[cfe-commits] r60995 - in /cfe/trunk: include/clang/Analysis/PathSensitive/MemRegion.h include/clang/Analysis/PathSensitive/Store.h lib/Analysis/BasicObjCFoundationChecks.cpp lib/Analysis/BasicStore.cpp lib/Analysis/CFRefCount.cpp lib/Analysis/GR

Ted Kremenek kremenek at apple.com
Mon Dec 15 21:55:13 PST 2008

On Dec 15, 2008, at 5:39 PM, Zhongxing Xu wrote:

> I agree in your example we should not convert p to point to the zero- 
> index element. But in my example:
> char * p = alloca(10);
> p[1] = 3;
> p *is* a pointer to 'char' when we do CastRegion.

Yes, but a "char*" can be either a pointer to an array or a single  
character.  In this case (with alloca) we know p is a pointer to an  
array of bytes, so it simplifies things, but if (for example) the  
region is symbolic we don't know if the void* is a pointer to a single  
character or to an array of bytes.

> And later in ArraySubscriptExpr we don't have a chance to do the  
> conversion.

Not true.  Just because there isn't a pointer-to-array cast in the AST  
doesn't mean we can't do the conversion.  We can do it when handling  
the ArraySubscriptExpr:

/// VisitArraySubscriptExpr - Transfer function for array accesses
void GRExprEngine::VisitArraySubscriptExpr(ArraySubscriptExpr* A,  
NodeTy* Pred,
                                            NodeSet& Dst, bool  
asLValue) {

   Expr* Base = A->getBase()->IgnoreParens();
   Expr* Idx  = A->getIdx()->IgnoreParens();
   NodeSet Tmp;
   Visit(Base, Pred, Tmp);   // Get Base's rvalue, which should be an  

   for (NodeSet::iterator I1=Tmp.begin(), E1=Tmp.end(); I1!=E1; ++I1) {
     NodeSet Tmp2;
     Visit(Idx, *I1, Tmp2);     // Evaluate the index.

     for (NodeSet::iterator I2=Tmp2.begin(), E2=Tmp2.end(); I2!=E2; + 
+I2) {
       const GRState* St = GetState(*I2);
       // **** Possible insert a call to StoreManager::PointerToArray  
here for the
       // ****  results of GetSVal(St, Base).
       SVal V = StateMgr.GetLValue(St, GetSVal(St, Base), GetSVal(St,  

I'm not saying this is the best solution; it just seems that using an  
ElementRegion early seems speculative and premature, especially if it  
really isn't an array.  Why not just do it lazily when a region is  
*used* as an array?

Of course, this leads to the question of how we handle general pointer  
arithmetic (one of those things we're basically punting on right now).

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