Detect dead code, and handle breaks and continues in inferrer.

sdk/lib/_internal/compiler/implementation/ssa/builder.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.
 
 part of ssa;
 
 /**
  * A special element for the extra parameter taken by intercepted
  * methods. We need to override [Element.computeType] because our
  * optimizers may look at its declared type.
@@ skipping 4256 matching lines @@
     }
     handleLoop(node, buildInitializer, buildCondition, () {}, buildBody);
   }
 
   visitLabel(Label node) {
     compiler.internalError('SsaBuilder.visitLabel', node: node);
   }
 
   visitLabeledStatement(LabeledStatement node) {
     Statement body = node.statement;
-    if (body is Loop || body is SwitchStatement) {
+    if (body is Loop
+        || body is SwitchStatement
+        || Elements.isUnusedLabel(node, elements)) {
       // Loops and switches handle their own labels.
       visit(body);
       return;
     }
-    // Non-loop statements can only be break targets, not continue targets.
     TargetElement targetElement = elements[body];
-    if (targetElement == null || !identical(targetElement.statement, body)) {
-      // Labeled statements with no element on the body have no breaks.
-      // A different target statement only happens if the body is itself
-      // a break or continue for a different target. In that case, this
-      // label is also always unused.
-      visit(body);
-      return;
-    }
     LocalsHandler beforeLocals = new LocalsHandler.from(localsHandler);
     assert(targetElement.isBreakTarget);
     JumpHandler handler = new JumpHandler(this, targetElement);
     // Introduce a new basic block.
     HBasicBlock entryBlock = openNewBlock();
     visit(body);
     SubGraph bodyGraph = new SubGraph(entryBlock, lastOpenedBlock);
 
     HBasicBlock joinBlock = graph.addNewBlock();
     List<LocalsHandler> breakHandlers = <LocalsHandler>[];
@@ skipping 1115 matching lines @@
           new HSubGraphBlockInformation(elseBranch.graph));
 
     HBasicBlock conditionStartBlock = conditionBranch.block;
     conditionStartBlock.setBlockFlow(info, joinBlock);
     SubGraph conditionGraph = conditionBranch.graph;
     HIf branch = conditionGraph.end.last;
     assert(branch is HIf);
     branch.blockInformation = conditionStartBlock.blockFlow;
   }
 }