clang  3.7.0
TransRetainReleaseDealloc.cpp
Go to the documentation of this file.
1 //===--- TransRetainReleaseDealloc.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 // removeRetainReleaseDealloc:
11 //
12 // Removes retain/release/autorelease/dealloc messages.
13 //
14 // return [[foo retain] autorelease];
15 // ---->
16 // return foo;
17 //
18 //===----------------------------------------------------------------------===//
19 
20 #include "Transforms.h"
21 #include "Internals.h"
22 #include "clang/AST/ASTContext.h"
23 #include "clang/AST/ParentMap.h"
25 #include "clang/Lex/Lexer.h"
27 #include "llvm/ADT/StringSwitch.h"
28 
29 using namespace clang;
30 using namespace arcmt;
31 using namespace trans;
32 
33 namespace {
34 
35 class RetainReleaseDeallocRemover :
36  public RecursiveASTVisitor<RetainReleaseDeallocRemover> {
37  Stmt *Body;
38  MigrationPass &Pass;
39 
40  ExprSet Removables;
41  std::unique_ptr<ParentMap> StmtMap;
42 
43  Selector DelegateSel, FinalizeSel;
44 
45 public:
46  RetainReleaseDeallocRemover(MigrationPass &pass)
47  : Body(nullptr), Pass(pass) {
48  DelegateSel =
49  Pass.Ctx.Selectors.getNullarySelector(&Pass.Ctx.Idents.get("delegate"));
50  FinalizeSel =
51  Pass.Ctx.Selectors.getNullarySelector(&Pass.Ctx.Idents.get("finalize"));
52  }
53 
54  void transformBody(Stmt *body, Decl *ParentD) {
55  Body = body;
56  collectRemovables(body, Removables);
57  StmtMap.reset(new ParentMap(body));
58  TraverseStmt(body);
59  }
60 
61  bool VisitObjCMessageExpr(ObjCMessageExpr *E) {
62  switch (E->getMethodFamily()) {
63  default:
64  if (E->isInstanceMessage() && E->getSelector() == FinalizeSel)
65  break;
66  return true;
67  case OMF_autorelease:
68  if (isRemovable(E)) {
69  if (!isCommonUnusedAutorelease(E)) {
70  // An unused autorelease is badness. If we remove it the receiver
71  // will likely die immediately while previously it was kept alive
72  // by the autorelease pool. This is bad practice in general, leave it
73  // and emit an error to force the user to restructure their code.
74  Pass.TA.reportError("it is not safe to remove an unused 'autorelease' "
75  "message; its receiver may be destroyed immediately",
76  E->getLocStart(), E->getSourceRange());
77  return true;
78  }
79  }
80  // Pass through.
81  case OMF_retain:
82  case OMF_release:
84  if (Expr *rec = E->getInstanceReceiver()) {
85  rec = rec->IgnoreParenImpCasts();
86  if (rec->getType().getObjCLifetime() == Qualifiers::OCL_ExplicitNone &&
87  (E->getMethodFamily() != OMF_retain || isRemovable(E))) {
88  std::string err = "it is not safe to remove '";
89  err += E->getSelector().getAsString() + "' message on "
90  "an __unsafe_unretained type";
91  Pass.TA.reportError(err, rec->getLocStart());
92  return true;
93  }
94 
95  if (isGlobalVar(rec) &&
96  (E->getMethodFamily() != OMF_retain || isRemovable(E))) {
97  std::string err = "it is not safe to remove '";
98  err += E->getSelector().getAsString() + "' message on "
99  "a global variable";
100  Pass.TA.reportError(err, rec->getLocStart());
101  return true;
102  }
103 
104  if (E->getMethodFamily() == OMF_release && isDelegateMessage(rec)) {
105  Pass.TA.reportError("it is not safe to remove 'retain' "
106  "message on the result of a 'delegate' message; "
107  "the object that was passed to 'setDelegate:' may not be "
108  "properly retained", rec->getLocStart());
109  return true;
110  }
111  }
112  case OMF_dealloc:
113  break;
114  }
115 
116  switch (E->getReceiverKind()) {
117  default:
118  return true;
120  Transaction Trans(Pass.TA);
121  clearDiagnostics(E->getSelectorLoc(0));
122  if (tryRemoving(E))
123  return true;
124  Pass.TA.replace(E->getSourceRange(), "self");
125  return true;
126  }
128  break;
129  }
130 
131  Expr *rec = E->getInstanceReceiver();
132  if (!rec) return true;
133 
134  Transaction Trans(Pass.TA);
135  clearDiagnostics(E->getSelectorLoc(0));
136 
137  ObjCMessageExpr *Msg = E;
138  Expr *RecContainer = Msg;
139  SourceRange RecRange = rec->getSourceRange();
140  checkForGCDOrXPC(Msg, RecContainer, rec, RecRange);
141 
142  if (Msg->getMethodFamily() == OMF_release &&
143  isRemovable(RecContainer) && isInAtFinally(RecContainer)) {
144  // Change the -release to "receiver = nil" in a finally to avoid a leak
145  // when an exception is thrown.
