TypeErasedDataflowAnalysis.h

Go to the documentation of this file.

//===- TypeErasedDataflowAnalysis.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 type-erased base types and functions for building dataflow
//  analyses that run over Control-Flow Graphs (CFGs).
//
//===----------------------------------------------------------------------===//
 
#ifndef LLVM_CLANG_ANALYSIS_FLOWSENSITIVE_TYPEERASEDDATAFLOWANALYSIS_H
#define LLVM_CLANG_ANALYSIS_FLOWSENSITIVE_TYPEERASEDDATAFLOWANALYSIS_H
 
#include <optional>
#include <utility>
#include <vector>
 
#include "clang/AST/ASTContext.h"
#include "clang/AST/Stmt.h"
#include "clang/Analysis/CFG.h"
#include "clang/Analysis/FlowSensitive/AdornedCFG.h"
#include "clang/Analysis/FlowSensitive/DataflowAnalysisContext.h"
#include "clang/Analysis/FlowSensitive/DataflowEnvironment.h"
#include "clang/Analysis/FlowSensitive/DataflowLattice.h"
#include "llvm/ADT/Any.h"
#include "llvm/Support/Error.h"
 
namespace clang {
namespace dataflow {
 
struct DataflowAnalysisOptions {
  /// Options for the built-in model, or empty to not apply them.
  // FIXME: Remove this option once the framework supports composing analyses
  // (at which point the built-in transfer functions can be simply a standalone
  // analysis).
  std::optional<DataflowAnalysisContext::Options> BuiltinOpts =
      DataflowAnalysisContext::Options{};
};
 
/// Type-erased lattice element container.
///
/// Requirements:
///
///  The type of the object stored in the container must be a bounded
///  join-semilattice.
struct TypeErasedLattice {
  llvm::Any Value;
};
 
/// Type-erased base class for dataflow analyses built on a single lattice type.
class TypeErasedDataflowAnalysis : public Environment::ValueModel {
  DataflowAnalysisOptions Options;
 
public:
  TypeErasedDataflowAnalysis() : Options({}) {}
 
  TypeErasedDataflowAnalysis(DataflowAnalysisOptions Options)
      : Options(Options) {}
 
  virtual ~TypeErasedDataflowAnalysis() {}
 
  /// Returns the `ASTContext` that is used by the analysis.
  virtual ASTContext &getASTContext() = 0;
 
  /// Returns a type-erased lattice element that models the initial state of a
  /// basic block.
  virtual TypeErasedLattice typeErasedInitialElement() = 0;
 
  /// Joins two type-erased lattice elements by computing their least upper
  /// bound. Places the join result in the left element and returns an effect
  /// indicating whether any changes were made to it.
  virtual TypeErasedLattice joinTypeErased(const TypeErasedLattice &,
                                           const TypeErasedLattice &) = 0;
 
  /// Chooses a lattice element that approximates the current element at a
  /// program point, given the previous element at that point. Places the
  /// widened result in the current element (`Current`). Widening is optional --
  /// it is only needed to either accelerate convergence (for lattices with
  /// non-trivial height) or guarantee convergence (for lattices with infinite
  /// height).
  ///
  /// Returns an indication of whether any changes were made to `Current` in
  /// order to widen. This saves a separate call to `isEqualTypeErased` after
  /// the widening.
  virtual LatticeJoinEffect
  widenTypeErased(TypeErasedLattice &Current,
                  const TypeErasedLattice &Previous) = 0;
 
  /// Returns true if and only if the two given type-erased lattice elements are
  /// equal.
  virtual bool isEqualTypeErased(const TypeErasedLattice &,
                                 const TypeErasedLattice &) = 0;
 
  /// Applies the analysis transfer function for a given control flow graph
  /// element and type-erased lattice element.
  virtual void transferTypeErased(const CFGElement &, TypeErasedLattice &,
                                  Environment &) = 0;
 
  /// Applies the analysis transfer function for a given edge from a CFG block
  /// of a conditional statement.
  /// @param Stmt The condition which is responsible for the split in the CFG.
  /// @param Branch True if the edge goes to the basic block where the
  /// condition is true.
  // FIXME: Change `Stmt` argument to a reference.
  virtual void transferBranchTypeErased(bool Branch, const Stmt *,
                                        TypeErasedLattice &, Environment &) = 0;
 
  /// If the built-in model is enabled, returns the options to be passed to
  /// them. Otherwise returns empty.
  const std::optional<DataflowAnalysisContext::Options> &
  builtinOptions() const {
    return Options.BuiltinOpts;
  }
};
 
/// Type-erased model of the program at a given program point.
struct TypeErasedDataflowAnalysisState {
  /// Type-erased model of a program property.
  TypeErasedLattice Lattice;
 
  /// Model of the state of the program (store and heap).
  Environment Env;
 
  TypeErasedDataflowAnalysisState(TypeErasedLattice Lattice, Environment Env)
      : Lattice(std::move(Lattice)), Env(std::move(Env)) {}
 
  TypeErasedDataflowAnalysisState fork() const {
    return TypeErasedDataflowAnalysisState(Lattice, Env.fork());
  }
};
 
/// 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. Returns an error if the
/// dataflow analysis cannot be performed successfully. Otherwise, calls
/// `PostVisitCFG` on each CFG element with the final analysis results at that
/// program point.
///
/// `MaxBlockVisits` caps the number of block visits during analysis. It doesn't
/// distinguish between repeat visits to the same block and visits to distinct
/// blocks. This parameter is a backstop to prevent infinite loops, in the case
/// of bugs in the lattice and/or transfer functions that prevent the analysis
/// from converging.
llvm::Expected<std::vector<std::optional<TypeErasedDataflowAnalysisState>>>
runTypeErasedDataflowAnalysis(
    const AdornedCFG &ACFG, TypeErasedDataflowAnalysis &Analysis,
    const Environment &InitEnv,
    std::function<void(const CFGElement &,
                       const TypeErasedDataflowAnalysisState &)>
        PostVisitCFG,
    std::int32_t MaxBlockVisits);
 
} // namespace dataflow
} // namespace clang
 
#endif // LLVM_CLANG_ANALYSIS_FLOWSENSITIVE_TYPEERASEDDATAFLOWANALYSIS_H