cps-ir: Implement string concatenation.

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 '../../js/js.dart' as js;
@@ skipping 117 matching lines @@
     return arguments.map(visitExpression).toList();
   }
 
   giveup(tree_ir.Node node,
          [String reason = 'unimplemented in CodeGenerator']) {
     throw new CodegenBailout(node, reason);
   }
 
   @override
   js.Expression visitConcatenateStrings(tree_ir.ConcatenateStrings node) {
-    return giveup(node);
-    // TODO: implement visitConcatenateStrings
+    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.expression.value.isString ||
+           input.expression.value.isInt ||
+           input.expression.value.isBool);
+      js.Expression value = visit(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));
   }
 
@@ skipping 366 matching lines @@
   void visitSetField(tree_ir.SetField node) {
     js.PropertyAccess field =
         new js.PropertyAccess.field(
             visitExpression(node.object),
             glue.instanceFieldPropertyName(node.field));
     js.Assignment asn = new js.Assignment(field, visitExpression(node.value));
     accumulator.add(new js.ExpressionStatement(asn));
     visitStatement(node.next);
   }
 }