RFR (S) 8222766: Shenandoah: streamline post-LRB CAS barrier

[Roman Kennke]

Hi Aleksey,

This looks good to me. One minor nit:

609   // to-space, and memory pointer is to-space as well. Nothing is 
able to store
610   // to-space ptr into memory anymore.

Should be: Nothing is able to store from-space ptr into memory anymore.

Also:

626   // and promote the result. Note that we handle the flag from any 
the CASes
627   // either from fast-path or retries.

'from any *of* the CASes'

I don't need to see it again for this.

Thanks,
Roman