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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("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:
83       if (E->getReceiverKind() == ObjCMessageExpr::Instance)
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;
119     case ObjCMessageExpr::SuperInstance: {
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     }
127     case ObjCMessageExpr::Instance:
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) || !tryRemoving(RecContainer))
154       Pass.TA.replace(RecContainer->getSourceRange(), RecRange);
155 
156     return true;
157   }
158 
159 private:
160   /// \brief Checks for idioms where an unused -autorelease is common.
161   ///
162   /// Returns true for this idiom which is common in property
163   /// setters:
164   ///
165   ///   [backingValue autorelease];
166   ///   backingValue = [newValue retain]; // in general a +1 assign
167   ///
168   /// For these as well:
169   ///
170   ///   [[var retain] autorelease];
171   ///   return var;
172   ///
isCommonUnusedAutorelease(ObjCMessageExpr * E)173   bool isCommonUnusedAutorelease(ObjCMessageExpr *E) {
174     return isPlusOneAssignBeforeOrAfterAutorelease(E) ||
175            isReturnedAfterAutorelease(E);
176   }
177 
isReturnedAfterAutorelease(ObjCMessageExpr * E)178   bool isReturnedAfterAutorelease(ObjCMessageExpr *E) {
179     Expr *Rec = E->getInstanceReceiver();
180     if (!Rec)
181       return false;
182 
183     Decl *RefD = getReferencedDecl(Rec);
184     if (!RefD)
185       return false;
186 
187     Stmt *nextStmt = getNextStmt(E);
188     if (!nextStmt)
189       return false;
190 
191     // Check for "return <variable>;".
192 
193     if (ReturnStmt *RetS = dyn_cast<ReturnStmt>(nextStmt))
194       return RefD == getReferencedDecl(RetS->getRetValue());
195 
196     return false;
197   }
198 
isPlusOneAssignBeforeOrAfterAutorelease(ObjCMessageExpr * E)199   bool isPlusOneAssignBeforeOrAfterAutorelease(ObjCMessageExpr *E) {
200     Expr *Rec = E->getInstanceReceiver();
201     if (!Rec)
202       return false;
203 
204     Decl *RefD = getReferencedDecl(Rec);
205     if (!RefD)
206       return false;
207 
208     Stmt *prevStmt, *nextStmt;
209     std::tie(prevStmt, nextStmt) = getPreviousAndNextStmt(E);
210 
211     return isPlusOneAssignToVar(prevStmt, RefD) ||
212            isPlusOneAssignToVar(nextStmt, RefD);
213   }
214 
isPlusOneAssignToVar(Stmt * S,Decl * RefD)215   bool isPlusOneAssignToVar(Stmt *S, Decl *RefD) {
216     if (!S)
217       return false;
218 
219     // Check for "RefD = [+1 retained object];".
220 
221     if (BinaryOperator *Bop = dyn_cast<BinaryOperator>(S)) {
222       return (RefD == getReferencedDecl(Bop->getLHS())) && isPlusOneAssign(Bop);
223     }
224 
225     if (DeclStmt *DS = dyn_cast<DeclStmt>(S)) {
226       if (DS->isSingleDecl() && DS->getSingleDecl() == RefD) {
227         if (VarDecl *VD = dyn_cast<VarDecl>(RefD))
228           return isPlusOne(VD->getInit());
229       }
230       return false;
231     }
232 
233     return false;
234   }
235 
getNextStmt(Expr * E)236   Stmt *getNextStmt(Expr *E) {
237     return getPreviousAndNextStmt(E).second;
238   }
239 
getPreviousAndNextStmt(Expr * E)240   std::pair<Stmt *, Stmt *> getPreviousAndNextStmt(Expr *E) {
241     Stmt *prevStmt = nullptr, *nextStmt = nullptr;
242     if (!E)
243       return std::make_pair(prevStmt, nextStmt);
244 
245     Stmt *OuterS = E, *InnerS;
246     do {
247       InnerS = OuterS;
248       OuterS = StmtMap->getParent(InnerS);
249     }
250     while (OuterS && (isa<ParenExpr>(OuterS) ||
251                       isa<CastExpr>(OuterS) ||
