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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



  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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