Re: [Cocci] Removing the last return statement from a void function
On Thu, 18 Mar 2021 at 19:24, Julia Lawall wrote:
> The ... in Coccinelle is based on control flow, so it is a bit hard to
> find the return at the bottom of the function. Actually, from
> Coccinelle's point of view, all returns are at the bottom of the function,
> because one leaves the function after a return.
Interesting, that helps me understand a little more about Coccinelle. Thanks.
> You can try the following:
>
> @r@
> position p;
> identifier f;
> }
>
> f(...) {
> <...
> { .. return@p; }
> ...>
> }
>
> @@
> position p != r.p;
> @@
>
> - return@p;
So I tried this:
@r@
position p;
identifier f;
@@
f(...) {
<...
{ ... return@p; }
...>
}
@@
position p != r.p;
@@
- return@p;
Which I ran as:
spatch --in-place --debug --iso-file contrib/coccinelle/empty.iso \
--sp-file ./contrib/coccinelle/remove-void-return.cocci --dir fvwm
With "--dir fvwm", I found that my CPU was being chewed at 100%, which I left
running overnight. Some 8 hours later, spatch was still running. Presumably,
Coccinelle is having an interesting time coordinating the positions?
Instead, I decided to loop over the .c files which "--dir fvwm" would have
done. What I found was that for some files, spatch took a few seconds, and
produced no output, yet for some, spatch was still running without any result
known (so I killed it).
Indeed, I'm attaching a debug run of spatch to this email (cocci-debug) for
one file that definitely has functions where I would expect Coccinelle to have
matched a "return;" statement to be removed, but this wasn't the case.
Would you be able to suggest what I might have done wrong, or if there's any
additional debugging I can provide?
Thanks,
Thomas
cocci-debug
Description: Binary data
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Re: [Cocci] Removing the last return statement from a void function
On Thu, 18 Mar 2021, Thomas Adam wrote:
> Hello all,
>
> I've another Coccinelle question I'm hoping you can help me with. The
> codebase I'm working on is old, and has some interesting styles which
> by themselves probably don't cause any problems, but newer C compilers
> are now starting to flag them.
>
> In particular, there seems to be a pattern in this code base of using
> explicit `return;` statements at the end of void functions. Here's an
> example:
>
> static void broadcast_mini_icon(FvwmWindow *fw)
> {
> if (!FMiniIconsSupported)
> {
> return;
> }
> if (fw->mini_pixmap_file && fw->mini_icon)
> {
> BroadcastFvwmPicture( M_MINI_ICON, FW_W(fw),
> FW_W_FRAME(fw), (unsigned long)fw,
> fw->mini_icon, fw->mini_pixmap_file);
> }
> return;
> }
>
> Here you can see the last return statement is not necessary.
>
> I'm trying to make coccinelle recognise this and remove such cases.
> Here's what I've tried:
>
> @@
> identifier f;
> @@
>
> void f(...) {
> <...
> - return;
> ...>
>
> }
>
> ... which sort of works, but proceeds to remove *all* `return;`
> statements from void functions, rather than the last occurance in the
> function.
>
> Am I on the right track with this approach, or do I need to do
> something more creative?
The ... in Coccinelle is based on control flow, so it is a bit hard to
find the return at the bottom of the function. Actually, from
Coccinelle's point of view, all returns are at the bottom of the function,
because one leaves the function after a return.
You can try the following:
@r@
position p;
identifier f;
}
f(...) {
<...
{ .. return@p; }
...>
}
@@
position p != r.p;
@@
- return@p;
Basically the first rule collects the position of all returns that are
inside a { }, and then the second rule removes the others.
However there is an isomorphism that makes a pattern with { ... S } match
just S, for any S, which you don't want. So you can make an empty file
called empty.iso, and then run the rule with the command-line argument
--iso-file empty.iso
julia
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[Cocci] Removing the last return statement from a void function
Hello all,
I've another Coccinelle question I'm hoping you can help me with. The
codebase I'm working on is old, and has some interesting styles which
by themselves probably don't cause any problems, but newer C compilers
are now starting to flag them.
In particular, there seems to be a pattern in this code base of using
explicit `return;` statements at the end of void functions. Here's an
example:
static void broadcast_mini_icon(FvwmWindow *fw)
{
if (!FMiniIconsSupported)
{
return;
}
if (fw->mini_pixmap_file && fw->mini_icon)
{
BroadcastFvwmPicture( M_MINI_ICON, FW_W(fw),
FW_W_FRAME(fw), (unsigned long)fw,
fw->mini_icon, fw->mini_pixmap_file);
}
return;
}
Here you can see the last return statement is not necessary.
I'm trying to make coccinelle recognise this and remove such cases.
Here's what I've tried:
@@
identifier f;
@@
void f(...) {
<...
- return;
...>
}
... which sort of works, but proceeds to remove *all* `return;`
statements from void functions, rather than the last occurance in the
function.
Am I on the right track with this approach, or do I need to do
something more creative?
Thanks once more for your help.
Thomas
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