1 //===--- TransBlockObjCVariable.cpp - Tranformations 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 // rewriteBlockObjCVariable:
11 //
12 // Adding __block to an obj-c variable could be either because the the variable
13 // is used for output storage or the user wanted to break a retain cycle.
14 // This transformation checks whether a reference of the variable for the block
15 // is actually needed (it is assigned to or its address is taken) or not.
16 // If the reference is not needed it will assume __block was added to break a
17 // cycle so it will remove '__block' and add __weak/__unsafe_unretained.
18 // e.g
19 //
20 // __block Foo *x;
21 // bar(^ { [x cake]; });
22 // ---->
23 // __weak Foo *x;
24 // bar(^ { [x cake]; });
25 //
26 //===----------------------------------------------------------------------===//
27
28 #include "Transforms.h"
29 #include "Internals.h"
30 #include "clang/Basic/SourceManager.h"
31
32 using namespace clang;
33 using namespace arcmt;
34 using namespace trans;
35
36 namespace {
37
38 class RootBlockObjCVarRewriter :
39 public RecursiveASTVisitor<RootBlockObjCVarRewriter> {
40 MigrationPass &Pass;
41 llvm::DenseSet<VarDecl *> &VarsToChange;
42
43 class BlockVarChecker : public RecursiveASTVisitor<BlockVarChecker> {
44 VarDecl *Var;
45
46 typedef RecursiveASTVisitor<BlockVarChecker> base;
47 public:
BlockVarChecker(VarDecl * var)48 BlockVarChecker(VarDecl *var) : Var(var) { }
49
TraverseImplicitCastExpr(ImplicitCastExpr * castE)50 bool TraverseImplicitCastExpr(ImplicitCastExpr *castE) {
51 if (DeclRefExpr *
52 ref = dyn_cast<DeclRefExpr>(castE->getSubExpr())) {
53 if (ref->getDecl() == Var) {
54 if (castE->getCastKind() == CK_LValueToRValue)
55 return true; // Using the value of the variable.
56 if (castE->getCastKind() == CK_NoOp && castE->isLValue() &&
57 Var->getASTContext().getLangOpts().CPlusPlus)
58 return true; // Binding to const C++ reference.
59 }
60 }
61
62 return base::TraverseImplicitCastExpr(castE);
63 }
64
VisitDeclRefExpr(DeclRefExpr * E)65 bool VisitDeclRefExpr(DeclRefExpr *E) {
66 if (E->getDecl() == Var)
67 return false; // The reference of the variable, and not just its value,
68 // is needed.
69 return true;
70 }
71 };
72
73 public:
RootBlockObjCVarRewriter(MigrationPass & pass,llvm::DenseSet<VarDecl * > & VarsToChange)74 RootBlockObjCVarRewriter(MigrationPass &pass,
75 llvm::DenseSet<VarDecl *> &VarsToChange)
76 : Pass(pass), VarsToChange(VarsToChange) { }
77
VisitBlockDecl(BlockDecl * block)78 bool VisitBlockDecl(BlockDecl *block) {
79 SmallVector<VarDecl *, 4> BlockVars;
80
81 for (BlockDecl::capture_iterator
82 I = block->capture_begin(), E = block->capture_end(); I != E; ++I) {
83 VarDecl *var = I->getVariable();
84 if (I->isByRef() &&
85 var->getType()->isObjCObjectPointerType() &&
86 isImplicitStrong(var->getType())) {
87 BlockVars.push_back(var);
88 }
89 }
90
91 for (unsigned i = 0, e = BlockVars.size(); i != e; ++i) {
92 VarDecl *var = BlockVars[i];
93
94 BlockVarChecker checker(var);
95 bool onlyValueOfVarIsNeeded = checker.TraverseStmt(block->getBody());
96 if (onlyValueOfVarIsNeeded)
97 VarsToChange.insert(var);
98 else
99 VarsToChange.erase(var);
100 }
101
102 return true;
103 }
104
105 private:
isImplicitStrong(QualType ty)106 bool isImplicitStrong(QualType ty) {
107 if (isa<AttributedType>(ty.getTypePtr()))
108 return false;
109 return ty.getLocalQualifiers().getObjCLifetime() == Qualifiers::OCL_Strong;
110 }
111 };
112
113 class BlockObjCVarRewriter : public RecursiveASTVisitor<BlockObjCVarRewriter> {
114 MigrationPass &Pass;
115 llvm::DenseSet<VarDecl *> &VarsToChange;
116
117 public:
BlockObjCVarRewriter(MigrationPass & pass,llvm::DenseSet<VarDecl * > & VarsToChange)118 BlockObjCVarRewriter(MigrationPass &pass,
119 llvm::DenseSet<VarDecl *> &VarsToChange)
120 : Pass(pass), VarsToChange(VarsToChange) { }
121
TraverseBlockDecl(BlockDecl * block)122 bool TraverseBlockDecl(BlockDecl *block) {
123 RootBlockObjCVarRewriter(Pass, VarsToChange).TraverseDecl(block);
124 return true;
125 }
126 };
127
128 } // anonymous namespace
129
traverseBody(BodyContext & BodyCtx)130 void BlockObjCVariableTraverser::traverseBody(BodyContext &BodyCtx) {
131 MigrationPass &Pass = BodyCtx.getMigrationContext().Pass;
132 llvm::DenseSet<VarDecl *> VarsToChange;
133
134 BlockObjCVarRewriter trans(Pass, VarsToChange);
135 trans.TraverseStmt(BodyCtx.getTopStmt());
136
137 for (llvm::DenseSet<VarDecl *>::iterator
138 I = VarsToChange.begin(), E = VarsToChange.end(); I != E; ++I) {
139 VarDecl *var = *I;
140 BlocksAttr *attr = var->getAttr<BlocksAttr>();
141 if(!attr)
142 continue;
143 bool useWeak = canApplyWeak(Pass.Ctx, var->getType());
144 SourceManager &SM = Pass.Ctx.getSourceManager();
145 Transaction Trans(Pass.TA);
146 Pass.TA.replaceText(SM.getExpansionLoc(attr->getLocation()),
147 "__block",
148 useWeak ? "__weak" : "__unsafe_unretained");
149 }
150 }
151