A simple PIC api

[Mark Roos]

Hi Jochen

I have to think about yours some more but I thought I would share mine.  I 
condensed it to 
make it easier to explain. 

regards
mark

I extended callsite to hold a bunch of values one of which is the depth.
And my model for the cache is up to 10 chained GWTs after that I drop the
chain and start over.

When I get a miss in the cache off to the fallback ( look below to see how 
this MH is made)
        static RtObject fallbackSelf(RtCallSite site, Object... args)

For each guard I create a test MH which takes all of the args and returns 
a bool.
Since I only look at the TOS it drops the rest,  yours is more 
complicated.  This can be
different for each guard in my case.
        RtObject rcvr=(RtObject)args[args.length - 1];  // top of stack
        test=MethodHandles.insertArguments(test, 0, rcvr.classField()); // 
the behavior field
       test=MethodHandles.dropArguments(test, 0, site.dropArray());     // 
match test signature

  then finds the code based on the site and the receiver in this case
        MethodHandle newTarget=rcvr.lookupSelf(site.getSelector());

  makes a new GWT with the existing chain as its slow path
  if the cache is full will make the bootstrap MH (see below) the target 
dropping the existing cache
        if(site._depth < 10)  
        MethodHandle gwt=MethodHandles.guardWithTest(test, newTarget, site
.getRealTarget());
        site._depth = site._depth + 1;  // bump the depth

  inserts it at the start of the chain by making it the new target
      site.setRealTarget(gwt);

  and invokes it ( has to spread the args here as they were compressed on 
the way to the fallback)
        MethodHandle     invoke=newTarget.asSpreader(Object[].class, site
.getAirity());
      result=(RtObject) invoke.invokeExact((Object[])args);

You probably need to see the bootstrap to understand the invoke.  To limit 
myself to only one fallback signature
I bind the callsite and collect the args

         MethodHandle mh=lookup.findStatic(RtCallSite.class, 
"fallbackSelf", mt); 
        MethodHandle mh2=MethodHandles.insertArguments(mh, 0, site); // 
insert the call site
        MethodHandle mh3=mh2.asCollector(RtObject[].class, site
.getAirity()); // combine the args into an array
        site.setBootstrapTarget(mh3);
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