Perf: SATB and WB coalescing

[Aleksey Shipilev]

On 01/10/2018 12:12 PM, Roman Kennke wrote:
> That confirms what I suspected since a while. And I also sorta hope that the traversal GC will solve
> it, because it only ever polls a single flag. We might even want to wrap RBs into evac-flag-checks
> initially, so that the optimizer can coalesce them too, and remove lone evac-checks-around-RBs after
> optimization.

Let's not conflate this with traversal GC: flag handling and coalescing barriers in important even
for our regular cycle. So I'd rather improve that part of the story, and then build traversal GC on top.

Do you have a separate patch that introduces a single flag instead of the assortment of
{mark,evac,updaterefs}-in-progress and fixes all the uses around? That would be a base for further
compiler optimizations, I think.

Thanks,
-Aleksey