[llvm] [AMDGPU] Do not erase KILLs that redefine a register in SIPostRABundler (PR #218349)

[Matt Arsenault via llvm-commits]

================
@@ -222,6 +222,12 @@ bool SIPostRABundler::run(MachineFunction &MF) {
 
           while (Next != E && Next->isKill()) {
             MachineInstr &Kill = *Next;
+
+            // KILL from an undef-source COPY keeps its def; must not erase it.
----------------
arsenm wrote:

KILL instructions can't have defs?

https://github.com/llvm/llvm-project/pull/218349