252                       isa<ExprWithCleanups>(OuterS)));
253 
254     if (!OuterS)
255       return std::make_pair(prevStmt, nextStmt);
256 
257     Stmt::child_iterator currChildS = OuterS->child_begin();
258     Stmt::child_iterator childE = OuterS->child_end();
259     Stmt::child_iterator prevChildS = childE;
260     for (; currChildS != childE; ++currChildS) {
261       if (*currChildS == InnerS)
262         break;
263       prevChildS = currChildS;
264     }
265 
266     if (prevChildS != childE) {
267       prevStmt = *prevChildS;
268       if (prevStmt)
269         prevStmt = prevStmt->IgnoreImplicit();
270     }
271 
272     if (currChildS == childE)
273       return std::make_pair(prevStmt, nextStmt);
274     ++currChildS;
275     if (currChildS == childE)
276       return std::make_pair(prevStmt, nextStmt);
277 
278     nextStmt = *currChildS;
279     if (nextStmt)
280       nextStmt = nextStmt->IgnoreImplicit();
281 
282     return std::make_pair(prevStmt, nextStmt);
283   }
284 
getReferencedDecl(Expr * E)285   Decl *getReferencedDecl(Expr *E) {
286     if (!E)
287       return nullptr;
288 
289     E = E->IgnoreParenCasts();
290     if (ObjCMessageExpr *ME = dyn_cast<ObjCMessageExpr>(E)) {
291       switch (ME->getMethodFamily()) {
292       case OMF_copy:
293       case OMF_autorelease:
294       case OMF_release:
295       case OMF_retain:
296         return getReferencedDecl(ME->getInstanceReceiver());
297       default:
298         return nullptr;
299       }
300     }
301     if (DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(E))
302       return DRE->getDecl();
303     if (MemberExpr *ME = dyn_cast<MemberExpr>(E))
304       return ME->getMemberDecl();
305     if (ObjCIvarRefExpr *IRE = dyn_cast<ObjCIvarRefExpr>(E))
306       return IRE->getDecl();
307 
308     return nullptr;
309   }
310 
311   /// \brief Check if the retain/release is due to a GCD/XPC macro that are
312   /// defined as:
313   ///
314   /// #define dispatch_retain(object) ({ dispatch_object_t _o = (object); _dispatch_object_validate(_o); (void)[_o retain]; })
315   /// #define dispatch_release(object) ({ dispatch_object_t _o = (object); _dispatch_object_validate(_o); [_o release]; })
316   /// #define xpc_retain(object) ({ xpc_object_t _o = (object); _xpc_object_validate(_o); [_o retain]; })
317   /// #define xpc_release(object) ({ xpc_object_t _o = (object); _xpc_object_validate(_o); [_o release]; })
318   ///
319   /// and return the top container which is the StmtExpr and the macro argument
320   /// expression.
checkForGCDOrXPC(ObjCMessageExpr * Msg,Expr * & RecContainer,Expr * & Rec,SourceRange & RecRange)321   void checkForGCDOrXPC(ObjCMessageExpr *Msg, Expr *&RecContainer,
322                         Expr *&Rec, SourceRange &RecRange) {
323     SourceLocation Loc = Msg->getExprLoc();
324     if (!Loc.isMacroID())
325       return;
326     SourceManager &SM = Pass.Ctx.getSourceManager();
327     StringRef MacroName = Lexer::getImmediateMacroName(Loc, SM,
328                                                      Pass.Ctx.getLangOpts());
329     bool isGCDOrXPC = llvm::StringSwitch<bool>(MacroName)
330         .Case("dispatch_retain", true)
331         .Case("dispatch_release", true)
332         .Case("xpc_retain", true)
333         .Case("xpc_release", true)
334         .Default(false);
335     if (!isGCDOrXPC)
336       return;
337 
338     StmtExpr *StmtE = nullptr;
339     Stmt *S = Msg;
340     while (S) {
341       if (StmtExpr *SE = dyn_cast<StmtExpr>(S)) {
342         StmtE = SE;
343         break;
344       }
345       S = StmtMap->getParent(S);
346     }
347 
348     if (!StmtE)
349       return;
