revng-revng/lib/EarlyFunctionAnalysis/ControlFlowGraph.cpp

/// \file ControlFlowGraph.cpp

//
// This file is distributed under the MIT License. See LICENSE.md for details.
//

#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/Support/DOTGraphTraits.h"
#include "llvm/Support/GraphWriter.h"
#include "llvm/Support/raw_os_ostream.h"

#include "revng/ADT/GenericGraph.h"
#include "revng/BasicAnalyses/GeneratedCodeBasicInfo.h"
#include "revng/EarlyFunctionAnalysis/CFGHelpers.h"
#include "revng/EarlyFunctionAnalysis/ControlFlowGraph.h"
#include "revng/Model/Binary.h"
#include "revng/Model/VerifyHelper.h"
#include "revng/Support/IRHelpers.h"

using namespace llvm;

namespace efa {

struct FunctionCFGNodeData {
  FunctionCFGNodeData(const efa::BasicBlock &BB, const MetaAddress &) :
    ID(BB.ID()) {}
  BasicBlockID ID;
};

using FunctionCFGNode = ForwardNode<FunctionCFGNodeData>;
using FunctionCFG = GenericGraph<FunctionCFGNode, 16, true>;

/// A helper data structure to simplify working with the graph
/// when verifying the CFG.
struct FunctionCFGVerificationHelper {
public:
  FunctionCFG Graph;
  std::map<BasicBlockID, FunctionCFGNode *> Map;

public:
  FunctionCFGVerificationHelper(const efa::ControlFlowGraph &Metadata,
                                const model::Binary &Binary) {
    using G = FunctionCFG;
    std::tie(Graph, Map) = buildControlFlowGraph<G>(Metadata.Blocks(),
                                                    Metadata.Entry(),
                                                    Binary);
  }

public:
  SmallVector<const FunctionCFGNode *, 4> unreachableNodes() const {
    revng_assert(Graph.size() == Map.size());
    if (Map.size() == 0)
      return {};

    // Ensure all the nodes are reachable from the entry node
    df_iterator_default_set<FunctionCFGNode *> Visited;
    revng_assert(Graph.getEntryNode() != nullptr);
    for (auto &Ignore : depth_first_ext(Graph.getEntryNode(), Visited))
      ;

    if (Visited.size() == Graph.size())
      return {};

    SmallVector<const FunctionCFGNode *, 4> Result;

    for (const FunctionCFGNode *Node : Graph.nodes())
      if (!Visited.contains(Node))
        Result.push_back(Node);

    return Result;
  }

  bool hasAtMostOneInvalidExit() const {
    FunctionCFGNode *Exit = nullptr;
    for (const auto &[Address, Node] : Map) {
      if (not Address.isValid()) {
        if (Node->hasSuccessors() || Exit != nullptr)
          return false;
        Exit = Node;
      } else {
        if (!Node->hasSuccessors())
          return false;
      }
    }

    return true;
  }
};

const efa::BasicBlock *ControlFlowGraph::findBlock(GeneratedCodeBasicInfo &GCBI,
                                                   llvm::BasicBlock *BB) const {
  const llvm::BasicBlock *JumpTargetBB = getJumpTargetBlock(BB);
  if (JumpTargetBB == nullptr)
    return nullptr;

  BasicBlockID CallerBlockID = getBasicBlockID(JumpTargetBB);
  revng_assert(CallerBlockID.isValid());
  auto It = Blocks().find(CallerBlockID);

  while (It == Blocks().end()) {

    const llvm::BasicBlock *PredecessorJumpTargetBB = nullptr;
    for (const llvm::BasicBlock *Predecessor : predecessors(JumpTargetBB)) {
      auto IBDHB = BlockType::IndirectBranchDispatcherHelperBlock;
      if (GCBI.isTranslated(Predecessor) or getType(Predecessor) == IBDHB) {
        const llvm::BasicBlock *NewJT = getJumpTargetBlock(Predecessor);
        if (PredecessorJumpTargetBB != nullptr) {
          revng_assert(PredecessorJumpTargetBB == NewJT,
                       "Jump target is not in the CFG but it has multiple "
                       "predecessors");
        }
        PredecessorJumpTargetBB = NewJT;
      }
    }
    JumpTargetBB = PredecessorJumpTargetBB;

    revng_assert(JumpTargetBB != nullptr);
    CallerBlockID = getBasicBlockID(JumpTargetBB);
    revng_assert(CallerBlockID.isValid());
    It = Blocks().find(CallerBlockID);
  }

  return &*It;
}

void ControlFlowGraph::serialize(GeneratedCodeBasicInfo &GCBI) const {
  using namespace llvm;
  using llvm::BasicBlock;

