RFR: 8221732: Introduce CollectedHeap::hash_oop()

[Per Liden]

Thanks Stefan!

/Per

On 4/1/19 1:04 PM, Stefan Karlsson wrote:
> Looks good.
> 
> StefanK
> 
> On 2019-04-01 09:39, Per Liden wrote:
>> The JVMTITagMap hashes oops by casts them to 32-bit unsigned integers. 
>> For ZGC, which has colored oop, this happens to work because all 
>> metadata bits are above 32-bit. In theory, ZGC could store its 
>> metadata bits in the lower 32-bit part of the address, in which case 
>> this hash scheme would break. Today we have an ugly assert in 
>> JvmtiTagHashmap::hash() to make sure this doesn't happen. However, the 
>> JVMITagMap should not make assumptions on what an oop looks like, and 
>> should instead delegate this hashing to CollectedHeap.
>>
>> Bug: https://bugs.openjdk.java.net/browse/JDK-8221732
>> Webrev: http://cr.openjdk.java.net/~pliden/8221732/webrev.0
>>
>> /Per