1 //===--- TransRetainReleaseDealloc.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 // removeRetainReleaseDealloc:
10 //
11 // Removes retain/release/autorelease/dealloc messages.
12 //
13 // return [[foo retain] autorelease];
14 // ---->
15 // return foo;
16 //
17 //===----------------------------------------------------------------------===//
18
19 #include "Transforms.h"
20 #include "Internals.h"
21 #include "clang/AST/ASTContext.h"
22 #include "clang/AST/ParentMap.h"
23 #include "clang/Basic/SourceManager.h"
24 #include "clang/Lex/Lexer.h"
25 #include "clang/Sema/SemaDiagnostic.h"
26 #include "llvm/ADT/StringSwitch.h"
27
28 using namespace clang;
29 using namespace arcmt;
30 using namespace trans;
31
32 namespace {
33
34 class RetainReleaseDeallocRemover :
35 public RecursiveASTVisitor<RetainReleaseDeallocRemover> {
36 Stmt *Body;
37 MigrationPass &Pass;
38
39 ExprSet Removables;
40 std::unique_ptr<ParentMap> StmtMap;
41
42 Selector DelegateSel, FinalizeSel;
43
44 public:
RetainReleaseDeallocRemover(MigrationPass & pass)45 RetainReleaseDeallocRemover(MigrationPass &pass)
46 : Body(nullptr), Pass(pass) {
47 DelegateSel =
48 Pass.Ctx.Selectors.getNullarySelector(&Pass.Ctx.Idents.get("delegate"));
49 FinalizeSel =
50 Pass.Ctx.Selectors.getNullarySelector(&Pass.Ctx.Idents.get("finalize"));
51 }
52
transformBody(Stmt * body,Decl * ParentD)53 void transformBody(Stmt *body, Decl *ParentD) {
54 Body = body;
55 collectRemovables(body, Removables);
56 StmtMap.reset(new ParentMap(body));
57 TraverseStmt(body);
58 }
59
VisitObjCMessageExpr(ObjCMessageExpr * E)60 bool VisitObjCMessageExpr(ObjCMessageExpr *E) {
61 switch (E->getMethodFamily()) {
62 default:
63 if (E->isInstanceMessage() && E->getSelector() == FinalizeSel)
64 break;
65 return true;
66 case OMF_autorelease:
67 if (isRemovable(E)) {
68 if (!isCommonUnusedAutorelease(E)) {
69 // An unused autorelease is badness. If we remove it the receiver
70 // will likely die immediately while previously it was kept alive
71 // by the autorelease pool. This is bad practice in general, leave it
72 // and emit an error to force the user to restructure their code.
73 Pass.TA.reportError(
74 "it is not safe to remove an unused 'autorelease' "
75 "message; its receiver may be destroyed immediately",
76 E->getBeginLoc(), E->getSourceRange());
77 return true;
78 }
79 }
80 // Pass through.
81 [[fallthrough]];
82 case OMF_retain:
83 case OMF_release:
84 if (E->getReceiverKind() == ObjCMessageExpr::Instance)
85 if (Expr *rec = E->getInstanceReceiver()) {
86 rec = rec->IgnoreParenImpCasts();
87 if (rec->getType().getObjCLifetime() == Qualifiers::OCL_ExplicitNone &&
88 (E->getMethodFamily() != OMF_retain || isRemovable(E))) {
89 std::string err = "it is not safe to remove '";
90 err += E->getSelector().getAsString() + "' message on "
91 "an __unsafe_unretained type";
92 Pass.TA.reportError(err, rec->getBeginLoc());
93 return true;
94 }
95
96 if (isGlobalVar(rec) &&
97 (E->getMethodFamily() != OMF_retain || isRemovable(E))) {
98 std::string err = "it is not safe to remove '";
99 err += E->getSelector().getAsString() + "' message on "
100 "a global variable";
101 Pass.TA.reportError(err, rec->getBeginLoc());
102 return true;
103 }
104
105 if (E->getMethodFamily() == OMF_release && isDelegateMessage(rec)) {
106 Pass.TA.reportError(
107 "it is not safe to remove 'retain' "
108 "message on the result of a 'delegate' message; "
109 "the object that was passed to 'setDelegate:' may not be "
110 "properly retained",
111 rec->getBeginLoc());
112 return true;
113 }
114 }
115 break;
116 case OMF_dealloc:
117 break;
118 }
119
120 switch (E->getReceiverKind()) {
121 default:
122 return true;
123 case ObjCMessageExpr::SuperInstance: {
124 Transaction Trans(Pass.TA);
125 clearDiagnostics(E->getSelectorLoc(0));
126 if (tryRemoving(E))
127 return true;
128 Pass.TA.replace(E->getSourceRange(), "self");
129 return true;
130 }
131 case ObjCMessageExpr::Instance:
132 break;
133 }
134
135 Expr *rec = E->getInstanceReceiver();
136 if (!rec) return true;
137
138 Transaction Trans(Pass.TA);
139 clearDiagnostics(E->getSelectorLoc(0));
140
141 ObjCMessageExpr *Msg = E;
142 Expr *RecContainer = Msg;
143 SourceRange RecRange = rec->getSourceRange();
144 checkForGCDOrXPC(Msg, RecContainer, rec, RecRange);
145
146 if (Msg->getMethodFamily() == OMF_release &&
147 isRemovable(RecContainer) && isInAtFinally(RecContainer)) {
148 // Change the -release to "receiver = nil" in a finally to avoid a leak
149 // when an exception is thrown.
