1//===- AdornedCFG.cpp ---------------------------------------------===//
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// This file defines an `AdornedCFG` class that is used by dataflow analyses
10// that run over Control-Flow Graphs (CFGs).
11//
12//===----------------------------------------------------------------------===//
13
14#include "clang/Analysis/FlowSensitive/AdornedCFG.h"
15#include "clang/AST/ASTContext.h"
16#include "clang/AST/Decl.h"
17#include "clang/AST/Stmt.h"
18#include "clang/Analysis/CFG.h"
19#include "llvm/ADT/BitVector.h"
20#include "llvm/ADT/DenseMap.h"
21#include "llvm/Support/Error.h"
22#include <utility>
23
24namespace clang {
25namespace dataflow {
26
27/// Returns a map from statements to basic blocks that contain them.
28static llvm::DenseMap<const Stmt *, const CFGBlock *>
29buildStmtToBasicBlockMap(const CFG &Cfg) {
30 llvm::DenseMap<const Stmt *, const CFGBlock *> StmtToBlock;
31 for (const CFGBlock *Block : Cfg) {
32 if (Block == nullptr)
33 continue;
34
35 for (const CFGElement &Element : *Block) {
36 auto Stmt = Element.getAs<CFGStmt>();
37 if (!Stmt)
38 continue;
39
40 StmtToBlock[Stmt->getStmt()] = Block;
41 }
42 }
43 // Some terminator conditions don't appear as a `CFGElement` anywhere else -
44 // for example, this is true if the terminator condition is a `&&` or `||`
45 // operator.
46 // We associate these conditions with the block the terminator appears in,
47 // but only if the condition has not already appeared as a regular
48 // `CFGElement`. (The `insert()` below does nothing if the key already exists
49 // in the map.)
50 for (const CFGBlock *Block : Cfg) {
51 if (Block != nullptr)
52 if (const Stmt *TerminatorCond = Block->getTerminatorCondition())
53 StmtToBlock.insert(KV: {TerminatorCond, Block});
54 }
55 // Terminator statements typically don't appear as a `CFGElement` anywhere
56 // else, so we want to associate them with the block that they terminate.
57 // However, there are some important special cases:
58 // - The conditional operator is a type of terminator, but it also appears
59 // as a regular `CFGElement`, and we want to associate it with the block
60 // in which it appears as a `CFGElement`.
61 // - The `&&` and `||` operators are types of terminators, but like the
62 // conditional operator, they can appear as a regular `CFGElement` or
63 // as a terminator condition (see above).
64 // We process terminators last to make sure that we only associate them with
65 // the block they terminate if they haven't previously occurred as a regular
66 // `CFGElement` or as a terminator condition.
67 for (const CFGBlock *Block : Cfg) {
68 if (Block != nullptr)
69 if (const Stmt *TerminatorStmt = Block->getTerminatorStmt())
70 StmtToBlock.insert(KV: {TerminatorStmt, Block});
71 }
72 return StmtToBlock;
73}
74
75static llvm::BitVector findReachableBlocks(const CFG &Cfg) {
76 llvm::BitVector BlockReachable(Cfg.getNumBlockIDs(), false);
77
78 llvm::SmallVector<const CFGBlock *> BlocksToVisit;
79 BlocksToVisit.push_back(Elt: &Cfg.getEntry());
80 while (!BlocksToVisit.empty()) {
81 const CFGBlock *Block = BlocksToVisit.back();
82 BlocksToVisit.pop_back();
83
84 if (BlockReachable[Block->getBlockID()])
85 continue;
86
87 BlockReachable[Block->getBlockID()] = true;
88
89 for (const CFGBlock *Succ : Block->succs())
90 if (Succ)
91 BlocksToVisit.push_back(Elt: Succ);
92 }
93
94 return BlockReachable;
95}
96
97static llvm::DenseSet<const CFGBlock *>
98buildContainsExprConsumedInDifferentBlock(
99 const CFG &Cfg, const internal::StmtToBlockMap &StmtToBlock) {
100 llvm::DenseSet<const CFGBlock *> Result;
101
102 auto CheckChildExprs = [&Result, &StmtToBlock](const Stmt *S,
103 const CFGBlock *Block) {
104 for (const Stmt *Child : S->children()) {
105 if (!isa_and_nonnull<Expr>(Val: Child))
106 continue;
107 const CFGBlock *ChildBlock = StmtToBlock.lookup(S: *Child);
108 if (ChildBlock != Block)
109 Result.insert(V: ChildBlock);
110 }
111 };
112
113 for (const CFGBlock *Block : Cfg) {
114 if (Block == nullptr)
115 continue;
116
117 for (const CFGElement &Element : *Block)
118 if (auto S = Element.getAs<CFGStmt>())
119 CheckChildExprs(S->getStmt(), Block);
120
121 if (const Stmt *TerminatorCond = Block->getTerminatorCondition())
122 CheckChildExprs(TerminatorCond, Block);
123 }
124
125 return Result;
126}
127
128namespace internal {
129
130StmtToBlockMap::StmtToBlockMap(const CFG &Cfg)
131 : StmtToBlock(buildStmtToBasicBlockMap(Cfg)) {}
132
133} // namespace internal
134
135llvm::Expected<AdornedCFG> AdornedCFG::build(const FunctionDecl &Func) {
136 if (!Func.doesThisDeclarationHaveABody())
137 return llvm::createStringError(
138 EC: std::make_error_code(e: std::errc::invalid_argument),
139 S: "Cannot analyze function without a body");
140
141 return build(D: Func, S&: *Func.getBody(), C&: Func.getASTContext());
142}
143
144llvm::Expected<AdornedCFG> AdornedCFG::build(const Decl &D, Stmt &S,
145 ASTContext &C) {
146 if (D.isTemplated())
147 return llvm::createStringError(
148 EC: std::make_error_code(e: std::errc::invalid_argument),
149 S: "Cannot analyze templated declarations");
150
151 // The shape of certain elements of the AST can vary depending on the
152 // language. We currently only support C++.
153 if (!C.getLangOpts().CPlusPlus || C.getLangOpts().ObjC)
154 return llvm::createStringError(
155 EC: std::make_error_code(e: std::errc::invalid_argument),
156 S: "Can only analyze C++");
157
158 CFG::BuildOptions Options;
159 Options.PruneTriviallyFalseEdges = true;
160 Options.AddImplicitDtors = true;
161 Options.AddTemporaryDtors = true;
162 Options.AddInitializers = true;
163 Options.AddCXXDefaultInitExprInCtors = true;
164 Options.AddLifetime = true;
165
166 // Ensure that all sub-expressions in basic blocks are evaluated.
167 Options.setAllAlwaysAdd();
168
169 auto Cfg = CFG::buildCFG(D: &D, AST: &S, C: &C, BO: Options);
170 if (Cfg == nullptr)
171 return llvm::createStringError(
172 EC: std::make_error_code(e: std::errc::invalid_argument),
173 S: "CFG::buildCFG failed");
174
175 internal::StmtToBlockMap StmtToBlock(*Cfg);
176
177 llvm::BitVector BlockReachable = findReachableBlocks(Cfg: *Cfg);
178
179 llvm::DenseSet<const CFGBlock *> ContainsExprConsumedInDifferentBlock =
180 buildContainsExprConsumedInDifferentBlock(Cfg: *Cfg, StmtToBlock);
181
182 return AdornedCFG(D, std::move(Cfg), std::move(StmtToBlock),
183 std::move(BlockReachable),
184 std::move(ContainsExprConsumedInDifferentBlock));
185}
186
187} // namespace dataflow
188} // namespace clang
189