Re: [RFC] Replacing special goto statements by direct returns?

[Julia Lawall]

On Tue, 3 Nov 2026, Markus Elfring wrote:

> Hello,
>
> The documentation for the Linux coding style contains the following information.
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/coding-style.rst?h=v7.4-rc1#n526
>
> “…
> The goto statement comes in handy when a function exits from multiple
> locations and some common work such as cleanup has to be done.  If there is no
> cleanup needed then just return directly.
> …”
>
>
> Thus it seems that the following script for the semantic patch language
> can work to some degree.
>
>
> @replacement exists@
> identifier label, var;
> @@
> -goto label;
> +return var;
>  ...
> -label:
>  return var;
>
>
>
> Unfortunately, patches would be generated then by such a simple SmPL code
> which would still preserve return statements that became unreachable.
>
> Test result example:
> Markus_Elfring@Sonne:…/Projekte/Linux/next-analyses> time spatch --allow-inconsistent-paths fs/xfs/libxfs/xfs_btree.c …/Projekte/Coccinelle/janitor/replace_goto_by_return2.cocci
> …
> @@ -1735,7 +1735,7 @@ xfs_btree_increment(
>                 --lev;
>                 error = xfs_btree_read_buf_block(cur, ptrp, 0, &block, &bp);
>                 if (error)
> -                       goto error0;
> +                       return error;
>
>                 xfs_btree_setbuf(cur, lev, bp);
>                 cur->bc_levels[lev].ptr = 1;
> @@ -1747,8 +1747,6 @@ out1:
>  out0:
>         *stat = 0;
>         return 0;
> -
> -error0:
>         return error;
>  }

I think you can do:

@useful@
statement S;
expression error;
identifier error0;
position p;
@@

S
error0:@p
  return error;

@useless@
position p1 != useful.p;
expression error;
identifier error0;
@@

f(...) {
(
<...
- goto error0;
+ return error;
...>
&
...
error0:@p1
  return error;
)
}

I have not tested this.  It might not work, or it might be very slow.

julia


> …
> real    0m1,074s
> user    0m0,995s
> sys     0m0,071s
>
>
>
> How should such a source code transformation approach be improved accordingly?
>
> Regards,
> Markus
>
>