review (S) for 6877221: Endless deoptimizations in OSR nmethod

[Tom Rodriguez]

On Feb 16, 2010, at 3:24 PM, Vladimir Kozlov wrote:

> Tom,
> 
> So making athrow non rerunnable will force to generate runtime call to trow
> instead of uncommon trap. Correct?

Yes and we'll get CatchProj's off the call to handle/describe all the exception edges.

tom

> 
> Otherwise looks fine.
> 
> Thanks,
> Vladimir
> 
> Tom Rodriguez wrote:
>> http://cr.openjdk.java.net/~never/6877221
>> 6877221: Endless deoptimizations in OSR nmethod
>> Reviewed-by:
>> When emitting the inline exception code if we can't handle all the
>> exception types inline we will try to fall back to an uncommon trap
>> for bytecodes that can be rerun to produce the exceptional condition.
>> All bytecodes except the various invokes can be handled this way.  The
>> cases we currently can't handle inline are unloaded catch classes,
>> which will require class loading during lookup and catch classes that
>> have subclasses.  That latter is a historical limitation from the
>> times when type checks were more expensive.  Currently athrow is
>> handled by rerunning it which means that any exception forwarding
>> logic that uses athrow will force us back into the interpreter for
>> every exception dispatch through this nmethod.  Since this fix will
>> likely be backported I want to do the simple fix of removing athrow
>> from the set of rerunnable bytecodes.  A more complete fix involving
>> rewriting catch_inline_exceptions to avoid the uncommon trap with
>> Action_none and to perform full type checks inline will be done for
>> hs18.
>> I collected some stats on how catch_inline_exceptions behaves to get
>> some sense of which paths are used.  These numbers are generated every
>> benchmark in reference_server plus specjvm2008.  In 22631 calls, 16050
>> terminate by unwinding the frame, 3280 dispatch to a default exception
>> handler, 3176 call the rethrow function, and 125 emit an uncommon
>> trap.  Of those uncommon traps the bytecode breakdown is this:
>>    14 anewarray
>>  52 athrow
>>  52 new
>>   7 newarray
>> Of the athrows, 43 are from unloaded classes and the other 9 are
>> because the catch class had subclasses.
>> src/share/vm/opto/parse1.cpp