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Kristof Umann7f7dd092019-05-15 15:06:25 +00001//===--- BranchCloneCheck.cpp - clang-tidy --------------------------------===//
2//
3// The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9
10#include "BranchCloneCheck.h"
11#include "clang/AST/ASTContext.h"
12#include "clang/ASTMatchers/ASTMatchFinder.h"
13#include "clang/Analysis/CloneDetection.h"
14#include "llvm/Support/Casting.h"
15
16using namespace clang;
17using namespace clang::ast_matchers;
18
19/// Returns true when the statements are Type I clones of each other.
20static bool areStatementsIdentical(const Stmt *LHS, const Stmt *RHS,
21 const ASTContext &Context) {
22 llvm::FoldingSetNodeID DataLHS, DataRHS;
23 LHS->Profile(DataLHS, Context, false);
24 RHS->Profile(DataRHS, Context, false);
25 return (DataLHS == DataRHS);
26}
27
28namespace {
29/// A branch in a switch may consist of several statements; while a branch in
30/// an if/else if/else chain is one statement (which may be a CompoundStmt).
31using SwitchBranch = llvm::SmallVector<const Stmt *, 2>;
32} // anonymous namespace
33
34/// Determines if the bodies of two branches in a switch statements are Type I
35/// clones of each other. This function only examines the body of the branch
36/// and ignores the `case X:` or `default:` at the start of the branch.
37static bool areSwitchBranchesIdentical(const SwitchBranch LHS,
38 const SwitchBranch RHS,
39 const ASTContext &Context) {
40 if (LHS.size() != RHS.size())
41 return false;
42
43 for (size_t i = 0, Size = LHS.size(); i < Size; i++) {
44 // NOTE: We strip goto labels and annotations in addition to stripping
45 // the `case X:` or `default:` labels, but it is very unlikely that this
46 // would casue false positives in real-world code.
47 if (!areStatementsIdentical(LHS[i]->stripLabelLikeStatements(),
48 RHS[i]->stripLabelLikeStatements(), Context)) {
49 return false;
50 }
51 }
52
53 return true;
54}
55
56namespace clang {
57namespace tidy {
58namespace bugprone {
59
60void BranchCloneCheck::registerMatchers(MatchFinder *Finder) {
61 Finder->addMatcher(
62 ifStmt(stmt().bind("if"),
63 hasParent(stmt(unless(ifStmt(hasElse(equalsBoundNode("if")))))),
64 hasElse(stmt().bind("else"))),
65 this);
66 Finder->addMatcher(switchStmt().bind("switch"), this);
67 Finder->addMatcher(conditionalOperator().bind("condOp"), this);
68}
69
70void BranchCloneCheck::check(const MatchFinder::MatchResult &Result) {
71 const ASTContext &Context = *Result.Context;
72
73 if (const auto *IS = Result.Nodes.getNodeAs<IfStmt>("if")) {
74 const Stmt *Then = IS->getThen();
75 assert(Then && "An IfStmt must have a `then` branch!");
76
77 const Stmt *Else = Result.Nodes.getNodeAs<Stmt>("else");
78 assert(Else && "We only look for `if` statements with an `else` branch!");
79
80 if (!isa<IfStmt>(Else)) {
81 // Just a simple if with no `else if` branch.
82 if (areStatementsIdentical(Then->IgnoreContainers(),
83 Else->IgnoreContainers(), Context)) {
84 diag(IS->getBeginLoc(), "if with identical then and else branches");
85 diag(IS->getElseLoc(), "else branch starts here", DiagnosticIDs::Note);
86 }
87 return;
88 }
89
90 // This is the complicated case when we start an if/else if/else chain.
91 // To find all the duplicates, we collect all the branches into a vector.
92 llvm::SmallVector<const Stmt *, 4> Branches;
93 const IfStmt *Cur = IS;
94 while (true) {
95 // Store the `then` branch.
96 Branches.push_back(Cur->getThen());
97
98 Else = Cur->getElse();
99 // The chain ends if there is no `else` branch.
100 if (!Else)
101 break;
102
103 // Check if there is another `else if`...
104 Cur = dyn_cast<IfStmt>(Else);
105 if (!Cur) {
106 // ...this is just a plain `else` branch at the end of the chain.
107 Branches.push_back(Else);
108 break;
109 }
110 }
111
112 size_t N = Branches.size();
113 llvm::BitVector KnownAsClone(N);
114
115 for (size_t i = 0; i + 1 < N; i++) {
116 // We have already seen Branches[i] as a clone of an earlier branch.
117 if (KnownAsClone[i])
118 continue;
119
120 int NumCopies = 1;
121
122 for (size_t j = i + 1; j < N; j++) {
123 if (KnownAsClone[j] ||
124 !areStatementsIdentical(Branches[i]->IgnoreContainers(),
125 Branches[j]->IgnoreContainers(), Context))
126 continue;
127
128 NumCopies++;
129 KnownAsClone[j] = true;
130
131 if (NumCopies == 2) {
132 // We report the first occurence only when we find the second one.
