linux-kernel - Re: [PATCH] sh: use generic uaccess

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Message-Id: <8d37ad26-efdf-4e10-9a72-d49e37de0307@app.fastmail.com>
Date: Tue, 23 Jan 2024 15:14:04 +0100
From: "Arnd Bergmann" <arnd@...db.de>
To: "John Paul Adrian Glaubitz" <glaubitz@...sik.fu-berlin.de>,
 "Arnd Bergmann" <arnd@...nel.org>,
 "Yoshinori Sato" <ysato@...rs.sourceforge.jp>,
 "Rich Felker" <dalias@...c.org>
Cc: linux-sh@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-riscv@...ts.infradead.org
Subject: Re: [PATCH] sh: use generic uaccess

On Tue, Jan 23, 2024, at 14:55, John Paul Adrian Glaubitz wrote:
>
> Wouldn't that make these operations slower or do you think that GCC is able
> to optimize this well enough?

It's only single load/store instructions, so it should make no
difference. If anything, the generic code should allow the compiler
to have better register allocation and produce better output than
the assembler version (which is how this avoids the ICE), but it's
unlikely to be noticeably either.

> Also, this is something that should definitely be boot-tested to make sure
> this doesn't introduce any regressions.

Agree.

      Arnd