dart2js cps: Refactor and optimize string concatenations.

pkg/compiler/lib/src/js_backend/codegen/codegen.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library code_generator;
 
 import 'glue.dart';
 
 import '../../tree_ir/tree_ir_nodes.dart' as tree_ir;
 import '../../tree_ir/tree_ir_nodes.dart' show BuiltinOperator;
@@ skipping 153 matching lines @@
         (int index) => visitExpression(expressions[index]),
         growable: false);
   }
 
   giveup(tree_ir.Node node,
          [String reason = 'unimplemented in CodeGenerator']) {
     throw new CodegenBailout(node, reason);
   }
 
   @override
-  js.Expression visitConcatenateStrings(tree_ir.ConcatenateStrings node) {
-    js.Expression addStrings(js.Expression left, js.Expression right) {
-      return new js.Binary('+', left, right);
-    }
-
-    js.Expression toString(tree_ir.Expression input) {
-      bool useDirectly = input is tree_ir.Constant &&
-          (input.value.isString ||
-           input.value.isInt ||
-           input.value.isBool);
-      js.Expression value = visitExpression(input);
-      if (useDirectly) {
-        return value;
-      } else {
-        Element convertToString = glue.getStringConversion();
-        registry.registerStaticUse(convertToString);
-        js.Expression access = glue.staticFunctionAccess(convertToString);
-        return (new js.Call(access, <js.Expression>[value]));
-      }
-    }
-
-    return node.arguments.map(toString).reduce(addStrings);
-  }
-
-  @override
   js.Expression visitConditional(tree_ir.Conditional node) {
     return new js.Conditional(
         visitExpression(node.condition),
         visitExpression(node.thenExpression),
         visitExpression(node.elseExpression));
   }
 
   js.Expression buildConstant(ConstantValue constant) {
     registry.registerCompileTimeConstant(constant);
     return glue.constantReference(constant);
@@ skipping 508 matching lines @@
       case BuiltinOperator.NumXor:
         return js.js('(# ^ #) >>> 0', args);
       case BuiltinOperator.NumLt:
         return new js.Binary('<', args[0], args[1]);
       case BuiltinOperator.NumLe:
         return new js.Binary('<=', args[0], args[1]);
       case BuiltinOperator.NumGt:
         return new js.Binary('>', args[0], args[1]);
       case BuiltinOperator.NumGe:
         return new js.Binary('>=', args[0], args[1]);
+      case BuiltinOperator.StringConcat:
+        if (args.isEmpty) return js.string('');
+        return args.reduce((e1,e2) => new js.Binary('+', e1, e2));
       case BuiltinOperator.StrictEq:
         return new js.Binary('===', args[0], args[1]);
       case BuiltinOperator.StrictNeq:
         return new js.Binary('!==', args[0], args[1]);
       case BuiltinOperator.LooseEq:
         return new js.Binary('==', args[0], args[1]);
       case BuiltinOperator.LooseNeq:
         return new js.Binary('!=', args[0], args[1]);
       case BuiltinOperator.IsFalsy:
         return new js.Prefix('!', args[0]);
       case BuiltinOperator.IsNumber:
         return js.js("typeof # === 'number'", args);
       case BuiltinOperator.IsNotNumber:
         return js.js("typeof # !== 'number'", args);
       case BuiltinOperator.IsFloor:
         return js.js("Math.floor(#) === #", args);
       case BuiltinOperator.IsNumberAndFloor:
         return js.js("typeof # === 'number' && Math.floor(#) === #", args);
     }
   }
 
   visitFunctionExpression(tree_ir.FunctionExpression node) {
     // FunctionExpressions are currently unused.
     // We might need them if we want to emit raw JS nested functions.
     throw 'FunctionExpressions should not be used';
   }
 }