The following invalid code snippet triggers an ICE since GCC 4.8.0:

========================================
struct A
{
  void operator= (const A& = A());
  void foo(const A&);
};

void A::foo(const A& = A()) {}
========================================

bug.cc:3:33: error: 'void A::operator=(const A&)' cannot have default arguments
   void operator= (const A& = A());
                                 ^
bug.cc:7:27: internal compiler error: canonical types differ for identical types 'void (A::)(const A&)' and 'void (A::)(const A&)'
 void A::foo(const A& = A()) {}
                           ^
0x9dc198 comptypes(tree_node*, tree_node*, int)
	../../gcc/gcc/cp/typeck.c:1480
0x89241a duplicate_decls(tree_node*, tree_node*, bool)
	../../gcc/gcc/cp/decl.c:2226
0x899062 grokfndecl
	../../gcc/gcc/cp/decl.c:9099
0x8a95f0 grokdeclarator(cp_declarator const*, cp_decl_specifier_seq*, decl_context, int, tree_node**)
	../../gcc/gcc/cp/decl.c:12429
0x8ac476 start_function(cp_decl_specifier_seq*, cp_declarator const*, tree_node*)
	../../gcc/gcc/cp/decl.c:15299
0x93c891 cp_parser_function_definition_from_specifiers_and_declarator
	../../gcc/gcc/cp/parser.c:26711
0x93c891 cp_parser_init_declarator
	../../gcc/gcc/cp/parser.c:19501
0x944508 cp_parser_simple_declaration
	../../gcc/gcc/cp/parser.c:13049
0x945318 cp_parser_block_declaration
	../../gcc/gcc/cp/parser.c:12874
0x9492a2 cp_parser_declaration
	../../gcc/gcc/cp/parser.c:12772
0x9496b1 cp_parser_declaration_seq_opt
	../../gcc/gcc/cp/parser.c:12648
0x9499a4 cp_parser_translation_unit
	../../gcc/gcc/cp/parser.c:4563
0x9499a4 c_parse_file()
	../../gcc/gcc/cp/parser.c:39016
0xa49636 c_common_parse_file()
	../../gcc/gcc/c-family/c-opts.c:1132
Please submit a full bug report, [etc.]