1 //===--- TransZeroOutPropsInDealloc.cpp - Transformations to ARC mode -----===//
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 // removeZeroOutPropsInDealloc:
11 //
12 // Removes zero'ing out "strong" @synthesized properties in a -dealloc method.
13 //
14 //===----------------------------------------------------------------------===//
15 
16 #include "Transforms.h"
17 #include "Internals.h"
18 #include "clang/AST/ASTContext.h"
19 
20 using namespace clang;
21 using namespace arcmt;
22 using namespace trans;
23 
24 namespace {
25 
26 class ZeroOutInDeallocRemover :
27                            public RecursiveASTVisitor<ZeroOutInDeallocRemover> {
28   typedef RecursiveASTVisitor<ZeroOutInDeallocRemover> base;
29 
30   MigrationPass &Pass;
31 
32   llvm::DenseMap<ObjCPropertyDecl*, ObjCPropertyImplDecl*> SynthesizedProperties;
33   ImplicitParamDecl *SelfD;
34   ExprSet Removables;
35   Selector FinalizeSel;
36 
37 public:
ZeroOutInDeallocRemover(MigrationPass & pass)38   ZeroOutInDeallocRemover(MigrationPass &pass) : Pass(pass), SelfD(nullptr) {
39     FinalizeSel =
40         Pass.Ctx.Selectors.getNullarySelector(&Pass.Ctx.Idents.get("finalize"));
41   }
42 
VisitObjCMessageExpr(ObjCMessageExpr * ME)43   bool VisitObjCMessageExpr(ObjCMessageExpr *ME) {
44     ASTContext &Ctx = Pass.Ctx;
45     TransformActions &TA = Pass.TA;
46 
47     if (ME->getReceiverKind() != ObjCMessageExpr::Instance)
48       return true;
49     Expr *receiver = ME->getInstanceReceiver();
50     if (!receiver)
51       return true;
52 
53     DeclRefExpr *refE = dyn_cast<DeclRefExpr>(receiver->IgnoreParenCasts());
54     if (!refE || refE->getDecl() != SelfD)
55       return true;
56 
57     bool BackedBySynthesizeSetter = false;
58     for (llvm::DenseMap<ObjCPropertyDecl*, ObjCPropertyImplDecl*>::iterator
59          P = SynthesizedProperties.begin(),
60          E = SynthesizedProperties.end(); P != E; ++P) {
61       ObjCPropertyDecl *PropDecl = P->first;
62       if (PropDecl->getSetterName() == ME->getSelector()) {
63         BackedBySynthesizeSetter = true;
64         break;
65       }
66     }
67     if (!BackedBySynthesizeSetter)
68       return true;
69 
70     // Remove the setter message if RHS is null
71     Transaction Trans(TA);
72     Expr *RHS = ME->getArg(0);
73     bool RHSIsNull =
74       RHS->isNullPointerConstant(Ctx,
75                                  Expr::NPC_ValueDependentIsNull);
76     if (RHSIsNull && isRemovable(ME))
77       TA.removeStmt(ME);
78 
79     return true;
80   }
81 
VisitPseudoObjectExpr(PseudoObjectExpr * POE)82   bool VisitPseudoObjectExpr(PseudoObjectExpr *POE) {
83     if (isZeroingPropIvar(POE) && isRemovable(POE)) {
84       Transaction Trans(Pass.TA);
85       Pass.TA.removeStmt(POE);
86     }
87 
88     return true;
89   }
90 
VisitBinaryOperator(BinaryOperator * BOE)91   bool VisitBinaryOperator(BinaryOperator *BOE) {
92     if (isZeroingPropIvar(BOE) && isRemovable(BOE)) {
93       Transaction Trans(Pass.TA);
94       Pass.TA.removeStmt(BOE);
95     }
96 
97     return true;
98   }
99 
TraverseObjCMethodDecl(ObjCMethodDecl * D)100   bool TraverseObjCMethodDecl(ObjCMethodDecl *D) {
101     if (D->getMethodFamily() != OMF_dealloc &&
102         !(D->isInstanceMethod() && D->getSelector() == FinalizeSel))
103       return true;
104     if (!D->hasBody())
105       return true;
106 
107     ObjCImplDecl *IMD = dyn_cast<ObjCImplDecl>(D->getDeclContext());
108     if (!IMD)
109       return true;
110 
111     SelfD = D->getSelfDecl();
112     collectRemovables(D->getBody(), Removables);
113 
114     // For a 'dealloc' method use, find all property implementations in
115     // this class implementation.
