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"
24 #include "clang/Basic/SourceManager.h"
25 #include "clang/Lex/Lexer.h"
26 #include "clang/Sema/SemaDiagnostic.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:
RetainReleaseDeallocRemover(MigrationPass & pass)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
transformBody(Stmt * body,Decl * ParentD)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
VisitObjCMessageExpr(ObjCMessageExpr * E)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(
75 "it is not safe to remove an unused 'autorelease' "
76 "message; its receiver may be destroyed immediately",
77 E->getBeginLoc(), E->getSourceRange());
78 return true;
79 }
80 }
81 // Pass through.
82 LLVM_FALLTHROUGH;
83 case OMF_retain:
84 case OMF_release:
85 if (E->getReceiverKind() == ObjCMessageExpr::Instance)
86 if (Expr *rec = E->getInstanceReceiver()) {
87 rec = rec->IgnoreParenImpCasts();
88 if (rec->getType().getObjCLifetime() == Qualifiers::OCL_ExplicitNone &&
89 (E->getMethodFamily() != OMF_retain || isRemovable(E))) {
90 std::string err = "it is not safe to remove '";
91 err += E->getSelector().getAsString() + "' message on "
92 "an __unsafe_unretained type";
93 Pass.TA.reportError(err, rec->getBeginLoc());
94 return true;
95 }
96
97 if (isGlobalVar(rec) &&
98 (E->getMethodFamily() != OMF_retain || isRemovable(E))) {
99 std::string err = "it is not safe to remove '";
100 err += E->getSelector().getAsString() + "' message on "
101 "a global variable";
102 Pass.TA.reportError(err, rec->getBeginLoc());
103 return true;
104 }
105
106 if (E->getMethodFamily() == OMF_release && isDelegateMessage(rec)) {
107 Pass.TA.reportError(
108 "it is not safe to remove 'retain' "
109 "message on the result of a 'delegate' message; "
110 "the object that was passed to 'setDelegate:' may not be "
111 "properly retained",
112 rec->getBeginLoc());
113 return true;
114 }
115 }
116 break;
117 case OMF_dealloc:
118 break;
119 }
120
121 switch (E->getReceiverKind()) {
122 default:
123 return true;
124 case ObjCMessageExpr::SuperInstance: {
125 Transaction Trans(Pass.TA);
126 clearDiagnostics(E->getSelectorLoc(0));
127 if (tryRemoving(E))
128 return true;
129 Pass.TA.replace(E->getSourceRange(), "self");
130 return true;
131 }
132 case ObjCMessageExpr::Instance:
133 break;
134 }
135
136 Expr *rec = E->getInstanceReceiver();
137 if (!rec) return true;
138
139 Transaction Trans(Pass.TA);
140 clearDiagnostics(E->getSelectorLoc(0));
141
142 ObjCMessageExpr *Msg = E;
143 Expr *RecContainer = Msg;
144 SourceRange RecRange = rec->getSourceRange();
145 checkForGCDOrXPC(Msg, RecContainer, rec, RecRange);
146
147 if (Msg->getMethodFamily() == OMF_release &&
148 isRemovable(RecContainer) && isInAtFinally(RecContainer)) {
149 // Change the -release to "receiver = nil" in a finally to avoid a leak
150 // when an exception is thrown.
151 Pass.TA.replace(RecContainer->getSourceRange(), RecRange);
152 std::string str = " = ";
153 str += getNilString(Pass);
154 Pass.TA.insertAfterToken(RecRange.getEnd(), str);
155 return true;
156 }
157
158 if (hasSideEffects(rec, Pass.Ctx) || !tryRemoving(RecContainer))
159 Pass.TA.replace(RecContainer->getSourceRange(), RecRange);
160
161 return true;
162 }
163
164 private:
165 /// Checks for idioms where an unused -autorelease is common.
