[mlir][debuginfo] Add support for subroutine annotations

LLVM already supports `DW_TAG_LLVM_annotation` entries for subroutines, but this hasn't been surfaced to the LLVM dialect.
I'm doing the minimal amount of work to support string-based annotations, which is useful for attaching metadata to
functions, which is useful for debuggers to offer features beyond basic DWARF.
As LLVM already supports this, this patch is not controversial.

Author: walter erquinigo

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

@@ -586,19 +586,20 @@ def LLVM_DISubprogramAttr : LLVM_Attr<"DISubprogram", "di_subprogram",
     OptionalParameter<"unsigned">:$scopeLine,
     OptionalParameter<"DISubprogramFlags">:$subprogramFlags,
     OptionalParameter<"DISubroutineTypeAttr">:$type,
-    OptionalArrayRefParameter<"DINodeAttr">:$retainedNodes
+    OptionalArrayRefParameter<"DINodeAttr">:$retainedNodes,
+    OptionalArrayRefParameter<"DINodeAttr">:$annotations
   );
   let builders = [
     AttrBuilder<(ins
       "DistinctAttr":$id, "DICompileUnitAttr":$compileUnit,
       "DIScopeAttr":$scope, "StringAttr":$name, "StringAttr":$linkageName,
       "DIFileAttr":$file, "unsigned":$line, "unsigned":$scopeLine,
       "DISubprogramFlags":$subprogramFlags, "DISubroutineTypeAttr":$type,
-      "ArrayRef<DINodeAttr>":$retainedNodes
+      "ArrayRef<DINodeAttr>":$retainedNodes, "ArrayRef<DINodeAttr>":$annotations
     ), [{
       return $_get($_ctxt, /*recId=*/nullptr, /*isRecSelf=*/false, id, compileUnit,
                    scope, name, linkageName, file, line, scopeLine,
-                   subprogramFlags, type, retainedNodes);
+                   subprogramFlags, type, retainedNodes, annotations);
     }]>
   ];
   let assemblyFormat = "`<` struct(params) `>`";
@@ -670,6 +671,21 @@ def LLVM_DIImportedEntityAttr : LLVM_Attr<"DIImportedEntity", "di_imported_entit
   let assemblyFormat = "`<` struct(params) `>`";
 }
 
+//===----------------------------------------------------------------------===//
+// DIStringAnnotationAttr
+//===----------------------------------------------------------------------===//
+
+def LLVM_DIStringAnnotationAttr : LLVM_Attr<"DIStringAnnotation",
+                                            "di_string_annotation",
+                                           /*traits=*/[], "DINodeAttr"> {
+  let parameters = (ins
+    "StringAttr":$name,
+    "StringAttr":$value
+  );
+
+  let assemblyFormat = "`<` struct(params) `>`";
+}
+
 //===----------------------------------------------------------------------===//
 // DISubrangeAttr
 //===----------------------------------------------------------------------===//

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

@@ -60,9 +60,9 @@ bool DINodeAttr::classof(Attribute attr) {
                    DIDerivedTypeAttr, DIFileAttr, DIGlobalVariableAttr,
                    DIImportedEntityAttr, DILabelAttr, DILexicalBlockAttr,
                    DILexicalBlockFileAttr, DILocalVariableAttr, DIModuleAttr,
-                   DINamespaceAttr, DINullTypeAttr, DIStringTypeAttr,
-                   DISubprogramAttr, DISubrangeAttr, DISubroutineTypeAttr>(
-      attr);
+                   DINamespaceAttr, DINullTypeAttr, DIStringAnnotationAttr,
+                   DIStringTypeAttr, DISubprogramAttr, DISubrangeAttr,
+                   DISubroutineTypeAttr>(attr);
 }
 
 //===----------------------------------------------------------------------===//
@@ -221,15 +221,16 @@ DICompositeTypeAttr::getRecSelf(DistinctAttr recId) {
 //===----------------------------------------------------------------------===//
 
 DIRecursiveTypeAttrInterface DISubprogramAttr::withRecId(DistinctAttr recId) {
-  return DISubprogramAttr::get(
-      getContext(), recId, getIsRecSelf(), getId(), getCompileUnit(),
-      getScope(), getName(), getLinkageName(), getFile(), getLine(),
-      getScopeLine(), getSubprogramFlags(), getType(), getRetainedNodes());
+  return DISubprogramAttr::get(getContext(), recId, getIsRecSelf(), getId(),
+                               getCompileUnit(), getScope(), getName(),
+                               getLinkageName(), getFile(), getLine(),
+                               getScopeLine(), getSubprogramFlags(), getType(),
+                               getRetainedNodes(), getAnnotations());
 }
 
 DIRecursiveTypeAttrInterface DISubprogramAttr::getRecSelf(DistinctAttr recId) {
   return DISubprogramAttr::get(recId.getContext(), recId, /*isRecSelf=*/true,
-                               {}, {}, {}, {}, {}, 0, 0, {}, {}, {}, {});
+                               {}, {}, {}, {}, {}, 0, 0, {}, {}, {}, {}, {});
 }
 
 //===----------------------------------------------------------------------===//

mlir/lib/Dialect/LLVMIR/Transforms/DIScopeForLLVMFuncOp.cpp

@@ -78,7 +78,7 @@ static void addScopeToFunction(LLVM::LLVMFuncOp llvmFunc,
   auto subprogramAttr = LLVM::DISubprogramAttr::get(
       context, id, compileUnitAttr, fileAttr, funcName, funcName, fileAttr,
       /*line=*/line, /*scopeline=*/col, subprogramFlags, subroutineTypeAttr,
-      /*retainedNodes=*/{});
+      /*retainedNodes=*/{}, /*annotations=*/{});
   llvmFunc->setLoc(FusedLoc::get(context, {loc}, subprogramAttr));
 }
 

mlir/lib/Target/LLVMIR/DebugTranslation.cpp

@@ -102,6 +102,13 @@ DebugTranslation::getMDTupleOrNull(ArrayRef<DINodeAttr> elements) {
     return nullptr;
   SmallVector<llvm::Metadata *> llvmElements = llvm::to_vector(
       llvm::map_range(elements, [&](DINodeAttr attr) -> llvm::Metadata * {
+        if (DIStringAnnotationAttr annAttr =
+                dyn_cast<DIStringAnnotationAttr>(attr)) {
+          llvm::Metadata *ops[2] = {
+              llvm::MDString::get(llvmCtx, annAttr.getName()),
+              llvm::MDString::get(llvmCtx, annAttr.getValue())};
+          return llvm::MDNode::get(llvmCtx, ops);
+        }
         return translate(attr);
       }));
   return llvm::MDNode::get(llvmCtx, llvmElements);
@@ -332,7 +339,8 @@ llvm::DISubprogram *DebugTranslation::translateImpl(DISubprogramAttr attr) {
       /*ThisAdjustment=*/0, llvm::DINode::FlagZero,
       static_cast<llvm::DISubprogram::DISPFlags>(attr.getSubprogramFlags()),
       compileUnit, /*TemplateParams=*/nullptr, /*Declaration=*/nullptr,
-      getMDTupleOrNull(attr.getRetainedNodes()));
+      getMDTupleOrNull(attr.getRetainedNodes()), nullptr,
+      getMDTupleOrNull(attr.getAnnotations()));
   if (attr.getId())
     distinctAttrToNode.try_emplace(attr.getId(), node);
   return node;