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From: Wilco Dijkstra <Wilco.Dijkstra@arm.com>
To: Richard Sandiford <Richard.Sandiford@arm.com>
Cc: GCC Patches <gcc-patches@gcc.gnu.org>,
	Kyrylo Tkachov <Kyrylo.Tkachov@arm.com>
Subject: Re: [PATCH] AArch64: Improve immediate expansion [PR105928]
Date: Tue, 19 Sep 2023 12:57:58 +0000	[thread overview]
Message-ID: <PAWPR08MB898295C7C7EF0E409EF13BE883FAA@PAWPR08MB8982.eurprd08.prod.outlook.com> (raw)
In-Reply-To: <mptled2im3l.fsf@arm.com>

Hi Richard,

>> Note that aarch64_internal_mov_immediate may be called after reload,
>> so it would end up even more complex.
>
> The sequence I quoted was supposed to work before and after reload.  The:
>
>                rtx tmp = aarch64_target_reg (dest, DImode);
>
> would create a fresh temporary before reload and reuse dest otherwise.
> So the sequence after reload would be the same as in your patch,
> but the sequence before reload would use a temporary.

aarch64_target_reg just returns the input register so it won't do that.
Also the movsi/movdi patterns only split if the destination register is physical.
That's typically after register allocation but not uniformly so (eg. immediates in
returns will get split early), which is inconsistent. Given we always emit register
notes it's not obvious whether splitting early or late is better overall.

Cheers,
Wilco

      reply	other threads:[~2023-09-19 12:58 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-09-14 15:24 Wilco Dijkstra
2023-09-17 11:04 ` Richard Sandiford
2023-09-18 17:41   ` Wilco Dijkstra
2023-09-19  8:49     ` Richard Sandiford
2023-09-19 12:57       ` Wilco Dijkstra [this message]

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