[Soot-list] Singleton ArrayLists

[Patrick Lam]

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Hi Ohad,

Thanks for the note and the profiling results. There is no particular
reason that some places in the code use singleton lists and others
don't. I think it just depended on when each piece of code was written.
Someone should go through and change the code to make it more
space-efficient.

pat

Ohad Shacham wrote:
> Hi,
> 
> We recently built a tool called Chameleon (
> http://www.research.ibm.com/qvm/chameleon.html) for automatically managing
> collections in Java. Running Chameleon on Soot, it reported, among other
> things, that in the following places a Singleton (non-modifiable) list
> should be used:
> 
> soot.jimple.internal.JIfStmt - targetBoxes
> soot.baf.internal.BLoadInst - useBoxes
> soot.jimple.internal.JIdentityStmt - defBoxes
> soot.baf.internal.BStoreInst - defBoxes
> soot.baf.internal.BIdentityInst - defBoxes
> 
> Checking the code, it seems that indeed there's no reason to use a
> full-fledged ArrayList in these places, as the collections are singletons
> and are immutable.
> 
> For example: in soot.jimple.internal.JIfStmt
> 
>   protected JIfStmt(ValueBox conditionBox, UnitBox targetBox)
>     {
>         this.conditionBox = conditionBox;
>         this.targetBox = targetBox;
> 
>         targetBoxes = new ArrayList();
>         targetBoxes.add(this. targetBox);
>         targetBoxes = Collections.unmodifiableList(targetBoxes);
>     }
> 
> This ArrayList allocates a default size of 10, and will always use only 1
> element in the underlying array. This might lead to significant waste of
> space.
> 
> We noticed that in some other places in Soot, the constructors are already
> using a SingletonList (e.g., JAssignStmt), and wondered what is the reason
> that the aforementioned locations remained as using ArrayLists?
> Thanks,
> Ohad
> 
> 
> 
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