From e5995e61687673dca684914b774d1456160f1891 Mon Sep 17 00:00:00 2001
From: Michael Woerister <michaelwoerister@posteo>
Date: Fri, 27 Jan 2023 15:29:04 +0000
Subject: [PATCH] Don't merge vtables when full debuginfo is enabled.

---
 compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs | 5 +++++
 tests/codegen/debug-vtable.rs                         | 8 ++++++++
 2 files changed, 13 insertions(+)

diff --git a/compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs b/compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs
index b6eb5ee183fa3..f73bbf3d22bd7 100644
--- a/compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs
+++ b/compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs
@@ -1499,6 +1499,11 @@ pub fn create_vtable_di_node<'ll, 'tcx>(
         return;
     }
 
+    // When full debuginfo is enabled, we want to try and prevent vtables from being
+    // merged. Otherwise debuggers will have a hard time mapping from dyn pointer
+    // to concrete type.
+    llvm::SetUnnamedAddress(vtable, llvm::UnnamedAddr::No);
+
     let vtable_name =
         compute_debuginfo_vtable_name(cx.tcx, ty, poly_trait_ref, VTableNameKind::GlobalVariable);
     let vtable_type_di_node = build_vtable_type_di_node(cx, ty, poly_trait_ref);
diff --git a/tests/codegen/debug-vtable.rs b/tests/codegen/debug-vtable.rs
index bdd312878ec88..d82b737de0b41 100644
--- a/tests/codegen/debug-vtable.rs
+++ b/tests/codegen/debug-vtable.rs
@@ -9,6 +9,14 @@
 // compile-flags: -Cdebuginfo=2 -Copt-level=0 -Csymbol-mangling-version=v0
 // ignore-tidy-linelength
 
+// Make sure that vtables don't have the unnamed_addr attribute when debuginfo is enabled.
+// This helps debuggers more reliably map from dyn pointer to concrete type.
+// CHECK: @vtable.0 = private constant <{
+// CHECK: @vtable.1 = private constant <{
+// CHECK: @vtable.2 = private constant <{
+// CHECK: @vtable.3 = private constant <{
+// CHECK: @vtable.4 = private constant <{
+
 // NONMSVC: ![[USIZE:[0-9]+]] = !DIBasicType(name: "usize"
 // MSVC: ![[USIZE:[0-9]+]] = !DIDerivedType(tag: DW_TAG_typedef, name: "usize"
 // NONMSVC: ![[PTR:[0-9]+]] = !DIDerivedType(tag: DW_TAG_pointer_type, name: "*const ()"