RFR: 8303040: linux PPC64le: Implementation of Foreign Function & Memory API (Preview)

[Martin Doerr]

On Wed, 22 Feb 2023 17:03:16 GMT, Jorn Vernee <jvernee at openjdk.org> wrote:

> I will do a more thorough review soon.

Thanks a lot!

> > The ABI has some tricky corner cases related to HFA (Homogeneous Float Aggregate). The same argument may need to get passed in both, a FP reg and a GP reg or stack slot (see "no partial DW rule"). This cases are not covered by the existing tests.
> 
> FWIW, we have to do this for Windows vararg floats as well ([here](https://github.com/openjdk/jdk/blob/master/src/java.base/share/classes/jdk/internal/foreign/abi/x64/windows/CallArranger.java#L231-L239))
> 
> This can be done by `dup`-ing the value, and using 2 `vmStore`s. (each `vmStore` corresponding to a single register/stack location). Doing something similar might be simpler than the `INTEGER_AND_FLOAT` and `STACK_AND_FLOAT` storage types you're using right now. I'm not sure if that is related to the other limitations you mention? Might be interesting to look into. (perhaps as a separate RFE. I don't have a big issue since the current approach stays in PPC-only code)

Maybe I need to think a bit more about it. I don't really like the extra cases for `INTEGER_AND_FLOAT` and `STACK_AND_FLOAT`. On the other side, doing it in the CallArranger would break the design of factoring out the allocation from the binding generation.
In addition, it seems like PPC64 is even more tricky than the Windows case. I need to pass 2 float arguments in a GP reg (or stack slot) plus one of these 2 floats in float register F13. I think this can get implemented more easily in the backend. Do you agree?

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PR: https://git.openjdk.org/jdk/pull/12708