150 Pass.TA.replace(RecContainer->getSourceRange(), RecRange);
151 std::string str = " = ";
152 str += getNilString(Pass);
153 Pass.TA.insertAfterToken(RecRange.getEnd(), str);
154 return true;
155 }
156
157 if (hasSideEffects(rec, Pass.Ctx) || !tryRemoving(RecContainer))
158 Pass.TA.replace(RecContainer->getSourceRange(), RecRange);
159
160 return true;
161 }
162
163 private:
164 /// Checks for idioms where an unused -autorelease is common.
165 ///
166 /// Returns true for this idiom which is common in property
167 /// setters:
168 ///
169 /// [backingValue autorelease];
170 /// backingValue = [newValue retain]; // in general a +1 assign
171 ///
172 /// For these as well:
173 ///
174 /// [[var retain] autorelease];
175 /// return var;
176 ///
isCommonUnusedAutorelease(ObjCMessageExpr * E)177 bool isCommonUnusedAutorelease(ObjCMessageExpr *E) {
178 return isPlusOneAssignBeforeOrAfterAutorelease(E) ||
179 isReturnedAfterAutorelease(E);
180 }
181
isReturnedAfterAutorelease(ObjCMessageExpr * E)182 bool isReturnedAfterAutorelease(ObjCMessageExpr *E) {
183 Expr *Rec = E->getInstanceReceiver();
184 if (!Rec)
185 return false;
186
187 Decl *RefD = getReferencedDecl(Rec);
188 if (!RefD)
189 return false;
190
191 Stmt *nextStmt = getNextStmt(E);
192 if (!nextStmt)
193 return false;
194
195 // Check for "return <variable>;".
196
197 if (ReturnStmt *RetS = dyn_cast<ReturnStmt>(nextStmt))
198 return RefD == getReferencedDecl(RetS->getRetValue());
199
200 return false;
201 }
202
isPlusOneAssignBeforeOrAfterAutorelease(ObjCMessageExpr * E)203 bool isPlusOneAssignBeforeOrAfterAutorelease(ObjCMessageExpr *E) {
204 Expr *Rec = E->getInstanceReceiver();
205 if (!Rec)
206 return false;
207
208 Decl *RefD = getReferencedDecl(Rec);
209 if (!RefD)
210 return false;
211
212 Stmt *prevStmt, *nextStmt;
213 std::tie(prevStmt, nextStmt) = getPreviousAndNextStmt(E);
214
215 return isPlusOneAssignToVar(prevStmt, RefD) ||
216 isPlusOneAssignToVar(nextStmt, RefD);
217 }
218
isPlusOneAssignToVar(Stmt * S,Decl * RefD)219 bool isPlusOneAssignToVar(Stmt *S, Decl *RefD) {
220 if (!S)
221 return false;
222
223 // Check for "RefD = [+1 retained object];".
