VM: Fix double comparisons using != and NaN in optimized code.

runtime/vm/flow_graph_compiler_x64.cc

 // Copyright (c) 2013, 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.
 
 #include "vm/globals.h"  // Needed here to get TARGET_ARCH_X64.
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/flow_graph_compiler.h"
 
 #include "vm/ast_printer.h"
@@ skipping 1641 matching lines @@
   branch->EmitBranchOnCondition(this, true_condition);
 }
 
 
 void FlowGraphCompiler::EmitDoubleCompareBool(Condition true_condition,
                                               FpuRegister left,
                                               FpuRegister right,
                                               Register result) {
   assembler()->comisd(left, right);
   Label is_false, is_true, done;
-  assembler()->j(PARITY_EVEN, &is_false, Assembler::kNearJump);  // NaN false;
+  // x == NaN -> false, x != NaN -> true.
+  Label* nan_label = (true_condition == NOT_EQUAL) ? &is_true : &is_false;
+  assembler()->j(PARITY_EVEN, nan_label, Assembler::kNearJump);
   assembler()->j(true_condition, &is_true, Assembler::kNearJump);
   assembler()->Bind(&is_false);
   assembler()->LoadObject(result, Bool::False(), PP);
   assembler()->jmp(&done);
   assembler()->Bind(&is_true);
   assembler()->LoadObject(result, Bool::True(), PP);
   assembler()->Bind(&done);
 }
 
 
@@ skipping 255 matching lines @@
   __ movups(reg, Address(RSP, 0));
   __ AddImmediate(RSP, Immediate(kFpuRegisterSize), PP);
 }
 
 
 #undef __
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64