[llvm] [AArch64] Only clear kill flags if necessary when merging str (PR #69680)

[Matthias Braun via llvm-commits]

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@@ -997,8 +997,17 @@ AArch64LoadStoreOpt::mergePairedInsns(MachineBasicBlock::iterator I,
       //   STRWui %w0, ...
       //   USE %w1
       //   STRWui kill %w1  ; need to clear kill flag when moving STRWui upwards
-      RegOp0.setIsKill(false);
-      RegOp1.setIsKill(false);
+      for (auto It = std::next(I);
+           It != Paired && (RegOp0.isKill() || RegOp1.isKill()); ++It) {
+        auto ClearKill = [](MachineInstr &MI, MachineOperand &MOP,
+                            const TargetRegisterInfo *TRI) {
+          Register Reg = MOP.getReg();
+          if (MI.readsRegister(Reg, TRI))
+            MOP.setIsKill(false);
+        };
+        ClearKill(*It, RegOp0, TRI);
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MatzeB wrote:

It's been a while since I worked on this, so I hope I am not missing anything. But intuitively you would only need to change the flags for operands that you move around the schedule (as in conceptually you are moving one store next to the other store before replacing it with the `strd`).

https://github.com/llvm/llvm-project/pull/69680