146  Pass.TA.replace(RecContainer->getSourceRange(), RecRange);
147  std::string str = " = ";
148  str += getNilString(Pass);
149  Pass.TA.insertAfterToken(RecRange.getEnd(), str);
150  return true;
151  }
152 
153  if (!hasSideEffects(rec, Pass.Ctx)) {
154  if (tryRemoving(RecContainer))
155  return true;
156  }
157  Pass.TA.replace(RecContainer->getSourceRange(), RecRange);
158 
159  return true;
160  }
161 
162 private:
163  /// \brief Checks for idioms where an unused -autorelease is common.
164  ///
165  /// Returns true for this idiom which is common in property
166  /// setters:
167  ///
168  /// [backingValue autorelease];
169  /// backingValue = [newValue retain]; // in general a +1 assign
170  ///
171  /// For these as well:
172  ///
173  /// [[var retain] autorelease];
174  /// return var;
175  ///
176  bool isCommonUnusedAutorelease(ObjCMessageExpr *E) {
177  if (isPlusOneAssignBeforeOrAfterAutorelease(E))
178  return true;
179  if (isReturnedAfterAutorelease(E))
180  return true;
181  return false;
182  }
183 
184  bool isReturnedAfterAutorelease(ObjCMessageExpr *E) {
185  Expr *Rec = E->getInstanceReceiver();
186  if (!Rec)
187  return false;
188 
189  Decl *RefD = getReferencedDecl(Rec);
190  if (!RefD)
191  return false;
192 
193  Stmt *nextStmt = getNextStmt(E);
194  if (!nextStmt)
195  return false;
196 
197  // Check for "return <variable>;".
198 
199  if (ReturnStmt *RetS = dyn_cast<ReturnStmt>(nextStmt))
200  return RefD == getReferencedDecl(RetS->getRetValue());
201 
202  return false;
203  }
204 
205  bool isPlusOneAssignBeforeOrAfterAutorelease(ObjCMessageExpr *E) {
206  Expr *Rec = E->getInstanceReceiver();
207  if (!Rec)
208  return false;
209 
210  Decl *RefD = getReferencedDecl(Rec);
211  if (!RefD)
212  return false;
213 
214  Stmt *prevStmt, *nextStmt;
215  std::tie(prevStmt, nextStmt) = getPreviousAndNextStmt(E);
216 
217  return isPlusOneAssignToVar(prevStmt, RefD) ||
218  isPlusOneAssignToVar(nextStmt, RefD);
219  }
220 
221  bool isPlusOneAssignToVar(Stmt *S, Decl *RefD) {
222  if (!S)
223  return false;
224 
225  // Check for "RefD = [+1 retained object];".
