linux-kernel - Re: [PATCH 1/6] staging: vt6655: Compress return logic

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Date:   Sat, 18 Feb 2017 12:51:15 -0800
From:   Joe Perches <joe@...ches.com>
To:     simran singhal <singhalsimran0@...il.com>,
        forest@...ttletooquiet.net
Cc:     gregkh@...uxfoundation.org, devel@...verdev.osuosl.org,
        linux-kernel@...r.kernel.org, outreachy-kernel@...glegroups.com
Subject: Re: [PATCH 1/6] staging: vt6655: Compress return logic

On Sun, 2017-02-19 at 01:50 +0530, simran singhal wrote:
> Simplify function returns by merging assignment and return into
> one command line.
> Found with Coccinelle
> @@
> local idexpression ret;
> expression e;
> @@
> 
> -ret =
> +return
>      e;
> -return ret;
[]
> diff --git a/drivers/staging/vt6655/card.c b/drivers/staging/vt6655/card.c
[]
> @@ -920,7 +920,7 @@ u64 CARDqGetTSFOffset(unsigned char byRxRate, u64 qwTSF1, u64 qwTSF2)
>  
>  	qwTSFOffset = qwTSF1 - qwTSF2;
>  
> -	return qwTSFOffset;
> +	return qwTSF1 - qwTSF2;
>  }

It's not a problem here but generically, this transformation may
introduce defects when the local idexpression being assigned to
is a smaller type than the return type.  e.g.:

u64 foo(u64 a, u64 b)
{
	u8 bar = a - b;
	return bar;
}