clang/lib/ARCMigrate/TransAutoreleasePool.cpp

   1 //===--- TransAutoreleasePool.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 // rewriteAutoreleasePool:
  10 //
  11 // Calls to NSAutoreleasePools will be rewritten as an @autorelease scope.
  12 //
  13 //  NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
  14 //  ...
  15 //  [pool release];
  16 // ---->
  17 //  @autorelease {
  18 //  ...
  19 //  }
  20 //
  21 // An NSAutoreleasePool will not be touched if:
  22 // - There is not a corresponding -release/-drain in the same scope
  23 // - Not all references of the NSAutoreleasePool variable can be removed
  24 // - There is a variable that is declared inside the intended @autorelease scope
  25 //   which is also used outside it.
  26 //
  27 //===----------------------------------------------------------------------===//
  28
  29 #include "Transforms.h"
  30 #include "Internals.h"
  31 #include "clang/AST/ASTContext.h"
  32 #include "clang/Basic/SourceManager.h"
  33 #include "clang/Sema/SemaDiagnostic.h"
  34 #include <map>
  35
  36 using namespace clang;
  37 using namespace arcmt;
  38 using namespace trans;
  39
  40 namespace {
  41
  42 class ReleaseCollector : public RecursiveASTVisitor<ReleaseCollector> {
  43   Decl *Dcl;
  44   SmallVectorImpl<ObjCMessageExpr *> &Releases;
  45
  46 public:
  47   ReleaseCollector(Decl *D, SmallVectorImpl<ObjCMessageExpr *> &releases)
  48     : Dcl(D), Releases(releases) { }
  49
  50   bool VisitObjCMessageExpr(ObjCMessageExpr *E) {
  51     if (!E->isInstanceMessage())
  52       return true;
  53     if (E->getMethodFamily() != OMF_release)
  54       return true;
  55     Expr *instance = E->getInstanceReceiver()->IgnoreParenCasts();
  56     if (DeclRefExpr *DE = dyn_cast<DeclRefExpr>(instance)) {
  57       if (DE->getDecl() == Dcl)
  58         Releases.push_back(E);
  59     }
  60     return true;
  61   }
  62 };
  63
  64 }
  65
  66 namespace {
  67
  68 class AutoreleasePoolRewriter
  69                          : public RecursiveASTVisitor<AutoreleasePoolRewriter> {
  70 public:
  71   AutoreleasePoolRewriter(MigrationPass &pass)
  72     : Body(nullptr), Pass(pass) {
  73     PoolII = &pass.Ctx.Idents.get("NSAutoreleasePool");
  74     DrainSel = pass.Ctx.Selectors.getNullarySelector(
  75                                                  &pass.Ctx.Idents.get("drain"));
  76   }
  77
  78   void transformBody(Stmt *body, Decl *ParentD) {
  79     Body = body;
  80     TraverseStmt(body);
  81   }
  82
  83   ~AutoreleasePoolRewriter() {
  84     SmallVector<VarDecl *, 8> VarsToHandle;
  85
  86     for (std::map<VarDecl *, PoolVarInfo>::iterator
  87            I = PoolVars.begin(), E = PoolVars.end(); I != E; ++I) {
  88       VarDecl *var = I->first;
  89       PoolVarInfo &info = I->second;
  90
  91       // Check that we can handle/rewrite all references of the pool.
  92
  93       clearRefsIn(info.Dcl, info.Refs);
  94       for (SmallVectorImpl<PoolScope>::iterator
  95              scpI = info.Scopes.begin(),
  96              scpE = info.Scopes.end(); scpI != scpE; ++scpI) {
  97         PoolScope &scope = *scpI;
  98         clearRefsIn(*scope.Begin, info.Refs);
  99         clearRefsIn(*scope.End, info.Refs);
 100         clearRefsIn(scope.Releases.begin(), scope.Releases.end(), info.Refs);
 101       }
 102
 103       // Even if one reference is not handled we will not do anything about that
 104       // pool variable.
 105       if (info.Refs.empty())
 106         VarsToHandle.push_back(var);
 107     }
 108
 109     for (unsigned i = 0, e = VarsToHandle.size(); i != e; ++i) {
 110       PoolVarInfo &info = PoolVars[VarsToHandle[i]];
 111
 112       Transaction Trans(Pass.TA);
 113
 114       clearUnavailableDiags(info.Dcl);
 115       Pass.TA.removeStmt(info.Dcl);
 116
 117       // Add "@autoreleasepool { }"
 118       for (SmallVectorImpl<PoolScope>::iterator
 119              scpI = info.Scopes.begin(),
 120              scpE = info.Scopes.end(); scpI != scpE; ++scpI) {
 121         PoolScope &scope = *scpI;
 122         clearUnavailableDiags(*scope.Begin);
 123         clearUnavailableDiags(*scope.End);
 124         if (scope.IsFollowedBySimpleReturnStmt) {
 125           // Include the return in the scope.
