[llvm] [BOLT] Improve DWARF CFI generation for pac-ret binaries (PR #163381)

[Paschalis Mpeis via llvm-commits]

================
@@ -104,32 +118,126 @@ void InsertNegateRAState::coverFunctionFragmentStart(BinaryFunction &BF,
                          MCCFIInstruction::createNegateRAState(nullptr));
 }
 
-void InsertNegateRAState::inferUnknownStates(BinaryFunction &BF) {
+std::optional<bool>
+InsertNegateRAState::getFirstKnownRAState(BinaryContext &BC,
+                                          BinaryBasicBlock &BB) {
+  for (const MCInst &Inst : BB) {
+    if (BC.MIB->isCFI(Inst))
+      continue;
+    std::optional<bool> RAState = BC.MIB->getRAState(Inst);
+    if (RAState.has_value())
+      return RAState;
+  }
+  return std::nullopt;
+}
+
+void InsertNegateRAState::fillUnknownStateInBB(BinaryContext &BC,
+                                               BinaryBasicBlock &BB) {
+
+  auto First = BB.getFirstNonPseudo();
+  if (First == BB.end())
+    return;
+  // If the first instruction has unknown RAState, we should copy the first
+  // known RAState.
+  std::optional<bool> RAState = BC.MIB->getRAState(*First);
+  if (!RAState.has_value()) {
+    std::optional<bool> FirstRAState = getFirstKnownRAState(BC, BB);
+    if (!FirstRAState.has_value())
+      // We fill unknown BBs later.
+      return;
+
+    BC.MIB->setRAState(*First, *FirstRAState);
+  }
+
+  // At this point we know the RAState of the first instruction,
+  // so we can propagate the RAStates to all subsequent unknown instructions.
+  MCInst Prev = *First;
+  for (auto It = First + 1; It != BB.end(); ++It) {
+    MCInst &Inst = *It;
+    if (BC.MIB->isCFI(Inst))
+      continue;
+
+    // No need to check for nullopt: we only entered this loop after the first
+    // instruction had its RAState set, and RAState is always set for the
+    // previous instruction in the previous iteration of the loop.
+    std::optional<bool> PrevRAState = BC.MIB->getRAState(Prev);
+
+    std::optional<bool> RAState = BC.MIB->getRAState(Inst);
+    if (!RAState.has_value()) {
+      if (BC.MIB->isPSignOnLR(Prev))
+        PrevRAState = true;
+      else if (BC.MIB->isPAuthOnLR(Prev))
+        PrevRAState = false;
+      BC.MIB->setRAState(Inst, *PrevRAState);
+    }
+    Prev = Inst;
+  }
+}
+
+bool InsertNegateRAState::isUnknownBlock(BinaryContext &BC,
----------------
paschalis-mpeis wrote:

Any differences from `getFirstKnownRAState`? We could maybe get away with one function, or have a thin wrapper here if it simplifies code parsing.

https://github.com/llvm/llvm-project/pull/163381