C2: Did something just happen to unrolling?

[Andrew Haley]

I'm working on a patch for AArch64 vector code, and I just rebased my patch on
mainline. The performance regression is shocking. On some machines I don't
see much difference, but on others I see almost 2*.

The cause of the difference seems to be that there is now much less unrolling,
so much that "before" I see an 8-lane vector op unrolled 8 times, and now
it's only unrolled twice.

So, does anyone here reading this have any idea what happened in the last month
or two? Did someone change the unrolling heuristics?

Thanks,

-- 
Andrew Haley  (he/him)
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
https://keybase.io/andrewhaley
EAC8 43EB D3EF DB98 CC77 2FAD A5CD 6035 332F A671