1//==- ObjCUnusedIVarsChecker.cpp - Check for unused ivars --------*- C++ -*-==//
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 a CheckObjCUnusedIvars, a checker that
10// analyzes an Objective-C class's interface/implementation to determine if it
11// has any ivars that are never accessed.
12//
13//===----------------------------------------------------------------------===//
14
15#include "clang/AST/Attr.h"
16#include "clang/AST/DeclObjC.h"
17#include "clang/AST/Expr.h"
18#include "clang/AST/ExprObjC.h"
19#include "clang/Analysis/PathDiagnostic.h"
20#include "clang/Basic/LangOptions.h"
21#include "clang/Basic/SourceManager.h"
22#include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
23#include "clang/StaticAnalyzer/Core/BugReporter/BugReporter.h"
24#include "clang/StaticAnalyzer/Core/Checker.h"
25#include "llvm/ADT/STLExtras.h"
26
27using namespace clang;
28using namespace ento;
29
30enum IVarState { Unused, Used };
31typedef llvm::DenseMap<const ObjCIvarDecl*,IVarState> IvarUsageMap;
32
33static void Scan(IvarUsageMap& M, const Stmt *S) {
34 if (!S)
35 return;
36
37 if (const ObjCIvarRefExpr *Ex = dyn_cast<ObjCIvarRefExpr>(Val: S)) {
38 const ObjCIvarDecl *D = Ex->getDecl();
39 IvarUsageMap::iterator I = M.find(Val: D);
40 if (I != M.end())
41 I->second = Used;
42 return;
43 }
44
45 // Blocks can reference an instance variable of a class.
46 if (const BlockExpr *BE = dyn_cast<BlockExpr>(Val: S)) {
47 Scan(M, S: BE->getBody());
48 return;
49 }
50
51 if (const PseudoObjectExpr *POE = dyn_cast<PseudoObjectExpr>(Val: S))
52 for (const Expr *sub : POE->semantics()) {
53 if (const OpaqueValueExpr *OVE = dyn_cast<OpaqueValueExpr>(Val: sub))
54 sub = OVE->getSourceExpr();
55 Scan(M, S: sub);
56 }
57
58 for (const Stmt *SubStmt : S->children())
59 Scan(M, S: SubStmt);
60}
61
62static void Scan(IvarUsageMap& M, const ObjCPropertyImplDecl *D) {
63 if (!D)
64 return;
65
66 const ObjCIvarDecl *ID = D->getPropertyIvarDecl();
67
68 if (!ID)
69 return;
70
71 IvarUsageMap::iterator I = M.find(Val: ID);
72 if (I != M.end())
73 I->second = Used;
74}
75
76static void Scan(IvarUsageMap& M, const ObjCContainerDecl *D) {
77 // Scan the methods for accesses.
78 for (const auto *I : D->instance_methods())
79 Scan(M, S: I->getBody());
80
81 if (const ObjCImplementationDecl *ID = dyn_cast<ObjCImplementationDecl>(Val: D)) {
82 // Scan for @synthesized property methods that act as setters/getters
83 // to an ivar.
84 for (const auto *I : ID->property_impls())
85 Scan(M, D: I);
86
87 // Scan the associated categories as well.
88 for (const auto *Cat : ID->getClassInterface()->visible_categories()) {
89 if (const ObjCCategoryImplDecl *CID = Cat->getImplementation())
90 Scan(M, D: CID);
91 }
92 }
93}
94
95static void Scan(IvarUsageMap &M, const DeclContext *C, const FileID FID,
96 const SourceManager &SM) {
97 for (const auto *I : C->decls())
98 if (const auto *FD = dyn_cast<FunctionDecl>(Val: I)) {
99 SourceLocation L = FD->getBeginLoc();
100 if (SM.getFileID(SpellingLoc: L) == FID)
101 Scan(M, S: FD->getBody());
102 }
103}
104
105static void checkObjCUnusedIvar(const ObjCImplementationDecl *D,
106 BugReporter &BR,
107 const CheckerBase *Checker) {
108
109 const ObjCInterfaceDecl *ID = D->getClassInterface();
110 IvarUsageMap M;
111
112 // Iterate over the ivars.
113 for (const auto *Ivar : ID->ivars()) {
114 // Ignore ivars that...
115 // (a) aren't private
116 // (b) explicitly marked unused
117 // (c) are iboutlets
118 // (d) are unnamed bitfields
119 if (Ivar->getAccessControl() != ObjCIvarDecl::Private ||
120 Ivar->hasAttr<UnusedAttr>() || Ivar->hasAttr<IBOutletAttr>() ||
121 Ivar->hasAttr<IBOutletCollectionAttr>() || Ivar->isUnnamedBitField())
122 continue;
123
124 M[Ivar] = Unused;
125 }
126
127 if (M.empty())
128 return;
129
130 // Now scan the implementation declaration.
131 Scan(M, D);
132
133 // Any potentially unused ivars?
134 bool hasUnused = false;
135 for (IVarState State : llvm::make_second_range(c&: M))
136 if (State == Unused) {
137 hasUnused = true;
138 break;
139 }
140
141 if (!hasUnused)
142 return;
143
144 // We found some potentially unused ivars. Scan the entire translation unit
145 // for functions inside the @implementation that reference these ivars.
146 // FIXME: In the future hopefully we can just use the lexical DeclContext
147 // to go from the ObjCImplementationDecl to the lexically "nested"
148 // C functions.
149 const SourceManager &SM = BR.getSourceManager();
150 Scan(M, C: D->getDeclContext(), FID: SM.getFileID(SpellingLoc: D->getLocation()), SM);
151
152 // Find ivars that are unused.
153 for (auto [Ivar, State] : M)
154 if (State == Unused) {
155 std::string sbuf;
156 llvm::raw_string_ostream os(sbuf);
157 os << "Instance variable '" << *Ivar << "' in class '" << *ID
158 << "' is never used by the methods in its @implementation "
159 "(although it may be used by category methods).";
160
161 PathDiagnosticLocation L =
162 PathDiagnosticLocation::create(D: Ivar, SM: BR.getSourceManager());
163 BR.EmitBasicReport(DeclWithIssue: ID, Checker, BugName: "Unused instance variable",
164 BugCategory: "Optimization", BugStr: os.str(), Loc: L);
165 }
166}
167
168//===----------------------------------------------------------------------===//
169// ObjCUnusedIvarsChecker
170//===----------------------------------------------------------------------===//
171
172namespace {
173class ObjCUnusedIvarsChecker : public Checker<
174 check::ASTDecl<ObjCImplementationDecl> > {
175public:
176 void checkASTDecl(const ObjCImplementationDecl *D, AnalysisManager& mgr,
177 BugReporter &BR) const {
178 checkObjCUnusedIvar(D, BR, Checker: this);
179 }
180};
181}
182
183void ento::registerObjCUnusedIvarsChecker(CheckerManager &mgr) {
184 mgr.registerChecker<ObjCUnusedIvarsChecker>();
185}
186
187bool ento::shouldRegisterObjCUnusedIvarsChecker(const CheckerManager &mgr) {
188 return true;
189}
190