re PR c++/63942 (constexpr conflicts with previous declaration)

	PR c++/63942
	* name-lookup.c (supplement_binding_1): Override a mangling alias.
	* mangle.c (implicit_alias_p, remove_implicit_alias): New.
	(mangle_decl): Avoid creating conflicting alias with
	-fabi-compat-version=0, too.
	* cp-tree.h: Adjust.

From-SVN: r217950

gcc/cp/ChangeLog

 2014-11-21  Jason Merrill  <jason@redhat.com>
 
+	PR c++/63942
+	* name-lookup.c (supplement_binding_1): Override a mangling alias.
+	* mangle.c (maybe_remove_implicit_alias): New.
+	(mangle_decl): Always avoid creating conflicting alias.
+	* cp-tree.h: Adjust.
+
 	PR c++/63849
 	* mangle.c (decl_mangling_context): Use template_type_parameter_p.
 

gcc/cp/cp-tree.h

@@ -6299,6 +6299,7 @@ extern tree add_exception_specifier		(tree, tree, int);
 extern tree merge_exception_specifiers		(tree, tree);
 
 /* in mangle.c */
+extern bool maybe_remove_implicit_alias		(tree);
 extern void init_mangle				(void);
 extern void mangle_decl				(tree);
 extern const char *mangle_type_string		(tree);

gcc/cp/mangle.c

@@ -3428,6 +3428,28 @@ get_mangled_id (tree decl)
   return targetm.mangle_decl_assembler_name (decl, id);
 }
 
+/* If DECL is a mangling alias, remove it from the symbol table and return
+   true; otherwise return false.  */
+
+bool
+maybe_remove_implicit_alias (tree decl)
+{
+  if (DECL_P (decl) && DECL_ARTIFICIAL (decl)
+      && DECL_IGNORED_P (decl)
+      && (TREE_CODE (decl) == FUNCTION_DECL
+	  || (TREE_CODE (decl) == VAR_DECL
+	      && TREE_STATIC (decl))))
+    {
+      symtab_node *n = symtab_node::get (decl);
+      if (n && n->cpp_implicit_alias)
+	{
+	  n->remove();
+	  return true;
+	}
+    }
+  return false;
+}
+
 /* Create an identifier for the external mangled name of DECL.  */
 
 void
@@ -3491,8 +3513,9 @@ mangle_decl (const tree decl)
 	}
 
 #ifdef ASM_OUTPUT_DEF
-      if (flag_abi_compat_version != 0
-	  && IDENTIFIER_GLOBAL_VALUE (id2))
+      /* If there's a declaration already using this mangled name,
+	 don't create a compatibility alias that conflicts.  */
+      if (IDENTIFIER_GLOBAL_VALUE (id2))
 	return;
 
       tree alias = make_alias_for (decl, id2);

gcc/cp/name-lookup.c

@@ -561,6 +561,12 @@ supplement_binding_1 (cxx_binding *binding, tree decl)
       region to refer only to the namespace to which it already
       refers.  */
     ok = false;
+  else if (maybe_remove_implicit_alias (bval))
+    {
+      /* There was a mangling compatibility alias using this mangled name,
+	 but now we have a real decl that wants to use it instead.  */
+      binding->value = decl;
+    }
   else
     {
       diagnose_name_conflict (decl, bval);

gcc/testsuite/g++.dg/cpp0x/nullptr32.C

+// PR c++/63942
+// A mangling alias for the first constructor was conflicting with the second.
+// { dg-do compile { target c++11 } }
+// { dg-options "-fno-inline" }
+
+int i;
+template <class T> struct A
+{
+  A(const T&) { i = 42; }
+  A(const A&) { i = 36; }
+};
+
+typedef A<decltype(nullptr)> An;
+
+int main()
+{
+  An a (nullptr);
+  if (i != 42) __builtin_abort();
+  An a2 (a);
+  if (i != 36) __builtin_abort();
+}