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

[Arseniy Obolenskiy via llvm-commits]

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@@ -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.
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aobolensk wrote:

TargetInstrInfo::lowerCopy turns an undef-source COPY into a KILL

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