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

[Vladimir Kozlov]

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)?

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.
>