[C++/84812] ICE with local fn decl

https://gcc.gnu.org/ml/gcc-patches/2018-03/msg00872.html
	PR c++/84812
	* name-lookup.c (set_local_extern_decl_linkage): Defend against
	ambiguous lookups.

	PR c++/84812
	* g++.dg/lookup/pr84812.C: New.

From-SVN: r258644

gcc/cp/ChangeLog

+2018-03-19  Nathan Sidwell  <nathan@acm.org>
+
+	PR c++/84812
+	* name-lookup.c (set_local_extern_decl_linkage): Defend against
+	ambiguous lookups.
+
 2018-03-16  Jakub Jelinek  <jakub@redhat.com>
 
 	PR c/84910

gcc/cp/name-lookup.c

@@ -2878,7 +2878,9 @@ set_local_extern_decl_linkage (tree decl, bool shadowed)
 	    = find_namespace_value (current_namespace, DECL_NAME (decl));
 	  loc_value = ns_value;
 	}
-      if (loc_value == error_mark_node)
+      if (loc_value == error_mark_node
+	  /* An ambiguous lookup.  */
+	  || (loc_value && TREE_CODE (loc_value) == TREE_LIST))
 	loc_value = NULL_TREE;
 
       for (ovl_iterator iter (loc_value); iter; ++iter)
@@ -2926,7 +2928,8 @@ set_local_extern_decl_linkage (tree decl, bool shadowed)
       if (ns_value == decl)
 	ns_value = find_namespace_value (current_namespace, DECL_NAME (decl));
 
-      if (ns_value == error_mark_node)
+      if (ns_value == error_mark_node
+	  || (ns_value && TREE_CODE (ns_value) == TREE_LIST))
 	ns_value = NULL_TREE;
 
       for (ovl_iterator iter (ns_value); iter; ++iter)

gcc/testsuite/ChangeLog

+2018-03-19  Nathan Sidwell  <nathan@acm.org>
+
+	PR c++/84812
+	* g++.dg/lookup/pr84812.C: New.
+
 2018-03-19  Richard Biener  <rguenther@suse.de>
 
 	PR tree-optimization/84929

gcc/testsuite/g++.dg/lookup/pr84812.C

+// PR 84812.  ICE determining implicit "C" linkage
+
+struct A { void foo(); };
+struct B { void foo(); };
+
+struct C : A, B
+{
+  void X ();
+};
+
+void C::X ()
+{
+  void foo (); // local decl of ::foo
+
+  foo ();
+}
+
+// { dg-final { scan-assembler "_Z3foov" } }