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//===- 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());
}
};
/// A callback to be called with the state before or after visiting a CFG
/// element.
using CFGEltCallbackTypeErased = std::function<void(
const CFGElement &, const TypeErasedDataflowAnalysisState &)>;
/// A pair of callbacks to be called with the state before and after visiting a
/// CFG element.
/// Either or both of the callbacks may be null.
struct CFGEltCallbacksTypeErased {
CFGEltCallbackTypeErased Before;
CFGEltCallbackTypeErased After;
};
/// 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
/// `PostAnalysisCallbacks` on each CFG element with the final analysis results
/// before and after 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,
const CFGEltCallbacksTypeErased &PostAnalysisCallbacks,
std::int32_t MaxBlockVisits);
} // namespace dataflow
} // namespace clang
#endif // LLVM_CLANG_ANALYSIS_FLOWSENSITIVE_TYPEERASEDDATAFLOWANALYSIS_H