1 //===--- TransUnbridgedCasts.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 // rewriteUnbridgedCasts:
11 //
12 // A cast of non-objc pointer to an objc one is checked. If the non-objc pointer
13 // is from a file-level variable, __bridge cast is used to convert it.
14 // For the result of a function call that we know is +1/+0,
15 // __bridge/CFBridgingRelease is used.
16 //
17 //  NSString *str = (NSString *)kUTTypePlainText;
18 //  str = b ? kUTTypeRTF : kUTTypePlainText;
19 //  NSString *_uuidString = (NSString *)CFUUIDCreateString(kCFAllocatorDefault,
20 //                                                         _uuid);
21 // ---->
22 //  NSString *str = (__bridge NSString *)kUTTypePlainText;
23 //  str = (__bridge NSString *)(b ? kUTTypeRTF : kUTTypePlainText);
24 // NSString *_uuidString = (NSString *)
25 //            CFBridgingRelease(CFUUIDCreateString(kCFAllocatorDefault, _uuid));
26 //
27 // For a C pointer to ObjC, for casting 'self', __bridge is used.
28 //
29 //  CFStringRef str = (CFStringRef)self;
30 // ---->
31 //  CFStringRef str = (__bridge CFStringRef)self;
32 //
33 // Uses of Block_copy/Block_release macros are rewritten:
34 //
35 //  c = Block_copy(b);
36 //  Block_release(c);
37 // ---->
38 //  c = [b copy];
39 //  <removed>
40 //
41 //===----------------------------------------------------------------------===//
42 
43 #include "Transforms.h"
44 #include "Internals.h"
45 #include "clang/AST/ASTContext.h"
46 #include "clang/AST/Attr.h"
47 #include "clang/AST/ParentMap.h"
48 #include "clang/Analysis/DomainSpecific/CocoaConventions.h"
49 #include "clang/Basic/SourceManager.h"
50 #include "clang/Lex/Lexer.h"
51 #include "clang/Sema/SemaDiagnostic.h"
52 #include "llvm/ADT/SmallString.h"
53 
54 using namespace clang;
55 using namespace arcmt;
56 using namespace trans;
57 
58 namespace {
59 
60 class UnbridgedCastRewriter : public RecursiveASTVisitor<UnbridgedCastRewriter>{
61   MigrationPass &Pass;
62   IdentifierInfo *SelfII;
63   std::unique_ptr<ParentMap> StmtMap;
64   Decl *ParentD;
65   Stmt *Body;
66   mutable std::unique_ptr<ExprSet> Removables;
67 
68 public:
69   UnbridgedCastRewriter(MigrationPass &pass)
70     : Pass(pass), ParentD(nullptr), Body(nullptr) {
71     SelfII = &Pass.Ctx.Idents.get("self");
72   }
73 
74   void transformBody(Stmt *body, Decl *ParentD) {
75     this->ParentD = ParentD;
76     Body = body;
77     StmtMap.reset(new ParentMap(body));
78     TraverseStmt(body);
79   }
80 
81   bool TraverseBlockDecl(BlockDecl *D) {
82     // ParentMap does not enter into a BlockDecl to record its stmts, so use a
83     // new UnbridgedCastRewriter to handle the block.
84     UnbridgedCastRewriter(Pass).transformBody(D->getBody(), D);
85     return true;
86   }
87 
88   bool VisitCastExpr(CastExpr *E) {
89     if (E->getCastKind() != CK_CPointerToObjCPointerCast &&
90         E->getCastKind() != CK_BitCast &&
91         E->getCastKind() != CK_AnyPointerToBlockPointerCast)
92       return true;
93 
94     QualType castType = E->getType();
95     Expr *castExpr = E->getSubExpr();
96     QualType castExprType = castExpr->getType();
97 
98     if (castType->isObjCRetainableType() == castExprType->isObjCRetainableType())
99       return true;
100 
101     bool exprRetainable = castExprType->isObjCIndirectLifetimeType();
102     bool castRetainable = castType->isObjCIndirectLifetimeType();
103     if (exprRetainable == castRetainable) return true;
104 
105     if (castExpr->isNullPointerConstant(Pass.Ctx,
106                                         Expr::NPC_ValueDependentIsNull))
107       return true;
108 
109     SourceLocation loc = castExpr->getExprLoc();
110     if (loc.isValid() && Pass.Ctx.getSourceManager().isInSystemHeader(loc))
111       return true;
112 
113     if (castType->isObjCRetainableType())
114       transformNonObjCToObjCCast(E);
115     else
116       transformObjCToNonObjCCast(E);
117 
118     return true;
119   }
120 
121 private:
122   void transformNonObjCToObjCCast(CastExpr *E) {
123     if (!E) return;
124 
125     // Global vars are assumed that are cast as unretained.
126     if (isGlobalVar(E))
127       if (E->getSubExpr()->getType()->isPointerType()) {
128         castToObjCObject(E, /*retained=*/false);
129         return;
130       }
131 
132     // If the cast is directly over the result of a Core Foundation function
133     // try to figure out whether it should be cast as retained or unretained.
134     Expr *inner = E->IgnoreParenCasts();
135     if (CallExpr *callE = dyn_cast<CallExpr>(inner)) {
136       if (FunctionDecl *FD = callE->getDirectCallee()) {
137         if (FD->hasAttr<CFReturnsRetainedAttr>()) {
138           castToObjCObject(E, /*retained=*/true);
139           return;
140         }
141         if (FD->hasAttr<CFReturnsNotRetainedAttr>()) {
142           castToObjCObject(E, /*retained=*/false);
143           return;
144         }
145         if (FD->isGlobal() &&
146             FD->getIdentifier() &&
147             ento::cocoa::isRefType(E->getSubExpr()->getType(), "CF",
148                                    FD->getIdentifier()->getName())) {
149           StringRef fname = FD->getIdentifier()->getName();
150           if (fname.endswith("Retain") ||
151               fname.find("Create") != StringRef::npos ||
152               fname.find("Copy") != StringRef::npos) {
153             // Do not migrate to couple of bridge transfer casts which
154             // cancel each other out. Leave it unchanged so error gets user
155             // attention instead.
156             if (FD->getName() == "CFRetain" &&
157                 FD->getNumParams() == 1 &&
158                 FD->getParent()->isTranslationUnit() &&
159                 FD->isExternallyVisible()) {
160               Expr *Arg = callE->getArg(0);
161               if (const ImplicitCastExpr *ICE = dyn_cast<ImplicitCastExpr>(Arg)) {
162                 const Expr *sub = ICE->getSubExpr();
163                 QualType T = sub->getType();
164                 if (T->isObjCObjectPointerType())
165                   return;
166               }
167             }
168             castToObjCObject(E, /*retained=*/true);
169             return;
170           }
171 
172           if (fname.find("Get") != StringRef::npos) {
173             castToObjCObject(E, /*retained=*/false);
174             return;
175           }
176         }
177       }
178     }
179 
180     // If returning an ivar or a member of an ivar from a +0 method, use
181     // a __bridge cast.
182     Expr *base = inner->IgnoreParenImpCasts();
183     while (isa<MemberExpr>(base))
184       base = cast<MemberExpr>(base)->getBase()->IgnoreParenImpCasts();
185     if (isa<ObjCIvarRefExpr>(base) &&
186         isa<ReturnStmt>(StmtMap->getParentIgnoreParenCasts(E))) {
187       if (ObjCMethodDecl *method = dyn_cast_or_null<ObjCMethodDecl>(ParentD)) {
188         if (!method->hasAttr<NSReturnsRetainedAttr>()) {
189           castToObjCObject(E, /*retained=*/false);
190           return;
191         }
192       }
193     }
194   }
195 
196   void castToObjCObject(CastExpr *E, bool retained) {
197     rewriteToBridgedCast(E, retained ? OBC_BridgeTransfer : OBC_Bridge);
198   }
199 
200   void rewriteToBridgedCast(CastExpr *E, ObjCBridgeCastKind Kind) {
201     Transaction Trans(Pass.TA);
202     rewriteToBridgedCast(E, Kind, Trans);
203   }
204 
205   void rewriteToBridgedCast(CastExpr *E, ObjCBridgeCastKind Kind,
206                             Transaction &Trans) {
207     TransformActions &TA = Pass.TA;
208 
209     // We will remove the compiler diagnostic.