 126           Pass.TA.replaceStmt(*scope.Begin, "@autoreleasepool {");
 127           Pass.TA.removeStmt(*scope.End);
 128           Stmt::child_iterator retI = scope.End;
 129           ++retI;
 130           SourceLocation afterSemi =
 131               findLocationAfterSemi((*retI)->getEndLoc(), Pass.Ctx);
 132           assert(afterSemi.isValid() &&
 133                  "Didn't we check before setting IsFollowedBySimpleReturnStmt "
 134                  "to true?");
 135           Pass.TA.insertAfterToken(afterSemi, "\n}");
 136           Pass.TA.increaseIndentation(
 137               SourceRange(scope.getIndentedRange().getBegin(),
 138                           (*retI)->getEndLoc()),
 139               scope.CompoundParent->getBeginLoc());
 140         } else {
 141           Pass.TA.replaceStmt(*scope.Begin, "@autoreleasepool {");
 142           Pass.TA.replaceStmt(*scope.End, "}");
 143           Pass.TA.increaseIndentation(scope.getIndentedRange(),
 144                                       scope.CompoundParent->getBeginLoc());
 145         }
 146       }
 147
 148       // Remove rest of pool var references.
 149       for (SmallVectorImpl<PoolScope>::iterator
 150              scpI = info.Scopes.begin(),
 151              scpE = info.Scopes.end(); scpI != scpE; ++scpI) {
 152         PoolScope &scope = *scpI;
 153         for (SmallVectorImpl<ObjCMessageExpr *>::iterator
 154                relI = scope.Releases.begin(),
 155                relE = scope.Releases.end(); relI != relE; ++relI) {
 156           clearUnavailableDiags(*relI);
 157           Pass.TA.removeStmt(*relI);
 158         }
 159       }
 160     }
 161   }
 162
 163   bool VisitCompoundStmt(CompoundStmt *S) {
 164     SmallVector<PoolScope, 4> Scopes;
 165
 166     for (Stmt::child_iterator
 167            I = S->body_begin(), E = S->body_end(); I != E; ++I) {
 168       Stmt *child = getEssential(*I);
 169       if (DeclStmt *DclS = dyn_cast<DeclStmt>(child)) {
 170         if (DclS->isSingleDecl()) {
 171           if (VarDecl *VD = dyn_cast<VarDecl>(DclS->getSingleDecl())) {
 172             if (isNSAutoreleasePool(VD->getType())) {
 173               PoolVarInfo &info = PoolVars[VD];
 174               info.Dcl = DclS;
 175               collectRefs(VD, S, info.Refs);
 176               // Does this statement follow the pattern:
 177               // NSAutoreleasePool * pool = [NSAutoreleasePool  new];
 178               if (isPoolCreation(VD->getInit())) {
 179                 Scopes.push_back(PoolScope());
 180                 Scopes.back().PoolVar = VD;
 181                 Scopes.back().CompoundParent = S;
 182                 Scopes.back().Begin = I;
 183               }
 184             }
 185           }
 186         }
 187       } else if (BinaryOperator *bop = dyn_cast<BinaryOperator>(child)) {
 188         if (DeclRefExpr *dref = dyn_cast<DeclRefExpr>(bop->getLHS())) {
 189           if (VarDecl *VD = dyn_cast<VarDecl>(dref->getDecl())) {
 190             // Does this statement follow the pattern:
 191             // pool = [NSAutoreleasePool  new];
 192             if (isNSAutoreleasePool(VD->getType()) &&
 193                 isPoolCreation(bop->getRHS())) {
 194               Scopes.push_back(PoolScope());
 195               Scopes.back().PoolVar = VD;
 196               Scopes.back().CompoundParent = S;
 197               Scopes.back().Begin = I;
 198             }
 199           }
 200         }
 201       }
 202
 203       if (Scopes.empty())
 204         continue;
 205
 206       if (isPoolDrain(Scopes.back().PoolVar, child)) {
 207         PoolScope &scope = Scopes.back();
 208         scope.End = I;
 209         handlePoolScope(scope, S);
 210         Scopes.pop_back();
 211       }
 212     }
 213     return true;
 214   }
 215
 216 private:
 217   void clearUnavailableDiags(Stmt *S) {
 218     if (S)
 219       Pass.TA.clearDiagnostic(diag::err_unavailable,
 220                               diag::err_unavailable_message,
 221                               S->getSourceRange());
 222   }
 223
 224   struct PoolScope {
