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:
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(
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   ///
178   bool isCommonUnusedAutorelease(ObjCMessageExpr *E) {
179     return isPlusOneAssignBeforeOrAfterAutorelease(E) ||
180            isReturnedAfterAutorelease(E);
181   }
182 
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 
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 
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 
241   Stmt *getNextStmt(Expr *E) {
242     return getPreviousAndNextStmt(E).second;
243   }
244 
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 
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.
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 
389   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 
396   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 
411   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 
423   bool isRemovable(Expr *E) const {
424     return Removables.count(E);
425   }
426 
427   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 
457 void trans::removeRetainReleaseDeallocFinalize(MigrationPass &pass) {
458   BodyTransform<RetainReleaseDeallocRemover> trans(pass);
459   trans.TraverseDecl(pass.Ctx.getTranslationUnitDecl());
460 }
461