[BOLT] Gadget scanner: analyze functions without CFG information

Support simple analysis of the functions for which BOLT is unable to
reconstruct the CFG. This patch is inspired by the approach implemented
by Kristof Beyls in the original prototype of gadget scanner, but a
CFG-unaware counterpart of the data-flow analysis is implemented
instead of separate version of gadget detector, as multiple gadget kinds
are detected now.

Author: atrosinenko

bolt/include/bolt/Core/BinaryFunction.h

@@ -793,6 +793,19 @@ class BinaryFunction {
     return iterator_range<const_cfi_iterator>(cie_begin(), cie_end());
   }
 
+  /// Iterate over instructions (only if CFG is unavailable or not built yet).
+  iterator_range<InstrMapType::iterator> instrs() {
+    assert(!hasCFG() && "Iterate over basic blocks instead");
+    return make_range(Instructions.begin(), Instructions.end());
+  }
+  iterator_range<InstrMapType::const_iterator> instrs() const {
+    assert(!hasCFG() && "Iterate over basic blocks instead");
+    return make_range(Instructions.begin(), Instructions.end());
+  }
+
+  /// Returns whether there are any labels at Offset.
+  bool hasLabelAt(unsigned Offset) const { return Labels.count(Offset) != 0; }
+
   /// Iterate over all jump tables associated with this function.
   iterator_range<std::map<uint64_t, JumpTable *>::const_iterator>
   jumpTables() const {

bolt/include/bolt/Passes/PAuthGadgetScanner.h

@@ -67,6 +67,14 @@ struct MCInstInBFReference {
   uint64_t Offset;
   MCInstInBFReference(BinaryFunction *BF, uint64_t Offset)
       : BF(BF), Offset(Offset) {}
+
+  static MCInstInBFReference get(const MCInst *Inst, BinaryFunction &BF) {
+    for (auto &I : BF.instrs())
+      if (Inst == &I.second)
+        return MCInstInBFReference(&BF, I.first);
+    return {};
+  }
+
   MCInstInBFReference() : BF(nullptr), Offset(0) {}
   bool operator==(const MCInstInBFReference &RHS) const {
     return BF == RHS.BF && Offset == RHS.Offset;
@@ -106,6 +114,12 @@ struct MCInstReference {
   MCInstReference(BinaryFunction *BF, uint32_t Offset)
       : MCInstReference(MCInstInBFReference(BF, Offset)) {}
 
+  static MCInstReference get(const MCInst *Inst, BinaryFunction &BF) {
+    if (BF.hasCFG())
+      return MCInstInBBReference::get(Inst, BF);
+    return MCInstInBFReference::get(Inst, BF);
+  }
+
   bool operator<(const MCInstReference &RHS) const {
     if (ParentKind != RHS.ParentKind)
       return ParentKind < RHS.ParentKind;
@@ -140,6 +154,16 @@ struct MCInstReference {
     llvm_unreachable("");
   }
 
+  operator bool() const {
+    switch (ParentKind) {
+    case BasicBlockParent:
+      return U.BBRef.BB != nullptr;
+    case FunctionParent:
+      return U.BFRef.BF != nullptr;
+    }
+    llvm_unreachable("");
+  }
+
   uint64_t getAddress() const {
     switch (ParentKind) {
     case BasicBlockParent: