Re: [Aarch64] Vector Function Application Binary Interface Specification for OpenMP

[Francesco Petrogalli <Francesco.Petrogalli@arm.com>]

Dear all,

I just want to let you know that we just published the final version of the Vector Function ABI specification. The call-clobbered and call-preserved lists of register has been updated (see section 2.1) .

The document is located at the same address:

https://developer.arm.com/products/software-development-tools/hpc/arm-compiler-for-hpc/vector-function-abi

Kind regards,

Francesco

> On May 16, 2018, at 11:21 AM, Steve Ellcey <sellcey@cavium.com> wrote:
> 
> On Tue, 2018-05-15 at 18:29 +0000, Francesco Petrogalli wrote:
> 
>> Hi Steve,
>> 
>> I am happy to let you know that the Vector Function ABI for AArch64
>> is now public and available via the link at [1].
>> 
>> Don’t hesitate to contact me in case you have any questions.
>> 
>> Kind regards,
>> 
>> Francesco
>> 
>> [1] https://developer.arm.com/products/software-development-tools/hpc
>> /arm-compiler-for-hpc/vector-function-abi
>> 
>>> 
>>> Steve Ellcey
>>> sellcey@cavium.com
> 
> Thanks for publishing this Francesco, it looks like the main issue for
> GCC is that the Vector Function ABI has different caller saved / callee
> saved register conventions than the standard ARM calling convention.
> 
> If I understand things correctly, in the standard calling convention
> the callee will only save the bottom 64 bits of V8-V15 and so the
> caller needs to save those registers if it is using the top half.  In
> the Vector calling convention the callee will save all 128 bits of
> these registers (and possibly more registers) so the caller does not
> have to save these registers at all, even if it is using all 128 bits
> of them.
> 
> It doesn't look like GCC has any existing mechanism for having different
> sets of caller saved/callee saved registers depending on the function
> attributes of the calling or called function.
> 
> Changing what registers a callee function saves and restores shouldn't
> be too difficult since that can be done when generating the prologue
> and epilogue code but changing what registers a caller saves/restores
> when doing the call seems trickier.  The macro
> TARGET_HARD_REGNO_CALL_PART_CLOBBERED doesn't know anything about the
> function being called.  It returns true/false depending on just the
> register number and mode.
> 
> Steve Ellcey
> sellcey@cavium.com