Using the Klass gap (Was: Master Thesis on Shenandoah)

[Martin Grajcar]

>* Am 08.11.2017 um 19:07 schrieb Dominik Inführ:*

I was pondering the idea to squeeze the fwd ptr into the so-called
> Klass-gap. This is 32 unused bits when the Klass* is compressed. It's
> only available for non-arrays, because for arrays, the array-length is
> squeezed into those 32bits.


A possibly stupid question, but shouldn't it be the other way round?

Currently, array length gets packed in a gap and you're thinking about
using the gap -- when available -- for the fwd ptr. This sounds slow and
complicated/

Can't you instead *always* use this gap for non-arrays and use a new slot
for the array length? This saves memory for non-arrays in exactly the same
way and needs no new conditional logic (I guess, arrays can already deal
with the case they need a new slot  for their length).