From 22e596e986511b6f7a4ef2ffbd7d6fefe5d02607 Mon Sep 17 00:00:00 2001
From: David Green <david.green@arm.com>
Date: Wed, 23 Aug 2023 11:49:36 +0100
Subject: [PATCH] [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 | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/llvm/lib/Target/AArch64/AArch64RedundantCopyElimination.cpp b/llvm/lib/Target/AArch64/AArch64RedundantCopyElimination.cpp
index 369801a8ea7c..1494312886a4 100644
--- a/llvm/lib/Target/AArch64/AArch64RedundantCopyElimination.cpp
+++ b/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))