226 
227  if (BinaryOperator *Bop = dyn_cast<BinaryOperator>(S)) {
228  if (RefD != getReferencedDecl(Bop->getLHS()))
229  return false;
230  if (isPlusOneAssign(Bop))
231  return true;
232  return false;
233  }
234 
235  if (DeclStmt *DS = dyn_cast<DeclStmt>(S)) {
236  if (DS->isSingleDecl() && DS->getSingleDecl() == RefD) {
237  if (VarDecl *VD = dyn_cast<VarDecl>(RefD))
238  return isPlusOne(VD->getInit());
239  }
240  return false;
241  }
242 
243  return false;
244  }
245 
246  Stmt *getNextStmt(Expr *E) {
247  return getPreviousAndNextStmt(E).second;
248  }
249 
250  std::pair<Stmt *, Stmt *> getPreviousAndNextStmt(Expr *E) {
251  Stmt *prevStmt = nullptr, *nextStmt = nullptr;
252  if (!E)
253  return std::make_pair(prevStmt, nextStmt);
254 
255  Stmt *OuterS = E, *InnerS;
256  do {
257  InnerS = OuterS;
258  OuterS = StmtMap->getParent(InnerS);
259  }
260  while (OuterS && (isa<ParenExpr>(OuterS) ||
261  isa<CastExpr>(OuterS) ||
262  isa<ExprWithCleanups>(OuterS)));
263 
264  if (!OuterS)
265  return std::make_pair(prevStmt, nextStmt);
266 
267  Stmt::child_iterator currChildS = OuterS->child_begin();
268  Stmt::child_iterator childE = OuterS->child_end();
269  Stmt::child_iterator prevChildS = childE;
270  for (; currChildS != childE; ++currChildS) {
271  if (*currChildS == InnerS)
272  break;
273  prevChildS = currChildS;
274  }
275 
276  if (prevChildS != childE) {
277  prevStmt = *prevChildS;
278  if (prevStmt)
279  prevStmt = prevStmt->IgnoreImplicit();
280  }
281 
282  if (currChildS == childE)
283  return std::make_pair(prevStmt, nextStmt);
284  ++currChildS;
285  if (currChildS == childE)
286  return std::make_pair(prevStmt, nextStmt);
287 
288  nextStmt = *currChildS;
289  if (nextStmt)
290  nextStmt = nextStmt->IgnoreImplicit();
291 
292  return std::make_pair(prevStmt, nextStmt);
293  }
294 
295  Decl *getReferencedDecl(Expr *E) {
296  if (!E)
297  return nullptr;
298 
299  E = E->IgnoreParenCasts();
300  if (ObjCMessageExpr *ME = dyn_cast<ObjCMessageExpr>(E)) {
301  switch (ME->getMethodFamily()) {
302  case OMF_copy:
303  case OMF_autorelease:
304  case OMF_release:
305  case OMF_retain:
306  return getReferencedDecl(ME->getInstanceReceiver());
307  default:
308  return nullptr;
309  }
310  }
311  if (DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(E))
312  return DRE->getDecl();
313  if (MemberExpr *ME = dyn_cast<MemberExpr>(E))
314  return ME->getMemberDecl();
315  if (ObjCIvarRefExpr *IRE = dyn_cast<ObjCIvarRefExpr>(E))
316  return IRE->getDecl();
317 
318  return nullptr;
319  }
320 
321  /// \brief Check if the retain/release is due to a GCD/XPC macro that are
322  /// defined as:
323  ///
324  /// #define dispatch_retain(object) ({ dispatch_object_t _o = (object); _dispatch_object_validate(_o); (void)[_o retain]; })
325  /// #define dispatch_release(object) ({ dispatch_object_t _o = (object); _dispatch_object_validate(_o); [_o release]; })
326  /// #define xpc_retain(object) ({ xpc_object_t _o = (object); _xpc_object_validate(_o); [_o retain]; })
327  /// #define xpc_release(object) ({ xpc_object_t _o = (object); _xpc_object_validate(_o); [_o release]; })
328  ///
329  /// and return the top container which is the StmtExpr and the macro argument
330  /// expression.
