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

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Message-ID: <aJ9hsHj9lsHvvhcA@gate>
Date: Fri, 15 Aug 2025 11:34:56 -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

Hi!

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,
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