> On Jan 7, 2022, at 4:06 PM, Iain Sandoe <i...@sandoe.co.uk> wrote:
>
> Hi Folks,
>
> In the aarch64 Darwin ABI we have an unusual (OK, several unusual) feature of
> the calling convention.
>
> When an argument is passed *in a register* and it is integral and less than
> SI it is promoted (with appropriate signedness) to SI. This applies when the
> function parm is named only.
>
> When the same argument would be placed on the stack (i.e. we ran out of
> registers) - it occupies its natural size, and is naturally aligned (so, for
> instance, 3 QI values could be passed as 3 registers - promoted to SI .. or
> packed into three adjacent bytes on the stack)..
>
> The key is that we need to know that the argument will be placed in a
> register before we decide whether to promote it.
> (similarly, the promotion is not done in the callee for the in-register case).
>
> I am trying to figure out where to implement this.
I don't remember the MIPS machinery well enough, but is that a similar case?
It too has register arguments (4 or 8 of them) along with stack arguments (for
the rest).
paul
