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

[Adrian Prantl via llvm-commits]

================
@@ -1227,6 +1261,30 @@ AArch64LoadStoreOpt::mergePairedInsns(MachineBasicBlock::iterator I,
             .addImm(0)
             .addImm(31);
     (void)MIBSXTW;
+
+    if (I->peekDebugInstrNum()) {
----------------
adrian-prantl wrote:

```suggestion
    if (auto InstrNum = I->peekDebugInstrNum()) {
```

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