RFR(M) 8148047: Move the vtable length field to Klass

[Mikael Gerdin]

Hi all,

Here's the second part of the set of changes to move most of the vtable 
related code to Klass.

This change consists of the following parts:
* Move the field _vtable_len to Klass, making its accessor nonvirtual.
  -> Ensure that this does not result in any footprint regression by 
moving TRACE_DEFINE_KLASS_TRACE_ID in Klass and _itable_len in 
InstanceKlass to fill out alignment gaps.
  -> Move vtable_length_offset to Klass. Move vtable_start_offset to 
Klass to keep the code consistent. vtable_start_offset depends on the 
size of InstanceKlass and must therefore be defined outside of klass.hpp.

* Update all locations to refer to Klass::vtable_{length,start}_offset 
instead of InstanceKlass.

* Modify SA to look for _vtable_len in Klass.

* Rename CompilerToVM::Data::InstanceKlass_vtable_{length,start}_offset
and 
jdk.vm.ci.hotspot.HotSpotVMConfig.instanceKlassVtable{Length,Start}Offset to 
properly represent where the offsets are coming from.


Webrev: http://cr.openjdk.java.net/~mgerdin/8148047/webrev.0/
Bug: https://bugs.openjdk.java.net/browse/JDK-8148047

Testing: JPRT on Oracle supported platforms.

As in the previous change I've updated the PPC64 and AARCH64 ports but I 
have not tested the changes. Build and test feedback from porters is 
most welcome!

Thanks
/Mikael