RFR: Fix full-gc matrix updates

[Aleksey Shipilev]

On 03/17/2017 10:16 PM, Roman Kennke wrote:
> Am 17.03.2017 um 22:10 schrieb Roman Kennke:
>> Am 17.03.2017 um 22:02 schrieb Roman Kennke:
>>> When running the adjust-pointers pass in full-gc, we're also updating
>>> the matrix. We're using the current oop* for from-region, and the new
>>> location of the object for to-region. However, the from-object is also
>>> going to move! We need to take this into account.
>>>
>>> It's fixed by computing the offset of the from-object and its new
>>> location, and subtracting this from the from-pointer in the closure.
>>>
>>> I also snuck in two minor improvements:
>>> - Remove some old redundant code (from last patch)
>>> - use encode_store_heap_oop_not_null() instead of encode_store_heap_oop().
>>>
>>> http://cr.openjdk.java.net/~rkennke/partial-fixfullgc/webrev.00/
>>> <http://cr.openjdk.java.net/%7Erkennke/partial-fixfullgc/webrev.00/>
>>>
>>> Ok?
>>>
>>> Roman
>>>
>>>
>> Two little changes:
>> - Use size_t instead of int, in case we need to address large memory.
>> - Don't cast HeapWord* to oop, just to cast it back to HeapWord*. ;-)
>>
>> http://cr.openjdk.java.net/~rkennke/partial-fixfullgc/webrev.01/
>> <http://cr.openjdk.java.net/%7Erkennke/partial-fixfullgc/webrev.01/>
> Ok, another last change (sorry, it's almost weekend), as chf suggested
> on IRC, let's use pointer_delta() instead of pointer subtraction.
> 
> http://cr.openjdk.java.net/~rkennke/partial-fixfullgc/webrev.02/

Put a comment there why this is safe, and we are good to go.

Thanks,
-Aleksey