  BasicBlock *BB = GCBI.getBlockAt(Entry());
  LLVMContext &Context = getContext(BB);
  std::string Buffer;
  {
    raw_string_ostream Stream(Buffer);
    ::serialize(Stream, *this);
  }

  Instruction *Term = BB->getTerminator();
  MDNode *Node = MDNode::get(Context, MDString::get(Context, Buffer));
  Term->setMetadata(ControlFlowGraphMDName, Node);
}

void ControlFlowGraph::simplify(const model::Binary &Binary) {
  // If A does not end with a call and A.end == B.start and A is the only
  // predecessor of B and B is the only successor of A, merge

  // Create quick map of predecessors
  std::map<BasicBlockID, SmallVector<BasicBlockID, 2>> Predecessors;
  for (efa::BasicBlock &Block : Blocks()) {
    for (auto &Successor : Block.Successors()) {
      if (Successor->Type() == efa::FunctionEdgeType::DirectBranch
          and Successor->Destination().isValid()) {
        Predecessors[Successor->Destination()].push_back(Block.ID());
      } else if (auto *Call = dyn_cast<efa::CallEdge>(Successor.get())) {
        if (not Call->IsTailCall()
            and not Call->hasAttribute(Binary,
                                       model::FunctionAttribute::NoReturn)) {
          Predecessors[Block.nextBlock()].push_back(Block.ID());
        }
      }
    }
  }

  // Identify blocks that need to be merged in their predecessor
  SmallVector<std::pair<BasicBlockID, BasicBlockID>, 4> ToMerge;
  for (efa::BasicBlock &Block : Blocks()) {
    // Ignore entry block entirely
    if (Block.End() == Entry())
      continue;

    // Do we have only one successor?
    if (Block.Successors().size() != 1)
      continue;

    // Is the successor a direct branch to the end of the block?
    auto &OnlySuccessor = *Block.Successors().begin();
    if (not(OnlySuccessor->Type() == efa::FunctionEdgeType::DirectBranch
            and OnlySuccessor->Destination() == Block.nextBlock()))
      continue;

    // Does the only successor has only one predecessor?
    auto PredecessorsAddress = Predecessors.at(Block.nextBlock());
    if (PredecessorsAddress.size() != 1)
      continue;

    // Are we the only predecessor?
    if (*PredecessorsAddress.begin() != Block.ID())
      continue;

    ToMerge.emplace_back(Block.ID(), Block.nextBlock());
  }

  for (auto &&[PredecessorAddress, BlockAddress] : llvm::reverse(ToMerge)) {
    efa::BasicBlock &Predecessor = Blocks().at(PredecessorAddress);
    efa::BasicBlock &Block = Blocks().at(BlockAddress);

    // Safety checks
    revng_assert(Predecessor.Successors().size() == 1);
    revng_assert(Predecessor.End() == Block.ID().start());

    // Merge Block into Predecessor
    Predecessor.End() = Block.End();
    Predecessor.Successors() = std::move(Block.Successors());

    // Drop Block
    Blocks().erase(BlockAddress);
  }
}

bool ControlFlowGraph::verify(const model::Binary &Binary) const {
  return verify(Binary, false);
}

bool ControlFlowGraph::verify(const model::Binary &Binary, bool Assert) const {
  model::VerifyHelper VH(Assert);
  return verify(Binary, VH);
}

bool ControlFlowGraph::verify(const model::Binary &Binary,
                              model::VerifyHelper &VH) const {
  if (Entry().isInvalid())
    return VH.fail("CFG can only be built for a valid function.", *this);

  if (not Binary.Functions().contains(Entry()))
    return VH.fail("CFG can only be built for a known function.", *this);

  const auto &Function = Binary.Functions().at(Entry());

  if (Blocks().size() == 0)
    return VH.fail("The function has no CFG", *this);

  // Populate graph
  FunctionCFGVerificationHelper Helper(*this, Binary);

  // Ensure all the nodes are reachable from the entry node
  auto UnreachableNodes = Helper.unreachableNodes();
  if (UnreachableNodes.size() > 0) {
    std::string Message = "The following nodes are unreachable:\n\n";
    for (const FunctionCFGNode *UnreachableNode : UnreachableNodes)
      Message += "  " + UnreachableNode->ID.toString() + "\n";
    return VH.fail(Message, *this);
  }

  // Ensure the only node with no successors is invalid
  if (not Helper.hasAtMostOneInvalidExit())
    return VH.fail("We have more than one invalid exit", *this);