 225     VarDecl *PoolVar;
 226     CompoundStmt *CompoundParent;
 227     Stmt::child_iterator Begin;
 228     Stmt::child_iterator End;
 229     bool IsFollowedBySimpleReturnStmt;
 230     SmallVector<ObjCMessageExpr *, 4> Releases;
 231
 232     PoolScope()
 233         : PoolVar(nullptr), CompoundParent(nullptr),
 234           IsFollowedBySimpleReturnStmt(false) {}
 235
 236     SourceRange getIndentedRange() const {
 237       Stmt::child_iterator rangeS = Begin;
 238       ++rangeS;
 239       if (rangeS == End)
 240         return SourceRange();
 241       Stmt::child_iterator rangeE = Begin;
 242       for (Stmt::child_iterator I = rangeS; I != End; ++I)
 243         ++rangeE;
 244       return SourceRange((*rangeS)->getBeginLoc(), (*rangeE)->getEndLoc());
 245     }
 246   };
 247
 248   class NameReferenceChecker : public RecursiveASTVisitor<NameReferenceChecker>{
 249     ASTContext &Ctx;
 250     SourceRange ScopeRange;
 251     SourceLocation &referenceLoc, &declarationLoc;
 252
 253   public:
 254     NameReferenceChecker(ASTContext &ctx, PoolScope &scope,
 255                          SourceLocation &referenceLoc,
 256                          SourceLocation &declarationLoc)
 257       : Ctx(ctx), referenceLoc(referenceLoc),
 258         declarationLoc(declarationLoc) {
 259       ScopeRange = SourceRange((*scope.Begin)->getBeginLoc(),
 260                                (*scope.End)->getBeginLoc());
 261     }
 262
 263     bool VisitDeclRefExpr(DeclRefExpr *E) {
 264       return checkRef(E->getLocation(), E->getDecl()->getLocation());
 265     }
 266
 267     bool VisitTypedefTypeLoc(TypedefTypeLoc TL) {
 268       return checkRef(TL.getBeginLoc(), TL.getTypedefNameDecl()->getLocation());
 269     }
 270
 271     bool VisitTagTypeLoc(TagTypeLoc TL) {
 272       return checkRef(TL.getBeginLoc(), TL.getDecl()->getLocation());
 273     }
 274
 275   private:
 276     bool checkRef(SourceLocation refLoc, SourceLocation declLoc) {
 277       if (isInScope(declLoc)) {
 278         referenceLoc = refLoc;
 279         declarationLoc = declLoc;
 280         return false;
 281       }
 282       return true;
 283     }
 284
 285     bool isInScope(SourceLocation loc) {
 286       if (loc.isInvalid())
 287         return false;
 288
 289       SourceManager &SM = Ctx.getSourceManager();
 290       if (SM.isBeforeInTranslationUnit(loc, ScopeRange.getBegin()))
 291         return false;
 292       return SM.isBeforeInTranslationUnit(loc, ScopeRange.getEnd());
 293     }
 294   };
 295
 296   void handlePoolScope(PoolScope &scope, CompoundStmt *compoundS) {
 297     // Check that all names declared inside the scope are not used
 298     // outside the scope.
 299     {
 300       bool nameUsedOutsideScope = false;
 301       SourceLocation referenceLoc, declarationLoc;
 302       Stmt::child_iterator SI = scope.End, SE = compoundS->body_end();
 303       ++SI;
 304       // Check if the autoreleasepool scope is followed by a simple return
 305       // statement, in which case we will include the return in the scope.
 306       if (SI != SE)
 307         if (ReturnStmt *retS = dyn_cast<ReturnStmt>(*SI))
 308           if ((retS->getRetValue() == nullptr ||
 309                isa<DeclRefExpr>(retS->getRetValue()->IgnoreParenCasts())) &&
 310               findLocationAfterSemi(retS->getEndLoc(), Pass.Ctx).isValid()) {
 311             scope.IsFollowedBySimpleReturnStmt = true;
 312             ++SI; // the return will be included in scope, don't check it.
 313           }
 314
 315       for (; SI != SE; ++SI) {
 316         nameUsedOutsideScope = !NameReferenceChecker(Pass.Ctx, scope,
 317                                                      referenceLoc,
 318                                               declarationLoc).TraverseStmt(*SI);
 319         if (nameUsedOutsideScope)
 320           break;
 321       }
 322
 323       // If not all references were cleared it means some variables/typenames/etc
 324       // declared inside the pool scope are used outside of it.
 325       // We won't try to rewrite the pool.
