RFR (S): 8198561: Make oop and narrowOop always have their own class type

[Erik Österlund]

Hi Coleen,

As I said to Roman: the studio compiler finds it ambiguous to have both 
const and const volatile implicit conversion overloads - you gotta pick 
your favourite. Seemingly same issue as oopDesc* -> void* where solaris 
is forced to pick just one. But my latest revision 
http://cr.openjdk.java.net/~eosterlund/8198561/webrev.01/ managed to get 
rid of it by introducing a new constructor accepting const volatile 
narrowOop& instead.

Thanks,
/Erik

On 2018-02-26 21:27, coleen.phillimore at oracle.com wrote:
> Yeah I forgot to ask for a comment why this is:
>
> http://cr.openjdk.java.net/~eosterlund/8198561/webrev.00/src/hotspot/share/oops/oopsHierarchy.hpp.udiff.html 
>
>
> +#ifndef SOLARIS
> + operator PrimitiveType () const { return _value; }
> +#endif
> + operator PrimitiveType () const volatile { return _value; }
>
> Thanks,
> Coleen
>
> On 2/26/18 3:11 PM, Roman Kennke wrote:
>> This is a very welcome change!
>> Changeset looks good to me (except I've no idea what the sparc part
>> does). Same question as Colleen though.
>>
>> Thanks,
>> Roman
>>
>> On Mon, Feb 26, 2018 at 8:55 PM, <coleen.phillimore at oracle.com> wrote:
>>> Hi Erik,
>>>
>>> This looks great.   I assume that the generated code (for these 
>>> classes vs.
>>> oopDesc* and juint) comes out the same?
>>>
>>> thanks,
>>> Coleen
>>>
>>>
>>> On 2/26/18 8:32 AM, Erik Österlund wrote:
>>>> Hi,
>>>>
>>>> Making oop sometimes map to class types and sometimes to primitives 
>>>> comes
>>>> with some unfortunate problems. Advantages of making them always 
>>>> have their
>>>> own type include:
>>>>
>>>> 1) Not getting compilation errors in configuration X but not Y
>>>> 2) Making it easier to adopt existing code to use Shenandoah equals
>>>> barriers
>>>> 3) Recognize oops and narrowOops safely in template
>>>>
>>>> Therefore, I would like to make both oop and narrowOop always map to a
>>>> class type consistently.
>>>>
>>>> Webrev:
>>>> http://cr.openjdk.java.net/~eosterlund/8198561/webrev.00/
>>>>
>>>> Bug:
>>>> https://bugs.openjdk.java.net/browse/JDK-8198561
>>>>
>>>> Thanks,
>>>> /Erik
>>>
>