linux-kernel - Re: [PATCH] Drop -Wdeclaration-after-statement

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Date:   Fri, 25 Feb 2022 17:10:04 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Alexey Dobriyan <adobriyan@...il.com>
Cc:     linux-kernel@...r.kernel.org,
        David Laight <David.Laight@...LAB.COM>
Subject: Re: [PATCH] Drop -Wdeclaration-after-statement

On Fri, 25 Feb 2022 11:15:58 +0300 Alexey Dobriyan <adobriyan@...il.com> wrote:

> Putting declarations before statement is relict of single pass compiler
> era. It was necessary to allocate stack slots before generating code.
> 
> Recently added static_assert() is a declaration. -Wdeclaration-after-statement
> prevents its placement anywhere in the code for no reason.
> 
> Placing variable declarations in the beginning of the block increases
> variable "LOC lifetime" so to speak and chances that it will be misused.
> This is very low probability bug but still. Declaring variables right
> before first use will make "LOC lifetime" smaller.
> 
> 	{
> 		int x;
> 		[x is misused due to a typo]
> 		f(x);	// first correct use
> 	}
> 
> vs
> 
> 	{
> 		[can't misuse undeclared variable]
> 		int x;
> 		f(x);	// first correct use
> 	}
> 

Oh man.  I so wish you'd cc'ed Linus on this one so we could admire his
reaction.