Introduce faster swapping primitives.

src/x64/codegen-x64.cc

Index: src/x64/codegen-x64.cc
diff --git a/src/x64/codegen-x64.cc b/src/x64/codegen-x64.cc
index 7a3278ca86259b9912ca9f51551da46e69765e53..13eec723eeb652cf15bb46129ce559a1037a3277 100644
--- a/src/x64/codegen-x64.cc
+++ b/src/x64/codegen-x64.cc
@@ -4362,6 +4362,20 @@ void CodeGenerator::GenerateNumberToString(ZoneList<Expression*>* args) {
 }
 
 
+void CodeGenerator::GenerateSwapElements(ZoneList<Expression*>* args) {
+  Comment cmnt(masm_, "[ GenerateSwapElements");
+
+  ASSERT_EQ(3, args->length());
+
+  Load(args->at(0));
+  Load(args->at(1));
+  Load(args->at(2));
+
+  Result result = frame_->CallRuntime(Runtime::kSwapElements, 3);
+  frame_->Push(&result);
+}
+
+
 void CodeGenerator::GenerateCallFunction(ZoneList<Expression*>* args) {
   Comment cmnt(masm_, "[ GenerateCallFunction");