Optimize Date construction and string concatenation with...

src/runtime.js

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 143 matching lines @@
   } else if (IS_STRING(b)) {
     return %StringAdd(%ToString(a), b);
   } else {
     return %NumberAdd(%ToNumber(a), %ToNumber(b));
   }
 }
 
 
 // Left operand (this) is already a string.
 function STRING_ADD_LEFT(y) {
-  if (!IS_STRING(y)) y = %ToString(%ToPrimitive(y, NO_HINT));
+  if (!IS_STRING(y)) {
+    if (IS_STRING_WRAPPER(y)) {
+      y = %_ValueOf(y);
+    } else {
+      y = IS_NUMBER(y)
+          ? %NumberToString(y)
+          : %ToString(%ToPrimitive(y, NO_HINT));
+    }
+  }
   return %StringAdd(this, y);
 }
 
 
 // Right operand (y) is already a string.
 function STRING_ADD_RIGHT(y) {
-  var x = IS_STRING(this) ? this : %ToString(%ToPrimitive(this, NO_HINT));
+  var x = this;
+  if (!IS_STRING(x)) {
+    if (IS_STRING_WRAPPER(x)) {
+      x = %_ValueOf(x);
+    } else {
+      x = IS_NUMBER(x)
+          ? %NumberToString(x)
+          : %ToString(%ToPrimitive(x, NO_HINT));
+    }
+  }
   return %StringAdd(x, y);
 }
 
 
 // ECMA-262, section 11.6.2, page 50.
 function SUB(y) {
   var x = IS_NUMBER(this) ? this : %ToNumber(this);
   if (!IS_NUMBER(y)) y = %ToNumber(y);
   return %NumberSub(x, y);
 }
@@ skipping 395 matching lines @@
   throw %MakeTypeError('cannot_convert_to_primitive', []);
 }
 
 
 // NOTE: Setting the prototype for Array must take place as early as
 // possible due to code generation for array literals.  When
 // generating code for a array literal a boilerplate array is created
 // that is cloned when running the code.  It is essiential that the
 // boilerplate gets the right prototype.
 %FunctionSetPrototype($Array, new $Array(0));