  // Verify blocks
  if (Blocks().size() > 0) {
    bool HasEntry = false;
    for (const BasicBlock &Block : Blocks()) {

      if (Block.ID() == BasicBlockID(Entry())) {
        if (HasEntry)
          return VH.fail("Multiple entry point blocks found, reporting the "
                         "second one",
                         Block);
        HasEntry = true;
      }

      if (Block.ID().isValid() and Block.End().isInvalid())
        return VH.fail("If a block has a beginning, it must also have an end.",
                       Block);

      if (Block.Successors().size() == 0)
        return VH.fail("A block has no successors", Block);

      for (const auto &Edge : Block.Successors())
        if (not Edge->verify(VH))
          return VH.fail("Invalid successor", Edge);
    }

    if (not HasEntry) {
      return VH.fail("The function CFG does not contain a block starting at "
                     "the entry point",
                     *this);
    }
  }

  // Check function calls
  for (const auto &Block : Blocks()) {
    for (const auto &Edge : Block.Successors()) {
      if (Edge->Type() == efa::FunctionEdgeType::FunctionCall) {
        // We're in a direct call, get the callee
        const auto *Call = dyn_cast<CallEdge>(Edge.get());

        if (not Call->DynamicFunction().empty()) {
          // It's a dynamic call
          auto &Function = Call->DynamicFunction();
          if (!Binary.ImportedDynamicFunctions().contains(Function))
            return VH.fail("Can't find callee \"" + Call->DynamicFunction()
                             + "\"",
                           Edge);
        } else if (Call->isDirect()) {
          // Regular call
          if (!Binary.Functions().contains(Call->Destination().start()))
            return VH.fail("Can't find callee", Edge);
        }
      }
    }
  }

  return true;
}

void ControlFlowGraph::dumpCFG(const model::Binary &Binary) const {
  auto &&[G, _] = buildControlFlowGraph<FunctionCFG>(Blocks(), Entry(), Binary);
  WriteGraph(&G, "function-metadata");
}

const CallEdge *FunctionEdgeBase::getCallEdge() const {
  return llvm::dyn_cast<CallEdge>(this);
}

bool FunctionEdgeBase::verify() const {
  return verify(false);
}

bool FunctionEdgeBase::verify(bool Assert) const {
  model::VerifyHelper VH(Assert);
  return verify(VH);
}

bool FunctionEdgeBase::verify(model::VerifyHelper &VH) const {
  using namespace efa::FunctionEdgeType;

  switch (Type()) {
  case Invalid:
  case Count:
  default:
    return VH.fail("Invalid edge type");

  case DirectBranch:
    if (not Destination().isValid())
      return VH.fail("Invalid destination in DirectBranch");
    break;

  case FunctionCall: {
    const auto &Call = cast<const CallEdge>(*this);
    if (Destination().isValid()) {
      if (not Call.DynamicFunction().empty())
        return VH.fail("Dynamic function has destination address");

      if (Destination().isInlined())
        return VH.fail("Callee block marked as inlined");
    }
  } break;

  case Return:
  case BrokenReturn:
  case LongJmp:
  case Killer:
  case Unreachable:
    if (Destination().isValid())
      return VH.fail("Unexpected destination, please use `:Invalid`.");
    break;
  }

  return true;
}

std::string BasicBlock::name() const {
  return "bb_" + ID().toString();
}

bool BasicBlock::verify() const {
  return verify(false);
}

bool BasicBlock::verify(bool Assert) const {
  model::VerifyHelper VH(Assert);
  return verify(VH);
}

bool BasicBlock::verify(model::VerifyHelper &VH) const {
  if (not ID().isValid() or End().isInvalid())
    return VH.fail("Invalid BasicBlock ID or End");

  for (auto &Edge : Successors())
    if (not Edge->verify(VH))
      return VH.fail();

  return true;
}

} // namespace efa

template<>
struct llvm::DOTGraphTraits<efa::FunctionCFG *> : public DefaultDOTGraphTraits {
  DOTGraphTraits(bool Simple = false) : DefaultDOTGraphTraits(Simple) {}

  static std::string getNodeLabel(const efa::FunctionCFGNode *Node,
                                  const efa::FunctionCFG *) {
    return Node->ID.toString();
  }

  static std::string getNodeAttributes(const efa::FunctionCFGNode *Node,
                                       const efa::FunctionCFG *Graph) {
    if (Node->ID == Graph->getEntryNode()->ID) {
      return "shape=box,peripheries=2";
    }

    return "";
  }
};