clang-tools  14.0.0git
ExprSequence.h
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1 //===------------- ExprSequence.h - clang-tidy ----------------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 
9 #ifndef LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_EXPRSEQUENCE_H
10 #define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_EXPRSEQUENCE_H
11 
12 #include "clang/Analysis/CFG.h"
13 #include "clang/Lex/Lexer.h"
14 #include "llvm/ADT/DenseMap.h"
15 #include "llvm/ADT/SmallPtrSet.h"
16 #include "llvm/ADT/SmallVector.h"
17 
18 #include "../ClangTidy.h"
19 
20 namespace clang {
21 namespace tidy {
22 namespace utils {
23 
24 /// Provides information about the evaluation order of (sub-)expressions within
25 /// a `CFGBlock`.
26 ///
27 /// While a `CFGBlock` does contain individual `CFGElement`s for some
28 /// sub-expressions, the order in which those `CFGElement`s appear reflects
29 /// only one possible order in which the sub-expressions may be evaluated.
30 /// However, we want to warn if any of the potential evaluation orders can lead
31 /// to a use-after-move, not just the one contained in the `CFGBlock`.
32 ///
33 /// This class implements only a simplified version of the C++ sequencing
34 /// rules. The main limitation is that we do not distinguish between value
35 /// computation and side effect -- see the "Implementation" section for more
36 /// details.
37 ///
38 /// Note: `SequenceChecker` from SemaChecking.cpp does a similar job (and much
39 /// more thoroughly), but using it would require
40 /// - Pulling `SequenceChecker` out into a header file (i.e. making it part of
41 /// the API),
42 /// - Removing the dependency of `SequenceChecker` on `Sema`, and
43 /// - (Probably) modifying `SequenceChecker` to make it suitable to be used in
44 /// this context.
45 /// For the moment, it seems preferable to re-implement our own version of
46 /// sequence checking that is special-cased to what we need here.
47 ///
48 /// Implementation
49 /// --------------
50 ///
51 /// `ExprSequence` uses two types of sequencing edges between nodes in the AST:
52 ///
53 /// - Every `Stmt` is assumed to be sequenced after its children. This is
54 /// overly optimistic because the standard only states that value computations
55 /// of operands are sequenced before the value computation of the operator,
56 /// making no guarantees about side effects (in general).
57 ///
58 /// For our purposes, this rule is sufficient, however, because this check is
59 /// interested in operations on objects, which are generally performed through
60 /// function calls (whether explicit and implicit). Function calls guarantee
61 /// that the value computations and side effects for all function arguments
62 /// are sequenced before the execution of the function.
63 ///
64 /// - In addition, some `Stmt`s are known to be sequenced before or after
65 /// their siblings. For example, the `Stmt`s that make up a `CompoundStmt`are
66 /// all sequenced relative to each other. The function
67 /// `getSequenceSuccessor()` implements these sequencing rules.
68 class ExprSequence {
69 public:
70  /// Initializes this `ExprSequence` with sequence information for the given
71  /// `CFG`. `Root` is the root statement the CFG was built from.
72  ExprSequence(const CFG *TheCFG, const Stmt *Root, ASTContext *TheContext);
73 
74  /// Returns whether \p Before is sequenced before \p After.
75  bool inSequence(const Stmt *Before, const Stmt *After) const;
76 
77  /// Returns whether \p After can potentially be evaluated after \p Before.
78  /// This is exactly equivalent to `!inSequence(After, Before)` but makes some
79  /// conditions read more naturally.
80  bool potentiallyAfter(const Stmt *After, const Stmt *Before) const;
81 
82 private:
83  // Returns the sibling of \p S (if any) that is directly sequenced after \p S,
84  // or nullptr if no such sibling exists. For example, if \p S is the child of
85  // a `CompoundStmt`, this would return the Stmt that directly follows \p S in
86  // the `CompoundStmt`.
87  //
88  // As the sequencing of many constructs that change control flow is already
89  // encoded in the `CFG`, this function only implements the sequencing rules
90  // for those constructs where sequencing cannot be inferred from the `CFG`.
91  const Stmt *getSequenceSuccessor(const Stmt *S) const;
92 
93  const Stmt *resolveSyntheticStmt(const Stmt *S) const;
94 
95  ASTContext *Context;
96  const Stmt *Root;
97 
98  llvm::DenseMap<const Stmt *, const Stmt *> SyntheticStmtSourceMap;
99 };
100 
101 /// Maps `Stmt`s to the `CFGBlock` that contains them. Some `Stmt`s may be
102 /// contained in more than one `CFGBlock`; in this case, they are mapped to the
103 /// innermost block (i.e. the one that is furthest from the root of the tree).
105 public:
106  /// Initializes the map for the given `CFG`.
107  StmtToBlockMap(const CFG *TheCFG, ASTContext *TheContext);
108 
109  /// Returns the block that \p S is contained in. Some `Stmt`s may be contained
110  /// in more than one `CFGBlock`; in this case, this function returns the
111  /// innermost block (i.e. the one that is furthest from the root of the tree).
112  const CFGBlock *blockContainingStmt(const Stmt *S) const;
113 
114 private:
115  ASTContext *Context;
116 
117  llvm::DenseMap<const Stmt *, const CFGBlock *> Map;
118 };
119 
120 } // namespace utils
121 } // namespace tidy
122 } // namespace clang
123 
124 #endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_EXPRSEQUENCE_H
Root
ASTNode Root
Definition: DumpAST.cpp:332
clang::tidy::utils::ExprSequence::potentiallyAfter
bool potentiallyAfter(const Stmt *After, const Stmt *Before) const
Returns whether After can potentially be evaluated after Before.
Definition: ExprSequence.cpp:96
clang::tidy::utils::ExprSequence
Provides information about the evaluation order of (sub-)expressions within a CFGBlock.
Definition: ExprSequence.h:68
clang::tidy::utils::StmtToBlockMap::blockContainingStmt
const CFGBlock * blockContainingStmt(const Stmt *S) const
Returns the block that S is contained in.
Definition: ExprSequence.cpp:197
clang::tidy::utils::StmtToBlockMap::StmtToBlockMap
StmtToBlockMap(const CFG *TheCFG, ASTContext *TheContext)
Initializes the map for the given CFG.
Definition: ExprSequence.cpp:187
clang::tidy::utils::ExprSequence::inSequence
bool inSequence(const Stmt *Before, const Stmt *After) const
Returns whether Before is sequenced before After.
Definition: ExprSequence.cpp:74
clang::tidy::utils::ExprSequence::ExprSequence
ExprSequence(const CFG *TheCFG, const Stmt *Root, ASTContext *TheContext)
Initializes this ExprSequence with sequence information for the given CFG.
Definition: ExprSequence.cpp:66
clang::tidy::utils::StmtToBlockMap
Maps Stmts to the CFGBlock that contains them.
Definition: ExprSequence.h:104
clang
===– Representation.cpp - ClangDoc Representation --------—*- C++ -*-===//
Definition: ApplyReplacements.h:27