linux-kernel - Re: Coccinelle: Checking the influence of “Grep query”

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Message-ID: <alpine.DEB.2.22.394.2010221434210.5113@hadrien>
Date:   Thu, 22 Oct 2020 14:35:03 +0200 (CEST)
From:   Julia Lawall <julia.lawall@...ia.fr>
To:     Markus Elfring <Markus.Elfring@....de>
cc:     Coccinelle <cocci@...teme.lip6.fr>,
        Gilles Muller <Gilles.Muller@...6.fr>,
        Julia Lawall <Julia.Lawall@...6.fr>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nicolas Palix <nicolas.palix@...g.fr>,
        Sumera Priyadarsini <sylphrenadin@...il.com>,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
        Denis Efremov <efremov@...ux.com>
Subject: Re: Coccinelle: Checking the influence of “Grep query”



On Thu, 22 Oct 2020, Markus Elfring wrote:

> > A disjunction is applied by this script for the semantic patch language.
> > This construct uses short-circuit evaluation. It has got the consequence
> > that the last element of the specified condition will only be checked
> > if all previous parts did not match. Such a technical detail leads to
> > a recommended ordering of condition parts if you would like to care for
> > optimal run time characteristics of SmPL code.
>
> I imagine that such information can trigger further software evolution
> at more places.
>
>
> > +++ b/scripts/coccinelle/iterators/for_each_child.cocci
>
> The software “Coccinelle 1.0.8-00177-g28737419” displays the following data.
>
> elfring@...ne:~/Projekte/Linux/next-patched> spatch -D patch --parse-cocci
> scripts/coccinelle/iterators/for_each_child.cocci
> …
> Grep query
> for_each_node_with_property || for_each_node_by_type || for_each_node_by_name ||
> for_each_matching_node_and_match || for_each_matching_node ||
> for_each_compatible_node || for_each_child_of_node ||
> for_each_available_child_of_node
>
>
> I suggest to take another closer look at the presented ordering for
> these identifiers.
> It deviates from the proposed listing for the SmPL disjunction.
> Now I am curious if this difference can be meaningful.
>
> If the exact “grep” is performed, it might happen that short-circuit evaluation
> would be applied also by the corresponding software component (or known tool).
> Will any adjustments become relevant then accordingly?

It doesn't matter.  The purpose is just to select files that are relevent
for consideration.  If a file is selected for two reasons instead of one
reason, it doesn't matter; it's still selected.

julia