RFR(M) 8208999 Some use of Klass* should be replaced by InstanceKlass*

[coleen.phillimore at oracle.com]

On 8/7/18 2:35 PM, Ioi Lam wrote:
>
>
> On 8/7/18 5:30 AM, coleen.phillimore at oracle.com wrote:
>>
>>
>> On 8/7/18 12:31 AM, Ioi Lam wrote:
>>> Hi Coleen,
>>>
>>> Thanks for the review. Updated webrev is here:
>>>
>>> http://cr.openjdk.java.net/~iklam/jdk12/8208999_klass_should_be_instanceklass.v02/ 
>>>
>>>
>>> More comments below
>>>
>>>
>>> On 8/6/18 3:36 PM, coleen.phillimore at oracle.com wrote:
>>>>
>>>> http://cr.openjdk.java.net/~iklam/jdk12/8208999_klass_should_be_instanceklass.v01/src/hotspot/share/classfile/systemDictionaryShared.cpp.udiff.html 
>>>>
>>>>
>>>> 1007 return entry != NULL ? entry->instance_klass() : 
>>>> (InstanceKlass*)NULL;
>>>>
>>>> do you need this cast here?
>>>>
>>> Removed.
>>>> http://cr.openjdk.java.net/~iklam/jdk12/8208999_klass_should_be_instanceklass.v01/src/hotspot/share/memory/metadataFactory.hpp.udiff.html 
>>>>
>>>>
>>>> + static void free_array(ClassLoaderData* loader_data, const 
>>>> Array<T>* data) {
>>>>
>>>>
>>>> But we are modifying the contents of the data (?).  This is for 
>>>> deleting secondary_supers?   I think maybe adding the const for 
>>>> them might be overkill.
>>>>
>>>> http://cr.openjdk.java.net/~iklam/jdk12/8208999_klass_should_be_instanceklass.v01/src/hotspot/share/oops/klass.hpp.udiff.html 
>>>>
>>>>
>>>> - Array<Klass*>* _secondary_supers;
>>>> + const Array<Klass*>* _secondary_supers;
>>>>
>>>> I think the improvement outweighs this messy part of this. This 
>>>> looks like a difficult thing to change.
>>>>
>>> I agree. I reverted the "const" for Klass::secondary_supers. I also 
>>> removed Array::as_const_array_of() since that will probably be 
>>> abused by people who don't read the comments. Instead, I added this 
>>> in InstanceKlass::compute_secondary_supers:
>>>
>>> set_secondary_supers((Array<Klass*>*)(address)interfaces);
>>>
>>> it's a little ugly but the effects are localized.
>>
>> I agree, and you can have a short comment above just that part why 
>> the cast is needed, and the if statement where you cast them both to 
>> address?
>>
>
>
> I added these comments. What do you think?
>
>     // The secondary super list is exactly the same as the transitive 
> interfaces, so
>     // let's use it instead of making a copy.
>     // Redefine classes has to be careful not to delete this!
>     // We need the cast because Array<Klass*> is NOT a supertype of 
> Array<InstanceKlass*>,
>     // (but it's safe to do here because we won't write into 
> _secondary_supers from this point on).
> set_secondary_supers((Array<Klass*>*)(address)interfaces);
>
>   if (secondary_supers() != NULL &&
>       secondary_supers() != Universe::the_empty_klass_array() &&
>       // see comments in compute_secondary_supers about the following 
> cast
>       (address)(secondary_supers()) != 
> (address)(transitive_interfaces()) &&
>

Yes, this looks good. thank you for adding the comments.
Coleen

>
> Thanks
> - Ioi
>
>
>> The as_const_array_of() will just give someone to something to puzzle 
>> over in the future without really increasing safety in my opinion.
>>>
>>>> http://cr.openjdk.java.net/~iklam/jdk12/8208999_klass_should_be_instanceklass.v01/src/hotspot/share/oops/arrayKlass.cpp.udiff.html 
>>>>
>>>>
>>>> + set_super(Universe::is_bootstrapping() ? (InstanceKlass*)NULL : 
>>>> SystemDictionary::Object_klass());
>>>>
>>>>
>>>> Do you need this cast?  Object_klass() returns InstanceKlass - all 
>>>> of these do.
>>>>
>>> Removed.
>>
>> Thanks!  Thank you for doing this change!
>> Coleen
>>>
>>> Thanks
>>> - Ioi
>>>
>>>>
>>>> This looks really good. Thank you for doing this!
>>>>
>>>> Coleen
>>>>
>>>>
>>>>
>>>> On 8/6/18 5:26 PM, Ioi Lam wrote:
>>>>> Hi, please review this clean up
>>>>>
>>>>> https://bugs.openjdk.java.net/browse/JDK-8208999
>>>>> http://cr.openjdk.java.net/~iklam/jdk12/8208999_klass_should_be_instanceklass.v01/ 
>>>>>
>>>>>
>>>>> I changed the following APIs so that we can avoid many unnecessary 
>>>>> type casts
>>>>> from Klass* -> InstanceKlass*.
>>>>>
>>>>>     Klass::java_super()                    -> now returns 
>>>>> InstanceKlass*
>>>>>     InstanceKlass::local_interfaces()      -> Array<InstanceKlass*>*
>>>>>     InstanceKlass::transitive_interfaces() -> Array<InstanceKlass*>*
>>>>>
>>>>> I also modified APIs in SystemSictionary and SystemSictionary to 
>>>>> return InstanceKlass*
>>>>> where possible.
>>>>>
>>>>> Most changes are mundane, but here are some notable changes:
>>>>>
>>>>> 1. To save space, Klass::_secondary_supers (an Array<Klass*>*) may 
>>>>> be pointing
>>>>>    to the same array as InstanceKlass::_transitive_interfaces (an
>>>>>    Array<InstanceKlass*>*).
>>>>>
>>>>>    To make this happen, I added Array::as_const_array_of().
>>>>>    See InstanceKlass::compute_secondary_supers() and array.h.
>>>>>
>>>>>    I've added enough 'const' and asserts to catch mis-uses of this 
>>>>> type
>>>>>    of casting. If someone has a better suggestion, please let me 
>>>>> know.
>>>>>
>>>>> 2. I changed Klass::_secondary_supers to 'const Array<Klass*>*' 
>>>>> because
>>>>>    of #1.
>>>>>
>>>>>    There are many pointers returned by Klass/InstanceKlass that 
>>>>> should be
>>>>>    'const', as most callers should read them only without 
>>>>> modifying, but that's
>>>>>    outside the scope of this RFE.
>>>>>
>>>>> 3. SystemDictionary::resolve_super_or_fail() currently accepts the 
>>>>> format
>>>>>    of "Ljava/lang/Object;" for the "super_name" parameter. I am 
>>>>> keeping the
>>>>>    same behavior in my patch. However, I wonder if this actually 
>>>>> correct
>>>>>    per JVMLS. I filed JDK-8209030.
>>>>>
>>>>>    See the call to resolve_instance_class_or_null_helper from 
>>>>> resolve_super_or_fail.
>>>>>
>>>>>
>>>>> Testing: hs tiers 1/2/3/4
>>>>>
>>>>> Thanks
>>>>> - Ioi
>>>>
>>>
>>
>