RFR[L]: 8237767 Field layout computation overhaul

[Aleksey Shipilev]

On 2/3/20 5:33 PM, Aleksey Shipilev wrote:
> As I look through the layouter going through my local Maven Central snapshot, this case does not
> look rare for us not to care. Looks like every class with a long and 3+ oop fields is regressing in
> instance size, which is in line with your explanation. I believe this needs to be resolved before
> releasing the new layouter in the wild.

To add some more data, out of ~15M classes, about 14K (~0.01%) are affected:
  https://cr.openjdk.java.net/~shade/8237767/classes-regression-1.txt

Of course, this does not mean we would have 0.01% footprint regression, because we don't know how
many instances of the affected class would be present. But browsing the list, it looks like plenty
of data classes, iterators, etc present.

For fun, here is some friendly fire: org.openjdk.tools.javac.code.Symbol -- it has long
Symbol.flags_field and plenty of oop fields.

-- 
Thanks,
-Aleksey