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Message-ID: <CAMuHMdULzic+NC+PA7fOZzaXbJnmW+MfCv05j3xJdj1qxPeyQQ@mail.gmail.com>
Date: Tue, 2 Jan 2024 11:49:03 +0100
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Vincent Mailhol <mailhol.vincent@...adoo.fr>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org,
Yury Norov <yury.norov@...il.com>, Nick Desaulniers <ndesaulniers@...gle.com>,
Douglas Anderson <dianders@...omium.org>, Kees Cook <keescook@...omium.org>,
Petr Mladek <pmladek@...e.com>, Randy Dunlap <rdunlap@...radead.org>,
Zhaoyang Huang <zhaoyang.huang@...soc.com>, Geert Uytterhoeven <geert+renesas@...der.be>,
Marco Elver <elver@...gle.com>, Brian Cain <bcain@...cinc.com>,
Matthew Wilcox <willy@...radead.org>, "Paul E . McKenney" <paulmck@...nel.org>, linux-hexagon@...r.kernel.org,
linux-m68k@...ts.linux-m68k.org
Subject: Re: [PATCH v3 2/5] m68k/bitops: use __builtin_{clz,ctzl,ffs} to
evaluate constant expressions
On Sun, Dec 17, 2023 at 8:13 AM Vincent Mailhol
<mailhol.vincent@...adoo.fr> wrote:
>
> The compiler is not able to do constant folding on "asm volatile" code.
>
> Evaluate whether or not the function argument is a constant expression
> and if this is the case, return an equivalent builtin expression.
>
> On an allyesconfig, with GCC 13.2.1, it saves roughly 8 KB.
>
> $ size --format=GNU vmlinux.before vmlinux.after
> text data bss total filename
> 60446534 70972412 2289596 133708542 vmlinux.before
> 60429746 70978876 2291676 133700298 vmlinux.after
Still a win with gcc 9.5.0-1ubuntu1~22.04:
allyesconfig:
text data bss total filename
58882250 72419706 2284004 133585960
vmlinux-v6.7-rc8-1-m68k-bitops-force-inlining
58863570 72419546 2285860 133568976
vmlinux-v6.7-rc8-2-m68k-bitops-use-__builtin_clz,ctzl,ffs
So an even bigger win...
atari_defconfig:
text data bss total filename
4117008 1579350 151680 5848038
vmlinux-v6.7-rc8-1-m68k-bitops-force-inlining
4116940 1579534 151712 5848186
vmlinux-v6.7-rc8-2-m68k-bitops-use-__builtin_clz,ctzl,ffs
... but a small size increase here.
>
> Reference: commit fdb6649ab7c1 ("x86/asm/bitops: Use __builtin_ctzl()
> to evaluate constant expressions")
Please don't split lines containing tags.
> Link: https://git.kernel.org/torvalds/c/fdb6649ab7c1
>
> Signed-off-by: Vincent Mailhol <mailhol.vincent@...adoo.fr>
Reviewed-by: Geert Uytterhoeven <geert@...ux-m68k.org>
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
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