ES6 symbols: Implement Symbol intrinsic and basic functionality

src/x64/builtins-x64.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 371 matching lines @@
     Label use_receiver, exit;
     // If the result is a smi, it is *not* an object in the ECMA sense.
     __ JumpIfSmi(rax, &use_receiver);
 
     // If the type of the result (stored in its map) is less than
     // FIRST_SPEC_OBJECT_TYPE, it is not an object in the ECMA sense.
     STATIC_ASSERT(LAST_SPEC_OBJECT_TYPE == LAST_TYPE);
     __ CmpObjectType(rax, FIRST_SPEC_OBJECT_TYPE, rcx);
     __ j(above_equal, &exit);
 
+    // Symbols are "objects".
+    __ CmpInstanceType(rcx, SYMBOL_TYPE);
+    __ j(equal, &exit);
+
     // Throw away the result of the constructor invocation and use the
     // on-stack receiver as the result.
     __ bind(&use_receiver);
     __ movq(rax, Operand(rsp, 0));
 
     // Restore the arguments count and leave the construct frame.
     __ bind(&exit);
     __ movq(rbx, Operand(rsp, kPointerSize));  // Get arguments count.
 
     // Leave construct frame.
@@ skipping 1433 matching lines @@
   Deoptimizer::EntryGenerator generator(masm, Deoptimizer::OSR);
   generator.Generate();
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64