//===- CFG.h ----------------------------------------------------*- 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
//
//===----------------------------------------------------------------------===//
/// \file
///
/// This file provides various utilities for inspecting and working with the
/// control flow graph in LLVM IR. This includes generic facilities for
/// iterating successors and predecessors of basic blocks, the successors of
/// specific terminator instructions, etc. It also defines specializations of
/// GraphTraits that allow Function and BasicBlock graphs to be treated as
/// proper graphs for generic algorithms.
///
//===----------------------------------------------------------------------===//

#ifndef LLVM_IR_CFG_H
#define LLVM_IR_CFG_H

#include "llvm/ADT/GraphTraits.h"
#include "llvm/ADT/iterator.h"
#include "llvm/ADT/iterator_range.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/Value.h"
#include <cassert>
#include <cstddef>
#include <iterator>

namespace llvm {

class Instruction;
class Use;

//===----------------------------------------------------------------------===//
// BasicBlock pred_iterator definition
//===----------------------------------------------------------------------===//

template <class Ptr, class USE_iterator> // Predecessor Iterator
class PredIterator {
public:
  using iterator_category = std::forward_iterator_tag;
  using value_type = Ptr *;
  using difference_type = std::ptrdiff_t;
  using pointer = Ptr **;
  using reference = Ptr *;

protected:
  using Self = PredIterator<Ptr, USE_iterator>;
  USE_iterator It;

public:
  PredIterator() = default;
  explicit inline PredIterator(Ptr *bb) : It(bb->user_begin()) {}
  inline PredIterator(Ptr *bb, bool) : It(bb->user_end()) {}

  inline bool operator==(const Self& x) const { return It == x.It; }
  inline bool operator!=(const Self& x) const { return !operator==(x); }

  inline reference operator*() const {
    assert(!It.atEnd() && "pred_iterator out of range!");
    auto *I = cast<Instruction>(*It);
    assert(I->isTerminator() && "BasicBlock used in non-terminator");
    return I->getParent();
  }
  inline pointer *operator->() const { return &operator*(); }

  inline Self& operator++() {   // Preincrement
    assert(!It.atEnd() && "pred_iterator out of range!");
    ++It;
    return *this;
  }

  inline Self operator++(int) { // Postincrement
    Self tmp = *this; ++*this; return tmp;
  }

  /// getOperandNo - Return the operand number in the predecessor's
  /// terminator of the successor.
  unsigned getOperandNo() const {
    return It.getOperandNo();
  }

  /// getUse - Return the operand Use in the predecessor's terminator
  /// of the successor.
  Use &getUse() const {
    return It.getUse();
  }
};

using pred_iterator = PredIterator<BasicBlock, Value::user_iterator>;
using const_pred_iterator =
    PredIterator<const BasicBlock, Value::const_user_iterator>;
using pred_range = iterator_range<pred_iterator>;
using const_pred_range = iterator_range<const_pred_iterator>;

inline pred_iterator pred_begin(BasicBlock *BB) { return pred_iterator(BB); }
inline const_pred_iterator pred_begin(const BasicBlock *BB) {
  return const_pred_iterator(BB);
}
inline pred_iterator pred_end(BasicBlock *BB) { return pred_iterator(BB, true);}
inline const_pred_iterator pred_end(const BasicBlock *BB) {
  return const_pred_iterator(BB, true);
}
inline bool pred_empty(const BasicBlock *BB) {
  return pred_begin(BB) == pred_end(BB);
}
/// Get the number of predecessors of \p BB. This is a linear time operation.
/// Use \ref BasicBlock::hasNPredecessors() or hasNPredecessorsOrMore if able.
inline unsigned pred_size(const BasicBlock *BB) {
  return std::distance(pred_begin(BB), pred_end(BB));
}
inline pred_range predecessors(BasicBlock *BB) {
  return pred_range(pred_begin(BB), pred_end(BB));
}
inline const_pred_range predecessors(const BasicBlock *BB) {
  return const_pred_range(pred_begin(BB), pred_end(BB));
}

