Fix a bug where a block would be visited twice: by a non-dominating loop, and by its dominator.

lib/compiler/implementation/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.
 
 class SsaCodeGeneratorTask extends CompilerTask {
   SsaCodeGeneratorTask(Compiler compiler) : super(compiler);
   String get name() => 'SSA code generator';
 
 
   String generateMethod(WorkItem work, HGraph graph) {
@@ skipping 831 matching lines @@
 
   visitLoopBranch(HLoopBranch node) {
     HBasicBlock branchBlock = currentBlock;
     handleLoopCondition(node);
     List<HBasicBlock> dominated = currentBlock.dominatedBlocks;
     // For a do while loop, the body has already been visited.
     if (!node.isDoWhile()) {
       visitBasicBlock(dominated[0]);
     }
     endLoop(node.block);
+
+    // If the branch does not dominate the code after the loop, the
+    // dominator will visit it.
+    if (branchBlock.successors[1].dominator !== branchBlock) return;
+
     visitBasicBlock(branchBlock.successors[1]);
     // With labeled breaks we can have more dominated blocks.
     if (dominated.length >= 3) {
       for (int i = 2; i < dominated.length; i++) {
         visitBasicBlock(dominated[i]);
       }
     }
   }
 
   visitNot(HNot node) {
@@ skipping 694 matching lines @@
       startBailoutSwitch();
     }
   }
 
   void endElse(HIf node) {
     if (node.elseBlock.hasGuards()) {
       endBailoutSwitch();
     }
   }
 }