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+//===------------- ExprSequence.h - clang-tidy ----------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#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 {
+namespace tidy {
+namespace 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 {
+public:
+  /// Initializes this `ExprSequence` with sequence information for the given
+  /// `CFG`.
+  ExprSequence(const CFG *TheCFG, ASTContext *TheContext);
+
+  /// Returns whether \p Before is sequenced before \p After.
+  bool inSequence(const Stmt *Before, const Stmt *After) const;
+
+  /// Returns whether \p After can potentially be evaluated after \p Before.
+  /// This is exactly equivalent to `!inSequence(After, Before)` but makes some
+  /// conditions read more naturally.
+  bool potentiallyAfter(const Stmt *After, const Stmt *Before) const;
+
+private:
+  // Returns the sibling of \p S (if any) that is directly sequenced after \p S,
+  // or nullptr if no such sibling exists. For example, if \p S is the child of
+  // a `CompoundStmt`, this would return the Stmt that directly follows \p S in
+  // the `CompoundStmt`.
+  //
+  // As the sequencing of many constructs that change control flow is already
+  // encoded in the `CFG`, this function only implements the sequencing rules
+  // for those constructs where sequencing cannot be inferred from the `CFG`.
+  const Stmt *getSequenceSuccessor(const Stmt *S) const;
+
+  const Stmt *resolveSyntheticStmt(const Stmt *S) const;
+
+  ASTContext *Context;
+
+  llvm::DenseMap<const Stmt *, const Stmt *> SyntheticStmtSourceMap;
+};
+
+/// 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 {
+public:
+  /// Initializes the map for the given `CFG`.
+  StmtToBlockMap(const CFG *TheCFG, ASTContext *TheContext);
+
+  /// Returns the block that \p S is contained in. Some `Stmt`s may be contained
+  /// in more than one `CFGBlock`; in this case, this function returns the
+  /// innermost block (i.e. the one that is furthest from the root of the tree).
+  const CFGBlock *blockContainingStmt(const Stmt *S) const;
+
+private:
+  ASTContext *Context;
+
+  llvm::DenseMap<const Stmt *, const CFGBlock *> Map;
+};
+
+} // namespace utils
+} // namespace tidy
+} // namespace clang
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_EXPRSEQUENCE_H