Use bit fields to calculate compare stub minor key

src/x64/codegen-x64.cc

Index: src/x64/codegen-x64.cc
===================================================================
--- src/x64/codegen-x64.cc	(revision 4200)
+++ src/x64/codegen-x64.cc	(working copy)
@@ -9105,11 +9105,13 @@
 
 
 int CompareStub::MinorKey() {
-  // Encode the three parameters in a unique 16 bit value.
+  // Encode the three parameters in a unique 16 bit value. To avoid duplicate
+  // stubs the never NaN NaN condition is only taken into account if the
+  // condition is equals.
   ASSERT(static_cast<unsigned>(cc_) < (1 << 14));
-  int nnn_value = (never_nan_nan_ ? 2 : 0);
-  if (cc_ != equal) nnn_value = 0;  // Avoid duplicate stubs.
-  return (static_cast<unsigned>(cc_) << 2) | nnn_value | (strict_ ? 1 : 0);
+  return ConditionField::encode(static_cast<unsigned>(cc_))
+         | StrictField::encode(strict_)
+         | NeverNanNanField::encode(cc_ == equal ? never_nan_nan_ : false);
 }