linux-kernel - Re: linux-6.12-rc1/drivers/iio/imu/bmi323/bmi323_core.c:133: Array contents defined but not used ?

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Message-ID: <7e9ae281-448c-429b-9ca5-86581f777f68@gmail.com>
Date: Mon, 30 Sep 2024 15:58:06 +0200
From: Javier Carrasco <javier.carrasco.cruz@...il.com>
To: David Binderman <dcb314@...mail.com>,
 "jagathjog1996@...il.com" <jagathjog1996@...il.com>,
 "jic23@...nel.org" <jic23@...nel.org>, "lars@...afoo.de" <lars@...afoo.de>,
 "linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
 Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: linux-6.12-rc1/drivers/iio/imu/bmi323/bmi323_core.c:133: Array
 contents defined but not used ?

On 30/09/2024 15:49, David Binderman wrote:
> Hello there,
> 
> I just tried to build linux-6.12-rc1 with clang. It said:
> 
> drivers/iio/imu/bmi323/bmi323_core.c:133:27: warning: variable 'bmi323_ext_reg_savestate' is not needed and will not be emitted [-Wunneeded-internal-declaration]
> 
> A grep for the identifier shows the following strange results::
> 
> inux-6.12-rc1 $ grep bmi323_ext_reg_savestate drivers/iio/imu/bmi323/bmi323_core.c
> static const unsigned int bmi323_ext_reg_savestate[] = {
> 	unsigned int ext_reg_settings[ARRAY_SIZE(bmi323_ext_reg_savestate)];
> 	for (unsigned int i = 0; i < ARRAY_SIZE(bmi323_ext_reg_savestate); i++) {
> 	for (unsigned int i = 0; i < ARRAY_SIZE(bmi323_ext_reg_savestate); i++) {
> linux-6.12-rc1 $ 
> 
> I see no mention of bmi323_ext_reg_savestate[ i]. Is there a possible
> cut'n'paste error in one of the two for loops ?
> 
> Regards
> 
> David Binderman

I think that is a bug in clang:

https://bugs.llvm.org/show_bug.cgi?id=33068

That happens because clang sees that bmi323_ext_reg_savestate is not
used but to gets its size, and that means for it that the variable is
not needed. That does not happen for example with
bmi323_ext_reg_savestate (right above bmi323_ext_reg_savestate) because
that one is used beyond ARRAY_SIZE.

Safe to ignore?

Best regards,
Javier Carrasco