Index: llvm/trunk/lib/CodeGen/BranchFolding.h
===================================================================
--- llvm/trunk/lib/CodeGen/BranchFolding.h
+++ llvm/trunk/lib/CodeGen/BranchFolding.h
@@ -11,6 +11,7 @@
 #define LLVM_LIB_CODEGEN_BRANCHFOLDING_H
 
 #include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/CodeGen/LivePhysRegs.h"
 #include "llvm/CodeGen/MachineBasicBlock.h"
 #include "llvm/Support/BlockFrequency.h"
 #include <vector>
@@ -21,7 +22,6 @@
   class MachineFunction;
   class MachineModuleInfo;
   class MachineLoopInfo;
-  class RegScavenger;
   class TargetInstrInfo;
   class TargetRegisterInfo;
 
@@ -98,11 +98,12 @@
     bool AfterBlockPlacement;
     bool EnableTailMerge;
     bool EnableHoistCommonCode;
+    bool UpdateLiveIns;
     const TargetInstrInfo *TII;
     const TargetRegisterInfo *TRI;
     MachineModuleInfo *MMI;
     MachineLoopInfo *MLI;
-    RegScavenger *RS;
+    LivePhysRegs LiveRegs;
 
   public:
     /// \brief This class keeps track of branch frequencies of newly created
@@ -130,8 +131,7 @@
     bool TryTailMergeBlocks(MachineBasicBlock* SuccBB,
                        MachineBasicBlock* PredBB);
     void setCommonTailEdgeWeights(MachineBasicBlock &TailMBB);
-    void MaintainLiveIns(MachineBasicBlock *CurMBB,
-                         MachineBasicBlock *NewMBB);
+    void computeLiveIns(MachineBasicBlock &MBB);
     void ReplaceTailWithBranchTo(MachineBasicBlock::iterator OldInst,
                                  MachineBasicBlock *NewDest);
     MachineBasicBlock *SplitMBBAt(MachineBasicBlock &CurMBB,
Index: llvm/trunk/lib/CodeGen/BranchFolding.cpp
===================================================================
--- llvm/trunk/lib/CodeGen/BranchFolding.cpp
+++ llvm/trunk/lib/CodeGen/BranchFolding.cpp
@@ -32,7 +32,6 @@
 #include "llvm/CodeGen/MachineRegisterInfo.h"
 #include "llvm/CodeGen/Passes.h"
 #include "llvm/CodeGen/TargetPassConfig.h"
-#include "llvm/CodeGen/RegisterScavenging.h"
 #include "llvm/IR/Function.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
@@ -212,13 +211,10 @@
   TRI = tri;
   MMI = mmi;
   MLI = mli;
-  RS = nullptr;
 
-  // Use a RegScavenger to help update liveness when required.
   MachineRegisterInfo &MRI = MF.getRegInfo();
-  if (MRI.tracksLiveness() && TRI->trackLivenessAfterRegAlloc(MF))
-    RS = new RegScavenger();
-  else
+  UpdateLiveIns = MRI.tracksLiveness() && TRI->trackLivenessAfterRegAlloc(MF);
+  if (!UpdateLiveIns)
     MRI.invalidateLiveness();
 
   // Fix CFG.  The later algorithms expect it to be right.
@@ -249,10 +245,8 @@
   // See if any jump tables have become dead as the code generator
   // did its thing.
   MachineJumpTableInfo *JTI = MF.getJumpTableInfo();
-  if (!JTI) {
-    delete RS;
+  if (!JTI)
     return MadeChange;
-  }
 
   // Walk the function to find jump tables that are live.
   BitVector JTIsLive(JTI->getJumpTables().size());
@@ -274,7 +268,6 @@
       MadeChange = true;
     }
 
-  delete RS;
   return MadeChange;
 }
 
@@ -406,15 +399,27 @@
   return TailLen;
 }
 
-void BranchFolder::MaintainLiveIns(MachineBasicBlock *CurMBB,
-                                   MachineBasicBlock *NewMBB) {
-  if (RS) {
-    RS->enterBasicBlock(*CurMBB);
-    if (!CurMBB->empty())
-      RS->forward(std::prev(CurMBB->end()));
-    for (unsigned int i = 1, e = TRI->getNumRegs(); i != e; i++)
-      if (RS->isRegUsed(i, false))
-        NewMBB->addLiveIn(i);
+void BranchFolder::computeLiveIns(MachineBasicBlock &MBB) {
+  if (!UpdateLiveIns)
+    return;
+
+  LiveRegs.init(TRI);
+  LiveRegs.addLiveOutsNoPristines(MBB);
+  for (MachineInstr &MI : make_range(MBB.rbegin(), MBB.rend()))
+    LiveRegs.stepBackward(MI);
+
+  for (unsigned Reg : LiveRegs) {
+    // Skip the register if we are about to add one of its super registers.
+    bool ContainsSuperReg = false;
+    for (MCSuperRegIterator SReg(Reg, TRI); SReg.isValid(); ++SReg) {
+      if (LiveRegs.contains(*SReg)) {
+        ContainsSuperReg = true;
+        break;
+      }
+    }
+    if (ContainsSuperReg)
+      continue;
+    MBB.addLiveIn(Reg);
   }
 }
 
@@ -422,12 +427,9 @@
 /// after it, replacing it with an unconditional branch to NewDest.
 void BranchFolder::ReplaceTailWithBranchTo(MachineBasicBlock::iterator OldInst,
                                            MachineBasicBlock *NewDest) {
-  MachineBasicBlock *CurMBB = OldInst->getParent();
-
   TII->ReplaceTailWithBranchTo(OldInst, NewDest);
 
-  // For targets that use the register scavenger, we must maintain LiveIns.
-  MaintainLiveIns(CurMBB, NewDest);
+  computeLiveIns(*NewDest);
 
   ++NumTailMerge;
 }
@@ -465,8 +467,7 @@
   // NewMBB inherits CurMBB's block frequency.
   MBBFreqInfo.setBlockFreq(NewMBB, MBBFreqInfo.getBlockFreq(&CurMBB));
 
-  // For targets that use the register scavenger, we must maintain LiveIns.
-  MaintainLiveIns(&CurMBB, NewMBB);
+  computeLiveIns(*NewMBB);
 
   // Add the new block to the funclet.
   const auto &FuncletI = FuncletMembership.find(&CurMBB);