Re: [PATCH] Analyzer: Pass the current TryCatchBlockNode to newControlFlowExceptionEdge

Hi,

thanks for this patch, I've committed it in the SVN repository

Eric

12/07/2011 15:20, Ivo Anjo wrote:
> Hello,
>
> I'm currently working on a project that heavily relies on the
> tree.analysis.Analyzer class to understand and modify classes.
>
> As you might know, when creating the control flow graph for exceptions,
> ASM calls analyzer.newControlFlowExceptionEdge(int insn, int successor),
> and uses its boolean return to decide if it should consider the edge
> valid or not.
>
> By default, this method simply returns "true". Because of the rules the
> JVM specification uses to decide which exception handler is active --
> for example if you add to the beginning of the exception table of a
> method an entry that covers the entire method, and catches
> java.lang.Throwable, none of the other handlers can ever be executed --
> this simplification might detect control flow edges that would never be
> possible.
>
> To implement the same rules the JVM uses, I do this:
>      protected boolean newControlFlowExceptionEdge(int src,
> TryCatchBlockNode tcb) {
>
>          for (TryCatchBlockNode handler : getHandlers(src)) {
>              if (handler.equals(tcb)) return true;
>              if (isSubTypeOf(tcb.type, handler.type)) return false;
>          }
>
>          throw new AssertionError();
>      }
>
> That is, I check if the current try catch block being "visited" is
> subsumed by some other that came before it (since getHandlers() gives me
> an ordered list, which is in the same order as the JVM uses).
>
> Unfortunately, the current code for newControlFlowExceptionEdge only
> supplies the src and dst; basically, the current instruction and
> insns.indexOf(tcb.handler).
> This is unsufficient information to perform this analysis -- especially
> since newControlFlowExceptionEdge might be called multiple times for the
> same handler, so it is very hard to know which handler is being referred
> to just by using the src and dst -- my first approach to this was
> counting the number of calls to newControlFlowExceptionEdge, and then I
> discovered that there can be multiple calls for the same block.
>
> This patch, then, adds a new method -- protected boolean
> newControlFlowExceptionEdge(int src, TryCatchBlockNode tcb), which by
> default delegates to the older newControlFlowExceptionEdge (which I
> suggest be deprecated, or even removed for ASM 4). Even so, the two
> methods can easily co-exist, and older code will still work perfectly;
> and a simple one-line change inside analyzer.analyze, since the code
> already knows that the current trycatchblock is.
>
> Hope it is acceptable, and thanks in advance,
> Ivo Anjo

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