RFC: loopnode.cpp clean up

[Roman Kennke]

This looks good to me. Thanks!

Roman

> http://cr.openjdk.java.net/~roland/shenandoah/gcinterface-loopopts/webrev.00/
> 
> This change includes some more gc interface entry point that I'd like to
> propose upstream.
> 
> The one for barrier expansion from:
> 
> http://mail.openjdk.java.net/pipermail/shenandoah-dev/2018-November/008288.html
> 
> is included.
> 
> There are also a couple for loop opts so we can call our own
> passes.
> 
> Also loopnode.cpp currently includes tweaks to loop strip mining
> verification code. Strip mined loops are only fully built late in the
> optimization process and the expectation is that we don't run loop opts
> after that but with shenandoah we do. This removes most of the changes
> in loopnode.cpp related to loop strip mining. I intend to propose the
> only remaining change.
> 
> Comments?
> 
> Roland.
>