1 //===--- TransZeroOutPropsInDealloc.cpp - Transformations to ARC mode -----===//
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 // removeZeroOutPropsInDealloc:
10 //
11 // Removes zero'ing out "strong" @synthesized properties in a -dealloc method.
12 //
13 //===----------------------------------------------------------------------===//
14 
15 #include "Transforms.h"
16 #include "Internals.h"
17 #include "clang/AST/ASTContext.h"
18 
19 using namespace clang;
20 using namespace arcmt;
21 using namespace trans;
22 
23 namespace {
24 
25 class ZeroOutInDeallocRemover :
26                            public RecursiveASTVisitor<ZeroOutInDeallocRemover> {
27   typedef RecursiveASTVisitor<ZeroOutInDeallocRemover> base;
28 
29   MigrationPass &Pass;
30 
31   llvm::DenseMap<ObjCPropertyDecl*, ObjCPropertyImplDecl*> SynthesizedProperties;
32   ImplicitParamDecl *SelfD;
33   ExprSet Removables;
34   Selector FinalizeSel;
35 
36 public:
37   ZeroOutInDeallocRemover(MigrationPass &pass) : Pass(pass), SelfD(nullptr) {
38     FinalizeSel =
39         Pass.Ctx.Selectors.getNullarySelector(&Pass.Ctx.Idents.get("finalize"));
40   }
41 
42   bool VisitObjCMessageExpr(ObjCMessageExpr *ME) {
43     ASTContext &Ctx = Pass.Ctx;
44     TransformActions &TA = Pass.TA;
45 
46     if (ME->getReceiverKind() != ObjCMessageExpr::Instance)
47       return true;
48     Expr *receiver = ME->getInstanceReceiver();
49     if (!receiver)
50       return true;
51 
52     DeclRefExpr *refE = dyn_cast<DeclRefExpr>(receiver->IgnoreParenCasts());
53     if (!refE || refE->getDecl() != SelfD)
54       return true;
55 
56     bool BackedBySynthesizeSetter = false;
57     for (llvm::DenseMap<ObjCPropertyDecl*, ObjCPropertyImplDecl*>::iterator
58          P = SynthesizedProperties.begin(),
59          E = SynthesizedProperties.end(); P != E; ++P) {
60       ObjCPropertyDecl *PropDecl = P->first;
61       if (PropDecl->getSetterName() == ME->getSelector()) {
62         BackedBySynthesizeSetter = true;
63         break;
64       }
65     }
66     if (!BackedBySynthesizeSetter)
67       return true;
68 
69     // Remove the setter message if RHS is null
70     Transaction Trans(TA);
71     Expr *RHS = ME->getArg(0);
72     bool RHSIsNull =
73       RHS->isNullPointerConstant(Ctx,
74                                  Expr::NPC_ValueDependentIsNull);
75     if (RHSIsNull && isRemovable(ME))
76       TA.removeStmt(ME);
77 
78     return true;
79   }
80 
81   bool VisitPseudoObjectExpr(PseudoObjectExpr *POE) {
82     if (isZeroingPropIvar(POE) && isRemovable(POE)) {
83       Transaction Trans(Pass.TA);
84       Pass.TA.removeStmt(POE);
85     }
86 
87     return true;
88   }
89 
90   bool VisitBinaryOperator(BinaryOperator *BOE) {
91     if (isZeroingPropIvar(BOE) && isRemovable(BOE)) {
92       Transaction Trans(Pass.TA);
93       Pass.TA.removeStmt(BOE);
94     }
95 
96     return true;
97   }
98 
99   bool TraverseObjCMethodDecl(ObjCMethodDecl *D) {
100     if (D->getMethodFamily() != OMF_dealloc &&
101         !(D->isInstanceMethod() && D->getSelector() == FinalizeSel))
102       return true;
103     if (!D->hasBody())
104       return true;
105 
106     ObjCImplDecl *IMD = dyn_cast<ObjCImplDecl>(D->getDeclContext());
107     if (!IMD)
108       return true;
109 
110     SelfD = D->getSelfDecl();
111     collectRemovables(D->getBody(), Removables);
112 
113     // For a 'dealloc' method use, find all property implementations in
114     // this class implementation.
