linux-kernel - Re: [PATCH v2] scripts: coccinelle: check for !(un)?likely usage

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Date:   Fri, 6 Sep 2019 22:19:21 +0200 (CEST)
From:   Julia Lawall <julia.lawall@...6.fr>
To:     Denis Efremov <efremov@...ux.com>
cc:     linux-kernel@...r.kernel.org, cocci@...teme.lip6.fr,
        Julia Lawall <Julia.Lawall@...6.fr>,
        Gilles Muller <Gilles.Muller@...6.fr>,
        Nicolas Palix <nicolas.palix@...g.fr>,
        Michal Marek <michal.lkml@...kovi.net>,
        Markus Elfring <Markus.Elfring@....de>,
        Joe Perches <joe@...ches.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: Re: [PATCH v2] scripts: coccinelle: check for !(un)?likely usage



On Thu, 29 Aug 2019, Denis Efremov wrote:

> This patch adds coccinelle script for detecting !likely and
> !unlikely usage. These notations are confusing. It's better
> to replace !likely(x) with unlikely(!x) and !unlikely(x) with
> likely(!x) for readability.
>
> The rule transforms !likely(x) to unlikely(!x) based on this logic:
>   !likely(x) iff
>   !__builtin_expect(!!(x), 1) iff
>    __builtin_expect(!!!(x), 0) iff
>   unlikely(!x)
>
> For !unlikely(x) to likely(!x):
>   !unlikely(x) iff
>   !__builtin_expect(!!(x), 0) iff
>   __builtin_expect(!!!(x), 1) iff
>   likely(!x)
>
> Signed-off-by: Denis Efremov <efremov@...ux.com>
> Cc: Julia Lawall <Julia.Lawall@...6.fr>
> Cc: Gilles Muller <Gilles.Muller@...6.fr>
> Cc: Nicolas Palix <nicolas.palix@...g.fr>
> Cc: Michal Marek <michal.lkml@...kovi.net>
> Cc: Markus Elfring <Markus.Elfring@....de>
> Cc: Joe Perches <joe@...ches.com>
> Cc: Rasmus Villemoes <linux@...musvillemoes.dk>

Acked-by: Julia Lawall <julia.lawall@...6.fr>

A small improvement though would be to improve the explicit dependency of
the last four python rules on r1 and r2.  Those rules won't execute unless
the inherited metavariable has a value, which makes the same dependency.

julia


> ---
>  scripts/coccinelle/misc/neg_unlikely.cocci | 89 ++++++++++++++++++++++
>  1 file changed, 89 insertions(+)
>  create mode 100644 scripts/coccinelle/misc/neg_unlikely.cocci
>
> diff --git a/scripts/coccinelle/misc/neg_unlikely.cocci b/scripts/coccinelle/misc/neg_unlikely.cocci
> new file mode 100644
> index 000000000000..9aac0a7ff042
> --- /dev/null
> +++ b/scripts/coccinelle/misc/neg_unlikely.cocci
> @@ -0,0 +1,89 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/// Use unlikely(!x) instead of !likely(x) and vice versa.
> +/// Notations !unlikely(x) and !likely(x) are confusing.
> +//
> +// Confidence: High
> +// Copyright: (C) 2019 Denis Efremov, ISPRAS.
> +// Options: --no-includes --include-headers
> +
> +virtual patch
> +virtual context
> +virtual org
> +virtual report
> +
> +//----------------------------------------------------------
> +//  For context mode
> +//----------------------------------------------------------
> +
> +@...ends on context disable unlikely@
> +expression E;
> +@@
> +
> +*! \( likely \| unlikely \) (E)
> +
> +//----------------------------------------------------------
> +//  For patch mode
> +//----------------------------------------------------------
> +
> +@...ends on patch disable unlikely@
> +expression E;
> +@@
> +
> +(
> +-!likely(!E)
> ++unlikely(E)
> +|
> +-!likely(E)
> ++unlikely(!E)
> +|
> +-!unlikely(!E)
> ++likely(E)
> +|
> +-!unlikely(E)
> ++likely(!E)
> +)
> +
> +//----------------------------------------------------------
> +//  For org and report mode
> +//----------------------------------------------------------
> +
> +@r1 depends on (org || report) disable unlikely@
> +expression E;
> +position p;
> +@@
> +
> +!likely@p(E)
> +
> +@r2 depends on (org || report) disable unlikely@
> +expression E;
> +position p;
> +@@
> +
> +!unlikely@p(E)
> +
> +@...ipt:python depends on org && r1@
> +p << r1.p;
> +@@
> +
> +coccilib.org.print_todo(p[0], "unlikely(!x) is more readable than !likely(x)")
> +
> +@...ipt:python depends on org && r2@
> +p << r2.p;
> +@@
> +
> +coccilib.org.print_todo(p[0], "likely(!x) is more readable than !unlikely(x)")
> +
> +@...ipt:python depends on report && r1@
> +p << r1.p;
> +@@
> +
> +coccilib.report.print_report(p[0],
> +	"unlikely(!x) is more readable than !likely(x)")
> +
> +@...ipt:python depends on report && r2@
> +p << r2.p;
> +@@
> +
> +coccilib.report.print_report(p[0],
> +	"likely(!x) is more readable than !unlikely(x)")
> +
> --
> 2.21.0
>
>