[turbofan][x64] Use the root register for comparisons with certain roots.

src/compiler/instruction-selector.cc

Index: src/compiler/instruction-selector.cc
diff --git a/src/compiler/instruction-selector.cc b/src/compiler/instruction-selector.cc
index b150725b2b20228d2127140d73e419119b3e0cff..9dc832bda162e7066c144fb3d067d333cf660fea 100644
--- a/src/compiler/instruction-selector.cc
+++ b/src/compiler/instruction-selector.cc
@@ -392,9 +392,13 @@ void InstructionSelector::SetEffectLevel(Node* node, int effect_level) {
 }
 
 bool InstructionSelector::CanAddressRelativeToRootsRegister() const {
-  return (enable_serialization_ == kDisableSerialization &&
-          (linkage()->GetIncomingDescriptor()->flags() &
-           CallDescriptor::kCanUseRoots));
+  return enable_serialization_ == kDisableSerialization &&
+         CanUseRootsRegister();
+}
+
+bool InstructionSelector::CanUseRootsRegister() const {
+  return linkage()->GetIncomingDescriptor()->flags() &
+         CallDescriptor::kCanUseRoots;
 }
 
 void InstructionSelector::MarkAsRepresentation(MachineRepresentation rep,