[Mlir-commits] [mlir] [MLIR][LLVM] Support Recursive DITypes (PR #80251)

[Tobias Gysi]

================
@@ -301,6 +301,70 @@ def LLVM_DIExpressionAttr : LLVM_Attr<"DIExpression", "di_expression"> {
   let assemblyFormat = "`<` ( `[` $operations^ `]` ) : (``)? `>`";
 }
 
+//===----------------------------------------------------------------------===//
+// DIRecursiveTypeAttr
+//===----------------------------------------------------------------------===//
+
+def LLVM_DIRecursiveTypeAttr : LLVM_Attr<"DIRecursiveType", "di_recursive_type",
+                                    /*traits=*/[], "DITypeAttr"> {
+  let description = [{
+    This attribute enables recursive DITypes. There are two modes for this
+    attribute.
+
+    1. If `baseType` is present:
+      - This type is considered a recursive declaration (rec-decl).
+      - The `baseType` is a self-recursive type identified by the `id` field.
+
+    2. If `baseType` is not present:
+      - This type is considered a recursive self reference (rec-self).
+      - This DIRecursiveType itself is a placeholder type that should be
+        conceptually replaced with the closet parent DIRecursiveType with the
+        same `id` field.
+
+    e.g. To represent a linked list struct:
+
+      #rec_self = di_recursive_type<self_id = 0>
+      #ptr = di_derived_type<baseType: #rec_self, ...>
+      #field = di_derived_type<name = "next", baseType: #ptr, ...>
+      #struct = di_composite_type<name = "Node", elements: #field, ...>
+      #rec = di_recursive_type<self_id = 0, baseType: #struct>
+
+      #var = di_local_variable<type = #struct_type, ...>
+
+    Note that the a rec-self without an outer rec-decl with the same id is
+    conceptually the same as an "unbound" variable. The context needs to provide
+    meaning to the rec-self.
+
+    This can be avoided by calling the `getUnfoldedBaseType()` method on a
+    rec-decl, which returns the `baseType` with all matching rec-self instances
+    replaced with this rec-decl again. This is useful, for example, for fetching
+    a field out of a recursive struct and maintaining the legality of the field
+    type.
+  }];
+
+  let parameters = (ins
+    "DistinctAttr":$id,
----------------
gysit wrote:

In other places, we use "DistinctAttr":$id to mark specific attributes as distinct in the LLVM sense. Here we use the id in a slightly different context. Do you know if a recursive composite type is always distinct? I guess so looking at the logic in DebugTranslation.cpp.

https://github.com/llvm/llvm-project/pull/80251