RFR(M): 6700100: optimize inline_native_clone() for small objects with exact klass

[Roland Westrelin]

Hi Vladimir,

Thanks for reviewing this.

> Sorry it took so long.

I sent this one yesterday so no, it didn’t take long! Maybe you’re thinking about 8054478 which has been out for a bit longer. I’m curious what you think about that one.

> Could you explain changes in fieldStreams.hpp? How it worked before?
> I see that the change only affects code in FieldStreamBase(Array<u2>* fields, constantPoolHandle constants, int start, int limit).

InternalFieldStream was not used anywhere and it’s broken. That change to FieldStreamBase fixes it.
InternalFieldStream starts iterating from k->java_fields_count() up to num_fields so num_fields must be the total number of fields.

> And can it be simple done as?:
> 
> return num_fields + _index;

I use the same code pattern as the next loop:

70     for (int i = _index; i*FieldInfo::field_slots < length; i++) {

76       num_fields ++;
77     }

But that doesn’t make much sense, you’re right. I’ll fix it.

> StressArrayCopyMacroNode flag is used in product code. Make it diagnostic.
> 
> Why you skip klasses with injected fields? I thought nof_nonstatic_fields() includes them. Add comment.

I skip them because they are rare and it seems simpler to simply skip them.
ciInstanceKlass::compute_nonstatic_fields_impl() uses JavaFieldStream that only iterates over regular java fields.

> 
> How we benefit from doing this optimization during parsing? Why you need StressArrayCopyMacroNode?

It’s a stress option. The Ideal transformation is often applied at parse time and I wanted to make sure I could stress test the Ideal transformation during IGVN because it performs somewhat trickier graph transformations. Why would I need to make it diagnostic?

Rolaand.

> 
> Otherwise changes looks reasonable.
> 
> Thanks,
> Vladimir
> 
> On 10/8/14 5:33 AM, Roland Westrelin wrote:
>> http://cr.openjdk.java.net/~roland/6700100/webrev.00/
>> 
>> Converts ArrayCopy nodes for small instance clones to series of loads/stores + a little bit of cleanup.
>> 
>> Small array clones & copies as loads/stores are coming next in another change.
>> 
>> Roland.
>>