linux-kernel - RE: [PATCH] bitops: Change function return types from long to int

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Date: Mon, 22 Apr 2024 05:24:39 +0000
From: "Wang, Xiao W" <xiao.w.wang@...el.com>
To: Thorsten Blum <thorsten.blum@...lux.com>, Arnd Bergmann <arnd@...db.de>
CC: Palmer Dabbelt <palmer@...osinc.com>, Charlie Jenkins
	<charlie@...osinc.com>, Namhyung Kim <namhyung@...nel.org>, Huacai Chen
	<chenhuacai@...nel.org>, Youling Tang <tangyouling@...ngson.cn>, Tiezhu Yang
	<yangtiezhu@...ngson.cn>, Jinyang He <hejinyang@...ngson.cn>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] bitops: Change function return types from long to int



> -----Original Message-----
> From: Thorsten Blum <thorsten.blum@...lux.com>
> Sent: Sunday, April 21, 2024 6:39 AM
> To: Arnd Bergmann <arnd@...db.de>
> Cc: Wang, Xiao W <xiao.w.wang@...el.com>; Palmer Dabbelt
> <palmer@...osinc.com>; Charlie Jenkins <charlie@...osinc.com>; Namhyung
> Kim <namhyung@...nel.org>; Huacai Chen <chenhuacai@...nel.org>; Youling
> Tang <tangyouling@...ngson.cn>; Tiezhu Yang <yangtiezhu@...ngson.cn>;
> Jinyang He <hejinyang@...ngson.cn>; linux-arch@...r.kernel.org; linux-
> kernel@...r.kernel.org; Thorsten Blum <thorsten.blum@...lux.com>
> Subject: [PATCH] bitops: Change function return types from long to int
> 
> Change the return types of bitops functions (ffs, fls, and fns) from
> long to int. The expected return values are in the range [0, 64], for
> which int is sufficient.
> 
> Additionally, int aligns well with the return types of the corresponding
> __builtin_* functions, potentially reducing overall type conversions.

Could we change the return types to "int", instead of "unsigned int"?
https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html says that these __builtin_*
functions return "int".

> 
> Many of the existing bitops functions already return an int and don't
> need to be changed. The bitops functions in arch/ should be considered
> separately.
> 
> Adjust some return variables to match the function return types.
> 
> With GCC 13 and defconfig, these changes reduced the size of a test
> kernel image by 5,432 bytes on arm64 and by 248 bytes on riscv; there
> were no changes in size on x86_64, powerpc, or m68k.

I guess your test is based on 64bit arch, right?

BRs,
Xiao