[llvm] [InstrRef] Preserve debug instr num in aarch64-ldst-opt. (PR #136009)

[Adrian Prantl via llvm-commits]

================
@@ -965,6 +965,40 @@ static void updateDefinedRegisters(MachineInstr &MI, LiveRegUnits &Units,
       Units.addReg(MOP.getReg());
 }
 
+/// Find the DBG_INSTR_REF instruction that references the \p InstrNum
----------------
adrian-prantl wrote:

Is there always at most one? If not, this should be "Scan for the first ... in MBB."

https://github.com/llvm/llvm-project/pull/136009