210     if (!TA.hasDiagnostic(diag::err_arc_mismatched_cast,
211                           diag::err_arc_cast_requires_bridge,
212                           E->getLocStart())) {
213       Trans.abort();
214       return;
215     }
216 
217     StringRef bridge;
218     switch(Kind) {
219     case OBC_Bridge:
220       bridge = "__bridge "; break;
221     case OBC_BridgeTransfer:
222       bridge = "__bridge_transfer "; break;
223     case OBC_BridgeRetained:
224       bridge = "__bridge_retained "; break;
225     }
226 
227     TA.clearDiagnostic(diag::err_arc_mismatched_cast,
228                        diag::err_arc_cast_requires_bridge,
229                        E->getLocStart());
230     if (Kind == OBC_Bridge || !Pass.CFBridgingFunctionsDefined()) {
231       if (CStyleCastExpr *CCE = dyn_cast<CStyleCastExpr>(E)) {
232         TA.insertAfterToken(CCE->getLParenLoc(), bridge);
233       } else {
234         SourceLocation insertLoc = E->getSubExpr()->getLocStart();
235         SmallString<128> newCast;
236         newCast += '(';
237         newCast += bridge;
238         newCast += E->getType().getAsString(Pass.Ctx.getPrintingPolicy());
239         newCast += ')';
240 
241         if (isa<ParenExpr>(E->getSubExpr())) {
242           TA.insert(insertLoc, newCast.str());
243         } else {
244           newCast += '(';
245           TA.insert(insertLoc, newCast.str());
246           TA.insertAfterToken(E->getLocEnd(), ")");
247         }
248       }
249     } else {
250       assert(Kind == OBC_BridgeTransfer || Kind == OBC_BridgeRetained);
251       SmallString<32> BridgeCall;
252 
253       Expr *WrapE = E->getSubExpr();
254       SourceLocation InsertLoc = WrapE->getLocStart();
255 
256       SourceManager &SM = Pass.Ctx.getSourceManager();
257       char PrevChar = *SM.getCharacterData(InsertLoc.getLocWithOffset(-1));
258       if (Lexer::isIdentifierBodyChar(PrevChar, Pass.Ctx.getLangOpts()))
259         BridgeCall += ' ';
260 
261       if (Kind == OBC_BridgeTransfer)
262         BridgeCall += "CFBridgingRelease";
263       else
264         BridgeCall += "CFBridgingRetain";
265 
266       if (isa<ParenExpr>(WrapE)) {
267         TA.insert(InsertLoc, BridgeCall);
268       } else {
269         BridgeCall += '(';
270         TA.insert(InsertLoc, BridgeCall);
271         TA.insertAfterToken(WrapE->getLocEnd(), ")");
272       }
273     }
274   }
275 
276   void rewriteCastForCFRetain(CastExpr *castE, CallExpr *callE) {
277     Transaction Trans(Pass.TA);
278     Pass.TA.replace(callE->getSourceRange(), callE->getArg(0)->getSourceRange());
279     rewriteToBridgedCast(castE, OBC_BridgeRetained, Trans);
280   }
281 
282   void getBlockMacroRanges(CastExpr *E, SourceRange &Outer, SourceRange &Inner) {
283     SourceManager &SM = Pass.Ctx.getSourceManager();
284     SourceLocation Loc = E->getExprLoc();
285     assert(Loc.isMacroID());
286     CharSourceRange MacroRange = SM.getImmediateExpansionRange(Loc);
287     SourceRange SubRange = E->getSubExpr()->IgnoreParenImpCasts()->getSourceRange();
288     SourceLocation InnerBegin = SM.getImmediateMacroCallerLoc(SubRange.getBegin());
289     SourceLocation InnerEnd = SM.getImmediateMacroCallerLoc(SubRange.getEnd());
290 
291     Outer = MacroRange.getAsRange();
292     Inner = SourceRange(InnerBegin, InnerEnd);
293   }
294 
295   void rewriteBlockCopyMacro(CastExpr *E) {
296     SourceRange OuterRange, InnerRange;
297     getBlockMacroRanges(E, OuterRange, InnerRange);
298 
299     Transaction Trans(Pass.TA);
