Add retguard for arm64.

Index: lib/Target/AArch64/AArch64FrameLowering.cpp
--- lib/Target/AArch64/AArch64FrameLowering.cpp.orig
+++ lib/Target/AArch64/AArch64FrameLowering.cpp
@@ -123,6 +123,7 @@
 #include "AArch64InstrInfo.h"
 #include "AArch64MachineFunctionInfo.h"
 #include "AArch64RegisterInfo.h"
+#include "AArch64ReturnProtectorLowering.h"
 #include "AArch64Subtarget.h"
 #include "AArch64TargetMachine.h"
 #include "MCTargetDesc/AArch64AddressingModes.h"
@@ -2753,6 +2754,10 @@ void AArch64FrameLowering::determineCalleeSaves(Machin
                                 ? RegInfo->getBaseRegister()
                                 : (unsigned)AArch64::NoRegister;
 
+  if (MFI.hasReturnProtectorRegister() && MFI.getReturnProtectorNeedsStore()) {
+    SavedRegs.set(MFI.getReturnProtectorRegister());
+  }
+
   unsigned ExtraCSSpill = 0;
   // Figure out which callee-saved registers to save/restore.
   for (unsigned i = 0; CSRegs[i]; ++i) {
@@ -3532,6 +3537,10 @@ unsigned AArch64FrameLowering::getWinEHFuncletFrameSiz
   // This is the amount of stack a funclet needs to allocate.
   return alignTo(CSSize + MF.getFrameInfo().getMaxCallFrameSize(),
                  getStackAlign());
+}
+
+const ReturnProtectorLowering *AArch64FrameLowering::getReturnProtector() const {
+  return &RPL;
 }
 
 namespace {