Index: llvm/trunk/include/llvm/CodeGen/MachineFunction.h
===================================================================
--- llvm/trunk/include/llvm/CodeGen/MachineFunction.h
+++ llvm/trunk/include/llvm/CodeGen/MachineFunction.h
@@ -106,11 +106,16 @@
 
   // Property descriptions:
   // IsSSA: True when the machine function is in SSA form and virtual registers
-  // have a single def.
-  // TracksLiveness: (currently unsued, intended to eventually replace
-  // MachineRegisterInfo::tracksLiveness())
+  //  have a single def.
+  // TracksLiveness: True when tracking register liveness accurately.
+  //  While this property is set, register liveness information in basic block
+  //  live-in lists and machine instruction operands (e.g. kill flags, implicit
+  //  defs) is accurate. This means it can be used to change the code in ways
+  //  that affect the values in registers, for example by the register
+  //  scavenger.
+  //  When this property is clear, liveness is no longer reliable.
   // AllVRegsAllocated: All virtual registers have been allocated; i.e. all
-  // register operands are physical registers.
+  //  register operands are physical registers.
   enum class Property : unsigned {
     IsSSA,
     TracksLiveness,
Index: llvm/trunk/include/llvm/CodeGen/MachineRegisterInfo.h
===================================================================
--- llvm/trunk/include/llvm/CodeGen/MachineRegisterInfo.h
+++ llvm/trunk/include/llvm/CodeGen/MachineRegisterInfo.h
@@ -50,11 +50,6 @@
   MachineFunction *MF;
   Delegate *TheDelegate;
 
-  /// TracksLiveness - True while register liveness is being tracked accurately.
-  /// Basic block live-in lists, kill flags, and implicit defs may not be
-  /// accurate when after this flag is cleared.
-  bool TracksLiveness;
-
   /// True if subregister liveness is tracked.
   bool TracksSubRegLiveness;
 
@@ -175,21 +170,21 @@
   }
 
   /// tracksLiveness - Returns true when tracking register liveness accurately.
-  ///
-  /// While this flag is true, register liveness information in basic block
-  /// live-in lists and machine instruction operands is accurate. This means it
-  /// can be used to change the code in ways that affect the values in
-  /// registers, for example by the register scavenger.
-  ///
-  /// When this flag is false, liveness is no longer reliable.
-  bool tracksLiveness() const { return TracksLiveness; }
+  /// (see MachineFUnctionProperties::Property description for details)
+  bool tracksLiveness() const {
+    return MF->getProperties().hasProperty(
+        MachineFunctionProperties::Property::TracksLiveness);
+  }
 
   /// invalidateLiveness - Indicates that register liveness is no longer being
   /// tracked accurately.
   ///
   /// This should be called by late passes that invalidate the liveness
   /// information.
-  void invalidateLiveness() { TracksLiveness = false; }
+  void invalidateLiveness() {
+    MF->getProperties().clear(
+        MachineFunctionProperties::Property::TracksLiveness);
+  }
 
   /// Returns true if liveness for register class @p RC should be tracked at
   /// the subregister level.
Index: llvm/trunk/lib/CodeGen/MachineFunction.cpp
===================================================================
--- llvm/trunk/lib/CodeGen/MachineFunction.cpp
+++ llvm/trunk/lib/CodeGen/MachineFunction.cpp
@@ -63,6 +63,9 @@
       case Property::IsSSA:
         ROS << (HasProperty ? "SSA, " : "Post SSA, ");
         break;
+      case Property::TracksLiveness:
+        ROS << (HasProperty ? "" : "not ") << "tracking liveness, ";
+        break;
       case Property::AllVRegsAllocated:
         ROS << (HasProperty ? "AllVRegsAllocated" : "HasVRegs");
         break;
@@ -95,8 +98,9 @@
                                  unsigned FunctionNum, MachineModuleInfo &mmi)
     : Fn(F), Target(TM), STI(TM.getSubtargetImpl(*F)), Ctx(mmi.getContext()),
       MMI(mmi) {
-  // Assume the function starts in SSA form.
+  // Assume the function starts in SSA form with correct liveness.
   Properties.set(MachineFunctionProperties::Property::IsSSA);
+  Properties.set(MachineFunctionProperties::Property::TracksLiveness);
   if (STI->getRegisterInfo())
     RegInfo = new (Allocator) MachineRegisterInfo(this);
   else
@@ -404,12 +408,7 @@
   OS << "# Machine code for function " << getName() << ": ";
   OS << "Properties: <";
   getProperties().print(OS);
-  OS << "> : ";
-  if (RegInfo) {
-    if (!RegInfo->tracksLiveness())
-      OS << "not tracking liveness";
-  }
-  OS << '\n';
+  OS << ">\n";
 
   // Print Frame Information
   FrameInfo->print(*this, OS);
Index: llvm/trunk/lib/CodeGen/MachineRegisterInfo.cpp
===================================================================
--- llvm/trunk/lib/CodeGen/MachineRegisterInfo.cpp
+++ llvm/trunk/lib/CodeGen/MachineRegisterInfo.cpp
@@ -25,8 +25,7 @@
 void MachineRegisterInfo::Delegate::anchor() {}
 
 MachineRegisterInfo::MachineRegisterInfo(MachineFunction *MF)
-  : MF(MF), TheDelegate(nullptr), TracksLiveness(true),
-    TracksSubRegLiveness(false) {
+    : MF(MF), TheDelegate(nullptr), TracksSubRegLiveness(false) {
   unsigned NumRegs = getTargetRegisterInfo()->getNumRegs();
   VRegInfo.reserve(256);
   RegAllocHints.reserve(256);