ES6 symbols: turn symbols into a proper primitive type

src/ia32/code-stubs-ia32.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 614 matching lines @@
   if (types_.Contains(STRING)) {
     // String value -> false iff empty.
     Label not_string;
     __ CmpInstanceType(map, FIRST_NONSTRING_TYPE);
     __ j(above_equal, &not_string, Label::kNear);
     __ mov(tos_, FieldOperand(argument, String::kLengthOffset));
     __ ret(1 * kPointerSize);  // the string length is OK as the return value
     __ bind(&not_string);
   }
 
+  if (types_.Contains(SYMBOL)) {
+    // Symbol value -> true.
+    Label not_symbol;
+    __ CmpInstanceType(map, SYMBOL_TYPE);
+    __ j(not_equal, &not_symbol, Label::kNear);
+    __ bind(&not_symbol);
+  }
+
   if (types_.Contains(HEAP_NUMBER)) {
     // heap number -> false iff +0, -0, or NaN.
     Label not_heap_number, false_result;
     __ cmp(map, factory->heap_number_map());
     __ j(not_equal, &not_heap_number, Label::kNear);
     __ fldz();
     __ fld_d(FieldOperand(argument, HeapNumber::kValueOffset));
     __ FCmp();
     __ j(zero, &false_result, Label::kNear);
     // argument contains the correct return value already.
@@ skipping 7226 matching lines @@
   // Restore ecx.
   __ pop(ecx);
   __ ret(0);
 }
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32