Re: CastCheckEliminator

[Archie Cobbs <archie@dellroad.org>]

Ondrej LHOTAK wrote:
> > > > Is it a well-known fact that CastCheckEliminator is broken [1]?
> > > > Just curious if so, and whether there are any plans to fix it.
> > > 
> > > It was not well-known that it's broken until I read your bug report this
> > > morning. I'm working on fixing it...

Thanks again for fixing that bug..

Now there appears to be another (I think much simpler) bug [1] in
CastCheckEliminator. It looks to me like it doesn' properly handle
the case where thing being cast is the null constant. E.g., I'm
getting this exception when analyzing a certain class (fyi it happens
to be polyglot/ext/jl/ast/AbstractDelFactory_c):

    java.lang.ClassCastException: soot.jimple.NullConstant
	at soot.jimple.toolkits.pointer.CastCheckEliminator.flowThrough(CastCheckEliminator.java:135)
	at soot.toolkits.scalar.ForwardBranchedFlowAnalysis.doAnalysis(ForwardBranchedFlowAnalysis.java:240)
	at soot.jimple.toolkits.pointer.CastCheckEliminator.<init>(CastCheckEliminator.java:38)
	at soot.jimple.toolkits.pointer.CastCheckEliminatorDumper.internalTransform(CastCheckEliminatorDumper.java:35
	)
	at soot.BodyTransformer.transform(BodyTransformer.java:51)

The relevant code is:

    132     CastExpr cast = (CastExpr) rhs;
    133     Type castType = cast.getCastType();
    134     if( castType instanceof RefType ) {
    135         out.localCopy( l, (Local) cast.getOp() );
    135         out.localMustBeSubtypeOf( l, (RefType) castType );
    137         out.localMustBeSubtypeOf( (Local) cast.getOp(),
    138                                   (RefType) castType );
    139     }

It's assuming cast.getOp() is a local, but it's a NullConstant.
Similar code appears on line 53:

    52      if( t instanceof RefType ) {
    52          Local l = (Local) cast.getOp();
    54          LocalTypeSet set = (LocalTypeSet) unitToBeforeFlow.get(s);
    55          s.addTag( new CastCheckTag( set.get( set.indexOf(
    56                                                           l, (RefType) t ) ) ) );
    57      }

-Archie

 [1] http://www.sable.mcgill.ca/sootbugs/incoming?id=95

__________________________________________________________________________
Archie Cobbs      *        CTO, Awarix        *      http://www.awarix.com