Fix type-warning.

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 buildJavaScriptFunction(FunctionElement element,
@@ skipping 1657 matching lines @@
     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) {
+    bool isBuiltinRelational(HInstruction instruction) {
+      if (instruction is !HRelational) return false;
+      HRelational relational = instruction;
+      return relational.builtin;
+    }
+
     assert(node.inputs.length == 1);
     HInstruction input = node.inputs[0];
     if (input is HBoolify && isGenerateAtUseSite(input)) {
       beginExpression(JSPrecedence.EQUALITY_PRECEDENCE);
       assert(node.inputs.length == 1);
       use(node.inputs[0], JSPrecedence.EQUALITY_PRECEDENCE);
       buffer.add(' !== true');
       endExpression(JSPrecedence.EQUALITY_PRECEDENCE);
-    } else if (input is HRelational &&
-               input.builtin &&
-               isGenerateAtUseSite(input)) {
+    } else if (isBuiltinRelational(input) && isGenerateAtUseSite(input)) {
       Map<String, String> inverseOperator = const <String>{
         "==" : "!=",
         "!=" : "==",
         "===": "!==",
         "!==": "===",
         "<"  : ">=",
         "<=" : ">",
         ">"  : "<=",
         ">=" : "<"
       };
+      HRelational relational = input;
       visitInvokeBinary(input,
-                        inverseOperator[input.operation.name.stringValue]);
+                        inverseOperator[relational.operation.name.stringValue]);
     } else {
       beginExpression(JSPrecedence.PREFIX_PRECEDENCE);
       buffer.add('!');
       use(input, JSPrecedence.PREFIX_PRECEDENCE);
       endExpression(JSPrecedence.PREFIX_PRECEDENCE);
     }
   }
 
   visitParameterValue(HParameterValue node) {
     assert(isGenerateAtUseSite(node));
@@ skipping 882 matching lines @@
       startBailoutSwitch();
     }
   }
 
   void endLabeledBlock(HLabeledBlockInformation labeledBlockInfo) {
     if (labeledBlockInfo.body.start.hasGuards()) {
       endBailoutSwitch();
     }
   }
 }