[llvm] [dsymutil] Fix linker's ODR uniquing for typedefs with different underlying types (PR #195749)

[via llvm-commits]

================
@@ -116,6 +116,28 @@ DeclContextTree::getChildDeclContext(DeclContext &Context, const DWARFDie &DIE,
     NameForUniquing = StringPool.internString(FullName ? *FullName : Name);
   }
 
+  // For typedefs, include the referenced type's tag and name in the uniquing
+  // key. Two typedefs with the same name (e.g. from preferred_name) but
+  // different DW_AT_type targets must get different DeclContexts, otherwise
+  // ODR deduplication can create self-referencing typedef cycles in the output
+  // DWARF. This mirrors the parallel linker fix in the parallel linker:
+  // https://github.com/llvm/llvm-project/pull/166767
+  if (Tag == dwarf::DW_TAG_typedef && !NameForUniquing.empty()) {
+    if (auto TypeAttr = DIE.find(dwarf::DW_AT_type)) {
+      if (auto RefDie = DIE.getAttributeValueAsReferencedDie(*TypeAttr)) {
+        StringRef RefName = RefDie.getShortName();
----------------
alx32 wrote:

Could this still miss typedefs through unnamed wrapper types, like `FooA *` vs `FooB *`, since `DW_TAG_pointer_type` has no short name here? It seems the parallel linker handles this by recursively adding referenced ODR DIE names and wrapper type prefixes in [`SyntheticTypeNameBuilder`](https://github.com/llvm/llvm-project/blob/main/llvm/lib/DWARFLinker/Parallel/SyntheticTypeNameBuilder.cpp#L276-L305) and [`addTypePrefix`](https://github.com/llvm/llvm-project/blob/main/llvm/lib/DWARFLinker/Parallel/SyntheticTypeNameBuilder.cpp#L433-L570).

https://github.com/llvm/llvm-project/pull/195749