llvm/clang-tools-extra/clang-tidy/utils/ExprSequence.h

//===------------- ExprSequence.h - clang-tidy ----------------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_EXPRSEQUENCE_H
#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_EXPRSEQUENCE_H

#include "clang/Analysis/CFG.h"
#include "clang/Lex/Lexer.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"

#include "../ClangTidy.h"

namespace clang::tidy::utils {

/// Provides information about the evaluation order of (sub-)expressions within
/// a `CFGBlock`.
///
/// While a `CFGBlock` does contain individual `CFGElement`s for some
/// sub-expressions, the order in which those `CFGElement`s appear reflects
/// only one possible order in which the sub-expressions may be evaluated.
/// However, we want to warn if any of the potential evaluation orders can lead
/// to a use-after-move, not just the one contained in the `CFGBlock`.
///
/// This class implements only a simplified version of the C++ sequencing
/// rules. The main limitation is that we do not distinguish between value
/// computation and side effect -- see the "Implementation" section for more
/// details.
///
/// Note: `SequenceChecker` from SemaChecking.cpp does a similar job (and much
/// more thoroughly), but using it would require
/// - Pulling `SequenceChecker` out into a header file (i.e. making it part of
///   the API),
/// - Removing the dependency of `SequenceChecker` on `Sema`, and
/// - (Probably) modifying `SequenceChecker` to make it suitable to be used in
///   this context.
/// For the moment, it seems preferable to re-implement our own version of
/// sequence checking that is special-cased to what we need here.
///
/// Implementation
/// --------------
///
/// `ExprSequence` uses two types of sequencing edges between nodes in the AST:
///
/// - Every `Stmt` is assumed to be sequenced after its children. This is
///   overly optimistic because the standard only states that value computations
///   of operands are sequenced before the value computation of the operator,
///   making no guarantees about side effects (in general).
///
///   For our purposes, this rule is sufficient, however, because this check is
///   interested in operations on objects, which are generally performed through
///   function calls (whether explicit and implicit). Function calls guarantee
///   that the value computations and side effects for all function arguments
///   are sequenced before the execution of the function.
///
/// - In addition, some `Stmt`s are known to be sequenced before or after
///   their siblings. For example, the `Stmt`s that make up a `CompoundStmt`are
///   all sequenced relative to each other. The function
///   `getSequenceSuccessor()` implements these sequencing rules.
class ExprSequence { … };

/// Maps `Stmt`s to the `CFGBlock` that contains them. Some `Stmt`s may be
/// contained in more than one `CFGBlock`; in this case, they are mapped to the
/// innermost block (i.e. the one that is furthest from the root of the tree).
class StmtToBlockMap { … };

} // namespace clang::tidy::utils

#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_EXPRSEQUENCE_H