From: Martin Uecker <muecker@gwdg.de>
To: "Rafał Pietrak" <embedded@ztk-rp.eu>,
"gcc@gcc.gnu.org" <gcc@gcc.gnu.org>
Subject: Re: wishlist: support for shorter pointers
Date: Wed, 28 Jun 2023 15:00:26 +0200 [thread overview]
Message-ID: <112e711791835d56cca38654f83a009cb46707d4.camel@gwdg.de> (raw)
In-Reply-To: <439affd4-11fe-de80-94c8-6fc64cbf76ec@ztk-rp.eu>
Sounds like named address spaces to me:
https://gcc.gnu.org/onlinedocs/gcc/Named-Address-Spaces.html
Best,
Martin
Am Dienstag, dem 27.06.2023 um 14:26 +0200 schrieb Rafał Pietrak via Gcc:
> Hello everybody,
>
> I'm not quite sure if this is correct mailbox for this suggestion (may
> be "embedded" would be better), but let me present it first (and while
> the examples is from ARM stm32 environment, the issue would equally
> apply to i386 or even amd64). So:
>
> 1. Small MPU (like stm32f103) would normally have small amount of RAM,
> and even somewhat larger variant do have its memory "partitioned/
> dedicated" to various subsystems (like CloseCoupledMemory, Ethernet
> buffers, USB buffs, etc).
>
> 2. to address any location within those sections of that memory (or
> their entire RAM) it would suffice to use 16-bit pointers.
>
> 3. still, declaring a pointer in GCC always allocate "natural" size of a
> pointer in given architecture. In case of ARM stm32 it would be 32-bits.
>
> 4. programs using pointers do keep them around in structures. So
> programs with heavy use of pointers have those structures like 2 times
> larger then necessary .... if only pointers were 16-bit. And memory in
> those devices is scarce.
>
> 5. the same thing applies to 64-bit world. Programs that don't require
> huge memories but do use pointers excessively, MUST take up 64-bit for a
> pointer no matter what.
>
> So I was wondering if it would be feasible for GCC to allow SEGMENT to
> be declared as "small" (like 16-bit addressable in 32-bit CPU, or 32-bit
> addressable in 64-bit CPU), and ANY pointer declared to reference
> location within them would then be appropriately reduced.
>
> In ARM world, the use of such pointers would require the use of an
> additional register (functionally being a "segment base address") to
> allow for data access using instructions like: "LD Rx, [Ry, Rz]" -
> meaning register index reference. Here Ry is the base of the SEGMENT in
> question. Or if (like inside a loop) the structure "pointed to" by Rz
> must be often used, just one operation "ADD Rz, Ry" will prep Rz for
> subsequent "ordinary" offset operations like: "LD Ra, [Rz, #member]" ...
> and reentering the loop by "LDH Rz, [Rz, #next]" does what's required by
> "x = x->next".
>
> Not having any experience in compiler implementations I have no idea if
> this is a big or a small change to compiler design.
>
> -R
next prev parent reply other threads:[~2023-06-28 13:00 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-27 12:26 Rafał Pietrak
2023-06-28 1:54 ` waffl3x
2023-06-28 7:13 ` Rafał Pietrak
2023-06-28 7:31 ` Jonathan Wakely
2023-06-28 8:35 ` Rafał Pietrak
2023-06-28 9:56 ` waffl3x
2023-06-28 10:43 ` Rafał Pietrak
2023-06-28 12:12 ` waffl3x
2023-06-28 12:23 ` Rafał Pietrak
2023-07-03 14:52 ` David Brown
2023-07-03 16:29 ` Rafał Pietrak
2023-07-04 14:20 ` Rafał Pietrak
2023-07-04 15:13 ` David Brown
2023-07-04 16:15 ` Rafał Pietrak
2023-06-28 7:34 ` waffl3x
2023-06-28 8:41 ` Rafał Pietrak
2023-06-28 13:00 ` Martin Uecker [this message]
2023-06-28 14:51 ` Rafał Pietrak
2023-06-28 15:44 ` Richard Earnshaw (lists)
2023-06-28 16:07 ` Martin Uecker
2023-06-28 16:49 ` Richard Earnshaw (lists)
2023-06-28 17:00 ` Martin Uecker
2023-06-28 16:48 ` Rafał Pietrak
2023-06-29 6:19 ` Rafał Pietrak
2023-07-03 15:07 ` Ian Lance Taylor
2023-07-03 16:42 ` Rafał Pietrak
2023-07-03 16:57 ` Richard Earnshaw (lists)
2023-07-03 17:34 ` Rafał Pietrak
2023-07-04 12:38 ` David Brown
2023-07-04 12:57 ` Oleg Endo
2023-07-04 14:46 ` Rafał Pietrak
2023-07-04 15:55 ` David Brown
2023-07-04 16:20 ` Rafał Pietrak
2023-07-04 22:57 ` Martin Uecker
2023-07-05 5:26 ` Rafał Pietrak
2023-07-05 7:29 ` Martin Uecker
2023-07-05 8:05 ` Rafał Pietrak
2023-07-05 9:11 ` David Brown
2023-07-05 9:25 ` Martin Uecker
2023-07-05 11:34 ` David Brown
2023-07-05 12:01 ` Martin Uecker
2023-07-05 9:42 ` Rafał Pietrak
2023-07-05 11:55 ` David Brown
2023-07-05 12:25 ` Rafał Pietrak
2023-07-05 12:57 ` David Brown
2023-07-05 13:29 ` Rafał Pietrak
2023-07-05 14:45 ` David Brown
2023-07-05 16:13 ` Rafał Pietrak
2023-07-05 17:39 ` David Brown
2023-07-06 7:00 ` Rafał Pietrak
2023-07-06 12:53 ` David Brown
2023-07-05 9:29 ` Martin Uecker
2023-07-05 10:17 ` Rafał Pietrak
2023-07-05 10:48 ` Martin Uecker
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