116     for (auto *PID : IMD->property_impls()) {
117       if (PID->getPropertyImplementation() ==
118           ObjCPropertyImplDecl::Synthesize) {
119         ObjCPropertyDecl *PD = PID->getPropertyDecl();
120         ObjCMethodDecl *setterM = PD->getSetterMethodDecl();
121         if (!(setterM && setterM->isDefined())) {
122           ObjCPropertyDecl::PropertyAttributeKind AttrKind =
123             PD->getPropertyAttributes();
124             if (AttrKind &
125                 (ObjCPropertyDecl::OBJC_PR_retain |
126                   ObjCPropertyDecl::OBJC_PR_copy   |
127                   ObjCPropertyDecl::OBJC_PR_strong))
128               SynthesizedProperties[PD] = PID;
129         }
130       }
131     }
132 
133     // Now, remove all zeroing of ivars etc.
134     base::TraverseObjCMethodDecl(D);
135 
136     // clear out for next method.
137     SynthesizedProperties.clear();
138     SelfD = nullptr;
139     Removables.clear();
140     return true;
141   }
142 
TraverseFunctionDecl(FunctionDecl * D)143   bool TraverseFunctionDecl(FunctionDecl *D) { return true; }
TraverseBlockDecl(BlockDecl * block)144   bool TraverseBlockDecl(BlockDecl *block) { return true; }
TraverseBlockExpr(BlockExpr * block)145   bool TraverseBlockExpr(BlockExpr *block) { return true; }
146 
147 private:
isRemovable(Expr * E) const148   bool isRemovable(Expr *E) const {
149     return Removables.count(E);
150   }
151 
isZeroingPropIvar(Expr * E)152   bool isZeroingPropIvar(Expr *E) {
153     E = E->IgnoreParens();
154     if (BinaryOperator *BO = dyn_cast<BinaryOperator>(E))
155       return isZeroingPropIvar(BO);
156     if (PseudoObjectExpr *PO = dyn_cast<PseudoObjectExpr>(E))
157       return isZeroingPropIvar(PO);
158     return false;
159   }
160 
isZeroingPropIvar(BinaryOperator * BOE)161   bool isZeroingPropIvar(BinaryOperator *BOE) {
162     if (BOE->getOpcode() == BO_Comma)
163       return isZeroingPropIvar(BOE->getLHS()) &&
164              isZeroingPropIvar(BOE->getRHS());
165 
166     if (BOE->getOpcode() != BO_Assign)
167       return false;
168 
169     Expr *LHS = BOE->getLHS();
170     if (ObjCIvarRefExpr *IV = dyn_cast<ObjCIvarRefExpr>(LHS)) {
171       ObjCIvarDecl *IVDecl = IV->getDecl();
172       if (!IVDecl->getType()->isObjCObjectPointerType())
173         return false;
174       bool IvarBacksPropertySynthesis = false;
175       for (llvm::DenseMap<ObjCPropertyDecl*, ObjCPropertyImplDecl*>::iterator
176            P = SynthesizedProperties.begin(),
177            E = SynthesizedProperties.end(); P != E; ++P) {
178         ObjCPropertyImplDecl *PropImpDecl = P->second;
179         if (PropImpDecl && PropImpDecl->getPropertyIvarDecl() == IVDecl) {
180           IvarBacksPropertySynthesis = true;
181           break;
182         }
183       }
184       if (!IvarBacksPropertySynthesis)
185         return false;
186     }
187     else
188         return false;
189 
190     return isZero(BOE->getRHS());
191   }
192 
isZeroingPropIvar(PseudoObjectExpr * PO)193   bool isZeroingPropIvar(PseudoObjectExpr *PO) {
194     BinaryOperator *BO = dyn_cast<BinaryOperator>(PO->getSyntacticForm());
195     if (!BO) return false;
196     if (BO->getOpcode() != BO_Assign) return false;
197 
198     ObjCPropertyRefExpr *PropRefExp =
199       dyn_cast<ObjCPropertyRefExpr>(BO->getLHS()->IgnoreParens());
200     if (!PropRefExp) return false;
201 
202     // TODO: Using implicit property decl.
203     if (PropRefExp->isImplicitProperty())
204       return false;
205 
206     if (ObjCPropertyDecl *PDecl = PropRefExp->getExplicitProperty()) {
207       if (!SynthesizedProperties.count(PDecl))
208         return false;
209     }
210 
211     return isZero(cast<OpaqueValueExpr>(BO->getRHS())->getSourceExpr());
212   }
213 
isZero(Expr * E)214   bool isZero(Expr *E) {
215     if (E->isNullPointerConstant(Pass.Ctx, Expr::NPC_ValueDependentIsNull))
216       return true;
217 
218     return isZeroingPropIvar(E);
219   }
220 };
221 
222 } // anonymous namespace
223 
removeZeroOutPropsInDeallocFinalize(MigrationPass & pass)224 void trans::removeZeroOutPropsInDeallocFinalize(MigrationPass &pass) {
225   ZeroOutInDeallocRemover trans(pass);
226   trans.TraverseDecl(pass.Ctx.getTranslationUnitDecl());
227 }
228