115     for (auto *PID : IMD->property_impls()) {
116       if (PID->getPropertyImplementation() ==
117           ObjCPropertyImplDecl::Synthesize) {
118         ObjCPropertyDecl *PD = PID->getPropertyDecl();
119         ObjCMethodDecl *setterM = PD->getSetterMethodDecl();
120         if (!(setterM && setterM->isDefined())) {
121           ObjCPropertyAttribute::Kind AttrKind = PD->getPropertyAttributes();
122           if (AttrKind & (ObjCPropertyAttribute::kind_retain |
123                           ObjCPropertyAttribute::kind_copy |
124                           ObjCPropertyAttribute::kind_strong))
125             SynthesizedProperties[PD] = PID;
126         }
127       }
128     }
129 
130     // Now, remove all zeroing of ivars etc.
131     base::TraverseObjCMethodDecl(D);
132 
133     // clear out for next method.
134     SynthesizedProperties.clear();
135     SelfD = nullptr;
136     Removables.clear();
137     return true;
138   }
139 
140   bool TraverseFunctionDecl(FunctionDecl *D) { return true; }
141   bool TraverseBlockDecl(BlockDecl *block) { return true; }
142   bool TraverseBlockExpr(BlockExpr *block) { return true; }
143 
144 private:
145   bool isRemovable(Expr *E) const {
146     return Removables.count(E);
147   }
148 
149   bool isZeroingPropIvar(Expr *E) {
150     E = E->IgnoreParens();
151     if (BinaryOperator *BO = dyn_cast<BinaryOperator>(E))
152       return isZeroingPropIvar(BO);
153     if (PseudoObjectExpr *PO = dyn_cast<PseudoObjectExpr>(E))
154       return isZeroingPropIvar(PO);
155     return false;
156   }
157 
158   bool isZeroingPropIvar(BinaryOperator *BOE) {
159     if (BOE->getOpcode() == BO_Comma)
160       return isZeroingPropIvar(BOE->getLHS()) &&
161              isZeroingPropIvar(BOE->getRHS());
162 
163     if (BOE->getOpcode() != BO_Assign)
164       return false;
165 
166     Expr *LHS = BOE->getLHS();
167     if (ObjCIvarRefExpr *IV = dyn_cast<ObjCIvarRefExpr>(LHS)) {
168       ObjCIvarDecl *IVDecl = IV->getDecl();
169       if (!IVDecl->getType()->isObjCObjectPointerType())
170         return false;
171       bool IvarBacksPropertySynthesis = false;
172       for (llvm::DenseMap<ObjCPropertyDecl*, ObjCPropertyImplDecl*>::iterator
173            P = SynthesizedProperties.begin(),
174            E = SynthesizedProperties.end(); P != E; ++P) {
175         ObjCPropertyImplDecl *PropImpDecl = P->second;
176         if (PropImpDecl && PropImpDecl->getPropertyIvarDecl() == IVDecl) {
177           IvarBacksPropertySynthesis = true;
178           break;
179         }
180       }
181       if (!IvarBacksPropertySynthesis)
182         return false;
183     }
184     else
185         return false;
186 
187     return isZero(BOE->getRHS());
188   }
189 
190   bool isZeroingPropIvar(PseudoObjectExpr *PO) {
191     BinaryOperator *BO = dyn_cast<BinaryOperator>(PO->getSyntacticForm());
192     if (!BO) return false;
193     if (BO->getOpcode() != BO_Assign) return false;
194 
195     ObjCPropertyRefExpr *PropRefExp =
196       dyn_cast<ObjCPropertyRefExpr>(BO->getLHS()->IgnoreParens());
197     if (!PropRefExp) return false;
198 
199     // TODO: Using implicit property decl.
200     if (PropRefExp->isImplicitProperty())
201       return false;
202 
203     if (ObjCPropertyDecl *PDecl = PropRefExp->getExplicitProperty()) {
204       if (!SynthesizedProperties.count(PDecl))
205         return false;
206     }
207 
208     return isZero(cast<OpaqueValueExpr>(BO->getRHS())->getSourceExpr());
209   }
210 
211   bool isZero(Expr *E) {
212     if (E->isNullPointerConstant(Pass.Ctx, Expr::NPC_ValueDependentIsNull))
213       return true;
214 
215     return isZeroingPropIvar(E);
216   }
217 };
218 
219 } // anonymous namespace
220 
221 void trans::removeZeroOutPropsInDeallocFinalize(MigrationPass &pass) {
222   ZeroOutInDeallocRemover trans(pass);
223   trans.TraverseDecl(pass.Ctx.getTranslationUnitDecl());
224 }
225