166 ///
167 /// Returns true for this idiom which is common in property
168 /// setters:
169 ///
170 /// [backingValue autorelease];
171 /// backingValue = [newValue retain]; // in general a +1 assign
172 ///
173 /// For these as well:
174 ///
175 /// [[var retain] autorelease];
176 /// return var;
177 ///
isCommonUnusedAutorelease(ObjCMessageExpr * E)178 bool isCommonUnusedAutorelease(ObjCMessageExpr *E) {
179 return isPlusOneAssignBeforeOrAfterAutorelease(E) ||
180 isReturnedAfterAutorelease(E);
181 }
182
isReturnedAfterAutorelease(ObjCMessageExpr * E)183 bool isReturnedAfterAutorelease(ObjCMessageExpr *E) {
184 Expr *Rec = E->getInstanceReceiver();
185 if (!Rec)
186 return false;
187
188 Decl *RefD = getReferencedDecl(Rec);
189 if (!RefD)
190 return false;
191
192 Stmt *nextStmt = getNextStmt(E);
193 if (!nextStmt)
194 return false;
195
196 // Check for "return <variable>;".
197
198 if (ReturnStmt *RetS = dyn_cast<ReturnStmt>(nextStmt))
199 return RefD == getReferencedDecl(RetS->getRetValue());
200
201 return false;
202 }
203
isPlusOneAssignBeforeOrAfterAutorelease(ObjCMessageExpr * E)204 bool isPlusOneAssignBeforeOrAfterAutorelease(ObjCMessageExpr *E) {
205 Expr *Rec = E->getInstanceReceiver();
206 if (!Rec)
207 return false;
208
209 Decl *RefD = getReferencedDecl(Rec);
210 if (!RefD)
211 return false;
212
213 Stmt *prevStmt, *nextStmt;
214 std::tie(prevStmt, nextStmt) = getPreviousAndNextStmt(E);
215
216 return isPlusOneAssignToVar(prevStmt, RefD) ||
217 isPlusOneAssignToVar(nextStmt, RefD);
218 }
219
isPlusOneAssignToVar(Stmt * S,Decl * RefD)220 bool isPlusOneAssignToVar(Stmt *S, Decl *RefD) {
221 if (!S)
222 return false;
223
224 // Check for "RefD = [+1 retained object];".
225
226 if (BinaryOperator *Bop = dyn_cast<BinaryOperator>(S)) {
227 return (RefD == getReferencedDecl(Bop->getLHS())) && isPlusOneAssign(Bop);
228 }
229
230 if (DeclStmt *DS = dyn_cast<DeclStmt>(S)) {
231 if (DS->isSingleDecl() && DS->getSingleDecl() == RefD) {
232 if (VarDecl *VD = dyn_cast<VarDecl>(RefD))
233 return isPlusOne(VD->getInit());
234 }
235 return false;
236 }
237
238 return false;
239 }
240
getNextStmt(Expr * E)241 Stmt *getNextStmt(Expr *E) {
242 return getPreviousAndNextStmt(E).second;
243 }
244
getPreviousAndNextStmt(Expr * E)245 std::pair<Stmt *, Stmt *> getPreviousAndNextStmt(Expr *E) {
246 Stmt *prevStmt = nullptr, *nextStmt = nullptr;
247 if (!E)
248 return std::make_pair(prevStmt, nextStmt);
249
250 Stmt *OuterS = E, *InnerS;
251 do {
252 InnerS = OuterS;
253 OuterS = StmtMap->getParent(InnerS);
254 }
255 while (OuterS && (isa<ParenExpr>(OuterS) ||
256 isa<CastExpr>(OuterS) ||
257 isa<FullExpr>(OuterS)));
258
259 if (!OuterS)
260 return std::make_pair(prevStmt, nextStmt);
261
262 Stmt::child_iterator currChildS = OuterS->child_begin();
263 Stmt::child_iterator childE = OuterS->child_end();
264 Stmt::child_iterator prevChildS = childE;
265 for (; currChildS != childE; ++currChildS) {
266 if (*currChildS == InnerS)
267 break;