 326       if (nameUsedOutsideScope) {
 327         Pass.TA.reportError("a name is referenced outside the "
 328             "NSAutoreleasePool scope that it was declared in", referenceLoc);
 329         Pass.TA.reportNote("name declared here", declarationLoc);
 330         Pass.TA.reportNote("intended @autoreleasepool scope begins here",
 331                            (*scope.Begin)->getBeginLoc());
 332         Pass.TA.reportNote("intended @autoreleasepool scope ends here",
 333                            (*scope.End)->getBeginLoc());
 334         return;
 335       }
 336     }
 337
 338     // Collect all releases of the pool; they will be removed.
 339     {
 340       ReleaseCollector releaseColl(scope.PoolVar, scope.Releases);
 341       Stmt::child_iterator I = scope.Begin;
 342       ++I;
 343       for (; I != scope.End; ++I)
 344         releaseColl.TraverseStmt(*I);
 345     }
 346
 347     PoolVars[scope.PoolVar].Scopes.push_back(scope);
 348   }
 349
 350   bool isPoolCreation(Expr *E) {
 351     if (!E) return false;
 352     E = getEssential(E);
 353     ObjCMessageExpr *ME = dyn_cast<ObjCMessageExpr>(E);
 354     if (!ME) return false;
 355     if (ME->getMethodFamily() == OMF_new &&
 356         ME->getReceiverKind() == ObjCMessageExpr::Class &&
 357         isNSAutoreleasePool(ME->getReceiverInterface()))
 358       return true;
 359     if (ME->getReceiverKind() == ObjCMessageExpr::Instance &&
 360         ME->getMethodFamily() == OMF_init) {
 361       Expr *rec = getEssential(ME->getInstanceReceiver());
 362       if (ObjCMessageExpr *recME = dyn_cast_or_null<ObjCMessageExpr>(rec)) {
 363         if (recME->getMethodFamily() == OMF_alloc &&
 364             recME->getReceiverKind() == ObjCMessageExpr::Class &&
 365             isNSAutoreleasePool(recME->getReceiverInterface()))
 366           return true;
 367       }
 368     }
 369
 370     return false;
 371   }
 372
 373   bool isPoolDrain(VarDecl *poolVar, Stmt *S) {
 374     if (!S) return false;
 375     S = getEssential(S);
 376     ObjCMessageExpr *ME = dyn_cast<ObjCMessageExpr>(S);
 377     if (!ME) return false;
 378     if (ME->getReceiverKind() == ObjCMessageExpr::Instance) {
 379       Expr *rec = getEssential(ME->getInstanceReceiver());
 380       if (DeclRefExpr *dref = dyn_cast<DeclRefExpr>(rec))
 381         if (dref->getDecl() == poolVar)
 382           return ME->getMethodFamily() == OMF_release ||
 383                  ME->getSelector() == DrainSel;
 384     }
 385
 386     return false;
 387   }
 388
 389   bool isNSAutoreleasePool(ObjCInterfaceDecl *IDecl) {
 390     return IDecl && IDecl->getIdentifier() == PoolII;
 391   }
 392
 393   bool isNSAutoreleasePool(QualType Ty) {
 394     QualType pointee = Ty->getPointeeType();
 395     if (pointee.isNull())
 396       return false;
 397     if (const ObjCInterfaceType *interT = pointee->getAs<ObjCInterfaceType>())
 398       return isNSAutoreleasePool(interT->getDecl());
 399     return false;
 400   }
 401
 402   static Expr *getEssential(Expr *E) {
 403     return cast<Expr>(getEssential((Stmt*)E));
 404   }
 405   static Stmt *getEssential(Stmt *S) {
 406     if (FullExpr *FE = dyn_cast<FullExpr>(S))
 407       S = FE->getSubExpr();
 408     if (Expr *E = dyn_cast<Expr>(S))
 409       S = E->IgnoreParenCasts();
 410     return S;
 411   }
 412
 413   Stmt *Body;
 414   MigrationPass &Pass;
 415
 416   IdentifierInfo *PoolII;
 417   Selector DrainSel;
 418
 419   struct PoolVarInfo {
 420     DeclStmt *Dcl;
 421     ExprSet Refs;
 422     SmallVector<PoolScope, 2> Scopes;
 423
 424     PoolVarInfo() : Dcl(nullptr) { }
 425   };
 426
 427   std::map<VarDecl *, PoolVarInfo> PoolVars;
 428 };
 429
 430 } // anonymous namespace
 431
 432 void trans::rewriteAutoreleasePool(MigrationPass &pass) {
 433   BodyTransform<AutoreleasePoolRewriter> trans(pass);
 434   trans.TraverseDecl(pass.Ctx.getTranslationUnitDecl());
 435 }