RFR(M) 8147461: Use byte offsets for vtable start and vtable length offsets

[Mikael Gerdin]

Hi again,

I've rebased the on hs-rt and had to include some additional changes for 
JVMCI.
I've also updated the copyright years.
Unfortunately I can't generate an incremental webrev since i rebased the 
patch and there's no good way that I know of to make that work with webrev.

New webrev at: http://cr.openjdk.java.net/~mgerdin/8147461/webrev.1/

Testing: JPRT again (which includes the JVMCI jtreg tests)

/Mikael

On 2016-01-15 18:04, Mikael Gerdin wrote:
> Hi all,
>
> As per the previous discussion in mid-December[0] about moving the
> _vtable_length field to class Klass, here's the first RFR and webrev,
> according to my suggested plan[1]:
>
>> My current plan is to first modify the vtable_length_offset accessor to
>> return a byte offset (which is what it's translated to by all callers).
>>
>> Then I'll tackle moving the _vtable_len field to Klass.
>>
>> Finally I'll try to consolidate the vtable related methods to Klass,
>> where they belong.
>
> This change actually consists of three changes:
> * modifying InstanceKlass::vtable_length_offset to become a byte offset
> and use the ByteSize type to communicate the scaling.
> * modifying InstanceKlass::vtable_start_offset to become a byte offset
> and use the ByteSize type, for symmetry reasons mainly.
> * adding a vtableEntry::size_in_bytes() since in many places the vtable
> entry size is used in combination with the vtable start to compute a
> byte offset for vtable lookups.
>
> I don't foresee any issues with the fact that the byte offset is
> represented as an int, for two reasons:
> 1) If the offset of any of these grows to over 2 gigabytes then we have
> a huge footprint problem with InstanceKlass
> 2) The offsets are converted to byte offsets and stored in ints already
> in the cpu specific code I've modified.
>
> Bug link: https://bugs.openjdk.java.net/browse/JDK-8147461
> Webrev: http://cr.openjdk.java.net/~mgerdin/8147461/webrev.0/
>
> Testing: JPRT on Oracle supported platforms, testing on AARCH64 and
> PPC64 would be much appreciated, appropriate mailing lists have been
> CC:ed to notify them of the request.
>
>
> [0]
> http://mail.openjdk.java.net/pipermail/hotspot-dev/2015-December/021152.html
>
> [1]
> http://mail.openjdk.java.net/pipermail/hotspot-dev/2015-December/021224.html
>
>
> Thanks!
> /Mikael