From: Paul Koning <paulkoning@comcast.net>
To: Iain Sandoe <iain@sandoe.co.uk>
Cc: GCC Development <gcc@gcc.gnu.org>
Subject: Re: Help with an ABI peculiarity
Date: Fri, 7 Jan 2022 16:55:06 -0500 [thread overview]
Message-ID: <DB1CB1BA-486C-4940-B824-FEC2ED9AD7EE@comcast.net> (raw)
In-Reply-To: <CD187C76-0620-457C-A0B7-B4ADBB6014FB@sandoe.co.uk>
> On Jan 7, 2022, at 4:06 PM, Iain Sandoe <iain@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
next prev parent reply other threads:[~2022-01-07 21:55 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-07 21:06 Iain Sandoe
2022-01-07 21:55 ` Paul Koning [this message]
2022-01-08 16:35 ` Jeff Law
2022-01-10 8:38 ` Florian Weimer
2022-01-10 13:27 ` Iain Sandoe
2022-01-10 13:46 ` Florian Weimer
2022-01-11 12:53 ` Eric Gallager
2022-01-11 11:57 ` Richard Earnshaw
2022-01-10 10:46 ` Richard Sandiford
2022-01-10 13:06 ` Iain Sandoe
2022-01-20 22:32 ` Richard Sandiford
2022-01-21 11:19 ` Iain Sandoe
2022-01-21 12:22 ` Richard Sandiford
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