Improve array to string conversion.

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 650337a29599fc09e685b0df7b08624e70e5b578..02d130e1c485b6536418e48370677fa5e6046b7c 100644
--- a/src/x64/full-codegen-x64.cc
+++ b/src/x64/full-codegen-x64.cc
@@ -3047,6 +3047,36 @@ void FullCodeGenerator::EmitDateField(CallRuntime* expr) {
 }
 
 
+void FullCodeGenerator::EmitOneByteSeqStringSetChar(CallRuntime* expr) {
+  ZoneList<Expression*>* args = expr->arguments();
+  ASSERT_EQ(3, args->length());
+
+  VisitForStackValue(args->at(1));  // index
+  VisitForStackValue(args->at(2));  // value
+  __ pop(rcx);
+  __ pop(rbx);
+  VisitForAccumulatorValue(args->at(0));  // string
+
+  SeqStringSetCharGenerator::Generate(masm_, true, rax, rbx, rcx);
+  context()->Plug(rax);
+}
+
+
+void FullCodeGenerator::EmitTwoByteSeqStringSetChar(CallRuntime* expr) {
+  ZoneList<Expression*>* args = expr->arguments();
+  ASSERT_EQ(3, args->length());
+
+  VisitForStackValue(args->at(1));  // index
+  VisitForStackValue(args->at(2));  // value
+  __ pop(rcx);
+  __ pop(rbx);
+  VisitForAccumulatorValue(args->at(0));  // string
+
+  SeqStringSetCharGenerator::Generate(masm_, false, rax, rbx, rcx);
+  context()->Plug(rax);
+}
+
+
 void FullCodeGenerator::EmitMathPow(CallRuntime* expr) {
   // Load the arguments on the stack and call the runtime function.
   ZoneList<Expression*>* args = expr->arguments();