331  void checkForGCDOrXPC(ObjCMessageExpr *Msg, Expr *&RecContainer,
332  Expr *&Rec, SourceRange &RecRange) {
333  SourceLocation Loc = Msg->getExprLoc();
334  if (!Loc.isMacroID())
335  return;
336  SourceManager &SM = Pass.Ctx.getSourceManager();
337  StringRef MacroName = Lexer::getImmediateMacroName(Loc, SM,
338  Pass.Ctx.getLangOpts());
339  bool isGCDOrXPC = llvm::StringSwitch<bool>(MacroName)
340  .Case("dispatch_retain", true)
341  .Case("dispatch_release", true)
342  .Case("xpc_retain", true)
343  .Case("xpc_release", true)
344  .Default(false);
345  if (!isGCDOrXPC)
346  return;
347 
348  StmtExpr *StmtE = nullptr;
349  Stmt *S = Msg;
350  while (S) {
351  if (StmtExpr *SE = dyn_cast<StmtExpr>(S)) {
352  StmtE = SE;
353  break;
354  }
355  S = StmtMap->getParent(S);
356  }
357 
358  if (!StmtE)
359  return;
360 
361  Stmt::child_range StmtExprChild = StmtE->children();
362  if (!StmtExprChild)
363  return;
364  CompoundStmt *CompS = dyn_cast_or_null<CompoundStmt>(*StmtExprChild);
365  if (!CompS)
366  return;
367 
368  Stmt::child_range CompStmtChild = CompS->children();
369  if (!CompStmtChild)
370  return;
371  DeclStmt *DeclS = dyn_cast_or_null<DeclStmt>(*CompStmtChild);
372  if (!DeclS)
373  return;
374  if (!DeclS->isSingleDecl())
375  return;
376  VarDecl *VD = dyn_cast_or_null<VarDecl>(DeclS->getSingleDecl());
377  if (!VD)
378  return;
379  Expr *Init = VD->getInit();
380  if (!Init)
381  return;
382 
383  RecContainer = StmtE;
384  Rec = Init->IgnoreParenImpCasts();
385  if (ExprWithCleanups *EWC = dyn_cast<ExprWithCleanups>(Rec))
386  Rec = EWC->getSubExpr()->IgnoreParenImpCasts();
387  RecRange = Rec->getSourceRange();
388  if (SM.isMacroArgExpansion(RecRange.getBegin()))
389  RecRange.setBegin(SM.getImmediateSpellingLoc(RecRange.getBegin()));
390  if (SM.isMacroArgExpansion(RecRange.getEnd()))
391  RecRange.setEnd(SM.getImmediateSpellingLoc(RecRange.getEnd()));
392  }
393 
394  void clearDiagnostics(SourceLocation loc) const {
395  Pass.TA.clearDiagnostic(diag::err_arc_illegal_explicit_message,
396  diag::err_unavailable,
397  diag::err_unavailable_message,
398  loc);
399  }
400 
401  bool isDelegateMessage(Expr *E) const {
402  if (!E) return false;
403 
404  E = E->IgnoreParenCasts();
405 
406  // Also look through property-getter sugar.
407  if (PseudoObjectExpr *pseudoOp = dyn_cast<PseudoObjectExpr>(E))
408  E = pseudoOp->getResultExpr()->IgnoreImplicit();
409 
410  if (ObjCMessageExpr *ME = dyn_cast<ObjCMessageExpr>(E))
411  return (ME->isInstanceMessage() && ME->getSelector() == DelegateSel);
412 
413  return false;
414  }
415 
416  bool isInAtFinally(Expr *E) const {
417  assert(E);
418  Stmt *S = E;
419  while (S) {
420  if (isa<ObjCAtFinallyStmt>(S))
421  return true;
422  S = StmtMap->getParent(S);
423  }
424 
425  return false;
426  }
427 
428  bool isRemovable(Expr *E) const {
429  return Removables.count(E);
430  }
431 
432  bool tryRemoving(Expr *E) const {
433  if (isRemovable(E)) {
434  Pass.TA.removeStmt(E);
435  return true;
436  }
437 
438  Stmt *parent = StmtMap->getParent(E);
439 
440  if (ImplicitCastExpr *castE = dyn_cast_or_null<ImplicitCastExpr>(parent))
441  return tryRemoving(castE);
442 
443  if (ParenExpr *parenE = dyn_cast_or_null<ParenExpr>(parent))
444  return tryRemoving(parenE);
445 
446  if (BinaryOperator *
447  bopE = dyn_cast_or_null<BinaryOperator>(parent)) {
448  if (bopE->getOpcode() == BO_Comma && bopE->getLHS() == E &&
449  isRemovable(bopE)) {
450  Pass.TA.replace(bopE->getSourceRange(), bopE->getRHS()->getSourceRange());
451  return true;
452  }
453  }
454 
455  return false;
456  }
457 
458 };
459 
460 } // anonymous namespace
461 
465 }
The receiver is the instance of the superclass object.
