linux-kernel - Re: [PATCH v2 0/4] s390: Fix and optimize _

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Message-ID: <c38409b1-fa4e-4fa6-94a8-51616bf1fd6a-agordeev@linux.ibm.com>
Date: Thu, 18 Sep 2025 16:19:22 +0200
From: Alexander Gordeev <agordeev@...ux.ibm.com>
To: Heiko Carstens <hca@...ux.ibm.com>
Cc: Nathan Chancellor <nathan@...nel.org>, Miguel Ojeda <ojeda@...nel.org>,
        Kees Cook <kees@...nel.org>,
        Nick Desaulniers <nick.desaulniers+lkml@...il.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Juergen Christ <jchrist@...ux.ibm.com>, linux-kernel@...r.kernel.org,
        linux-s390@...r.kernel.org, Sven Schnelle <svens@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>
Subject: Re: [PATCH v2 0/4] s390: Fix and optimize __flogr() inline assembly

On Tue, Sep 16, 2025 at 03:47:59PM +0200, Heiko Carstens wrote:
> A recent optimization of the s390 specific ffs() and ffs64()
> implementations leads to a new compiler warning. Instead of reverting the
> optimization address this with the rather new assume attribute, which
> generates even better code, if supported by compilers.
> 
> Since the assume attribute may be useful for others as well, add the
> __assume macro to compiler attributes, so it is kernel wide available,
> instead of adding an s390 specific optimization.
> 
> Heiko Carstens (4):
>   s390/bitops: Limit return value range of __flogr()
>   compiler_types: Add __assume macro
>   s390/bitops: Use __assume() for __flogr() inline assembly return value
>   s390/bitops: Cleanup __flogr()
> 
>  arch/s390/include/asm/bitops.h | 21 ++++++++++++++-------
>  include/linux/compiler_types.h | 23 +++++++++++++++++++++++
>  init/Kconfig                   | 10 ++++++++++
>  3 files changed, 47 insertions(+), 7 deletions(-)

Applied, thanks!