Optimize ToString and NonStringToString.

src/runtime.js

Index: src/runtime.js
diff --git a/src/runtime.js b/src/runtime.js
index dd776dbc8c354722c692c3580914398e5de26d30..e70666817321d2d60c7b7256ae9d20953663d8cc 100644
--- a/src/runtime.js
+++ b/src/runtime.js
@@ -766,7 +766,6 @@ function ToPrimitive(x, hint) {
   if (IS_STRING(x)) return x;
   // Normal behavior.
   if (!IS_SPEC_OBJECT(x)) return x;
-  if (IS_SYMBOL_WRAPPER(x)) throw MakeTypeError(kSymbolToPrimitive);

[bbudge, 2015/07/28 19:07:30]

Is this error part of the Spec? If so, we have to keep this line.

[rossberg, 2015/07/29 11:49:11]

No, the spec doesn't even recognise the existence of error messages.

   if (IS_FLOAT32X4(x)) return x;
   if (hint == NO_HINT) hint = (IS_DATE(x)) ? STRING_HINT : NUMBER_HINT;
   return (hint == NUMBER_HINT) ? DefaultNumber(x) : DefaultString(x);
@@ -816,7 +815,7 @@ function ToString(x) {
   if (IS_NUMBER(x)) return %_NumberToString(x);
   if (IS_BOOLEAN(x)) return x ? 'true' : 'false';
   if (IS_UNDEFINED(x)) return 'undefined';
-  if (IS_SYMBOL(x)) throw MakeTypeError(kSymbolToString);
+  // Types that can't be converted to string are caught in DefaultString.
   return (IS_NULL(x)) ? 'null' : ToString(DefaultString(x));
 }
 
@@ -824,7 +823,7 @@ function NonStringToString(x) {
   if (IS_NUMBER(x)) return %_NumberToString(x);
   if (IS_BOOLEAN(x)) return x ? 'true' : 'false';
   if (IS_UNDEFINED(x)) return 'undefined';
-  if (IS_SYMBOL(x)) throw MakeTypeError(kSymbolToString);
+  // Types that can't be converted to string are caught in DefaultString.
   return (IS_NULL(x)) ? 'null' : ToString(DefaultString(x));
 }
 
@@ -963,6 +962,7 @@ function DefaultNumber(x) {
 // ECMA-262, section 8.6.2.6, page 28.
 function DefaultString(x) {
   if (!IS_SYMBOL_WRAPPER(x)) {
+    if (IS_SYMBOL(x)) throw MakeTypeError(kSymbolToString);
     var toString = x.toString;
     if (IS_SPEC_FUNCTION(toString)) {
       var s = %_CallFunction(x, toString);