Definition: ExprObjC.h:1006
Defines the clang::ASTContext interface.
SourceLocation getEnd() const
The receiver is an object instance.
Definition: ExprObjC.h:1002
Smart pointer class that efficiently represents Objective-C method names.
bool isMacroID() const
ObjCMethodFamily getMethodFamily() const
Definition: ExprObjC.h:1267
SourceLocation getImmediateSpellingLoc(SourceLocation Loc) const
Given a SourceLocation object, return the spelling location referenced by the ID. ...
Defines the SourceManager interface.
const Expr * getInit() const
Definition: Decl.h:1068
Expr * IgnoreImplicit() LLVM_READONLY
Definition: Expr.h:694
void setBegin(SourceLocation b)
child_range children()
Definition: Expr.h:3429
bool TraverseDecl(Decl *D)
Recursively visit a declaration, by dispatching to Traverse*Decl() based on the argument's dynamic ty...
bool isGlobalVar(Expr *E)
Definition: Transforms.cpp:204
void removeRetainReleaseDeallocFinalize(MigrationPass &pass)
A builtin binary operation expression such as "x + y" or "x <= y".
Definition: Expr.h:2918
Selector getSelector() const
Definition: Expr.cpp:3718
Expr * IgnoreParenCasts() LLVM_READONLY
Definition: Expr.cpp:2439
child_range children()
Definition: Stmt.h:641
A class that does preorder depth-first traversal on the entire Clang AST and visits each node...
bool isPlusOneAssign(const BinaryOperator *E)
Definition: Transforms.cpp:71
StringRef getNilString(MigrationPass &Pass)
Returns "nil" or "0" if 'nil' macro is not actually defined.
Definition: Transforms.cpp:216
bool isInstanceMessage() const
Determine whether this is an instance message to either a computed object or to super.
Definition: ExprObjC.h:1140
SourceManager & SM
void collectRemovables(Stmt *S, ExprSet &exprs)
Definition: Transforms.cpp:315
TranslationUnitDecl * getTranslationUnitDecl() const
Definition: ASTContext.h:812
An expression that sends a message to the given Objective-C object or class.
Definition: ExprObjC.h:858
Encodes a location in the source. The SourceManager can decode this to get at the full include stack...
bool isSingleDecl() const
Definition: Stmt.h:463
std::string getAsString() const
Derive the full selector name (e.g. "foo:bar:") and return it as an std::string.
SourceLocation getBegin() const
static StringRef getImmediateMacroName(SourceLocation Loc, const SourceManager &SM, const LangOptions &LangOpts)
Retrieve the name of the immediate macro expansion.
Definition: Lexer.cpp:956
const Decl * getSingleDecl() const
Definition: Stmt.h:467
SourceLocation getExprLoc() const LLVM_READONLY
Definition: Expr.cpp:193
Expr * getInstanceReceiver()
Returns the object expression (receiver) for an instance message, or null for a message that is not a...
Definition: ExprObjC.h:1152
bool hasSideEffects(Expr *E, ASTContext &Ctx)
Definition: Transforms.cpp:175
SourceLocation getSelectorLoc(unsigned Index) const
Definition: ExprObjC.h:1314
SourceLocation getLocStart() const LLVM_READONLY
Definition: ExprObjC.h:1340
bool isPlusOne(const Expr *E)
Definition: Transforms.cpp:78
Expr * IgnoreParenImpCasts() LLVM_READONLY
Definition: Expr.cpp:2526
ObjCIvarRefExpr - A reference to an ObjC instance variable.
Definition: ExprObjC.h:474
void setEnd(SourceLocation e)
A reference to a declared variable, function, enum, etc. [C99 6.5.1p2].
Definition: Expr.h:899
A trivial tuple used to represent a source range.
ReceiverKind getReceiverKind() const
Determine the kind of receiver that this message is being sent to.
Definition: ExprObjC.h:1133
This class handles loading and caching of source files into memory.
bool isMacroArgExpansion(SourceLocation Loc) const
Tests whether the given source location represents a macro argument's expansion into the function-lik...