On Sun, Dec 17, 2023 at 8:13 AM Vincent Mailhol
<mailhol.vincent@xxxxxxxxxx> 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@xxxxxxxxxx>
Reviewed-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
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
