RFR: 8304986: Upcall stubs should support capureCallState

[ExE Boss]

On Fri, 21 Apr 2023 18:25:32 GMT, Jorn Vernee <jvernee at openjdk.org> wrote:

> Implement captureCallState support for upcall stubs.
> 
> The method handle of an upcall stub linked with this linker option has an additional leading memory segment parameter into which the capture state (e.g. errno) should be written. After returning from Java, this value is then actually written to the corresponding execution state.

test/jdk/java/foreign/capturecallstate/TestCaptureCallState.java line 89:

> 87:         FunctionDescriptor downcallDesc = testCase.retValueLayout()
> 88:                 .map(rl -> FunctionDescriptor.of(rl, JAVA_INT, rl))
> 89:                 .orElse(FunctionDescriptor.ofVoid(JAVA_INT));

Using [`Optional::orElseGet(…)`] avoids allocating the `FunctionDescriptor` corresponding to `(int)void` when `testCase.retValueLayout()` is present:
Suggestion:

                .orElseGet(() -> FunctionDescriptor.ofVoid(JAVA_INT));


[`Optional::orElseGet(…)`]: https://docs.oracle.com/en/java/javase/20/docs/api/java.base/java/util/Optional.html#orElseGet(java.util.function.Supplier)

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PR Review Comment: https://git.openjdk.org/jdk/pull/13588#discussion_r1174607193