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

[Billy Zhu]

================
@@ -342,3 +342,63 @@ llvm.func @func_line_tables() {
 llvm.func @func_debug_directives() {
   llvm.return
 } loc(fused<#di_subprogram_2>["foo2.mlir":0:0])
+
+// -----
+
+// Ensure recursive types with multiple external references work.
+
+// Common base nodes.
+#di_file = #llvm.di_file<"test.mlir" in "/">
+#di_null_type = #llvm.di_null_type
+#di_compile_unit = #llvm.di_compile_unit<id = distinct[1]<>, sourceLanguage = DW_LANG_C, file = #di_file, isOptimized = false, emissionKind = None>
+
+// Recursive type itself.
+#di_rec_self = #llvm.di_recursive_type<id = distinct[0]<>>
+#di_ptr_inner = #llvm.di_derived_type<tag = DW_TAG_pointer_type, baseType = #di_rec_self, sizeInBits = 64>
+#di_subroutine_inner = #llvm.di_subroutine_type<types = #di_null_type, #di_ptr_inner>
+#di_subprogram_inner = #llvm.di_subprogram<
+  id = distinct[2]<>,
+  compileUnit = #di_compile_unit,
+  scope = #di_rec_self,
+  name = "class_method",
+  file = #di_file,
+  subprogramFlags = Definition,
+  type = #di_subroutine_inner>
+#di_struct = #llvm.di_composite_type<
+  tag = DW_TAG_class_type,
+  name = "class_name",
+  file = #di_file,
+  line = 42,
+  flags = "TypePassByReference|NonTrivial",
+  elements = #di_subprogram_inner>
+#di_rec_struct = #llvm.di_recursive_type<id = distinct[0]<>, baseType = #di_struct>
+
+// Outer types referencing the entire recursive type.
+#di_ptr_outer = #llvm.di_derived_type<tag = DW_TAG_pointer_type, baseType = #di_rec_struct, sizeInBits = 64>
+#di_subroutine_outer = #llvm.di_subroutine_type<types = #di_null_type, #di_ptr_outer>
+#di_subprogram_outer = #llvm.di_subprogram<
+  id = distinct[2]<>,
+  compileUnit = #di_compile_unit,
+  scope = #di_rec_struct,
----------------
zyx-billy wrote:

yeah that's right. `#di_rec_self` can only occur inside `#di_rec_struct`. Since the rec_self is given meaning by the surrounding rec-type with the same id, it requires anyone traversing DI attrs to maintain a "context" dictionary, and it's illegal if it's possible to visit a rec_self without its id already in the context. If we ever write a legalization pass, this is what it'll check.

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