text: //=-- ExprEngineObjC.cpp - ExprEngine support for Objective-C ---*- C++ -*-===//
  //
  //                     The LLVM Compiler Infrastructure
  //
  // This file is distributed under the University of Illinois Open Source
  // License. See LICENSE.TXT for details.
  //
  //===----------------------------------------------------------------------===//
  //
  //  This file defines ExprEngine's support for Objective-C expressions.
  //
  //===----------------------------------------------------------------------===//
  
  #include "clang/AST/StmtObjC.h"
  #include "clang/StaticAnalyzer/Core/CheckerManager.h"
  #include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h"
  #include "clang/StaticAnalyzer/Core/PathSensitive/ExprEngine.h"
  
  using namespace clang;
  using namespace ento;
  
  void ExprEngine::VisitLvalObjCIvarRefExpr(const ObjCIvarRefExpr *Ex, 
                                            ExplodedNode *Pred,
                                            ExplodedNodeSet &Dst) {
    ProgramStateRef state = Pred->getState();
    const LocationContext *LCtx = Pred->getLocationContext();
    SVal baseVal = state->getSVal(Ex->getBase(), LCtx);
    SVal location = state->getLValue(Ex->getDecl(), baseVal);
    
    ExplodedNodeSet dstIvar;
    StmtNodeBuilder Bldr(Pred, dstIvar, *currBldrCtx);
    Bldr.generateNode(Ex, Pred, state->BindExpr(Ex, LCtx, location));
    
    // Perform the post-condition check of the ObjCIvarRefExpr and store
    // the created nodes in 'Dst'.
    getCheckerManager().runCheckersForPostStmt(Dst, dstIvar, Ex, *this);
  }
  
  void ExprEngine::VisitObjCAtSynchronizedStmt(const ObjCAtSynchronizedStmt *S,
                                               ExplodedNode *Pred,
                                               ExplodedNodeSet &Dst) {
    getCheckerManager().runCheckersForPreStmt(Dst, Pred, S, *this);
  }
  
  void ExprEngine::VisitObjCForCollectionStmt(const ObjCForCollectionStmt *S,
                                              ExplodedNode *Pred,
                                              ExplodedNodeSet &Dst) {
    
    // ObjCForCollectionStmts are processed in two places.  This method
    // handles the case where an ObjCForCollectionStmt* occurs as one of the
    // statements within a basic block.  This transfer function does two things:
    //
    //  (1) binds the next container value to 'element'.  This creates a new
    //      node in the ExplodedGraph.
    //
    //  (2) binds the value 0/1 to the ObjCForCollectionStmt* itself, indicating
    //      whether or not the container has any more elements.  This value
    //      will be tested in ProcessBranch.  We need to explicitly bind
    //      this value because a container can contain nil elements.
    //
    // FIXME: Eventually this logic should actually do dispatches to
    //   'countByEnumeratingWithState:objects:count:' (NSFastEnumeration).
    //   This will require simulating a temporary NSFastEnumerationState, either
    //   through an SVal or through the use of MemRegions.  This value can
    //   be affixed to the ObjCForCollectionStmt* instead of 0/1; when the loop
    //   terminates we reclaim the temporary (it goes out of scope) and we
    //   we can test if the SVal is 0 or if the MemRegion is null (depending
    //   on what approach we take).
    //
    //  For now: simulate (1) by assigning either a symbol or nil if the
    //    container is empty.  Thus this transfer function will by default
    //    result in state splitting.
  
    const Stmt *elem = S->getElement();
    ProgramStateRef state = Pred->getState();
    SVal elementV;
    
    if (const DeclStmt *DS = dyn_cast<DeclStmt>(elem)) {
      const VarDecl *elemD = cast<VarDecl>(DS->getSingleDecl());
      assert(elemD->getInit() == 0);
      elementV = state->getLValue(elemD, Pred->getLocationContext());
    }
    else {
      elementV = state->getSVal(elem, Pred->getLocationContext());
    }
    
    ExplodedNodeSet dstLocation;
    evalLocation(dstLocation, S, elem, Pred, state, elementV, NULL, false);
  
    ExplodedNodeSet Tmp;
    StmtNodeBuilder Bldr(Pred, Tmp, *currBldrCtx);
  
    for (ExplodedNodeSet::iterator NI = dstLocation.begin(),
         NE = dstLocation.end(); NI!=NE; ++NI) {
      Pred = *NI;
      ProgramStateRef state = Pred->getState();
      const LocationContext *LCtx = Pred->getLocationContext();
      
      // Handle the case where the container still has elements.
      SVal TrueV = svalBuilder.makeTruthVal(1);
      ProgramStateRef hasElems = state->BindExpr(S, LCtx, TrueV);
      
