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

[Vladimir Kozlov]

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.
>>>
>