[foreign-memaccess+abi] RFR: Check for mixed access - remove mem barriers

[Paul Sandoz]

On Sat, 24 Jul 2021 16:07:09 GMT, Radoslaw Smogura <github.com+7535718+rsmogura at openjdk.org> wrote:

> That's for previous PR, which I destroyed with bad merge from master.
> 
> I wonder if this can look like this?
> 
> 
> Benchmark                               (size)  Mode  Cnt   Score    Error  Units
> ByteBufferVectorAccess.directBuffers      1024  avgt   10  27.119 ?  0.186  ns/op
> ByteBufferVectorAccess.heapBuffers        1024  avgt   10  28.501 ?  0.118  ns/op
> ByteBufferVectorAccess.pollutedBuffers    1024  avgt   10  64.354 ? 27.778  ns/op
> Finished running test 'micro:ByteBufferVectorAccess'
> 
> 
> https://github.com/openjdk/panama-foreign/pull/566

That's a neat trick, but it will not work if the heap buffer is read only. But you could extract the array (or base) using unsafe access.

It would be preferable if we can tunnel this through the intrinsic, rather than branching on buffer state. VarHandle buffer/segment accessors uniformly go through unsafe for heap and direct. So in theory it should be possible for intrinsic vector access to achieve the same degree of functionality as intrinsic unsafe access.

(Note that for any integration we need to push first to the `panama-vector/vectorIntrinsics` branch)

-------------

PR: https://git.openjdk.java.net/panama-foreign/pull/573