[strong] Simplify (and sortof optimize) string addition for strong mode.

src/runtime.js

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This files contains runtime support implemented in JavaScript.
 
 // CAUTION: Some of the functions specified in this file are called
 // directly from compiled code. These are the functions with names in
 // ALL CAPS. The compiled code passes the first argument in 'this'.
 
 
 /* -----------------------------------
    - - -   C o m p a r i s o n   - - -
    -----------------------------------
 */
 
 // The following declarations are shared with other native JS files.
 // They are all declared at this one spot to avoid redeclaration errors.
 var EQUALS;
 var STRICT_EQUALS;
 var COMPARE;
 var COMPARE_STRONG;
 var ADD;
 var ADD_STRONG;
 var STRING_ADD_LEFT;
-var STRING_ADD_LEFT_STRONG;
 var STRING_ADD_RIGHT;
-var STRING_ADD_RIGHT_STRONG;
 var SUB;
 var SUB_STRONG;
 var MUL;
 var MUL_STRONG;
 var DIV;
 var DIV_STRONG;
 var MOD;
 var MOD_STRONG;
 var BIT_OR;
 var BIT_OR_STRONG;
@@ skipping 216 matching lines @@
     } else {
       y = IS_NUMBER(y)
           ? %_NumberToString(y)
           : %$toString(%$toPrimitive(y, NO_HINT));
     }
   }
   return %_StringAdd(this, y);
 }
 
 
-// Left operand (this) is already a string.
-STRING_ADD_LEFT_STRONG = function STRING_ADD_LEFT_STRONG(y) {
-  if (IS_STRING(y)) {
-    return %_StringAdd(this, y);
-  }
-  throw %MakeTypeError(kStrongImplicitConversion);
-}
-
-
 // Right operand (y) is already a string.
 STRING_ADD_RIGHT = function STRING_ADD_RIGHT(y) {
   var x = this;
   if (!IS_STRING(x)) {
     if (IS_STRING_WRAPPER(x) && %_IsStringWrapperSafeForDefaultValueOf(x)) {
       x = %_ValueOf(x);
     } else {
       x = IS_NUMBER(x)
           ? %_NumberToString(x)
           : %$toString(%$toPrimitive(x, NO_HINT));
     }
   }
   return %_StringAdd(x, y);
 }
 
 
-// Right operand (y) is already a string.
-STRING_ADD_RIGHT_STRONG = function STRING_ADD_RIGHT_STRONG(y) {
-  if (IS_STRING(this)) {
-    return %_StringAdd(this, y);
-  }
-  throw %MakeTypeError(kStrongImplicitConversion);
-}
-
-
 // ECMA-262, section 11.6.2, page 50.
 SUB = function SUB(y) {
   var x = IS_NUMBER(this) ? this : %$nonNumberToNumber(this);
   if (!IS_NUMBER(y)) y = %$nonNumberToNumber(y);
   return %NumberSub(x, y);
 }
 
 
 // Strong mode SUB throws if an implicit conversion would be performed
 SUB_STRONG = function SUB_STRONG(y) {
@@ skipping 646 matching lines @@
 $toBoolean = ToBoolean;
 $toInteger = ToInteger;
 $toLength = ToLength;
 $toName = ToName;
 $toNumber = ToNumber;
 $toPositiveInteger = ToPositiveInteger;
 $toPrimitive = ToPrimitive;
 $toString = ToString;
 
 })