Don't duplicate switch case code if we fall through to the default case.

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

 // Copyright (c) 2012, 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.
 
 import 'dart:math' as math;
 import 'dart:collection' show Queue;
 import '../common.dart';
 import '../common/codegen.dart' show CodegenRegistry, CodegenWorkItem;
 import '../common/tasks.dart' show CompilerTask;
 import '../constants/constant_system.dart';
@@ skipping 747 matching lines @@
     if (!isExpression) {
       generateStatements(info.expression);
     }
 
     if (isExpression) {
       push(generateExpression(info.expression));
     } else {
       use(info.expression.conditionExpression);
     }
     js.Expression key = pop();
+    bool handledDefault = false;
     List<js.SwitchClause> cases = <js.SwitchClause>[];
     HSwitch switchInstruction = info.expression.end.last;
     List<HInstruction> inputs = switchInstruction.inputs;
     List<HBasicBlock> successors = switchInstruction.block.successors;
 
     js.Block oldContainer = currentContainer;
     for (int inputIndex = 1, statementIndex = 0;
         inputIndex < inputs.length;
         statementIndex++) {
       HBasicBlock successor = successors[inputIndex - 1];
       // If liveness analysis has figured out that this case is dead,
       // omit the code for it.
       if (successor.isLive) {
         do {
           visit(inputs[inputIndex]);
           currentContainer = new js.Block.empty();
           cases.add(new js.Case(pop(), currentContainer));
           inputIndex++;
         } while ((successors[inputIndex - 1] == successor) &&
             (inputIndex < inputs.length));
 
+        // If this is the last statement, then these cases also belong to the
+        // default block.
+        if (statementIndex == info.statements.length - 1) {
+          currentContainer = new js.Block.empty();
+          cases.add(new js.Default(currentContainer));
+          handledDefault = true;
+        }
+
         generateStatements(info.statements[statementIndex]);
       } else {
         // Skip all the case statements that belong to this
         // block.
         while ((successors[inputIndex - 1] == successor) &&
             (inputIndex < inputs.length)) {
           ++inputIndex;
         }
       }
     }
 
     // If the default case is dead, we omit it. Likewise, if it is an
     // empty block, we omit it, too.
-    if (info.statements.last.start.isLive) {
+    if (info.statements.last.start.isLive && !handledDefault) {
       currentContainer = new js.Block.empty();
       generateStatements(info.statements.last);
       if (currentContainer.statements.isNotEmpty) {
         cases.add(new js.Default(currentContainer));
       }
     }
 
     currentContainer = oldContainer;
 
     js.Statement result = new js.Switch(key, cases);
@@ skipping 2217 matching lines @@
     return _closedWorld.anyStrictSubclassOf(cls, (ClassEntity subclass) {
       return !_rtiSubstitutions.isTrivialSubstitution(subclass, cls);
     });
   }
 
   @override
   void visitRef(HRef node) {
     visit(node.value);
   }
 }