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

[Roland Westrelin]

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.
>>