diff --git a/lib/CodeGen/MachineCSE.cpp b/lib/CodeGen/MachineCSE.cpp
index ae26967b235..29604089ad8 100644
--- a/lib/CodeGen/MachineCSE.cpp
+++ b/lib/CodeGen/MachineCSE.cpp
@@ -451,6 +451,7 @@ bool MachineCSE::ProcessBlock(MachineBasicBlock *MBB) {
 
   SmallVector<std::pair<unsigned, unsigned>, 8> CSEPairs;
   SmallVector<unsigned, 2> ImplicitDefsToUpdate;
+  SmallVector<unsigned, 2> ImplicitDefs;
   for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end(); I != E; ) {
     MachineInstr *MI = &*I;
     ++I;
@@ -542,6 +543,12 @@ bool MachineCSE::ProcessBlock(MachineBasicBlock *MBB) {
       // we should make sure it is not dead at CSMI.
       if (MO.isImplicit() && !MO.isDead() && CSMI->getOperand(i).isDead())
         ImplicitDefsToUpdate.push_back(i);
+
+      // Keep track of implicit defs of CSMI and MI, to clear possibly
+      // made-redundant kill flags.
+      if (MO.isImplicit() && !MO.isDead() && OldReg == NewReg)
+        ImplicitDefs.push_back(OldReg);
+
       if (OldReg == NewReg) {
         --NumDefs;
         continue;
@@ -582,6 +589,29 @@ bool MachineCSE::ProcessBlock(MachineBasicBlock *MBB) {
       for (unsigned i = 0, e = ImplicitDefsToUpdate.size(); i != e; ++i)
         CSMI->getOperand(ImplicitDefsToUpdate[i]).setIsDead(false);
 
+      // Go through implicit defs of CSMI and MI, and clear the kill flags on
+      // their uses in all the instructions between CSMI and MI.
+      // We might have made some of the kill flags redundant, consider:
+      //   subs  ... %NZCV<imp-def>        <- CSMI
+      //   csinc ... %NZCV<imp-use,kill>   <- this kill flag isn't valid anymore
+      //   subs  ... %NZCV<imp-def>        <- MI, to be eliminated
+      //   csinc ... %NZCV<imp-use,kill>
+      // Since we eliminated MI, and reused a register imp-def'd by CSMI
+      // (here %NZCV), that register, if it was killed before MI, should have
+      // that kill flag removed, because it's lifetime was extended.
+      if (CSMI->getParent() == MI->getParent()) {
+        for (MachineBasicBlock::iterator II = CSMI, IE = MI; II != IE; ++II)
+          for (auto ImplicitDef : ImplicitDefs)
+            if (MachineOperand *MO = II->findRegisterUseOperand(
+                    ImplicitDef, /*isKill=*/true, TRI))
+              MO->setIsKill(false);
+      } else {
+        // If the instructions aren't in the same BB, bail out and clear the
+        // kill flag on all uses of the imp-def'd register.
+        for (auto ImplicitDef : ImplicitDefs)
+          MRI->clearKillFlags(ImplicitDef);
+      }
+
       if (CrossMBBPhysDef) {
         // Add physical register defs now coming in from a predecessor to MBB
         // livein list.
@@ -606,6 +636,7 @@ bool MachineCSE::ProcessBlock(MachineBasicBlock *MBB) {
     }
     CSEPairs.clear();
     ImplicitDefsToUpdate.clear();
+    ImplicitDefs.clear();
   }
 
   return Changed;
diff --git a/test/CodeGen/AArch64/machine_cse_impdef_killflags.ll b/test/CodeGen/AArch64/machine_cse_impdef_killflags.ll
new file mode 100644
index 00000000000..e77824f5f14
--- /dev/null
+++ b/test/CodeGen/AArch64/machine_cse_impdef_killflags.ll
@@ -0,0 +1,26 @@
+; RUN: llc < %s -mtriple=aarch64-apple-ios -fast-isel -verify-machineinstrs | FileCheck %s
+
+; Check that the kill flag is cleared between CSE'd instructions on their
+; imp-def'd registers.
+; The verifier would complain otherwise.
+define i64 @csed-impdef-killflag(i64 %a) {
+; CHECK-LABEL: csed-impdef-killflag
+; CHECK-DAG:  mov    [[REG0:w[0-9]+]], wzr
+; CHECK-DAG:  orr    [[REG1:w[0-9]+]], wzr, #0x1
+; CHECK-DAG:  orr    [[REG2:x[0-9]+]], xzr, #0x2
+; CHECK-DAG:  orr    [[REG3:x[0-9]+]], xzr, #0x3
+; CHECK:      cmp    x0, #0
+; CHECK-DAG:  csel   w[[SELECT_WREG_1:[0-9]+]], [[REG0]], [[REG1]], ne
+; CHECK-DAG:  csel   [[SELECT_XREG_2:x[0-9]+]], [[REG2]], [[REG3]], ne
+; CHECK:      ubfx   [[SELECT_XREG_1:x[0-9]+]], x[[SELECT_WREG_1]], #0, #32
+; CHECK-NEXT: add    x0, [[SELECT_XREG_2]], [[SELECT_XREG_1]]
+; CHECK-NEXT: ret
+
+  %1 = icmp ne i64 %a, 0
+  %2 = select i1 %1, i32 0, i32 1
+  %3 = icmp ne i64 %a, 0
+  %4 = select i1 %3, i64 2, i64 3
+  %5 = zext i32 %2 to i64
+  %6 = add i64 %4, %5
+  ret i64 %6
+}