[runtime] Add %ToString and %_ToString and remove the TO_STRING builtin.

src/arm64/code-stubs-arm64.cc

Index: src/arm64/code-stubs-arm64.cc
diff --git a/src/arm64/code-stubs-arm64.cc b/src/arm64/code-stubs-arm64.cc
index 4555a81c5eaa7947b6849d0ed67da08dd147619c..62d68fdb8f9b35042a03c8db03a40469ea771ac3 100644
--- a/src/arm64/code-stubs-arm64.cc
+++ b/src/arm64/code-stubs-arm64.cc
@@ -3999,6 +3999,38 @@ void ToNumberStub::Generate(MacroAssembler* masm) {
 }
 
 
+void ToStringStub::Generate(MacroAssembler* masm) {
+  // The ToString stub takes one argument in x0.
+  Label is_number;
+  __ JumpIfSmi(x0, &is_number);
+
+  Label not_string;
+  __ JumpIfObjectType(x0, x1, x1, FIRST_NONSTRING_TYPE, &not_string, hs);
+  // x0: receiver
+  // x1: receiver instance type
+  __ Ret();
+  __ Bind(&not_string);
+
+  Label not_heap_number;
+  __ Cmp(x1, HEAP_NUMBER_TYPE);
+  __ B(ne, &not_heap_number);
+  __ Bind(&is_number);
+  NumberToStringStub stub(isolate());
+  __ TailCallStub(&stub);
+  __ Bind(&not_heap_number);
+
+  Label not_oddball;
+  __ Cmp(x1, ODDBALL_TYPE);
+  __ B(ne, &not_oddball);
+  __ Ldr(x0, FieldMemOperand(x0, Oddball::kToStringOffset));
+  __ Ret();
+  __ Bind(&not_oddball);
+
+  __ Push(x0);  // Push argument.
+  __ TailCallRuntime(Runtime::kToString, 1, 1);
+}
+
+
 void StringHelper::GenerateFlatOneByteStringEquals(
     MacroAssembler* masm, Register left, Register right, Register scratch1,
     Register scratch2, Register scratch3) {