ES6 symbols: Implement Symbol intrinsic and basic functionality

src/x64/full-codegen-x64.cc

Index: src/x64/full-codegen-x64.cc
diff --git a/src/x64/full-codegen-x64.cc b/src/x64/full-codegen-x64.cc
index eef9dc2afae81008138a6cdb61bf1330dbe68d18..34de83346151f9cb5b6b784669fc7cf0eadc7d43 100644
--- a/src/x64/full-codegen-x64.cc
+++ b/src/x64/full-codegen-x64.cc
@@ -2660,6 +2660,28 @@ void FullCodeGenerator::EmitIsStringWrapperSafeForDefaultValueOf(
 }
 
 
+void FullCodeGenerator::EmitIsSymbol(CallRuntime* expr) {
+  ZoneList<Expression*>* args = expr->arguments();
+  ASSERT(args->length() == 1);
+
+  VisitForAccumulatorValue(args->at(0));
+
+  Label materialize_true, materialize_false;
+  Label* if_true = NULL;
+  Label* if_false = NULL;
+  Label* fall_through = NULL;
+  context()->PrepareTest(&materialize_true, &materialize_false,
+                         &if_true, &if_false, &fall_through);
+
+  __ JumpIfSmi(rax, if_false);
+  __ CmpObjectType(rax, SYMBOL_TYPE, rbx);
+  PrepareForBailoutBeforeSplit(expr, true, if_true, if_false);
+  Split(equal, if_true, if_false, fall_through);
+
+  context()->Plug(if_true, if_false);
+}
+
+
 void FullCodeGenerator::EmitIsFunction(CallRuntime* expr) {
   ZoneList<Expression*>* args = expr->arguments();
   ASSERT(args->length() == 1);
@@ -4259,6 +4281,10 @@ void FullCodeGenerator::EmitLiteralCompareTypeof(Expression* expr,
       __ CompareRoot(rax, Heap::kNullValueRootIndex);
       __ j(equal, if_true);
     }
+    if (FLAG_harmony_symbols) {
+      __ CmpObjectType(rax, SYMBOL_TYPE, rdx);
+      __ j(equal, if_true);
+    }
     __ CmpObjectType(rax, FIRST_NONCALLABLE_SPEC_OBJECT_TYPE, rdx);
     __ j(below, if_false);
     __ CmpInstanceType(rdx, LAST_NONCALLABLE_SPEC_OBJECT_TYPE);