Re: [PATCH] shm: Remove silly double assignment

[Andrew Morton <akpm@linux-foundation.org>]

On Tue, 10 Jun 2008 08:53:39 -0400 Neil Horman <nhorman@tuxdriver.com> wrote:

>     Found a silly double assignment of err is do_shmat.  Silly, but good to clean up
>     the useless code.
>     
>     Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
> 
> diff --git a/ipc/shm.c b/ipc/shm.c
> index 554429a..d05f6b5 100644
> --- a/ipc/shm.c
> +++ b/ipc/shm.c
> @@ -894,8 +894,6 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr)
>  	if (!sfd)
>  		goto out_put_dentry;
>  
> -	err = -ENOMEM;
> -
>  	file = alloc_file(path.mnt, path.dentry, f_mode, &shm_file_operations);
>  	if (!file)
>  		goto out_free;

Not silly, really.  Look:

	err = -ENOMEM;
	if (expr1)
		goto out;

	err = -ENOMEM;
	if (expr2)
		goto out;

each of these two units is a separate, self-contained clause.  Removing
the second assignment to `err' breaks that separation and will make one
clause undesirably dependent upon the other.

Example: if someone later comes up and does

	err = -ENOMEM;
	if (expr1)
		goto out;

+	er = -EINVAL;
+	if (expr3)
+		goto out;

	if (expr2)
		goto out;

then whoops, it broke.

The compiler should optimise away the second assignment anyway.