linux-kernel - Re: [PATCH v2 4/6] bitops: define const

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Date:   Mon, 13 Jun 2022 16:30:34 +0200
From:   Alexander Lobakin <alexandr.lobakin@...el.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Alexander Lobakin <alexandr.lobakin@...el.com>,
        Arnd Bergmann <arnd@...db.de>,
        Yury Norov <yury.norov@...il.com>,
        "Mark Rutland" <mark.rutland@....com>,
        Matt Turner <mattst88@...il.com>,
        Brian Cain <bcain@...cinc.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        "Yoshinori Sato" <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>,
        "David S. Miller" <davem@...emloft.net>,
        Kees Cook <keescook@...omium.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Marco Elver <elver@...gle.com>, Borislav Petkov <bp@...e.de>,
        Tony Luck <tony.luck@...el.com>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        linux-alpha@...r.kernel.org, linux-hexagon@...r.kernel.org,
        linux-ia64@...r.kernel.org, linux-m68k@...ts.linux-m68k.org,
        linux-sh@...r.kernel.org, sparclinux@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/6] bitops: define const_*() versions of the non-atomics

From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Date: Fri, 10 Jun 2022 16:56:28 +0300

> On Fri, Jun 10, 2022 at 01:34:25PM +0200, Alexander Lobakin wrote:
> > Define const_*() variants of the non-atomic bitops to be used when
> > the input arguments are compile-time constants, so that the compiler
> > will be always to resolve those to compile-time constants as well.
> > Those are mostly direct aliases for generic_*() with one exception
> > for const_test_bit(): the original one is declared atomic-safe and
> > thus doesn't discard the `volatile` qualifier, so in order to let
> > optimize the code, define it separately disregarding the qualifier.
> > Add them to the compile-time type checks as well just in case.
> 
> ...
> 
> >  /* Check that the bitops prototypes are sane */
> >  #define __check_bitop_pr(name)						\
> > -	static_assert(__same_type(arch_##name, generic_##name) &&	\
> > +	static_assert(__same_type(const_##name, generic_##name) &&	\
> > +		      __same_type(arch_##name, generic_##name) &&	\
> >  		      __same_type(name, generic_##name))
> 
> Can't it be a one line change and actually keeping ordering at the same time?

Sure. Wanted to sort them "semantically", but it doesn't really make
any sense in here.

> 
> -- 
> With Best Regards,
> Andy Shevchenko

Thanks,
Olek