Re: Help with an ABI peculiarity

[Iain Sandoe <iain@sandoe.co.uk>]

Hi Richard,

> On 20 Jan 2022, at 22:32, Richard Sandiford <richard.sandiford@arm.com> wrote:
> 
> Iain Sandoe <iain@sandoe.co.uk> writes:
>>> On 10 Jan 2022, at 10:46, Richard Sandiford <richard.sandiford@arm.com> wrot>> An alternative might be to make promote_function_arg a “proper”
>>> ABI hook, taking a cumulative_args_t and a function_arg_info.
>>> Perhaps the return case should become a separate hook at the
>>> same time.
>>> 
>>> That would probably require more extensive changes than just
>>> updating the call sites, and I haven't really checked how much
>>> work it would be, but hopefully it wouldn't be too bad.
>>> 
>>> The new hook would still be called before function_arg, but that
>>> should no longer be a problem, since the new hook arguments would
>>> give the target the information it needs to decide whether the
>>> argument is passed in registers.
>> 
>> Yeah, this was my next port of call (I have looked at it ~10 times and then
>> decided “not today, maybe there’s a simpler way”).

… and I did not have a chance to look at this in the meantime …

> BTW, finally catching up on old email, I see this is essentially also
> the approach that Maxim was taking with the TARGET_FUNCTION_ARG_BOUNDARY
> patches.  What's the situation with those? 

I have the patches plus amendments to make use of their new functionality on the
development branch, which is actually in pretty good shape (not much difference
in testsuite results from other Darwin sub-ports).

Maxim and I need to discuss amending the TARGET_FUNCTION_ARG_BOUNDARY
changes to account for Richard (B)’s comments.

Likewise, I need to tweak the support for heap allocation of nested function trampolines
to account for review comments.

As always, it’s a question of fitting everything in…
thanks
Iain