RFA: Changes to interpreter to avoid non-debugging slowdown

[Kyle Galloway]

Tom Tromey wrote:
>>>>>> "Kyle" == Kyle Galloway <kgallowa@redhat.com> writes:
>>>>>>             
>
> Tom> We talked about it offline and the idea is, we need to track the types
> Tom> of stack and local variable slots while interpreting if the debugging
> Tom> code is enabled.  However, we don't want to do this unconditionally as
> Tom> it adds overhead to interpretation.
>
> So, I looked at JVMTI a little more.  It seems that we only need to
> know the types of locals, is that correct?
>
> I'm wondering now if it is worthwhile to make an entire second
> interpreter just for this.  Perhaps an extra store in the various
> 'store' instructions is not too much overhead.
>   
There are other reasons for this as well, in addition to what Keith 
said.  If we want the full suite of event notifications, we need to add 
code to check for them so it could mean a slew of conditional checks to 
see if we are debugging.  If we instead can just #ifdef this code into 
the debugging version, it will mean we don't have to do conditional 
checks in either case since we will know at the invocation of run() or 
run_debug() whether we should report debug info or not.
> That said, your updated patch is looking pretty good to me.
> One more addition I didn't think of yesterday: you have to update
> stacktrace.cc to account for the new interpreter.
>   
Small oversight on my part, I've fixed it.  I had also forgot about the 
change in ncode() in the changelog.  New changelog and new patch attached.

2006-07-28  Kyle Galloway  <kgallowa@redhat.com>

   * /include/java-interp.h (_Jv_InterpMethod::run_debug): New method.
   * /interpret.cc: Added placeholder for debug variable type info to STORE*
   macros.
   (_Jv_InterpMethod::run_debug): New method.
   (_Jv_InterpMethod::run_sync_object_debug): New method.
   (_Jv_InterpMethod::run_sync_class_debug): New method.
   (_Jv_InterpMethod::run_normal_debug): New method.
   (_Jv_InterpMethod::run_class_debug): New method.
   (_Jv_InterpMethod::ncode ()): Changed to select either debug or normal
   versions of these functions.
   * /interpret-run.cc: New file, holds contents of old 
_Jv_InterpMethod::run
   method.
   * /stacktrace.cc (_Jv_StackTrace::UnwindTraceFn): Changed to select
   appropriate function for debug or normal mode.