268 prevChildS = currChildS;
269 }
270
271 if (prevChildS != childE) {
272 prevStmt = *prevChildS;
273 if (prevStmt)
274 prevStmt = prevStmt->IgnoreImplicit();
275 }
276
277 if (currChildS == childE)
278 return std::make_pair(prevStmt, nextStmt);
279 ++currChildS;
280 if (currChildS == childE)
281 return std::make_pair(prevStmt, nextStmt);
282
283 nextStmt = *currChildS;
284 if (nextStmt)
285 nextStmt = nextStmt->IgnoreImplicit();
286
287 return std::make_pair(prevStmt, nextStmt);
288 }
289
getReferencedDecl(Expr * E)290 Decl *getReferencedDecl(Expr *E) {
291 if (!E)
292 return nullptr;
293
294 E = E->IgnoreParenCasts();
295 if (ObjCMessageExpr *ME = dyn_cast<ObjCMessageExpr>(E)) {
296 switch (ME->getMethodFamily()) {
297 case OMF_copy:
298 case OMF_autorelease:
299 case OMF_release:
300 case OMF_retain:
301 return getReferencedDecl(ME->getInstanceReceiver());
302 default:
303 return nullptr;
304 }
305 }
306 if (DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(E))
307 return DRE->getDecl();
308 if (MemberExpr *ME = dyn_cast<MemberExpr>(E))
309 return ME->getMemberDecl();
310 if (ObjCIvarRefExpr *IRE = dyn_cast<ObjCIvarRefExpr>(E))
311 return IRE->getDecl();
312
313 return nullptr;
314 }
315
316 /// Check if the retain/release is due to a GCD/XPC macro that are
317 /// defined as:
318 ///
319 /// #define dispatch_retain(object) ({ dispatch_object_t _o = (object); _dispatch_object_validate(_o); (void)[_o retain]; })
320 /// #define dispatch_release(object) ({ dispatch_object_t _o = (object); _dispatch_object_validate(_o); [_o release]; })
321 /// #define xpc_retain(object) ({ xpc_object_t _o = (object); _xpc_object_validate(_o); [_o retain]; })
322 /// #define xpc_release(object) ({ xpc_object_t _o = (object); _xpc_object_validate(_o); [_o release]; })
323 ///
324 /// and return the top container which is the StmtExpr and the macro argument
325 /// expression.
checkForGCDOrXPC(ObjCMessageExpr * Msg,Expr * & RecContainer,Expr * & Rec,SourceRange & RecRange)326 void checkForGCDOrXPC(ObjCMessageExpr *Msg, Expr *&RecContainer,
327 Expr *&Rec, SourceRange &RecRange) {
328 SourceLocation Loc = Msg->getExprLoc();
329 if (!Loc.isMacroID())
330 return;
331 SourceManager &SM = Pass.Ctx.getSourceManager();
332 StringRef MacroName = Lexer::getImmediateMacroName(Loc, SM,
333 Pass.Ctx.getLangOpts());
334 bool isGCDOrXPC = llvm::StringSwitch<bool>(MacroName)
335 .Case("dispatch_retain", true)
336 .Case("dispatch_release", true)
337 .Case("xpc_retain", true)
338 .Case("xpc_release", true)
339 .Default(false);
340 if (!isGCDOrXPC)
341 return;
342
343 StmtExpr *StmtE = nullptr;
344 Stmt *S = Msg;
345 while (S) {
346 if (StmtExpr *SE = dyn_cast<StmtExpr>(S)) {
347 StmtE = SE;
348 break;
349 }
350 S = StmtMap->getParent(S);
351 }
352
353 if (!StmtE)
354 return;
355
356 Stmt::child_range StmtExprChild = StmtE->children();
357 if (StmtExprChild.begin() == StmtExprChild.end())
358 return;
359 auto *CompS = dyn_cast_or_null<CompoundStmt>(*StmtExprChild.begin());