133 diag(Branches[i]->getBeginLoc(),
134 "repeated branch in conditional chain");
Nathan Huckleberryb53e13c2019-07-17 17:22:43 +0000135 SourceLocation End =
136 Lexer::getLocForEndOfToken(Branches[i]->getEndLoc(), 0,
137 *Result.SourceManager, getLangOpts());
138 if (End.isValid()) {
139 diag(End, "end of the original", DiagnosticIDs::Note);
140 }
Kristof Umann7f7dd092019-05-15 15:06:25 +0000141 }
142
143 diag(Branches[j]->getBeginLoc(), "clone %0 starts here",
144 DiagnosticIDs::Note)
145 << (NumCopies - 1);
146 }
147 }
148 return;
149 }
150
151 if (const auto *CO = Result.Nodes.getNodeAs<ConditionalOperator>("condOp")) {
152 // We do not try to detect chains of ?: operators.
153 if (areStatementsIdentical(CO->getTrueExpr(), CO->getFalseExpr(), Context))
154 diag(CO->getQuestionLoc(),
155 "conditional operator with identical true and false expressions");
156
157 return;
158 }
159
160 if (const auto *SS = Result.Nodes.getNodeAs<SwitchStmt>("switch")) {
161 const CompoundStmt *Body = dyn_cast_or_null<CompoundStmt>(SS->getBody());
162
163 // Code like
164 // switch (x) case 0: case 1: foobar();
165 // is legal and calls foobar() if and only if x is either 0 or 1;
166 // but we do not try to distinguish branches in such code.
167 if (!Body)
168 return;
169
170 // We will first collect the branches of the switch statements. For the
171 // sake of simplicity we say that branches are delimited by the SwitchCase
172 // (`case:` or `default:`) children of Body; that is, we ignore `case:` or
173 // `default:` labels embedded inside other statements and we do not follow
174 // the effects of `break` and other manipulation of the control-flow.
175 llvm::SmallVector<SwitchBranch, 4> Branches;
176 for (const Stmt *S : Body->body()) {
177 // If this is a `case` or `default`, we start a new, empty branch.
178 if (isa<SwitchCase>(S))
179 Branches.emplace_back();
180
181 // There may be code before the first branch (which can be dead code
182 // and can be code reached either through goto or through case labels
183 // that are embedded inside e.g. inner compound statements); we do not
184 // store those statements in branches.
185 if (!Branches.empty())
186 Branches.back().push_back(S);
187 }
188
189 auto End = Branches.end();
190 auto BeginCurrent = Branches.begin();
191 while (BeginCurrent < End) {
192 auto EndCurrent = BeginCurrent + 1;
193 while (EndCurrent < End &&
194 areSwitchBranchesIdentical(*BeginCurrent, *EndCurrent, Context)) {
195 ++EndCurrent;
196 }
197 // At this point the iterator range {BeginCurrent, EndCurrent} contains a
198 // complete family of consecutive identical branches.
199 if (EndCurrent > BeginCurrent + 1) {
200 diag(BeginCurrent->front()->getBeginLoc(),
201 "switch has %0 consecutive identical branches")
202 << static_cast<int>(std::distance(BeginCurrent, EndCurrent));
203
204 SourceLocation EndLoc = (EndCurrent - 1)->back()->getEndLoc();
205 // If the case statement is generated from a macro, it's SourceLocation
206 // may be invalid, resuling in an assertation failure down the line.
207 // While not optimal, try the begin location in this case, it's still
208 // better then nothing.
209 if (EndLoc.isInvalid())
210 EndLoc = (EndCurrent - 1)->back()->getBeginLoc();
211
212 if (EndLoc.isMacroID())
213 EndLoc = Context.getSourceManager().getExpansionLoc(EndLoc);
Nathan Huckleberryb53e13c2019-07-17 17:22:43 +0000214 EndLoc = Lexer::getLocForEndOfToken(EndLoc, 0, *Result.SourceManager,
215 getLangOpts());
Kristof Umann7f7dd092019-05-15 15:06:25 +0000216
Nathan Huckleberryb53e13c2019-07-17 17:22:43 +0000217 if (EndLoc.isValid()) {
218 diag(EndLoc, "last of these clones ends here", DiagnosticIDs::Note);
219 }
Kristof Umann7f7dd092019-05-15 15:06:25 +0000220 }
221 BeginCurrent = EndCurrent;
222 }
223 return;
224 }
225
226 llvm_unreachable("No if statement and no switch statement.");
227}
228
229} // namespace bugprone
230} // namespace tidy
231} // namespace clang