (function.getFunctionMetadataAttr())
+      return function.emitError()
+             << "not yet implemented: translating function_metadata to LLVM IR";
     addRuntimePreemptionSpecifier(function.getDsoLocal(), llvmFunc);
 
     // Convert function attributes.

mlir/test/Dialect/LLVMIR/invalid.mlir

@@ -1847,6 +1847,26 @@ llvm.mlir.alias external @y5 : i32 {
 
 // -----
 
+// expected-error@+1{{attribute 'function_metadata' failed to satisfy constraint: array of #llvm.func_metadata attributes}}
+llvm.func @function_metadata_value() attributes {function_metadata = [#llvm.md_string<"int">]}
+
+// -----
+
+// expected-error@+1{{function_metadata entry name must not be empty}}
+llvm.func @empty_function_metadata_name() attributes {function_metadata = [#llvm.func_metadata<"", #llvm.md_node<#llvm.md_string<"x">>>]}
+
+// -----
+
+// expected-error@+1{{reserved function_metadata entry 'dbg' must use a dedicated LLVM dialect representation}}
+llvm.func @reserved_dbg_function_metadata() attributes {function_metadata = [#llvm.func_metadata<"dbg", #llvm.md_node<#llvm.md_string<"x">>>]}
+
+// -----
+
+// expected-error@+1{{reserved function_metadata entry 'prof' must use a dedicated LLVM dialect representation}}
+llvm.func @reserved_prof_function_metadata() attributes {function_metadata = [#llvm.func_metadata<"prof", #llvm.md_node<#llvm.md_string<"function_entry_count">, #llvm.md_const<1 : i64>>>]}
+
+// -----
+
 // expected-error@+1{{attribute 'nodes' failed to satisfy constraint: array of #llvm.md_node attributes}}
 llvm.named_metadata "not_node" [#llvm.md_string<"int">]
 

mlir/test/Dialect/LLVMIR/roundtrip.mlir

@@ -1244,3 +1244,25 @@ llvm.named_metadata "foo.kernel" [
     >
   >
 ]
+
+// CHECK-LABEL: llvm.func @generic_function_metadata
+// CHECK-SAME: function_metadata
+// CHECK-SAME: #llvm.func_metadata<"annotation", <#llvm.md_string<"function annotation">>>
+// CHECK-SAME: #llvm.func_metadata<"type", <#llvm.md_const<0 : i64>, #llvm.md_string<"typeid">>>
+llvm.func @generic_function_metadata() attributes {
+  function_metadata = [
+    #llvm.func_metadata<"annotation", #llvm.md_node<#llvm.md_string<"function annotation">>>,
+    #llvm.func_metadata<"type", #llvm.md_node<#llvm.md_const<0 : i64>, #llvm.md_string<"typeid">>>
+  ]
+}
+
+// CHECK-LABEL: llvm.func @repeated_function_metadata
+// CHECK-SAME: function_metadata
+// CHECK-SAME: #llvm.func_metadata<"type", <#llvm.md_const<0 : i64>, #llvm.md_string<"typeid0">>>
+// CHECK-SAME: #llvm.func_metadata<"type", <#llvm.md_const<0 : i64>, #llvm.md_string<"typeid1">>>
+llvm.func @repeated_function_metadata() attributes {
+  function_metadata = [
+    #llvm.func_metadata<"type", #llvm.md_node<#llvm.md_const<0 : i64>, #llvm.md_string<"typeid0">>>,
+    #llvm.func_metadata<"type", #llvm.md_node<#llvm.md_const<0 : i64>, #llvm.md_string<"typeid1">>>
+  ]
+}