[llvm] [BOLT][AArch64] Add more heuristics on epilogue determination (PR #167077)

[Gergely Bálint via llvm-commits]

================
@@ -164,11 +164,53 @@ class AArch64MCPlusBuilder : public MCPlusBuilder {
 
   bool isPush(const MCInst &Inst) const override {
     return isStoreToStack(Inst);
-  };
+  }
 
   bool isPop(const MCInst &Inst) const override {
     return isLoadFromStack(Inst);
-  };
+  }
+
+  // We look for instructions that load from stack or make stack pointer
+  // adjustment, and assume the basic block is an epilogue if and only if
+  // such instructions are present and also immediately precede the branch
+  // instruction that ends the basic block.
+  bool isEpilogue(const BinaryBasicBlock &BB) const override {
+    if (BB.succ_size())
+      return false;
+
+    bool SeenLoadFromStack = false;
+    bool SeenStackPointerAdjustment = false;
+    for (const MCInst &Instr : BB) {
+      // Skip CFI pseudo instruction.
+      if (isCFI(Instr))
+        continue;
+
+      bool IsPop = isPop(Instr);
+      // A load from stack instruction could do SP adjustment in pre-index or
+      // post-index form, which we can skip to check for epilogue recognition
+      // purpose.
+      bool IsSPAdj = (isADD(Instr) || isMOVW(Instr)) &&
+                     Instr.getOperand(0).isReg() &&
+                     Instr.getOperand(0).getReg() == AArch64::SP;
+      SeenLoadFromStack |= IsPop;
+      SeenStackPointerAdjustment |= IsSPAdj;
+
+      if (!SeenLoadFromStack && !SeenStackPointerAdjustment)
+        continue;
+      if (IsPop || IsSPAdj || isPAuthOnLR(Instr))
+        continue;
+      if (isReturn(Instr) || isPAuthAndRet(Instr))
----------------
bgergely0 wrote:

```suggestion
      if (isReturn(Instr))
```

https://github.com/llvm/llvm-project/pull/167077