Index: include/llvm/CodeGen/MachineBasicBlock.h
===================================================================
--- include/llvm/CodeGen/MachineBasicBlock.h
+++ include/llvm/CodeGen/MachineBasicBlock.h
@@ -307,9 +307,7 @@
   livein_iterator livein_begin() const { return LiveIns.begin(); }
   livein_iterator livein_end()   const { return LiveIns.end(); }
   bool            livein_empty() const { return LiveIns.empty(); }
-  iterator_range<livein_iterator> liveins() const {
-    return make_range(livein_begin(), livein_end());
-  }
+  iterator_range<livein_iterator> liveins() const;
 
   /// Get the clobber mask for the start of this basic block. Funclets use this
   /// to prevent register allocation across funclet transitions.
Index: lib/CodeGen/MachineBasicBlock.cpp
===================================================================
--- lib/CodeGen/MachineBasicBlock.cpp
+++ lib/CodeGen/MachineBasicBlock.cpp
@@ -1297,3 +1297,11 @@
   // care what kind of return it is, putting a mask after it is a no-op.
   return isReturnBlock() && !succ_empty() ? TRI->getNoPreservedMask() : nullptr;
 }
+
+iterator_range<MachineBasicBlock::livein_iterator>
+MachineBasicBlock::liveins() const {
+  assert(getParent()->getProperties().hasProperty(
+      MachineFunctionProperties::Property::TracksLiveness) &&
+      "Liveness information is accurate");
+  return make_range(livein_begin(), livein_end());
+}
Index: lib/CodeGen/MachineVerifier.cpp
===================================================================
--- lib/CodeGen/MachineVerifier.cpp
+++ lib/CodeGen/MachineVerifier.cpp
@@ -565,7 +565,7 @@
   FirstTerminator = nullptr;
 
   if (!MF->getProperties().hasProperty(
-      MachineFunctionProperties::Property::NoPHIs)) {
+      MachineFunctionProperties::Property::NoPHIs) && MRI->tracksLiveness()) {
     // If this block has allocatable physical registers live-in, check that
     // it is an entry block or landing pad.
     for (const auto &LI : MBB->liveins()) {
@@ -740,14 +740,16 @@
   }
 
   regsLive.clear();
-  for (const auto &LI : MBB->liveins()) {
-    if (!TargetRegisterInfo::isPhysicalRegister(LI.PhysReg)) {
-      report("MBB live-in list contains non-physical register", MBB);
-      continue;
+  if (MRI->tracksLiveness()) {
+    for (const auto &LI : MBB->liveins()) {
+      if (!TargetRegisterInfo::isPhysicalRegister(LI.PhysReg)) {
+        report("MBB live-in list contains non-physical register", MBB);
+        continue;
+      }
+      for (MCSubRegIterator SubRegs(LI.PhysReg, TRI, /*IncludeSelf=*/true);
+           SubRegs.isValid(); ++SubRegs)
+        regsLive.insert(*SubRegs);
     }
-    for (MCSubRegIterator SubRegs(LI.PhysReg, TRI, /*IncludeSelf=*/true);
-         SubRegs.isValid(); ++SubRegs)
-      regsLive.insert(*SubRegs);
   }
   regsLiveInButUnused = regsLive;
 
Index: lib/CodeGen/VirtRegMap.cpp
===================================================================
--- lib/CodeGen/VirtRegMap.cpp
+++ lib/CodeGen/VirtRegMap.cpp
@@ -225,8 +225,11 @@
   // Add kill flags while we still have virtual registers.
   LIS->addKillFlags(VRM);
 
-  // Live-in lists on basic blocks are required for physregs.
-  addMBBLiveIns();
+  if (TRI->trackLivenessAfterRegAlloc(*MF)) {
+    addMBBLiveIns();
+  } else {
+    MRI->invalidateLiveness();
+  }
 
   // Rewrite virtual registers.
   rewrite();