JDK 9 rampdown and a plea for mercy

[Roland Westrelin]

> Roland has had a look at what is happening, and he thinks that this
> can be fixed fairly quickly: he already has a working patch.  Is there
> any way that we can get it in?

The 3 changes I think are needed are:

- we add MemBarCPUOrder around accesses when we don't know whether they
  are on heap or off heap (i.e. if base == null or not). That hurts
  optimizations a lot. I'd like to enable profiling of arguments at
  calls to unsafe methods so we can have speculative data on base and
  can then null check it if profiling tells us it's not null.

- We add MemBarCPUOrder around all "mismatched" accesses (integer write
  to byte array). That seems too strong to me for arrays. I'd like to
  relax that.

- There's an addressing shape that's not supported by superword that
  prevent vectorization from triggering with ByteBuffers. I think that
  can be fixed.

Roland.