[AArch64] Fix debug printing crash in AArch64RedundantCopyElimination

The LastChange can be MBB->end(), so it is not valid to dereference it for
printing. Fix the DEBUG statement to check for end() and handle it specially.

llvm/lib/Target/AArch64/AArch64RedundantCopyElimination.cpp

@@ -462,7 +462,9 @@ bool AArch64RedundantCopyElimination::optimizeBlock(MachineBasicBlock *MBB) {
   // Clear kills in the range where changes were made.  This is conservative,
   // but should be okay since kill markers are being phased out.
   LLVM_DEBUG(dbgs() << "Clearing kill flags.\n\tFirstUse: " << *FirstUse
-                    << "\tLastChange: " << *LastChange);
+                    << "\tLastChange: ";
+             if (LastChange == MBB->end()) dbgs() << "<end>\n";
+             else dbgs() << *LastChange);
   for (MachineInstr &MMI : make_range(FirstUse, PredMBB->end()))
     MMI.clearKillInfo();
   for (MachineInstr &MMI : make_range(MBB->begin(), LastChange))