RFR: 8303040: linux PPC64le: Implementation of Foreign Function & Memory API (Preview) [v35]

[Richard Reingruber]

On Tue, 23 May 2023 07:37:37 GMT, Richard Reingruber <rrich at openjdk.org> wrote:

>> Martin Doerr has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Parameter Save Area is the correct name.
>
> src/hotspot/cpu/ppc/downcallLinker_ppc.cpp line 163:
> 
>> 161:   // The Parameter Save Area needs to be at least 8 slots for ABIv1.
>> 162:   // ABIv2 allows omitting it when all parameters can get passed in registers. We currently don't optimize this.
>> 163:   // For ABIv2, we only need (_input_registers.length() > 8) ? _input_registers.length() : 0
> 
> The PSA is also needed if the parameter list is variable in length. Is the expression `(_input_registers.length() > 8) ? _input_registers.length() : 0` correct in that case too?
> Otherwise: `ABIv2 allows omitting it if the callee's prototype indicates that stack parameters are not expected. We currently don't optimize this.`

Ok, I see now. This is not obvious though. There are a few layers of abstraction at play which hide this. A comment is needed. Maybe like this:
```c++
            // With ABIv1 a Parameter Save Area of at least 8 double words is always needed.
            // ABIv2 allows omitting it if the callee's prototype indicates that stack parameters are not expected.
            // We currently don't optimize this (see DowncallStubGenerator in the backend).
            if (reg == null) return stack;

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PR Review Comment: https://git.openjdk.org/jdk/pull/12708#discussion_r1201706335