224
225 if (BinaryOperator *Bop = dyn_cast<BinaryOperator>(S)) {
226 return (RefD == getReferencedDecl(Bop->getLHS())) && isPlusOneAssign(Bop);
227 }
228
229 if (DeclStmt *DS = dyn_cast<DeclStmt>(S)) {
230 if (DS->isSingleDecl() && DS->getSingleDecl() == RefD) {
231 if (VarDecl *VD = dyn_cast<VarDecl>(RefD))
232 return isPlusOne(VD->getInit());
233 }
234 return false;
235 }
236
237 return false;
238 }
239
getNextStmt(Expr * E)240 Stmt *getNextStmt(Expr *E) {
241 return getPreviousAndNextStmt(E).second;
242 }
243
getPreviousAndNextStmt(Expr * E)244 std::pair<Stmt *, Stmt *> getPreviousAndNextStmt(Expr *E) {
245 Stmt *prevStmt = nullptr, *nextStmt = nullptr;
246 if (!E)
247 return std::make_pair(prevStmt, nextStmt);
248
249 Stmt *OuterS = E, *InnerS;
250 do {
251 InnerS = OuterS;
252 OuterS = StmtMap->getParent(InnerS);
253 }
254 while (OuterS && (isa<ParenExpr>(OuterS) ||
255 isa<CastExpr>(OuterS) ||
256 isa<FullExpr>(OuterS)));
257
258 if (!OuterS)
259 return std::make_pair(prevStmt, nextStmt);
260
261 Stmt::child_iterator currChildS = OuterS->child_begin();
262 Stmt::child_iterator childE = OuterS->child_end();
263 Stmt::child_iterator prevChildS = childE;
264 for (; currChildS != childE; ++currChildS) {
265 if (*currChildS == InnerS)
266 break;
267 prevChildS = currChildS;
268 }
269
270 if (prevChildS != childE) {
271 prevStmt = *prevChildS;
272 if (auto *E = dyn_cast_or_null<Expr>(prevStmt))
273 prevStmt = E->IgnoreImplicit();
274 }
275
276 if (currChildS == childE)
277 return std::make_pair(prevStmt, nextStmt);
278 ++currChildS;
279 if (currChildS == childE)
280 return std::make_pair(prevStmt, nextStmt);
281
282 nextStmt = *currChildS;
283 if (auto *E = dyn_cast_or_null<Expr>(nextStmt))
284 nextStmt = E->IgnoreImplicit();
285
286 return std::make_pair(prevStmt, nextStmt);
287 }
288
getReferencedDecl(Expr * E)289 Decl *getReferencedDecl(Expr *E) {
290 if (!E)
291 return nullptr;
292
293 E = E->IgnoreParenCasts();
294 if (ObjCMessageExpr *ME = dyn_cast<ObjCMessageExpr>(E)) {
295 switch (ME->getMethodFamily()) {
296 case OMF_copy:
297 case OMF_autorelease:
298 case OMF_release:
299 case OMF_retain:
300 return getReferencedDecl(ME->getInstanceReceiver());
301 default:
302 return nullptr;
303 }
304 }
305 if (DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(E))
306 return DRE->getDecl();
307 if (MemberExpr *ME = dyn_cast<MemberExpr>(E))
308 return ME->getMemberDecl();
309 if (ObjCIvarRefExpr *IRE = dyn_cast<ObjCIvarRefExpr>(E))
310 return IRE->getDecl();
311
312 return nullptr;
313 }
314
315 /// Check if the retain/release is due to a GCD/XPC macro that are
316 /// defined as:
317 ///
318 /// #define dispatch_retain(object) ({ dispatch_object_t _o = (object); _dispatch_object_validate(_o); (void)[_o retain]; })
319 /// #define dispatch_release(object) ({ dispatch_object_t _o = (object); _dispatch_object_validate(_o); [_o release]; })
320 /// #define xpc_retain(object) ({ xpc_object_t _o = (object); _xpc_object_validate(_o); [_o retain]; })
321 /// #define xpc_release(object) ({ xpc_object_t _o = (object); _xpc_object_validate(_o); [_o release]; })
322 ///
323 /// and return the top container which is the StmtExpr and the macro argument
324 /// expression.
