RFR(XS): 8209686: cleanup arguments to PhaseIdealLoop() constructor

[Per Liden]

Hi Roland,

On 08/20/2018 10:32 AM, Roland Westrelin wrote:
> 
> http://cr.openjdk.java.net/~roland/8209686/webrev.00/

Do we really want to encode ZGC into LoopOptsZgcLastRound? Shouldn't it 
be just LoopOptsLastRound? I'm thinking this has little to do with ZGC, 
except that ZGC happens to be the only user of it at the moment.

cheers,
Per

> 
> Instead of using 3 boolean arguments to PhaseIdealLoop(), I propose
> using a single enum argument that designate what level of loop opts to
> execute. This is another small change from the shenandoah repo where we
> have a few extra ways of triggering loop opts.
> 
> Roland.
>