//===----------------------------------------------------------------------===//
// Instruction and BasicBlock succ_iterator helpers
//===----------------------------------------------------------------------===//

using succ_iterator = Instruction::succ_iterator;
using const_succ_iterator = Instruction::const_succ_iterator;
using succ_range = iterator_range<succ_iterator>;
using const_succ_range = iterator_range<const_succ_iterator>;

inline succ_iterator succ_begin(Instruction *I) {
  return I->successors().begin();
}
inline const_succ_iterator succ_begin(const Instruction *I) {
  return I->successors().begin();
}
inline succ_iterator succ_end(Instruction *I) { return I->successors().end(); }
inline const_succ_iterator succ_end(const Instruction *I) {
  return I->successors().end();
}
inline bool succ_empty(const Instruction *I) {
  return succ_begin(I) == succ_end(I);
}
inline unsigned succ_size(const Instruction *I) {
  return std::distance(succ_begin(I), succ_end(I));
}
inline succ_range successors(Instruction *I) { return I->successors(); }
inline const_succ_range successors(const Instruction *I) {
  return I->successors();
}

inline succ_iterator succ_begin(BasicBlock *BB) {
  return succ_begin(BB->getTerminator());
}
inline const_succ_iterator succ_begin(const BasicBlock *BB) {
  return succ_begin(BB->getTerminator());
}
inline succ_iterator succ_end(BasicBlock *BB) {
  return succ_end(BB->getTerminator());
}
inline const_succ_iterator succ_end(const BasicBlock *BB) {
  return succ_end(BB->getTerminator());
}
inline bool succ_empty(const BasicBlock *BB) {
  return succ_begin(BB) == succ_end(BB);
}
inline unsigned succ_size(const BasicBlock *BB) {
  return std::distance(succ_begin(BB), succ_end(BB));
}
inline succ_range successors(BasicBlock *BB) {
  return successors(BB->getTerminator());
}
inline const_succ_range successors(const BasicBlock *BB) {
  return successors(BB->getTerminator());
}

//===--------------------------------------------------------------------===//
// GraphTraits specializations for basic block graphs (CFGs)
//===--------------------------------------------------------------------===//

// Provide specializations of GraphTraits to be able to treat a function as a
// graph of basic blocks...

template <> struct GraphTraits<BasicBlock*> {
  using NodeRef = BasicBlock *;
  using ChildIteratorType = succ_iterator;

  static NodeRef getEntryNode(BasicBlock *BB) { return BB; }
  static ChildIteratorType child_begin(NodeRef N) { return succ_begin(N); }
  static ChildIteratorType child_end(NodeRef N) { return succ_end(N); }

  static unsigned getNumber(const BasicBlock *BB) { return BB->getNumber(); }
};

static_assert(GraphHasNodeNumbers<BasicBlock *>,
              "GraphTraits getNumber() not detected");

template <> struct GraphTraits<const BasicBlock*> {
  using NodeRef = const BasicBlock *;
  using ChildIteratorType = const_succ_iterator;

  static NodeRef getEntryNode(const BasicBlock *BB) { return BB; }

  static ChildIteratorType child_begin(NodeRef N) { return succ_begin(N); }
  static ChildIteratorType child_end(NodeRef N) { return succ_end(N); }

  static unsigned getNumber(const BasicBlock *BB) { return BB->getNumber(); }
};

static_assert(GraphHasNodeNumbers<const BasicBlock *>,
              "GraphTraits getNumber() not detected");

// Provide specializations of GraphTraits to be able to treat a function as a
// graph of basic blocks... and to walk it in inverse order.  Inverse order for
// a function is considered to be when traversing the predecessor edges of a BB
// instead of the successor edges.
//
template <> struct GraphTraits<Inverse<BasicBlock*>> {
  using NodeRef = BasicBlock *;
  using ChildIteratorType = pred_iterator;

  static NodeRef getEntryNode(Inverse<BasicBlock *> G) { return G.Graph; }
  static ChildIteratorType child_begin(NodeRef N) { return pred_begin(N); }
  static ChildIteratorType child_end(NodeRef N) { return pred_end(N); }

