[foreign-abi] RFR: 8254260: Consider splitting binding recipe operators that serve a dual role

[Jorn Vernee]

On Thu, 8 Oct 2020 20:39:14 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

>> Hi,
>> 
>> This patch splits the binding recipe operators that currently serve a dual purpose into 2 operators each:
>> - MOVE -> VM_STORE and VM_LOAD
>> - DEREFERENCE -> BUFFER_STORE and BUFFER_LOAD
>> - CONVERT_ADDRESS -> BOX_ADDRESS and UNBOX_ADDRESS
>> 
>> Note that I also added a TO_SEGMENT operator which converts a MemoryAddress into a MemorySegment. This was previously
>> done as part of the COPY operator, but only for upcalls, so I had to split out this functionality so that COPY could
>> have only one interpretation as well. This will also enable some more optimizations down the line, such as merely
>> wrapping a by-value struct passed as a pointer in a MemorySegment, instead of having to make a copy.  This also
>> regularized the use of allocators by the operators. Now an allocator is always passed as an argument, and that's what
>> is used to do allocations, instead of relying implicitly on MemorySegment::allocateNative. (The index of the allocator
>> argument is now also always passed when specializing an operator, to indicate the dependency, and so that operator
>> impls don't have to 'guess' which argument index is the allocator (see for instance the implementation of
>> Copy::specialize).  The rest of the patch is more or less a mechanical renaming, and updating the tests/CallArrangers
>> to use the different operator names.  Thanks, Jorn
>
> src/jdk.incubator.foreign/share/classes/jdk/internal/foreign/abi/CallingSequenceBuilder.java line 107:
> 
>> 105:
>> 106:     private static void verifyBoxBindings(Class<?> expectedReturnType, List<Binding> bindings) {
>> 107:         Deque<Class<?>> stack = new ArrayDeque<>();
> 
> I've seen in the code that the verifyUnbox method speaks about a `returnType` parameter - should it be an `outType` for
> symmetry (since, I guess, we use this more than just for returns - e.g. we use it for args in upcalls).

I'll change the name. FWIW, `returnType` refers to the type 'returned' by the chain of operations.

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

PR: https://git.openjdk.java.net/panama-foreign/pull/375