[RFR] (M) 8143608: Don't 64-bit align start of InstanceKlass vtable, itable, and nonstatic_oopmap on 32-bit systems

[Chris Plummer]

Hello,

Please review the following:

https://bugs.openjdk.java.net/browse/JDK-8143608
http://cr.openjdk.java.net/~cjplummer/8143608/webrev.00/webrev.hotspot/

A bit of background would help. The InstanceKlass object has a number of 
variable length fields that are laid out after the declared fields. When 
an InstanceKlass object is allocated, extra memory is allocated for it 
to leave room for these fields. The first three of these fields are 
vtable, itable, and nonstatic_oopmap. They are all arrays of HeapWord 
sized values, which means void* size, which means they only need 32-bit 
alignment on 32-bit systems. However, they have always been 64-bit 
aligned. This webrev removes the forced 64-bit alignment on 32-bit 
systems, saving footprint.

This change affects all 32-bit platforms. It should have no net impact 
on 64-bit platforms since the fields remain (naturally) 64-bit aligned 
(unless of course I've introduced a bug). The intent is to not change 
what is done for 64-bit platforms.

BTW, there is a change to AARCH64, which may seem odd at first. It just 
removes an "if" block where the condition should always have evaluated 
to false, so it should have no net affect.

Tested with JPRT "-testset hotspot". Please let me know if you think 
there are any additional tests that should be run.

thanks,

Chris