RFR(L) Take 2 of Valhalla support for AArch64

[Tobias Hartmann]

Hi Dmitry,

this looks good to me but probably someone more familiar with the aarch64 architecture should have a
look as well.

Please don't completely remove the @requires os.simpleArch from the tests because we still don't
want to run them on other architectures like Sparc or ppc.

On 27.03.19 16:14, Dmitry Samersoff wrote:
> 2. Support for ValueTypePassFieldsAsArgs and ValueTypeReturnedAsFields
> is implemented but there are some issues
> 
>   I'll send a separate letter about it. I'll be happy if someone with
> good C2 knowledge chimes in with thoughts on it

I can help with that.

Unfortunately, the implementation is quite complex and things might change depending on how we
decide to handle null-ok value types in the feature. I also have some cleanup/refactoring related to
the calling convention on my To-Do list.

> 3. One test still fails
> 
>    compiler/valhalla/valuetypes/TestNewAcmp.java (one test within it)

We also see failures in our testing that are due to the interpreter not yet implementing the
substitutability test (only C2) does.

Best regards,
Tobias