Add test inspired by Leg bug.

dart/frog/leg/ssa/optimize.dart

 // Copyright (c) 2011, 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 SsaOptimizerTask extends CompilerTask {
   SsaOptimizerTask(Compiler compiler) : super(compiler);
   String get name() => 'SSA optimizer';
 
   void optimize(WorkItem work, HGraph graph) {
     measure(() {
@@ skipping 228 matching lines @@
     node.block.remove(node);
   }
 }
 
 class SsaDeadCodeEliminator extends HGraphVisitor {
   static bool isDeadCode(HInstruction instruction) {
     // TODO(ngeoffray): the way we handle side effects is not right
     // (e.g. branching instructions have side effects).
     return !instruction.hasSideEffects()
            && instruction.usedBy.isEmpty()
-           && instruction is !HCheck;
+           && instruction is !HCheck
+           && instruction is !HTypeGuard;
   }
 
   void visitGraph(HGraph graph) {
     visitPostDominatorTree(graph);
   }
 
   void visitBasicBlock(HBasicBlock block) {
     HInstruction instruction = block.last;
     while (instruction !== null) {
       var previous = instruction.previous;
@@ skipping 351 matching lines @@
         }
       }
       if (!canBeMoved) continue;
 
       // This is safe because we are running after GVN.
       // TODO(ngeoffray): ensure GVN has been run.
       set_.add(current);
     }
   }
 }