TransBlockObjCVariable.cpp source code [clang_source_code/lib/ARCMigrate/TransBlockObjCVariable.cpp]

1	//===--- TransBlockObjCVariable.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	// rewriteBlockObjCVariable:
10	//
11	// Adding __block to an obj-c variable could be either because the variable
12	// is used for output storage or the user wanted to break a retain cycle.
13	// This transformation checks whether a reference of the variable for the block
14	// is actually needed (it is assigned to or its address is taken) or not.
15	// If the reference is not needed it will assume __block was added to break a
16	// cycle so it will remove '__block' and add __weak/__unsafe_unretained.
17	// e.g
18	//
19	// __block Foo *x;
20	// bar(^ { [x cake]; });
21	// ---->
22	// __weak Foo *x;
23	// bar(^ { [x cake]; });
24	//
25	//===----------------------------------------------------------------------===//
26
27	#include "Transforms.h"
28	#include "Internals.h"
29	#include "clang/AST/ASTContext.h"
30	#include "clang/AST/Attr.h"
31	#include "clang/Basic/SourceManager.h"
32
33	using namespace clang;
34	using namespace arcmt;
35	using namespace trans;
36
37	namespace {
38
39	class RootBlockObjCVarRewriter :
40	public RecursiveASTVisitor<RootBlockObjCVarRewriter> {
41	llvm::DenseSet<VarDecl *> &VarsToChange;
42
43	class BlockVarChecker : public RecursiveASTVisitor<BlockVarChecker> {
44	VarDecl *Var;
45
46	typedef RecursiveASTVisitor<BlockVarChecker> base;
47	public:
48	BlockVarChecker(VarDecl *var) : Var(var) { }
49
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
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:
74	RootBlockObjCVarRewriter(llvm::DenseSet<VarDecl *> &VarsToChange)
75	: VarsToChange(VarsToChange) { }
76
77	bool VisitBlockDecl(BlockDecl *block) {
78	SmallVector<VarDecl *, 4> BlockVars;
79
80	for (const auto &I : block->captures()) {
81	VarDecl *var = I.getVariable();
82	if (I.isByRef() &&
83	var->getType()->isObjCObjectPointerType() &&
84	isImplicitStrong(var->getType())) {
85	BlockVars.push_back(var);
86	}
87	}
88
89	for (unsigned i = 0, e = BlockVars.size(); i != e; ++i) {
90	VarDecl *var = BlockVars[i];
91
92	BlockVarChecker checker(var);
93	bool onlyValueOfVarIsNeeded = checker.TraverseStmt(block->getBody());
94	if (onlyValueOfVarIsNeeded)
95	VarsToChange.insert(var);
96	else
97	VarsToChange.erase(var);
98	}
99
100	return true;
101	}
102
103	private:
104	bool isImplicitStrong(QualType ty) {
105	if (isa<AttributedType>(ty.getTypePtr()))
106	return false;
107	return ty.getLocalQualifiers().getObjCLifetime() == Qualifiers::OCL_Strong;
108	}
109	};
110
111	class BlockObjCVarRewriter : public RecursiveASTVisitor<BlockObjCVarRewriter> {
112	llvm::DenseSet<VarDecl *> &VarsToChange;
113
114	public:
115	BlockObjCVarRewriter(llvm::DenseSet<VarDecl *> &VarsToChange)
116	: VarsToChange(VarsToChange) { }
117
118	bool TraverseBlockDecl(BlockDecl *block) {
119	RootBlockObjCVarRewriter(VarsToChange).TraverseDecl(block);
120	return true;
121	}
122	};
123
124	} // anonymous namespace
125
126	void BlockObjCVariableTraverser::traverseBody(BodyContext &BodyCtx) {
127	MigrationPass &Pass = BodyCtx.getMigrationContext().Pass;
128	llvm::DenseSet<VarDecl *> VarsToChange;
129
130	BlockObjCVarRewriter trans(VarsToChange);
131	trans.TraverseStmt(BodyCtx.getTopStmt());
132
133	for (llvm::DenseSet<VarDecl *>::iterator
134	I = VarsToChange.begin(), E = VarsToChange.end(); I != E; ++I) {
135	VarDecl var = I;
136	BlocksAttr *attr = var->getAttr<BlocksAttr>();
137	if(!attr)
138	continue;
139	bool useWeak = canApplyWeak(Pass.Ctx, var->getType());
140	SourceManager &SM = Pass.Ctx.getSourceManager();
141	Transaction Trans(Pass.TA);
142	Pass.TA.replaceText(SM.getExpansionLoc(attr->getLocation()),
143	"__block",
144	useWeak ? "__weak" : "__unsafe_unretained");
145	}
146	}
147

clang::arcmt::trans::BlockObjCVariableTraverser::traverseBody

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