1//===--- TransBlockObjCVariable.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// rewriteBlockObjCVariable:
11//
12// Adding __block to an obj-c variable could be either because 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/AST/ASTContext.h"
31#include "clang/AST/Attr.h"
32#include "clang/Basic/SourceManager.h"
33
34using namespace clang;
35using namespace arcmt;
36using namespace trans;
37
38namespace {
39
40class RootBlockObjCVarRewriter :
41                          public RecursiveASTVisitor<RootBlockObjCVarRewriter> {
42  llvm::DenseSet<VarDecl *> &VarsToChange;
43
44  class BlockVarChecker : public RecursiveASTVisitor<BlockVarChecker> {
45    VarDecl *Var;
46
47    typedef RecursiveASTVisitor<BlockVarChecker> base;
48  public:
49    BlockVarChecker(VarDecl *var) : Var(var) { }
50
51    bool TraverseImplicitCastExpr(ImplicitCastExpr *castE) {
52      if (DeclRefExpr *
53            ref = dyn_cast<DeclRefExpr>(castE->getSubExpr())) {
54        if (ref->getDecl() == Var) {
55          if (castE->getCastKind() == CK_LValueToRValue)
56            return true; // Using the value of the variable.
57          if (castE->getCastKind() == CK_NoOp && castE->isLValue() &&
58              Var->getASTContext().getLangOpts().CPlusPlus)
59            return true; // Binding to const C++ reference.
60        }
61      }
62
63      return base::TraverseImplicitCastExpr(castE);
64    }
65
66    bool VisitDeclRefExpr(DeclRefExpr *E) {
67      if (E->getDecl() == Var)
68        return false; // The reference of the variable, and not just its value,
69                      //  is needed.
70      return true;
71    }
72  };
73
74public:
75  RootBlockObjCVarRewriter(llvm::DenseSet<VarDecl *> &VarsToChange)
76    : VarsToChange(VarsToChange) { }
77
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
105private:
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
113class BlockObjCVarRewriter : public RecursiveASTVisitor<BlockObjCVarRewriter> {
114  llvm::DenseSet<VarDecl *> &VarsToChange;
115
116public:
117  BlockObjCVarRewriter(llvm::DenseSet<VarDecl *> &VarsToChange)
118    : VarsToChange(VarsToChange) { }
119
120  bool TraverseBlockDecl(BlockDecl *block) {
121    RootBlockObjCVarRewriter(VarsToChange).TraverseDecl(block);
122    return true;
123  }
124};
125
126} // anonymous namespace
127
128void BlockObjCVariableTraverser::traverseBody(BodyContext &BodyCtx) {
129  MigrationPass &Pass = BodyCtx.getMigrationContext().Pass;
130  llvm::DenseSet<VarDecl *> VarsToChange;
131
132  BlockObjCVarRewriter trans(VarsToChange);
133  trans.TraverseStmt(BodyCtx.getTopStmt());
134
135  for (llvm::DenseSet<VarDecl *>::iterator
136         I = VarsToChange.begin(), E = VarsToChange.end(); I != E; ++I) {
137    VarDecl *var = *I;
138    BlocksAttr *attr = var->getAttr<BlocksAttr>();
139    if(!attr)
140      continue;
141    bool useWeak = canApplyWeak(Pass.Ctx, var->getType());
142    SourceManager &SM = Pass.Ctx.getSourceManager();
143    Transaction Trans(Pass.TA);
144    Pass.TA.replaceText(SM.getExpansionLoc(attr->getLocation()),
145                        "__block",
146                        useWeak ? "__weak" : "__unsafe_unretained");
147  }
148}
149