From: Wilco Dijkstra <Wilco.Dijkstra@arm.com>
To: Kyrylo Tkachov <Kyrylo.Tkachov@arm.com>,
GCC Patches <gcc-patches@gcc.gnu.org>
Cc: Richard Sandiford <Richard.Sandiford@arm.com>,
Richard Earnshaw <Richard.Earnshaw@arm.com>
Subject: Re: [PATCH] AArch64: Cleanup memset expansion
Date: Fri, 10 Nov 2023 10:17:36 +0000 [thread overview]
Message-ID: <PAWPR08MB898208A63C705C93E1DF86DF83AEA@PAWPR08MB8982.eurprd08.prod.outlook.com> (raw)
In-Reply-To: <PAXPR08MB69265FEE42BFED937A5D977A93AEA@PAXPR08MB6926.eurprd08.prod.outlook.com>
Hi Kyrill,
> + /* Reduce the maximum size with -Os. */
> + if (optimize_function_for_size_p (cfun))
> + max_set_size = 96;
> +
> .... This is a new "magic" number in this code. It looks sensible, but how did you arrive at it?
We need 1 instruction to create the value to store (DUP or MOVI) and 1 STP
for every 32 bytes, so the 96 means 4 instructions for typical sizes (sizes not
a multiple of 16 can add one extra instruction).
I checked codesize on SPECINT2017, and 96 had practically identical size.
Using 128 would also be a reasonable Os value with a very slight size increase,
and 384 looks good for O2 - however I didn't want to tune these values as this
is a cleanup patch.
Cheers,
Wilco
next prev parent reply other threads:[~2023-11-10 10:17 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-19 12:51 Wilco Dijkstra
2023-11-06 12:11 ` Wilco Dijkstra
2023-11-10 9:50 ` Kyrylo Tkachov
2023-11-10 10:17 ` Wilco Dijkstra [this message]
2023-11-10 11:30 ` Richard Earnshaw
2023-11-10 14:46 ` Kyrylo Tkachov
2023-11-10 15:13 ` Richard Earnshaw
2023-11-14 16:23 ` [PATCH v2] " Wilco Dijkstra
2023-11-14 16:36 ` Richard Earnshaw
2023-11-14 16:56 ` Wilco Dijkstra
2023-12-22 14:25 ` [PATCH v3] " Wilco Dijkstra
2024-01-05 10:53 ` Richard Sandiford
2024-01-09 20:51 ` [PATCH v4] " Wilco Dijkstra
2024-01-10 18:13 ` Richard Sandiford
2024-01-30 15:51 ` Wilco Dijkstra
2024-02-01 17:32 ` Richard Sandiford
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