[foreign-memaccess+abi] RFR: 8275644: Replace VMReg in shuffling code with something more fine grained. [v5]

[Nick Gasson]

On Mon, 5 Sep 2022 14:34:57 GMT, Jorn Vernee <jvernee at openjdk.org> wrote:

>> This patch replaces `VMReg` with a new `VMStorage` class in the C++ code, which can be used to represent stack arguments of different sizes, as well as allowing finer grained stack addressing.
>> 
>> The old masm code that used `VMReg` for moving values is also replaced with new code that uses `VMStorage`. And `VMReg` is changed to `VMStorage` everywhere.
>> 
>> The `vmstorageBase` class was added in C++ to mirror the `jdk.internal.foreign.VMStorage`. That class now also has an additional field to encode the size of a stack argument, or a register mask, which can also be used to encode the size of a register argument. This also leads to some stubs needing to be updated on unsupported platforms.
>> 
>> Lastly, instead of encoding stack indexes as 64-bit slots as we did before, they are now encoded as byte offsets, which allows finer grained stack addressing. (this leads to a bunch of values being multiplied by 8 in the Java code as well).
>> 
>> ---
>> 
>> This change is needed to address https://bugs.openjdk.org/browse/JDK-8275584 as well as adding support for `long double` as well as more exotic ABIs that take arguments as vectors.
>
> Jorn Vernee has updated the pull request incrementally with one additional commit since the last revision:
> 
>   fix MSVC compilation

The AArch64-specific changes look sensible to me!

src/hotspot/cpu/aarch64/foreignGlobals_aarch64.cpp line 100:

> 98: }
> 99: 
> 100: constexpr int RFP_BIAS = 16; // skip old rfp and lr

Should this be `static constexpr`?

src/hotspot/cpu/aarch64/vmstorage_aarch64.inline.hpp line 25:

> 23: 
> 24: #ifndef SHARE_PRIMS_VMSTORAGE_AARCH64
> 25: #define SHARE_PRIMS_VMSTORAGE_AARCH64

Should this be `CPU_AARCH64_VMSTORAGE_AARCH64_HPP`?

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Marked as reviewed by ngasson (Committer).

PR: https://git.openjdk.org/panama-foreign/pull/699