360 if (!CompS)
361 return;
362
363 Stmt::child_range CompStmtChild = CompS->children();
364 if (CompStmtChild.begin() == CompStmtChild.end())
365 return;
366 auto *DeclS = dyn_cast_or_null<DeclStmt>(*CompStmtChild.begin());
367 if (!DeclS)
368 return;
369 if (!DeclS->isSingleDecl())
370 return;
371 VarDecl *VD = dyn_cast_or_null<VarDecl>(DeclS->getSingleDecl());
372 if (!VD)
373 return;
374 Expr *Init = VD->getInit();
375 if (!Init)
376 return;
377
378 RecContainer = StmtE;
379 Rec = Init->IgnoreParenImpCasts();
380 if (FullExpr *FE = dyn_cast<FullExpr>(Rec))
381 Rec = FE->getSubExpr()->IgnoreParenImpCasts();
382 RecRange = Rec->getSourceRange();
383 if (SM.isMacroArgExpansion(RecRange.getBegin()))
384 RecRange.setBegin(SM.getImmediateSpellingLoc(RecRange.getBegin()));
385 if (SM.isMacroArgExpansion(RecRange.getEnd()))
386 RecRange.setEnd(SM.getImmediateSpellingLoc(RecRange.getEnd()));
387 }
388
clearDiagnostics(SourceLocation loc) const389 void clearDiagnostics(SourceLocation loc) const {
390 Pass.TA.clearDiagnostic(diag::err_arc_illegal_explicit_message,
391 diag::err_unavailable,
392 diag::err_unavailable_message,
393 loc);
394 }
395
isDelegateMessage(Expr * E) const396 bool isDelegateMessage(Expr *E) const {
397 if (!E) return false;
398
399 E = E->IgnoreParenCasts();
400
401 // Also look through property-getter sugar.
402 if (PseudoObjectExpr *pseudoOp = dyn_cast<PseudoObjectExpr>(E))
403 E = pseudoOp->getResultExpr()->IgnoreImplicit();
404
405 if (ObjCMessageExpr *ME = dyn_cast<ObjCMessageExpr>(E))
406 return (ME->isInstanceMessage() && ME->getSelector() == DelegateSel);
407
408 return false;
409 }
410
isInAtFinally(Expr * E) const411 bool isInAtFinally(Expr *E) const {
412 assert(E);
413 Stmt *S = E;
414 while (S) {
415 if (isa<ObjCAtFinallyStmt>(S))
416 return true;
417 S = StmtMap->getParent(S);
418 }
419
420 return false;
421 }
422
isRemovable(Expr * E) const423 bool isRemovable(Expr *E) const {
424 return Removables.count(E);
425 }
426
tryRemoving(Expr * E) const427 bool tryRemoving(Expr *E) const {
428 if (isRemovable(E)) {
429 Pass.TA.removeStmt(E);
430 return true;
431 }
432
433 Stmt *parent = StmtMap->getParent(E);
434
435 if (ImplicitCastExpr *castE = dyn_cast_or_null<ImplicitCastExpr>(parent))
436 return tryRemoving(castE);
437
438 if (ParenExpr *parenE = dyn_cast_or_null<ParenExpr>(parent))
439 return tryRemoving(parenE);
440
441 if (BinaryOperator *
442 bopE = dyn_cast_or_null<BinaryOperator>(parent)) {
443 if (bopE->getOpcode() == BO_Comma && bopE->getLHS() == E &&
444 isRemovable(bopE)) {
445 Pass.TA.replace(bopE->getSourceRange(), bopE->getRHS()->getSourceRange());
446 return true;
447 }
448 }
449
450 return false;
451 }
452
453 };
454
455 } // anonymous namespace
456
removeRetainReleaseDeallocFinalize(MigrationPass & pass)457 void trans::removeRetainReleaseDeallocFinalize(MigrationPass &pass) {
458 BodyTransform<RetainReleaseDeallocRemover> trans(pass);
459 trans.TraverseDecl(pass.Ctx.getTranslationUnitDecl());
460 }
461