[mlir][debuginfo] Add support for subprogram annotations (#110946)

LLVM already supports `DW_TAG_LLVM_annotation` entries for subprograms,
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-c/Dialect/LLVM.h

@@ -325,7 +325,12 @@ MLIR_CAPI_EXPORTED MlirAttribute mlirLLVMDISubprogramAttrGet(
     MlirAttribute compileUnit, MlirAttribute scope, MlirAttribute name,
     MlirAttribute linkageName, MlirAttribute file, unsigned int line,
     unsigned int scopeLine, uint64_t subprogramFlags, MlirAttribute type,
-    intptr_t nRetainedNodes, MlirAttribute const *retainedNodes);
+    intptr_t nRetainedNodes, MlirAttribute const *retainedNodes,
+    intptr_t nAnnotations, MlirAttribute const *annotations);
+
+/// Creates a LLVM DIAnnotation attribute.
+MLIR_CAPI_EXPORTED MlirAttribute mlirLLVMDIAnnotationAttrGet(
+    MlirContext ctx, MlirAttribute name, MlirAttribute value);
 
 /// Gets the scope from this DISubprogramAttr.
 MLIR_CAPI_EXPORTED MlirAttribute

mlir/lib/CAPI/Dialect/LLVM.cpp

@@ -303,9 +303,14 @@ MlirAttribute mlirLLVMDISubprogramAttrGet(
     MlirAttribute compileUnit, MlirAttribute scope, MlirAttribute name,
     MlirAttribute linkageName, MlirAttribute file, unsigned int line,
     unsigned int scopeLine, uint64_t subprogramFlags, MlirAttribute type,
-    intptr_t nRetainedNodes, MlirAttribute const *retainedNodes) {
+    intptr_t nRetainedNodes, MlirAttribute const *retainedNodes,
+    intptr_t nAnnotations, MlirAttribute const *annotations) {
   SmallVector<Attribute> nodesStorage;
   nodesStorage.reserve(nRetainedNodes);
+
+  SmallVector<Attribute> annotationsStorage;
+  annotationsStorage.reserve(nAnnotations);
+
   return wrap(DISubprogramAttr::get(
       unwrap(ctx), cast<DistinctAttr>(unwrap(recId)), isRecSelf,
       cast<DistinctAttr>(unwrap(id)),
@@ -316,6 +321,9 @@ MlirAttribute mlirLLVMDISubprogramAttrGet(
       cast<DISubroutineTypeAttr>(unwrap(type)),
       llvm::map_to_vector(
           unwrapList(nRetainedNodes, retainedNodes, nodesStorage),
+          [](Attribute a) { return cast<DINodeAttr>(a); }),
+      llvm::map_to_vector(
+          unwrapList(nAnnotations, annotations, annotationsStorage),
           [](Attribute a) { return cast<DINodeAttr>(a); })));
 }
 
@@ -375,3 +383,9 @@ MlirAttribute mlirLLVMDIImportedEntityAttrGet(
       llvm::map_to_vector(unwrapList(nElements, elements, elementsStorage),
                           [](Attribute a) { return cast<DINodeAttr>(a); })));
 }
+
+MlirAttribute mlirLLVMDIAnnotationAttrGet(MlirContext ctx, MlirAttribute name,
+                                          MlirAttribute value) {
+  return wrap(DIAnnotationAttr::get(unwrap(ctx), cast<StringAttr>(unwrap(name)),
+                                    cast<StringAttr>(unwrap(value))));
+}