linux-kernel - Re: [PATCH] coresight: cti: Remove unnecessary NULL check in cti_sig_type

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Message-ID: <CAKwvOdn8SgY-C1YRGOcCnTn84MHHGirkDHPfg=mCONmUV_wqSQ@mail.gmail.com>
Date:   Mon, 2 Mar 2020 13:51:07 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     Mathieu Poirier <mathieu.poirier@...aro.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Mike Leach <mike.leach@...aro.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH] coresight: cti: Remove unnecessary NULL check in cti_sig_type_name

On Mon, Mar 2, 2020 at 1:34 PM Nathan Chancellor
<natechancellor@...il.com> wrote:
>
> Clang warns:
>
> drivers/hwtracing/coresight/coresight-cti-sysfs.c:948:11: warning:
> address of array 'grp->sig_types' will always evaluate to 'true'
> [-Wpointer-bool-conversion]
>         if (grp->sig_types) {
>         ~~  ~~~~~^~~~~~~~~
> 1 warning generated.
>
> sig_types is at the end of a struct so it cannot be NULL.
>
> Fixes: 85b6684eab65 ("coresight: cti: Add connection information to sysfs")
> Link: https://github.com/ClangBuiltLinux/linux/issues/914
> Signed-off-by: Nathan Chancellor <natechancellor@...il.com>

Yep, GCC and Clang both eliminate the false case as impossible:
https://godbolt.org/z/tjbDqR
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>

> ---
>  drivers/hwtracing/coresight/coresight-cti-sysfs.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/hwtracing/coresight/coresight-cti-sysfs.c b/drivers/hwtracing/coresight/coresight-cti-sysfs.c
> index abb7f492c2cb..214d6552b494 100644
> --- a/drivers/hwtracing/coresight/coresight-cti-sysfs.c
> +++ b/drivers/hwtracing/coresight/coresight-cti-sysfs.c
> @@ -945,10 +945,8 @@ cti_sig_type_name(struct cti_trig_con *con, int used_count, bool in)
>         int idx = 0;
>         struct cti_trig_grp *grp = in ? con->con_in : con->con_out;
>
> -       if (grp->sig_types) {
> -               if (used_count < grp->nr_sigs)
> -                       idx = grp->sig_types[used_count];
> -       }
> +       if (used_count < grp->nr_sigs)
> +               idx = grp->sig_types[used_count];
>         return sig_type_names[idx];
>  }
>
> --


-- 
Thanks,
~Nick Desaulniers