//===- 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/ControlFlowContext.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"

#include "llvm/Support/Error.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;

///   * `void transfer(const Stmt *, LatticeT &, Environment &)` - applies the

///     analysis transfer function for a given statement and lattice element.

///

///  `Derived` can optionally override the following members:

///   * `bool merge(QualType, const Value &, const Value &, Value &,

///     Environment &)` -  joins distinct values. This could be a strict

///     lattice join or a more general widening operation.

///

///  `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) {}

  explicit DataflowAnalysis(ASTContext &Context, bool ApplyBuiltinTransfer)

      : TypeErasedDataflowAnalysis(ApplyBuiltinTransfer), Context(Context) {}

  ASTContext &getASTContext() final { return Context; }

  TypeErasedLattice 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;

  }

  void transferTypeErased(const Stmt *Stmt, TypeErasedLattice &E,

                          Environment &Env) final {

    Lattice &L = llvm::any_cast<Lattice &>(E.Value);

    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. The

/// returned vector, if any, will have the same size as the number of CFG

/// blocks, with indices corresponding to basic block IDs. Returns an error if

/// the dataflow analysis cannot be performed successfully. Otherwise, calls

/// `PostVisitStmt` on each statement with the final analysis results at that

/// program point.

template <typename AnalysisT>

llvm::Expected<std::vector<

    llvm::Optional<DataflowAnalysisState<typename AnalysisT::Lattice>>>>

runDataflowAnalysis(

    const ControlFlowContext &CFCtx, AnalysisT &Analysis,

    const Environment &InitEnv,

    std::function<void(const Stmt *, const DataflowAnalysisState<

                                         typename AnalysisT::Lattice> &)>

        PostVisitStmt = nullptr) {

  std::function<void(const Stmt *, const TypeErasedDataflowAnalysisState &)>

      PostVisitStmtClosure = nullptr;

  if (PostVisitStmt != nullptr) {

    PostVisitStmtClosure = [&PostVisitStmt](

                               const Stmt *Stmt,

                               const TypeErasedDataflowAnalysisState &State) {

      auto *Lattice =

          llvm::any_cast<typename AnalysisT::Lattice>(&State.Lattice.Value);

      PostVisitStmt(Stmt, DataflowAnalysisState<typename AnalysisT::Lattice>{

                              *Lattice, State.Env});

    };

  }

  auto TypeErasedBlockStates = runTypeErasedDataflowAnalysis(

      CFCtx, Analysis, InitEnv, PostVisitStmtClosure);

  if (!TypeErasedBlockStates)

    return TypeErasedBlockStates.takeError();

  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;

}

/// Abstract base class for dataflow "models": reusable analysis components that

/// model a particular aspect of program semantics in the `Environment`. For

/// example, a model may capture a type and its related functions.

class DataflowModel : public Environment::ValueModel {

public:

  /// Return value indicates whether the model processed the `Stmt`.

  virtual bool transfer(const Stmt *Stmt, Environment &Env) = 0;

};

} // namespace dataflow

} // namespace clang

#endif // LLVM_CLANG_ANALYSIS_FLOWSENSITIVE_DATAFLOWANALYSIS_H