review(S): 7058510: multinewarray with 6 dimensions uncommon traps in server compiler

Igor Veresov igor.veresov at
Fri Jul 1 12:55:39 PDT 2011

Following the advise of John Rose I made arguments transfer via java 
array for arrays with > 5 dimensions.



On 6/27/11 2:47 PM, Igor Veresov wrote:
> Thanks for the review, Tom!
> I'll try to implement the vararg calls.
> igor
> On 6/27/11 1:41 PM, Tom Rodriguez wrote:
>> Is there any easy way to just make C2 support a varargs style call for
>> multianewarray? C1 just does a funny calling convention where it
>> passes a pointer a stack allocated array which is obviously possible
>> with C2 though we don't have anything like it right now. I can see how
>> to do this by cons'ing up type signatures as need with extra count and
>> pointer arguments and then modifying the c_calling_convention to
>> switch to the stack only calling convention after the first two. The
>> only extra trick would be getting the address of the stack arguments
>> into the call when it's converted into a MachCall. We don't really
>> have a way to express that using MachNodes since stack slots are
>> virtual are that point. Maybe it could simply be handled at the ad
>> file level.
>> So something like a new MachCallRuntimeVarargsNode with an index
>> indicating which argument is the last real one, the
>> c_calling_convention modified to take an index indicating when it
>> should force a switch to stack only, and the ins_encode for that match
>> inserting the right address computation for the address. Is that too
>> complex for the limited benefit? Maybe compared to the complexity of
>> the existing machinery, it's not too bad.
>> As far as your webrev, I don't think you want to do this:
>> + if (per_bc_reason == Reason_unhandled) {
>> + make_not_compilable = true;
>> + }
>> There are other uses of Reason_unhandled and it's not clear the
>> stopping compilation is the right action for those other cases. Maybe
>> you need another action? Or maybe the actions need to be interpreted
>> specially for Reason_unhandled. Doing a make_not_entrant doesn't seem
>> like the right action for some of the other Reason_unhandleds.
>> I do like the trap_state changes if it allows us to move
>> Reason_loop_predicate and Reason_loop_limit_check into the per bci
>> section.
>> tom
>> On Jun 27, 2011, at 12:07 PM, Igor Veresov wrote:
>>> Problem: multinewarray with>= 6 dimensions is not supported by c2 and
>>> is plugged with uncommon trap. When executed in the main code path
>>> this yields performance far worse than even interpreter.
>>> Solution: Count these traps per bci and when the number exceeds
>>> PerBytecodeTrapLimit make it not compilable. With tiered it would
>>> result in recompilation at level 1 (pure C1), with regular scheme the
>>> method will continue in the interpreter.
>>> Webrev:
>>> Thanks,
>>> igor

More information about the hotspot-compiler-dev mailing list