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

[Jorn Vernee]

On Wed, 7 Oct 2020 11:39:50 GMT, Maurizio Cimadamore <mcimadamore 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).

Marked as reviewed by jvernee (Committer).

src/jdk.incubator.foreign/share/classes/jdk/internal/foreign/PlatformLayouts.java line 100:

> 98:      * @return the newly created ValueLayout
> 99:      */
> 100:     public static ValueLayout ofPointer(ByteOrder order, long bitSize) {

Looks like this can be private? (and in that case I think it's okay to drop the javadoc as well, since none of the
other factories have it either.)

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?

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