      // Handle the case where the container has no elements.
      SVal FalseV = svalBuilder.makeTruthVal(0);
      ProgramStateRef noElems = state->BindExpr(S, LCtx, FalseV);
  
      if (Optional<loc::MemRegionVal> MV = elementV.getAs<loc::MemRegionVal>())
        if (const TypedValueRegion *R = 
            dyn_cast<TypedValueRegion>(MV->getRegion())) {
          // FIXME: The proper thing to do is to really iterate over the
          //  container.  We will do this with dispatch logic to the store.
          //  For now, just 'conjure' up a symbolic value.
          QualType T = R->getValueType();
          assert(Loc::isLocType(T));
          SymbolRef Sym = SymMgr.conjureSymbol(elem, LCtx, T,
                                               currBldrCtx->blockCount());
          SVal V = svalBuilder.makeLoc(Sym);
          hasElems = hasElems->bindLoc(elementV, V);
          
          // Bind the location to 'nil' on the false branch.
          SVal nilV = svalBuilder.makeIntVal(0, T);
          noElems = noElems->bindLoc(elementV, nilV);
        }
      
      // Create the new nodes.
      Bldr.generateNode(S, Pred, hasElems);
      Bldr.generateNode(S, Pred, noElems);
    }
  
    // Finally, run any custom checkers.
    // FIXME: Eventually all pre- and post-checks should live in VisitStmt.
    getCheckerManager().runCheckersForPostStmt(Dst, Tmp, S, *this);
  }
  
  void ExprEngine::VisitObjCMessage(const ObjCMessageExpr *ME,
                                    ExplodedNode *Pred,
                                    ExplodedNodeSet &Dst) {
    CallEventManager &CEMgr = getStateManager().getCallEventManager();
    CallEventRef<ObjCMethodCall> Msg =
      CEMgr.getObjCMethodCall(ME, Pred->getState(), Pred->getLocationContext());
  
    // Handle the previsits checks.
    ExplodedNodeSet dstPrevisit;
    getCheckerManager().runCheckersForPreObjCMessage(dstPrevisit, Pred,
                                                     *Msg, *this);
    ExplodedNodeSet dstGenericPrevisit;
    getCheckerManager().runCheckersForPreCall(dstGenericPrevisit, dstPrevisit,
                                              *Msg, *this);
  
    // Proceed with evaluate the message expression.
    ExplodedNodeSet dstEval;
    StmtNodeBuilder Bldr(dstGenericPrevisit, dstEval, *currBldrCtx);
  
    for (ExplodedNodeSet::iterator DI = dstGenericPrevisit.begin(),
         DE = dstGenericPrevisit.end(); DI != DE; ++DI) {
      ExplodedNode *Pred = *DI;
      ProgramStateRef State = Pred->getState();
      CallEventRef<ObjCMethodCall> UpdatedMsg = Msg.cloneWithState(State);
      
      if (UpdatedMsg->isInstanceMessage()) {
        SVal recVal = UpdatedMsg->getReceiverSVal();
        if (!recVal.isUndef()) {
          // Bifurcate the state into nil and non-nil ones.
          DefinedOrUnknownSVal receiverVal =
              recVal.castAs<DefinedOrUnknownSVal>();
  
          ProgramStateRef notNilState, nilState;
          llvm::tie(notNilState, nilState) = State->assume(receiverVal);
          
          // There are three cases: can be nil or non-nil, must be nil, must be
          // non-nil. We ignore must be nil, and merge the rest two into non-nil.
          // FIXME: This ignores many potential bugs (<rdar://problem/11733396>).
          // Revisit once we have lazier constraints.
          if (nilState && !notNilState) {
            continue;
          }
          
          // Check if the "raise" message was sent.
          assert(notNilState);
          if (ObjCNoRet.isImplicitNoReturn(ME)) {
            // If we raise an exception, for now treat it as a sink.
            // Eventually we will want to handle exceptions properly.
            Bldr.generateSink(ME, Pred, State);
            continue;
          }
          
          // Generate a transition to non-Nil state.
          if (notNilState != State) {
            Pred = Bldr.generateNode(ME, Pred, notNilState);
            assert(Pred && "Should have cached out already!");
          }
        }
      } else {
        // Check for special class methods that are known to not return
        // and that we should treat as a sink.
        if (ObjCNoRet.isImplicitNoReturn(ME)) {
          // If we raise an exception, for now treat it as a sink.
          // Eventually we will want to handle exceptions properly.
          Bldr.generateSink(ME, Pred, Pred->getState());
          continue;
        }
      }
  
      defaultEvalCall(Bldr, Pred, *UpdatedMsg);
    }
    
    ExplodedNodeSet dstPostvisit;
    getCheckerManager().runCheckersForPostCall(dstPostvisit, dstEval,
                                               *Msg, *this);
  
    // Finally, perform the post-condition check of the ObjCMessageExpr and store
    // the created nodes in 'Dst'.
    getCheckerManager().runCheckersForPostObjCMessage(Dst, dstPostvisit,
                                                      *Msg, *this);
  }
  