RFR: 8314949: linux PPC64 Big Endian: Implementation of Foreign Function & Memory API [v3]

[Jorn Vernee]

On Mon, 4 Sep 2023 12:19:42 GMT, Martin Doerr <mdoerr at openjdk.org> wrote:

>> src/java.base/share/classes/jdk/internal/foreign/abi/Binding.java line 398:
>> 
>>> 396:                 bindings.add(Binding.cast(type, int.class));
>>> 397:                 type = int.class;
>>> 398:             }
>> 
>> Part of the casts are handled here with explicit cast bindings, but the widening from int -> long, and narrowing from long -> int are handled implicitly as part of the ShiftLeft implementation. I'd much prefer if all the type conversions are handled with explicit cast bindings. This would also semantically simplify the shift operator, since it would just handle the actual shifting.
>
> I guess we would need to add additional bindings for that? Is is worth adding more just for a big endian corner case? Or can that be done with the existing ones?

A `Cast` case for int -> long and long -> int would need to be added. Given the existing setup, that should only be a few lines of code for each. (See e.g. for int -> long https://github.com/openjdk/jdk/compare/master...JornVernee:jdk:I2L). I don't think the cost is that high.

> Is is worth adding more just for a big endian corner case?

I think it's worth it in order to have a cleaner contract for the shift ops, should we want to use them for anything else in the future, but also just to make them easier to understand for future readers.

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PR Review Comment: https://git.openjdk.org/jdk/pull/15417#discussion_r1314892030