Undo optimization in cases where NaN might be involved.

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 1671 matching lines @@
     }
 
     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(input.inputs[0], JSPrecedence.EQUALITY_PRECEDENCE);
       buffer.add(' !== true');
       endExpression(JSPrecedence.EQUALITY_PRECEDENCE);
-    } else if (isBuiltinRelational(input) && isGenerateAtUseSite(input)) {
+    } else if (isBuiltinRelational(input) &&
+               isGenerateAtUseSite(input) &&
+               !input.inputs[0].isDouble() &&
+               !input.inputs[0].isTypeUnknown()) {

[ngeoffray, 2012/05/10 10:41:13]

I think this will cover 'conflicting'. What you should use is
input.inputs[0].propagatedType.isUseful()

+      // This optimization doesn't work for NaN, so we don't do it if the
+      // type isn't known to be non-Double.
       Map<String, String> inverseOperator = const <String>{
         "==" : "!=",
         "!=" : "==",
         "===": "!==",
         "!==": "===",
         "<"  : ">=",
         "<=" : ">",
         ">"  : "<=",
         ">=" : "<"
       };
@@ skipping 895 matching lines @@
       startBailoutSwitch();
     }
   }
 
   void endLabeledBlock(HLabeledBlockInformation labeledBlockInfo) {
     if (labeledBlockInfo.body.start.hasGuards()) {
       endBailoutSwitch();
     }
   }
 }