Improve handling of unary plus.

src/parser.cc

 // Copyright 2012 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 3268 matching lines @@
     // "delete identifier" is a syntax error in strict mode.
     if (op == Token::DELETE && !top_scope_->is_classic_mode()) {
       VariableProxy* operand = expression->AsVariableProxy();
       if (operand != NULL && !operand->is_this()) {
         ReportMessage("strict_delete", Vector<const char*>::empty());
         *ok = false;
         return NULL;
       }
     }
 
+    // Desugar '+foo' into 'foo*1', this enables the collection of type feedback
+    // without any special stub and the multiplication is removed later in
+    // Crankshaft's canonicalization pass.
+    if (op == Token::ADD) {
+      return factory()->NewBinaryOperation(Token::MUL,
+                                           expression,
+                                           factory()->NewNumberLiteral(1),
+                                           position);
+    }
+
     return factory()->NewUnaryOperation(op, expression, position);
 
   } else if (Token::IsCountOp(op)) {
     op = Next();
     Expression* expression = ParseUnaryExpression(CHECK_OK);
     // Signal a reference error if the expression is an invalid
     // left-hand side expression.  We could report this as a syntax
     // error here but for compatibility with JSC we choose to report the
     // error at runtime.
     if (expression == NULL || !expression->IsValidLeftHandSide()) {
@@ skipping 2708 matching lines @@
       ASSERT(info()->isolate()->has_pending_exception());
     } else {
       result = ParseProgram();
     }
   }
   info()->SetFunction(result);
   return (result != NULL);
 }
 
 } }  // namespace v8::internal