[foreign-memaccess] RFR 8225172: Add way to create deref VarHandles without using the Layout API

[Jorn Vernee]

Forgot to 'hg add' one file. See updated webrev: 
http://cr.openjdk.java.net/~jvernee/panama/webrevs/8225172/webrev.02/

Thanks,
Jorn

Jorn Vernee schreef op 2019-06-03 18:38:
> Hi,
> 
> I've implemented an alternative way of creating memory access
> VarHandles, which bypasses the Layout API. One reason for having such
> an alternative API is that it offers users the opportunity to use
> their own (pre-existing) layout APIs when creating VarHandles. This
> mainly consists of a builder API called MemoryAccessVarHandleBuilder,
> which can be used similarly to LayoutPath to construct a VarHandle.
> 
> As a side effect I've removed the dependency on Layout/LayoutPath from
> VarHandles::makeMemoryAddressViewHandle. I think this decoupling makes
> this API point more suited to what's possible to do with memory access
> VarHandles.
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8225172
> Webrev: 
> http://cr.openjdk.java.net/~jvernee/panama/webrevs/8225172/webrev.01/
> 
> Added tests are pretty minimal since the resulting VarHandle is
> already tested by the existing tests using the Layout API.
> 
> This also opens up the possibility of removing the Layout API
> altogether if we wanted. Another TODO is adding a way to disable
> alignment checking upon access (which would need changes to the
> VarHandle impl classes I think).
> 
> Thanks,
> Jorn