  static unsigned getNumber(const BasicBlock *BB) { return BB->getNumber(); }
};

static_assert(GraphHasNodeNumbers<Inverse<BasicBlock *>>,
              "GraphTraits getNumber() not detected");

template <> struct GraphTraits<Inverse<const BasicBlock*>> {
  using NodeRef = const BasicBlock *;
  using ChildIteratorType = const_pred_iterator;

  static NodeRef getEntryNode(Inverse<const BasicBlock *> G) { return G.Graph; }
  static ChildIteratorType child_begin(NodeRef N) { return pred_begin(N); }
  static ChildIteratorType child_end(NodeRef N) { return pred_end(N); }

  static unsigned getNumber(const BasicBlock *BB) { return BB->getNumber(); }
};

static_assert(GraphHasNodeNumbers<Inverse<const BasicBlock *>>,
              "GraphTraits getNumber() not detected");

//===--------------------------------------------------------------------===//
// GraphTraits specializations for function basic block graphs (CFGs)
//===--------------------------------------------------------------------===//

// Provide specializations of GraphTraits to be able to treat a function as a
// graph of basic blocks... these are the same as the basic block iterators,
// except that the root node is implicitly the first node of the function.
//
template <> struct GraphTraits<Function*> : public GraphTraits<BasicBlock*> {
  static NodeRef getEntryNode(Function *F) { return &F->getEntryBlock(); }

  // nodes_iterator/begin/end - Allow iteration over all nodes in the graph
  using nodes_iterator = pointer_iterator<Function::iterator>;

  static nodes_iterator nodes_begin(Function *F) {
    return nodes_iterator(F->begin());
  }

  static nodes_iterator nodes_end(Function *F) {
    return nodes_iterator(F->end());
  }

  static size_t size(Function *F) { return F->size(); }

  static unsigned getMaxNumber(const Function *F) {
    return F->getMaxBlockNumber();
  }
  static unsigned getNumberEpoch(const Function *F) {
    return F->getBlockNumberEpoch();
  }
};
template <> struct GraphTraits<const Function*> :
  public GraphTraits<const BasicBlock*> {
  static NodeRef getEntryNode(const Function *F) { return &F->getEntryBlock(); }

  // nodes_iterator/begin/end - Allow iteration over all nodes in the graph
  using nodes_iterator = pointer_iterator<Function::const_iterator>;

  static nodes_iterator nodes_begin(const Function *F) {
    return nodes_iterator(F->begin());
  }

  static nodes_iterator nodes_end(const Function *F) {
    return nodes_iterator(F->end());
  }

  static size_t size(const Function *F) { return F->size(); }

  static unsigned getMaxNumber(const Function *F) {
    return F->getMaxBlockNumber();
  }
  static unsigned getNumberEpoch(const Function *F) {
    return F->getBlockNumberEpoch();
  }
};

// Provide specializations of GraphTraits to be able to treat a function as a
// graph of basic blocks... and to walk it in inverse order.  Inverse order for
// a function is considered to be when traversing the predecessor edges of a BB
// instead of the successor edges.
//
template <> struct GraphTraits<Inverse<Function*>> :
  public GraphTraits<Inverse<BasicBlock*>> {
  static NodeRef getEntryNode(Inverse<Function *> G) {
    return &G.Graph->getEntryBlock();
  }

  static unsigned getMaxNumber(const Function *F) {
    return F->getMaxBlockNumber();
  }
  static unsigned getNumberEpoch(const Function *F) {
    return F->getBlockNumberEpoch();
  }
};
template <> struct GraphTraits<Inverse<const Function*>> :
  public GraphTraits<Inverse<const BasicBlock*>> {
  static NodeRef getEntryNode(Inverse<const Function *> G) {
    return &G.Graph->getEntryBlock();
  }

  static unsigned getMaxNumber(const Function *F) {
    return F->getMaxBlockNumber();
  }
  static unsigned getNumberEpoch(const Function *F) {
    return F->getBlockNumberEpoch();
  }
};

} // end namespace llvm

#endif // LLVM_IR_CFG_H