RFR(L): 8031755: Type speculation should be used to optimize explicit null checks

[Roland Westrelin]

I need another review for this. Anyone?

Roland.

On Mar 26, 2014, at 9:55 AM, Roland Westrelin <roland.westrelin at oracle.com> wrote:

> Thanks for the review, Vladimir.
> 
> Roland.
> 
> 
> On Mar 26, 2014, at 1:43 AM, Vladimir Kozlov <vladimir.kozlov at oracle.com> wrote:
> 
>> It is good.
>> 
>> Thanks,
>> Vladimir
>> 
>> On 3/25/14 7:53 AM, Roland Westrelin wrote:
>>> Thanks for reviewing this, Vladimir!
>>> 
>>>> Looks good. I see next expression several times:
>>>> 
>>>> speculative ? Deoptimization::Reason_speculate_null_check : Deoptimization::Reason_null_check
>>>> 
>>>> Can you put it into method Deoptimization::reason_null_check(speculative)?
>>> 
>>> Here it is:
>>> 
>>> http://cr.openjdk.java.net/~roland/8031755/webrev.02/
>>> 
>>> I did the same for Reason_speculate_class_check & Deoptimization::Reason_class_check.
>>> 
>>> Roland.
>>> 
>>>> 
>>>> Thanks,
>>>> Vladimir
>>>> 
>>>> On 3/20/14 4:52 AM, Roland Westrelin wrote:
>>>>>>> I made the following change:
>>>>>>> 
>>>>>>> *** 3561,3571 ****
>>>>>>> 
>>>>>>> 
>>>>>>>      // Since klasses are different, we require a LCA in the Java
>>>>>>>      // class hierarchy - which means we have to fall to at least NotNull.
>>>>>>>      if( ptr == TopPTR || ptr == AnyNull || ptr == Constant )
>>>>>>>        ptr = NotNull;
>>>>>>> 
>>>>>>> -     instance_id = InstanceBot;
>>>>>>> 
>>>>>>> 
>>>>>>>      // Now we find the LCA of Java classes
>>>>>>>      ciKlass* k = this_klass->least_common_ancestor(tinst_klass);
>>>>>>>      return make(ptr, k, false, NULL, off, instance_id, speculative, depth);
>>>>>>>    } // End of case InstPtr
>>>>>>> 
>>>>>>> --- 3706,3715 ——
>>>>>>> 
>>>>>>> because I hit a type not symmetric failure that I think it causes:
>>>>>>> 
>>>>>>> === Meet Not Symmetric ===
>>>>>>> t   =                   javax/management/openmbean/OpenType:AnyNull * (inline_depth=-2)
>>>>>>> this=                   javax/management/openmbean/ArrayType:TopPTR *,iid=top (inline_depth=InlineDepthTop)
>>>>>>> mt=(t meet this)=       javax/management/openmbean/ArrayType:AnyNull * (inline_depth=-2)
>>>>>>> t_dual=                 javax/management/openmbean/OpenType:NotNull *,iid=top (inline_depth=2)
>>>>>>> this_dual=              javax/management/openmbean/ArrayType *
>>>>>>> mt_dual=                javax/management/openmbean/ArrayType:NotNull *,iid=top (inline_depth=2)
>>>>>>> mt_dual meet t_dual=    javax/management/openmbean/OpenType:NotNull * (inline_depth=2)
>>>>>>> mt_dual meet this_dual= javax/management/openmbean/ArrayType *
>>>>>> 
>>>>>> The question is why OpenType:AnyNull does not have iid=top. It is in upper type lattice.
>>>>> 
>>>>> http://cr.openjdk.java.net/~roland/8031755/TestMeetInstanceId.java
>>>>> 
>>>>> triggers this. But while working on reproducing it, I noticed a bug in the previous webrev:
>>>>> 
>>>>> if (!speculative_maybe_null) {
>>>>> 
>>>>> in TypePtr::would_improve_ptr() should have been:
>>>>> 
>>>>> if (!speculative_maybe_null()) {
>>>>> 
>>>>> with that fixed, the bug doesn’t reproduce. I also think we should drop the speculative type, if it is above the center line. So here is a new webrev with:
>>>>> instance_id = InstanceBot;
>>>>> back where it was.
>>>>> 
>>>>> http://cr.openjdk.java.net/~roland/8031755/webrev.01/
>>>>> 
>>>>> Roland.
>>>>> 
>>> 
>