[foreign] RFR: 8223808: initial port for AArch64

[Nick Gasson]

Hi Jorn and Maurizio,

Thanks for the feedback!

>>
>> If r8 is the first integer argument register this would work, but this 
>> doesn't seem to be the case? I think a quick-fix for this is adding a 
>> sorting pass of the bindings by storage index to 
>> CallingSequenceBuilder::build. 

This works but now it seems a bit of a kludge as r8 isn't normally an 
integer argument register.

> 
> Right - it seems like we should have separate treatment for return in 
> memory bindings in CallingSequenceBuilder too - e.g. instead of assume 
> that we can just add another argument binding for it, we should add a 
> 'return in memory' binding (which then on Windows/SysV will just 
> delegate to addArgumentBindings).
> 

Do you mean add a separate BindingsComputer for returns in memroy bindings?

I tried a different approach today of adding a new StorageClass 
INDIRECT_RESULT_REGISTER that is used in StorageCalculator::addBindings 
if forArguments && arg.argumentIndex() == -1. And then in 
universalNativeInvoker_aarch64.cpp we can load this directly into r8.

This seems quite neat to me, and adding a new storage class matches the 
ABI document more closely. Although we need to change the x86 to ignore 
this class.

With the changes to box/unboxValue from Windowsx64ABI, the 
StructByValueTest case passes now. If you're happy with this approach I 
can tidy it up and update the webrev?


Thanks,
Nick