netdev - Re: [PATCH] net/sch_generic.h: use sizeof_member() and get rid of unused variable

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Message-Id: <20200520.111717.835995575109387492.davem@davemloft.net>
Date:   Wed, 20 May 2020 11:17:17 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     a@...table.cc
Cc:     netdev@...r.kernel.org, cake@...ts.bufferbloat.net, toke@...e.dk,
        jhs@...atatu.com, xiyou.wangcong@...il.com, jiri@...nulli.us,
        stephen@...workplumber.org
Subject: Re: [PATCH] net/sch_generic.h: use sizeof_member() and get rid of
 unused variable

From: Antonio Quartulli <a@...table.cc>
Date: Wed, 20 May 2020 10:39:33 +0200

> I don't think it's BUILD_BUG_ON()'s fault, because qcb->data is passed
> to sizeof() first.
> 
> My best guess is that gcc is somewhat optimizing the sizeof(gcb->data)
> and thus leaving the gcb variable unused.

If you remove the argument from the function but leave the BUILD_BUG_ON()
calls the same, the compilation will fail.

Any such optimization is therefore unreasonable.

The variable is used otherwise compilation would not fail when you
remove it right?