350 
351     Stmt::child_range StmtExprChild = StmtE->children();
352     if (StmtExprChild.begin() == StmtExprChild.end())
353       return;
354     auto *CompS = dyn_cast_or_null<CompoundStmt>(*StmtExprChild.begin());
355     if (!CompS)
356       return;
357 
358     Stmt::child_range CompStmtChild = CompS->children();
359     if (CompStmtChild.begin() == CompStmtChild.end())
360       return;
361     auto *DeclS = dyn_cast_or_null<DeclStmt>(*CompStmtChild.begin());
362     if (!DeclS)
363       return;
364     if (!DeclS->isSingleDecl())
365       return;
366     VarDecl *VD = dyn_cast_or_null<VarDecl>(DeclS->getSingleDecl());
367     if (!VD)
368       return;
369     Expr *Init = VD->getInit();
370     if (!Init)
371       return;
372 
373     RecContainer = StmtE;
374     Rec = Init->IgnoreParenImpCasts();
375     if (ExprWithCleanups *EWC = dyn_cast<ExprWithCleanups>(Rec))
376       Rec = EWC->getSubExpr()->IgnoreParenImpCasts();
377     RecRange = Rec->getSourceRange();
378     if (SM.isMacroArgExpansion(RecRange.getBegin()))
379       RecRange.setBegin(SM.getImmediateSpellingLoc(RecRange.getBegin()));
380     if (SM.isMacroArgExpansion(RecRange.getEnd()))
381       RecRange.setEnd(SM.getImmediateSpellingLoc(RecRange.getEnd()));
382   }
383 
clearDiagnostics(SourceLocation loc) const384   void clearDiagnostics(SourceLocation loc) const {
385     Pass.TA.clearDiagnostic(diag::err_arc_illegal_explicit_message,
386                             diag::err_unavailable,
387                             diag::err_unavailable_message,
388                             loc);
389   }
390 
isDelegateMessage(Expr * E) const391   bool isDelegateMessage(Expr *E) const {
392     if (!E) return false;
393 
394     E = E->IgnoreParenCasts();
395 
396     // Also look through property-getter sugar.
397     if (PseudoObjectExpr *pseudoOp = dyn_cast<PseudoObjectExpr>(E))
398       E = pseudoOp->getResultExpr()->IgnoreImplicit();
399 
400     if (ObjCMessageExpr *ME = dyn_cast<ObjCMessageExpr>(E))
401       return (ME->isInstanceMessage() && ME->getSelector() == DelegateSel);
402 
403     return false;
404   }
405 
isInAtFinally(Expr * E) const406   bool isInAtFinally(Expr *E) const {
407     assert(E);
408     Stmt *S = E;
409     while (S) {
410       if (isa<ObjCAtFinallyStmt>(S))
411         return true;
412       S = StmtMap->getParent(S);
413     }
414 
415     return false;
416   }
417 
isRemovable(Expr * E) const418   bool isRemovable(Expr *E) const {
419     return Removables.count(E);
420   }
421 
tryRemoving(Expr * E) const422   bool tryRemoving(Expr *E) const {
423     if (isRemovable(E)) {
424       Pass.TA.removeStmt(E);
425       return true;
426     }
427 
428     Stmt *parent = StmtMap->getParent(E);
429 
430     if (ImplicitCastExpr *castE = dyn_cast_or_null<ImplicitCastExpr>(parent))
431       return tryRemoving(castE);
432 
433     if (ParenExpr *parenE = dyn_cast_or_null<ParenExpr>(parent))
434       return tryRemoving(parenE);
435 
436     if (BinaryOperator *
437           bopE = dyn_cast_or_null<BinaryOperator>(parent)) {
438       if (bopE->getOpcode() == BO_Comma && bopE->getLHS() == E &&
439           isRemovable(bopE)) {
440         Pass.TA.replace(bopE->getSourceRange(), bopE->getRHS()->getSourceRange());
441         return true;
442       }
443     }
444 
445     return false;
446   }
447 
448 };
449 
450 } // anonymous namespace
451 
removeRetainReleaseDeallocFinalize(MigrationPass & pass)452 void trans::removeRetainReleaseDeallocFinalize(MigrationPass &pass) {
453   BodyTransform<RetainReleaseDeallocRemover> trans(pass);
454   trans.TraverseDecl(pass.Ctx.getTranslationUnitDecl());
455 }
456