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//===- PostOrderCFGView.h - Post order view of CFG blocks -------*- C++ -*-===//

//

// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.

// See https://llvm.org/LICENSE.txt for license information.

// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

//

//===----------------------------------------------------------------------===//

//

// This file implements post order view of the blocks in a CFG.

//

//===----------------------------------------------------------------------===//

#ifndef LLVM_CLANG_ANALYSIS_ANALYSES_POSTORDERCFGVIEW_H

#define LLVM_CLANG_ANALYSIS_ANALYSES_POSTORDERCFGVIEW_H

#include "clang/Analysis/AnalysisDeclContext.h"

#include "clang/Analysis/CFG.h"

#include "clang/Basic/LLVM.h"

#include "llvm/ADT/BitVector.h"

#include "llvm/ADT/DenseMap.h"

#include "llvm/ADT/PostOrderIterator.h"

#include <utility>

#include <vector>

namespace clang {

class PostOrderCFGView : public ManagedAnalysis {

  virtual void anchor();

public:

  /// Implements a set of CFGBlocks using a BitVector.

  ///

  /// This class contains a minimal interface, primarily dictated by the SetType

  /// template parameter of the llvm::po_iterator template, as used with

  /// external storage. We also use this set to keep track of which CFGBlocks we

  /// visit during the analysis.

  class CFGBlockSet {

    llvm::BitVector VisitedBlockIDs;

  public:

    // po_iterator requires this iterator, but the only interface needed is the

    // value_type type.

    struct iterator { using value_type = const CFGBlock *; };

    CFGBlockSet() = default;

    CFGBlockSet(const CFG *G) : VisitedBlockIDs(G->getNumBlockIDs(), false) {}

    /// Set the bit associated with a particular CFGBlock.

    /// This is the important method for the SetType template parameter.

    std::pair<std::nullopt_t, bool> insert(const CFGBlock *Block) {

      // Note that insert() is called by po_iterator, which doesn't check to

      // make sure that Block is non-null.  Moreover, the CFGBlock iterator will

      // occasionally hand out null pointers for pruned edges, so we catch those

      // here.

      if (!Block)

        return std::make_pair(std::nullopt,

                              false); // if an edge is trivially false.

      if (VisitedBlockIDs.test(Block->getBlockID()))

        return std::make_pair(std::nullopt, false);

      VisitedBlockIDs.set(Block->getBlockID());

      return std::make_pair(std::nullopt, true);

    }

    /// Check if the bit for a CFGBlock has been already set.

    /// This method is for tracking visited blocks in the main threadsafety

    /// loop. Block must not be null.

    bool alreadySet(const CFGBlock *Block) {

      return VisitedBlockIDs.test(Block->getBlockID());

    }

  };

private:

  using po_iterator = llvm::po_iterator<const CFG *, CFGBlockSet, true>;

  std::vector<const CFGBlock *> Blocks;

  using BlockOrderTy = llvm::DenseMap<const CFGBlock *, unsigned>;

  BlockOrderTy BlockOrder;

public:

  friend struct BlockOrderCompare;

  using iterator = std::vector<const CFGBlock *>::reverse_iterator;

  using const_iterator = std::vector<const CFGBlock *>::const_reverse_iterator;

  PostOrderCFGView(const CFG *cfg);

  iterator begin() { return Blocks.rbegin(); }

  iterator end() { return Blocks.rend(); }

  const_iterator begin() const { return Blocks.rbegin(); }

  const_iterator end() const { return Blocks.rend(); }

  bool empty() const { return begin() == end(); }

  struct BlockOrderCompare {

    const PostOrderCFGView &POV;

  public:

    BlockOrderCompare(const PostOrderCFGView &pov) : POV(pov) {}

    bool operator()(const CFGBlock *b1, const CFGBlock *b2) const;

  };

  BlockOrderCompare getComparator() const {

    return BlockOrderCompare(*this);

  }

  // Used by AnalyisContext to construct this object.

  static const void *getTag();

  static std::unique_ptr<PostOrderCFGView>

  create(AnalysisDeclContext &analysisContext);

};

} // namespace clang

#endif // LLVM_CLANG_ANALYSIS_ANALYSES_POSTORDERCFGVIEW_H