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

[Roland Westrelin]

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.
>>>> 
>>