[foreign-abi] RFR: 8254156: Simplify ABI classification logic

[Maurizio Cimadamore]

On Wed, 7 Oct 2020 11:50:37 GMT, Jorn Vernee <jvernee at openjdk.org> wrote:

>> This patch reverts recent changes to introduce a public CValueLayout class; the realization here is that, after all,
>> CValueLayout exposes a public `Type` enum which is used by ABI classification. So, instead of using subclassing (which
>> is messy and tedious with immutable data structures with covariant overrides), let's just double down on layout
>> attributes, get rid of CValueLayout and simply expose the Type enum (now renamed to TypeKind).
>
> src/jdk.incubator.foreign/share/classes/jdk/internal/foreign/abi/aarch64/TypeClass.java line 46:
> 
>> 44:     private static TypeClass classifyValueType(ValueLayout type) {
>> 45:         CLinker.TypeKind kind = (CLinker.TypeKind)type.attribute(CLinker.TypeKind.ATTR_NAME).orElseThrow(
>> 46:                 () -> { throw new IllegalStateException("Unexpected value layout: could not determine ABI class");
>> });
> 
> Note that orElseThrow takes a `Supplier<Throwable>` (basically), so this can be simplified to return the new exception
> instance instead of throwing it.
> Also, this code is copied in the other TypeClass classes, so might be good to create a helper method in SharedUtils for
> it instead?

Done

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PR: https://git.openjdk.java.net/panama-foreign/pull/371