//===- DataflowAnalysis.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
//
//===----------------------------------------------------------------------===//
//
//  This file defines base types and functions for building dataflow analyses
//  that run over Control-Flow Graphs (CFGs).
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_CLANG_ANALYSIS_FLOWSENSITIVE_DATAFLOWANALYSIS_H
#define LLVM_CLANG_ANALYSIS_FLOWSENSITIVE_DATAFLOWANALYSIS_H

#include <iterator>
#include <utility>
#include <vector>

#include "clang/AST/ASTContext.h"
#include "clang/AST/Stmt.h"
#include "clang/Analysis/CFG.h"
#include "clang/Analysis/FlowSensitive/DataflowEnvironment.h"
#include "clang/Analysis/FlowSensitive/TypeErasedDataflowAnalysis.h"
#include "llvm/ADT/Any.h"
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/STLExtras.h"

namespace clang {
namespace dataflow {

/// Base class template for dataflow analyses built on a single lattice type.
///
/// Requirements:
///
///  `Derived` must be derived from a specialization of this class template and
///  must provide the following public members:
///   * `LatticeT initialElement()` - returns a lattice element that models the
///     initial state of a basic block;
///   * `LatticeT transfer(const Stmt *, const LatticeT &, Environment &)` -
///     applies the analysis transfer function for a given statement and lattice
///     element.
///
///  `LatticeT` is a bounded join-semilattice that is used by `Derived` and must
///  provide the following public members:
///   * `LatticeJoinEffect join(const LatticeT &)` - joins the object and the
///     argument by computing their least upper bound, modifies the object if
///     necessary, and returns an effect indicating whether any changes were
///     made to it;
///   * `bool operator==(const LatticeT &) const` - returns true if and only if
///     the object is equal to the argument.
template <typename Derived, typename LatticeT>
class DataflowAnalysis : public TypeErasedDataflowAnalysis {
public:
  /// Bounded join-semilattice that is used in the analysis.
  using Lattice = LatticeT;

  explicit DataflowAnalysis(ASTContext &Context) : Context(Context) {}

  ASTContext &getASTContext() final { return Context; }

  AnyLatticeElement typeErasedInitialElement() final {
    return {static_cast<Derived *>(this)->initialElement()};
  }

  LatticeJoinEffect joinTypeErased(TypeErasedLattice &E1,
                                   const TypeErasedLattice &E2) final {
    Lattice &L1 = llvm::any_cast<Lattice &>(E1.Value);
    const Lattice &L2 = llvm::any_cast<const Lattice &>(E2.Value);
    return L1.join(L2);
  }

  bool isEqualTypeErased(const TypeErasedLattice &E1,
                         const TypeErasedLattice &E2) final {
    const Lattice &L1 = llvm::any_cast<const Lattice &>(E1.Value);
    const Lattice &L2 = llvm::any_cast<const Lattice &>(E2.Value);
    return L1 == L2;
  }

  AnyLatticeElement transferTypeErased(const Stmt *Stmt,
                                       const AnyLatticeElement &E,
                                       Environment &Env) final {
    const Lattice &L = llvm::any_cast<const Lattice &>(E.Value);
    return {static_cast<Derived *>(this)->transfer(Stmt, L, Env)};
  }

private:
  ASTContext &Context;
};

// Model of the program at a given program point.
template <typename LatticeT> struct DataflowAnalysisState {
  // Model of a program property.
  LatticeT Lattice;

  // Model of the state of the program (store and heap).
  Environment Env;
};

/// Performs dataflow analysis and returns a mapping from basic block IDs to
/// dataflow analysis states that model the respective basic blocks. Indices
/// of the returned vector correspond to basic block IDs.
///
/// Requirements:
///
///  `Cfg` must have been built with `CFG::BuildOptions::setAllAlwaysAdd()` to
///  ensure that all sub-expressions in a basic block are evaluated.
template <typename AnalysisT>
std::vector<llvm::Optional<DataflowAnalysisState<typename AnalysisT::Lattice>>>
runDataflowAnalysis(const CFG &Cfg, AnalysisT &Analysis,
                    const Environment &InitEnv) {
  auto TypeErasedBlockStates =
      runTypeErasedDataflowAnalysis(Cfg, Analysis, InitEnv);
  std::vector<
      llvm::Optional<DataflowAnalysisState<typename AnalysisT::Lattice>>>
      BlockStates;
  BlockStates.reserve(TypeErasedBlockStates.size());
  llvm::transform(std::move(TypeErasedBlockStates),
                  std::back_inserter(BlockStates), [](auto &OptState) {
                    return std::move(OptState).map([](auto &&State) {
                      return DataflowAnalysisState<typename AnalysisT::Lattice>{
                          llvm::any_cast<typename AnalysisT::Lattice>(
                              std::move(State.Lattice.Value)),
                          std::move(State.Env)};
                    });
                  });
  return BlockStates;
}

} // namespace dataflow
} // namespace clang

#endif // LLVM_CLANG_ANALYSIS_FLOWSENSITIVE_DATAFLOWANALYSIS_H