--- gcc/cp/decl2.cc.jj	2024-04-23 14:49:41.933186265 +0200
+++ gcc/cp/decl2.cc	2024-04-24 15:17:09.043625729 +0200
@@ -3314,7 +3314,16 @@ tentative_decl_linkage (tree decl)
 	     to mark the functions at this point.  */
 	  if (DECL_DECLARED_INLINE_P (decl)
 	      && (!DECL_IMPLICIT_INSTANTIATION (decl)
-		  || DECL_DEFAULTED_FN (decl)))
+		  || DECL_DEFAULTED_FN (decl)
+		  /* For implicit instantiations of cdtors,
+		     if import_export_decl would use comdat linkage,
+		     make sure to use it right away, so that maybe_clone_body
+		     can use aliases.  See PR113208.  */
+		  || (DECL_MAYBE_IN_CHARGE_CDTOR_P (decl)
+		      && (flag_implicit_templates
+			  || flag_implicit_inline_templates)
+		      && flag_weak
+		      && TARGET_SUPPORTS_ALIASES)))
 	    {
 	      /* This function must have external linkage, as
 		 otherwise DECL_INTERFACE_KNOWN would have been
--- gcc/cp/optimize.cc.jj	2024-04-24 13:44:26.456634100 +0200
+++ gcc/cp/optimize.cc	2024-04-24 14:46:13.050371557 +0200
@@ -717,6 +717,10 @@ maybe_clone_body (tree fn)
       else
 	expand_or_defer_fn (clone);
       first = false;
+      if (DECL_INTERFACE_KNOWN (fn)
+	  && DECL_NOT_REALLY_EXTERN (fn)
+	  && DECL_DEFER_OUTPUT (fn))
+	note_vague_linkage_fn (clone);
     }
   pop_from_top_level ();
 
--- gcc/cp/decl.cc.jj	2024-04-23 08:31:05.515161033 +0200
+++ gcc/cp/decl.cc	2024-04-24 15:15:34.401951491 +0200
@@ -19254,6 +19254,14 @@ cxx_comdat_group (tree decl)
 	  else
 	    break;
 	}
+      /* If a ctor/dtor has already set the comdat group by
+	 maybe_clone_body, don't override it.  */
+      if (SUPPORTS_ONE_ONLY
+	  && TREE_CODE (decl) == FUNCTION_DECL
+	  && DECL_CLONED_FUNCTION_P (decl)
+	  && SUPPORTS_ONE_ONLY)
+	if (tree comdat = DECL_COMDAT_GROUP (decl))
+	  return comdat;
     }
 
   return decl;
--- gcc/testsuite/g++.dg/abi/comdat2.C.jj	2024-04-24 13:44:11.054849035 +0200
+++ gcc/testsuite/g++.dg/abi/comdat2.C	2024-04-24 13:44:11.054849035 +0200
@@ -0,0 +1,26 @@
+// PR lto/113208
+// { dg-do compile { target { c++11 && { *-*-*gnu* } } } }
+// { dg-additional-options "-O2 -fkeep-inline-functions" }
+// { dg-final { scan-assembler "_ZN1BI1CEC5ERKS1_,comdat" } }
+// { dg-final { scan-assembler-not "_ZN1BI1CEC1ERKS1_,comdat" } }
+// { dg-final { scan-assembler-not "_ZN1BI1CEC2ERKS1_,comdat" } }
+
+template <typename T>
+struct A {
+  int foo () const;
+  A (int, int);
+};
+template <typename T>
+struct B : A<T> {
+  constexpr B (const B &x) : A<T> (1, x.foo ()) {}
+  B () : A<T> (1, 2) {}
+};
+struct C;
+struct D : B<C> {};
+void bar (D);
+
+void
+baz (D x)
+{
+  bar (x);
+}
--- gcc/testsuite/g++.dg/abi/comdat3.C.jj	2024-04-24 15:23:58.829885362 +0200
+++ gcc/testsuite/g++.dg/abi/comdat3.C	2024-04-24 15:24:46.088223353 +0200
@@ -0,0 +1,22 @@
+// PR lto/113208
+// { dg-do compile { target { c++11 && { *-*-*gnu* } } } }
+// { dg-additional-options "-O2" }
+// { dg-final { scan-assembler "_ZN1M1SINS_1P1TELN1N1LE2EEC5Ev,comdat" } }
+// { dg-final { scan-assembler-not "_ZN1M1SINS_1P1TELN1N1LE2EEC1Ev,comdat" } }
+// { dg-final { scan-assembler-not "_ZN1M1SINS_1P1TELN1N1LE2EEC2Ev,comdat" } }
+
+namespace N { enum L { L1, L2, L3 } const O = L3; }
+namespace M {
+  using N::O;
+  using N::L;
+  template <typename, L = O>
+  struct S { constexpr S () {} };
+  namespace P {
+    struct T;
+    struct U { S<T> u; };
+    void foo () { U (); }
+  }
+  extern template class S<P::T>;
+}
+namespace p = M::P;
+template class M::S<p::T>;
--- gcc/testsuite/g++.dg/lto/pr113208_0.C.jj	2024-04-24 13:43:17.887591040 +0200
+++ gcc/testsuite/g++.dg/lto/pr113208_0.C	2024-04-24 13:44:11.055849021 +0200
@@ -0,0 +1,13 @@
+// { dg-lto-do link }
+// { dg-lto-options { {-O1 -std=c++20 -flto}} }
+// { dg-extra-ld-options "-r -nostdlib -flinker-output=nolto-rel" }
+// { dg-require-linker-plugin "" }
+
+#define CONSTEXPR constexpr
+#include "pr113208.h"
+
+struct QualityValue;
+struct k : vector<QualityValue> {};
+
+void m(k);
+void n(k i) { m(i); }
--- gcc/testsuite/g++.dg/lto/pr113208_1.C.jj	2024-04-24 13:43:17.887591040 +0200
+++ gcc/testsuite/g++.dg/lto/pr113208_1.C	2024-04-24 13:44:11.055849021 +0200
@@ -0,0 +1,6 @@
+#define CONSTEXPR 
+#include "pr113208.h"
+
+struct QualityValue;
+vector<QualityValue> values1;
+vector<QualityValue> values{values1};
--- gcc/testsuite/g++.dg/lto/pr113208.h.jj	2024-04-24 13:43:17.887591040 +0200
+++ gcc/testsuite/g++.dg/lto/pr113208.h	2024-04-24 13:44:11.054849035 +0200
@@ -0,0 +1,10 @@
+template <typename _Tp> struct _Vector_base {
+  int g() const;
+  _Vector_base(int, int);
+};
+template <typename _Tp>
+struct vector : _Vector_base<_Tp> {
+  CONSTEXPR vector(const vector &__x)
+      : _Vector_base<_Tp>(1, __x.g()) {}
+ vector() : _Vector_base<_Tp>(1, 2) {}
+};