checkForGCDOrXPC(ObjCMessageExpr * Msg,Expr * & RecContainer,Expr * & Rec,SourceRange & RecRange)325 void checkForGCDOrXPC(ObjCMessageExpr *Msg, Expr *&RecContainer,
326 Expr *&Rec, SourceRange &RecRange) {
327 SourceLocation Loc = Msg->getExprLoc();
328 if (!Loc.isMacroID())
329 return;
330 SourceManager &SM = Pass.Ctx.getSourceManager();
331 StringRef MacroName = Lexer::getImmediateMacroName(Loc, SM,
332 Pass.Ctx.getLangOpts());
333 bool isGCDOrXPC = llvm::StringSwitch<bool>(MacroName)
334 .Case("dispatch_retain", true)
335 .Case("dispatch_release", true)
336 .Case("xpc_retain", true)
337 .Case("xpc_release", true)
338 .Default(false);
339 if (!isGCDOrXPC)
340 return;
341
342 StmtExpr *StmtE = nullptr;
343 Stmt *S = Msg;
344 while (S) {
345 if (StmtExpr *SE = dyn_cast<StmtExpr>(S)) {
346 StmtE = SE;
347 break;
348 }
349 S = StmtMap->getParent(S);
350 }
351
352 if (!StmtE)
353 return;
354
355 Stmt::child_range StmtExprChild = StmtE->children();
356 if (StmtExprChild.begin() == StmtExprChild.end())
357 return;
358 auto *CompS = dyn_cast_or_null<CompoundStmt>(*StmtExprChild.begin());
359 if (!CompS)
360 return;
361
362 Stmt::child_range CompStmtChild = CompS->children();
363 if (CompStmtChild.begin() == CompStmtChild.end())
364 return;
365 auto *DeclS = dyn_cast_or_null<DeclStmt>(*CompStmtChild.begin());
366 if (!DeclS)
367 return;
368 if (!DeclS->isSingleDecl())
369 return;
370 VarDecl *VD = dyn_cast_or_null<VarDecl>(DeclS->getSingleDecl());
371 if (!VD)
372 return;
373 Expr *Init = VD->getInit();
374 if (!Init)
375 return;
376
377 RecContainer = StmtE;
378 Rec = Init->IgnoreParenImpCasts();
379 if (FullExpr *FE = dyn_cast<FullExpr>(Rec))
380 Rec = FE->getSubExpr()->IgnoreParenImpCasts();
381 RecRange = Rec->getSourceRange();
382 if (SM.isMacroArgExpansion(RecRange.getBegin()))
383 RecRange.setBegin(SM.getImmediateSpellingLoc(RecRange.getBegin()));
384 if (SM.isMacroArgExpansion(RecRange.getEnd()))
385 RecRange.setEnd(SM.getImmediateSpellingLoc(RecRange.getEnd()));
386 }
387
clearDiagnostics(SourceLocation loc) const388 void clearDiagnostics(SourceLocation loc) const {
389 Pass.TA.clearDiagnostic(diag::err_arc_illegal_explicit_message,
390 diag::err_unavailable,
391 diag::err_unavailable_message,
392 loc);
393 }
394
isDelegateMessage(Expr * E) const395 bool isDelegateMessage(Expr *E) const {
396 if (!E) return false;
397
398 E = E->IgnoreParenCasts();
399
400 // Also look through property-getter sugar.
401 if (PseudoObjectExpr *pseudoOp = dyn_cast<PseudoObjectExpr>(E))
402 E = pseudoOp->getResultExpr()->IgnoreImplicit();
403
404 if (ObjCMessageExpr *ME = dyn_cast<ObjCMessageExpr>(E))
405 return (ME->isInstanceMessage() && ME->getSelector() == DelegateSel);
406
407 return false;
408 }
409
isInAtFinally(Expr * E) const410 bool isInAtFinally(Expr *E) const {
411 assert(E);
412 Stmt *S = E;
413 while (S) {
414 if (isa<ObjCAtFinallyStmt>(S))
415 return true;
416 S = StmtMap->getParent(S);
417 }
418
419 return false;
420 }
421
isRemovable(Expr * E) const422 bool isRemovable(Expr *E) const {
423 return Removables.count(E);
424 }
425
tryRemoving(Expr * E) const426 bool tryRemoving(Expr *E) const {
427 if (isRemovable(E)) {
428 Pass.TA.removeStmt(E);
429 return true;
430 }
431
432 Stmt *parent = StmtMap->getParent(E);
433
434 if (ImplicitCastExpr *castE = dyn_cast_or_null<ImplicitCastExpr>(parent))
435 return tryRemoving(castE);
436
437 if (ParenExpr *parenE = dyn_cast_or_null<ParenExpr>(parent))
438 return tryRemoving(parenE);
439
440 if (BinaryOperator *
441 bopE = dyn_cast_or_null<BinaryOperator>(parent)) {
442 if (bopE->getOpcode() == BO_Comma && bopE->getLHS() == E &&
443 isRemovable(bopE)) {
444 Pass.TA.replace(bopE->getSourceRange(), bopE->getRHS()->getSourceRange());
445 return true;
446 }
447 }
448
449 return false;
450 }
451
452 };
453
454 } // anonymous namespace
455
removeRetainReleaseDeallocFinalize(MigrationPass & pass)456 void trans::removeRetainReleaseDeallocFinalize(MigrationPass &pass) {
457 BodyTransform<RetainReleaseDeallocRemover> trans(pass);
458 trans.TraverseDecl(pass.Ctx.getTranslationUnitDecl());
459 }
460