RFR: some C2 cleanup

[Aleksey Shipilev]

On 10/09/2018 09:48 AM, Roland Westrelin wrote:
> http://cr.openjdk.java.net/~roland/shenandoah/c2-cleanups/webrev.00/

Looks nice! Roman might want to take a look too.

Minor nits:

 *) Let's make the flag diagnostic, and description less specific: "Try to reuse after-barrier
values to reduce register pressure":

 431   product(bool, ShenandoahDecreaseRegisterPressure, false,                  \
 432           "Try to use v'=rb(v) instead of v to not keep both v and v' live")\

Thanks,
-Aleksey