125 lines
5.2 KiB
C++
125 lines
5.2 KiB
C++
//===------------- ExprSequence.h - clang-tidy ----------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_EXPRSEQUENCE_H
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#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_EXPRSEQUENCE_H
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#include "clang/Analysis/CFG.h"
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#include "clang/Lex/Lexer.h"
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/ADT/SmallVector.h"
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#include "../ClangTidy.h"
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namespace clang {
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namespace tidy {
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namespace utils {
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/// Provides information about the evaluation order of (sub-)expressions within
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/// a `CFGBlock`.
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///
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/// While a `CFGBlock` does contain individual `CFGElement`s for some
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/// sub-expressions, the order in which those `CFGElement`s appear reflects
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/// only one possible order in which the sub-expressions may be evaluated.
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/// However, we want to warn if any of the potential evaluation orders can lead
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/// to a use-after-move, not just the one contained in the `CFGBlock`.
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///
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/// This class implements only a simplified version of the C++ sequencing
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/// rules. The main limitation is that we do not distinguish between value
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/// computation and side effect -- see the "Implementation" section for more
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/// details.
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///
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/// Note: `SequenceChecker` from SemaChecking.cpp does a similar job (and much
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/// more thoroughly), but using it would require
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/// - Pulling `SequenceChecker` out into a header file (i.e. making it part of
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/// the API),
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/// - Removing the dependency of `SequenceChecker` on `Sema`, and
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/// - (Probably) modifying `SequenceChecker` to make it suitable to be used in
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/// this context.
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/// For the moment, it seems preferable to re-implement our own version of
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/// sequence checking that is special-cased to what we need here.
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///
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/// Implementation
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/// --------------
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///
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/// `ExprSequence` uses two types of sequencing edges between nodes in the AST:
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///
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/// - Every `Stmt` is assumed to be sequenced after its children. This is
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/// overly optimistic because the standard only states that value computations
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/// of operands are sequenced before the value computation of the operator,
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/// making no guarantees about side effects (in general).
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///
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/// For our purposes, this rule is sufficient, however, because this check is
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/// interested in operations on objects, which are generally performed through
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/// function calls (whether explicit and implicit). Function calls guarantee
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/// that the value computations and side effects for all function arguments
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/// are sequenced before the execution of the function.
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///
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/// - In addition, some `Stmt`s are known to be sequenced before or after
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/// their siblings. For example, the `Stmt`s that make up a `CompoundStmt`are
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/// all sequenced relative to each other. The function
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/// `getSequenceSuccessor()` implements these sequencing rules.
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class ExprSequence {
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public:
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/// Initializes this `ExprSequence` with sequence information for the given
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/// `CFG`. `Root` is the root statement the CFG was built from.
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ExprSequence(const CFG *TheCFG, const Stmt *Root, ASTContext *TheContext);
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/// Returns whether \p Before is sequenced before \p After.
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bool inSequence(const Stmt *Before, const Stmt *After) const;
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/// Returns whether \p After can potentially be evaluated after \p Before.
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/// This is exactly equivalent to `!inSequence(After, Before)` but makes some
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/// conditions read more naturally.
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bool potentiallyAfter(const Stmt *After, const Stmt *Before) const;
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private:
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// Returns the sibling of \p S (if any) that is directly sequenced after \p S,
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// or nullptr if no such sibling exists. For example, if \p S is the child of
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// a `CompoundStmt`, this would return the Stmt that directly follows \p S in
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// the `CompoundStmt`.
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//
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// As the sequencing of many constructs that change control flow is already
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// encoded in the `CFG`, this function only implements the sequencing rules
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// for those constructs where sequencing cannot be inferred from the `CFG`.
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const Stmt *getSequenceSuccessor(const Stmt *S) const;
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const Stmt *resolveSyntheticStmt(const Stmt *S) const;
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ASTContext *Context;
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const Stmt *Root;
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llvm::DenseMap<const Stmt *, const Stmt *> SyntheticStmtSourceMap;
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};
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/// Maps `Stmt`s to the `CFGBlock` that contains them. Some `Stmt`s may be
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/// contained in more than one `CFGBlock`; in this case, they are mapped to the
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/// innermost block (i.e. the one that is furthest from the root of the tree).
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class StmtToBlockMap {
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public:
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/// Initializes the map for the given `CFG`.
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StmtToBlockMap(const CFG *TheCFG, ASTContext *TheContext);
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/// Returns the block that \p S is contained in. Some `Stmt`s may be contained
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/// in more than one `CFGBlock`; in this case, this function returns the
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/// innermost block (i.e. the one that is furthest from the root of the tree).
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const CFGBlock *blockContainingStmt(const Stmt *S) const;
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private:
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ASTContext *Context;
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llvm::DenseMap<const Stmt *, const CFGBlock *> Map;
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};
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} // namespace utils
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} // namespace tidy
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} // namespace clang
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#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_EXPRSEQUENCE_H
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