[llvm] [BOLT][binary-analysis] Add initial pac-ret gadget scanner (PR #122304)

[Anatoly Trosinenko via llvm-commits]

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@@ -148,6 +148,69 @@ class AArch64MCPlusBuilder : public MCPlusBuilder {
     return false;
   }
 
+  MCPhysReg getAuthenticatedReg(const MCInst &Inst) const override {
+    switch (Inst.getOpcode()) {
+    case AArch64::AUTIAZ:
+    case AArch64::AUTIBZ:
+    case AArch64::AUTIASP:
+    case AArch64::AUTIBSP:
+    case AArch64::RETAA:
+    case AArch64::RETAB:
+      return AArch64::LR;
+    case AArch64::AUTIA1716:
+    case AArch64::AUTIB1716:
+      return AArch64::X17;
+    case AArch64::ERETAA:
+    case AArch64::ERETAB:
+      return AArch64::LR;
+
+    case AArch64::AUTIA:
+    case AArch64::AUTIB:
+    case AArch64::AUTDA:
+    case AArch64::AUTDB:
+    case AArch64::AUTIZA:
+    case AArch64::AUTIZB:
+    case AArch64::AUTDZA:
+    case AArch64::AUTDZB:
+      assert(Inst.getOperand(0).isReg());
+      return Inst.getOperand(0).getReg();
+
+    default:
+      return getNoRegister();
+    }
+  }
+
+  bool isAuthenticationOfReg(const MCInst &Inst,
+                             const unsigned RegAuthenticated) const override {
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atrosinenko wrote:

```suggestion
  bool isAuthenticationOfReg(const MCInst &Inst,
                             MCPhysReg RegAuthenticated) const override {
```

https://github.com/llvm/llvm-project/pull/122304