linux-kernel - Re: [PATCH 05/17] powerpc: Add __attribute_const_

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Message-ID: <aJ9jV80oYG6rPN1o@gate>
Date: Fri, 15 Aug 2025 11:41:59 -0500
From: Segher Boessenkool <segher@...nel.crashing.org>
To: Madhavan Srinivasan <maddy@...ux.ibm.com>
Cc: Kees Cook <kees@...nel.org>, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-alpha@...r.kernel.org, linux-csky@...r.kernel.org,
        linux-hexagon@...r.kernel.org, linux-m68k@...r.kernel.org,
        linux-mips@...r.kernel.org, linux-openrisc@...r.kernel.org,
        linux-parisc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-riscv@...ts.infradead.org, linux-s390@...r.kernel.org,
        linux-sh@...r.kernel.org, sparclinux@...r.kernel.org,
        llvm@...ts.linux.dev, linux-hardening@...r.kernel.org
Subject: Re: [PATCH 05/17] powerpc: Add __attribute_const__ to ffs()-family
 implementations

On Fri, Aug 15, 2025 at 11:34:56AM -0500, Segher Boessenkool wrote:
> On Thu, Aug 07, 2025 at 03:16:35PM +0530, Madhavan Srinivasan wrote:
> > making them eligible for compiler optimization.
> 
> You can instead use GCC for this.  __builtin_ffs () exists since 2003,

Erm, 1992 actually, but stuff has moved around since then :-)

> and has this attribute built-in, as well as tens of other optimisations
> that the kernel thing misses.
> 
> Of course using existing stuff instead of cobbling together something
> half working prevents you from having a lot of fun ;-)


Segher