300     Pass.TA.replace(OuterRange, InnerRange);
301     Pass.TA.insert(InnerRange.getBegin(), "[");
302     Pass.TA.insertAfterToken(InnerRange.getEnd(), " copy]");
303     Pass.TA.clearDiagnostic(diag::err_arc_mismatched_cast,
304                             diag::err_arc_cast_requires_bridge,
305                             OuterRange);
306   }
307 
308   void removeBlockReleaseMacro(CastExpr *E) {
309     SourceRange OuterRange, InnerRange;
310     getBlockMacroRanges(E, OuterRange, InnerRange);
311 
312     Transaction Trans(Pass.TA);
313     Pass.TA.clearDiagnostic(diag::err_arc_mismatched_cast,
314                             diag::err_arc_cast_requires_bridge,
315                             OuterRange);
316     if (!hasSideEffects(E, Pass.Ctx)) {
317       if (tryRemoving(cast<Expr>(StmtMap->getParentIgnoreParenCasts(E))))
318         return;
319     }
320     Pass.TA.replace(OuterRange, InnerRange);
321   }
322 
323   bool tryRemoving(Expr *E) const {
324     if (!Removables) {
325       Removables.reset(new ExprSet);
326       collectRemovables(Body, *Removables);
327     }
328 
329     if (Removables->count(E)) {
330       Pass.TA.removeStmt(E);
331       return true;
332     }
333 
334     return false;
335   }
336 
337   void transformObjCToNonObjCCast(CastExpr *E) {
338     SourceLocation CastLoc = E->getExprLoc();
339     if (CastLoc.isMacroID()) {
340       StringRef MacroName = Lexer::getImmediateMacroName(CastLoc,
341                                                     Pass.Ctx.getSourceManager(),
342                                                     Pass.Ctx.getLangOpts());
343       if (MacroName == "Block_copy") {
344         rewriteBlockCopyMacro(E);
345         return;
346       }
347       if (MacroName == "Block_release") {
348         removeBlockReleaseMacro(E);
349         return;
350       }
351     }
352 
353     if (isSelf(E->getSubExpr()))
354       return rewriteToBridgedCast(E, OBC_Bridge);
355 
356     CallExpr *callE;
357     if (isPassedToCFRetain(E, callE))
358       return rewriteCastForCFRetain(E, callE);
359 
360     ObjCMethodFamily family = getFamilyOfMessage(E->getSubExpr());
361     if (family == OMF_retain)
362       return rewriteToBridgedCast(E, OBC_BridgeRetained);
363 
364     if (family == OMF_autorelease || family == OMF_release) {
365       std::string err = "it is not safe to cast to '";
366       err += E->getType().getAsString(Pass.Ctx.getPrintingPolicy());
367       err += "' the result of '";
368       err += family == OMF_autorelease ? "autorelease" : "release";
369       err += "' message; a __bridge cast may result in a pointer to a "
370           "destroyed object and a __bridge_retained may leak the object";
371       Pass.TA.reportError(err, E->getLocStart(),
372                           E->getSubExpr()->getSourceRange());
373       Stmt *parent = E;
374       do {
375         parent = StmtMap->getParentIgnoreParenImpCasts(parent);
376       } while (parent && isa<ExprWithCleanups>(parent));
377 
378       if (ReturnStmt *retS = dyn_cast_or_null<ReturnStmt>(parent)) {
379         std::string note = "remove the cast and change return type of function "
380             "to '";
381         note += E->getSubExpr()->getType().getAsString(Pass.Ctx.getPrintingPolicy());
382         note += "' to have the object automatically autoreleased";
383         Pass.TA.reportNote(note, retS->getLocStart());
384       }
385     }
386 
387     Expr *subExpr = E->getSubExpr();
388 
389     // Look through pseudo-object expressions.
390     if (PseudoObjectExpr *pseudo = dyn_cast<PseudoObjectExpr>(subExpr)) {
391       subExpr = pseudo->getResultExpr();
392       assert(subExpr && "no result for pseudo-object of non-void type?");
393     }
394 
395     if (ImplicitCastExpr *implCE = dyn_cast<ImplicitCastExpr>(subExpr)) {
396       if (implCE->getCastKind() == CK_ARCConsumeObject)
397         return rewriteToBridgedCast(E, OBC_BridgeRetained);
398       if (implCE->getCastKind() == CK_ARCReclaimReturnedObject)
399         return rewriteToBridgedCast(E, OBC_Bridge);
400     }
401 
402     bool isConsumed = false;
403     if (isPassedToCParamWithKnownOwnership(E, isConsumed))
404       return rewriteToBridgedCast(E, isConsumed ? OBC_BridgeRetained
405                                                 : OBC_Bridge);
406   }
407 
408   static ObjCMethodFamily getFamilyOfMessage(Expr *E) {
409     E = E->IgnoreParenCasts();
410     if (ObjCMessageExpr *ME = dyn_cast<ObjCMessageExpr>(E))
411       return ME->getMethodFamily();
412 
413     return OMF_None;
414   }
415 
416   bool isPassedToCFRetain(Expr *E, CallExpr *&callE) const {
417     if ((callE = dyn_cast_or_null<CallExpr>(
418                                      StmtMap->getParentIgnoreParenImpCasts(E))))
419       if (FunctionDecl *
420             FD = dyn_cast_or_null<FunctionDecl>(callE->getCalleeDecl()))
421         if (FD->getName() == "CFRetain" && FD->getNumParams() == 1 &&
422             FD->getParent()->isTranslationUnit() &&
423             FD->isExternallyVisible())
424           return true;
425 
426     return false;
427   }
428 
429   bool isPassedToCParamWithKnownOwnership(Expr *E, bool &isConsumed) const {
430     if (CallExpr *callE = dyn_cast_or_null<CallExpr>(
431                                      StmtMap->getParentIgnoreParenImpCasts(E)))
432       if (FunctionDecl *
433             FD = dyn_cast_or_null<FunctionDecl>(callE->getCalleeDecl())) {
434         unsigned i = 0;
435         for (unsigned e = callE->getNumArgs(); i != e; ++i) {
436           Expr *arg = callE->getArg(i);
437           if (arg == E || arg->IgnoreParenImpCasts() == E)
438             break;
439         }
440         if (i < callE->getNumArgs() && i < FD->getNumParams()) {
441           ParmVarDecl *PD = FD->getParamDecl(i);
442           if (PD->hasAttr<CFConsumedAttr>()) {
443             isConsumed = true;
444             return true;
445           }
446         }
447       }
448 
449     return false;
450   }
451 
452   bool isSelf(Expr *E) const {
453     E = E->IgnoreParenLValueCasts();
454     if (DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(E))
455       if (ImplicitParamDecl *IPD = dyn_cast<ImplicitParamDecl>(DRE->getDecl()))
456         if (IPD->getIdentifier() == SelfII)
457           return true;
458 
459     return false;
460   }
461 };
462 
463 } // end anonymous namespace
464 
465 void trans::rewriteUnbridgedCasts(MigrationPass &pass) {
466   BodyTransform<UnbridgedCastRewriter> trans(pass);
467   trans.TraverseDecl(pass.Ctx.getTranslationUnitDecl());
468 }
469