Re: [Cocci] Re: [PATCH v2] coccinelle: if (ret) return ret; return ret; semantic patch

[Greg Dietsche <greg@farmergreg.com>]

On 06/15/2011 12:58 AM, Julia Lawall wrote:
> On Tue, 14 Jun 2011, Greg Dietsche wrote:
>
>>
>>
>> On 06/14/2011 04:24 PM, Greg Dietsche wrote:
>>> On 06/14/2011 12:50 AM, Julia Lawall wrote:
>>>> On Mon, 13 Jun 2011, Greg Dietsche wrote:
>>>>> just curious... i see you usually just write "return ret;" here when
>>>>> posting.
>>>>> I've assumed that's because it will 1) work and 2) is close enough.
>>>>>
>>>>> You'll notice I've been doing:
>>>>> -return ret;
>>>>> +return ret;
>>>>> because it seems to help coccinelle realize that it can get rid of
>>>>> extra line
>>>>> feeds - does this make sense - or should i just be doing a "return ret"?
>>>> I wondered why you were doing that :)
>>>>
>>>> Is the problem that the removed if is being replaced by a blank line? If
>>>> so, that is not intentional. I will look into it. If it doesn't happen
>>>> always, an example where it does happen could be helpful.
>>>>
>>>
>>> Some times it gets it right, so it's not always wrong. For example:
>>>
>>> diff -u -p a/arch/m68k/math-emu/fp_log.c b/arch/m68k/math-emu/fp_log.c
>>> --- a/arch/m68k/math-emu/fp_log.c 2011-06-13 14:06:37.943954469 -0500
>>> +++ b/arch/m68k/math-emu/fp_log.c 2011-06-14 16:07:22.394954040 -0500
>>> @@ -105,9 +105,6 @@ fp_fetoxm1(struct fp_ext *dest, struct f
>>>
>>> fp_monadic_check(dest, src);
>>>
>>> - if (IS_ZERO(dest))
>>> - return dest;
>>> -
>>> return dest;
>>> }
>>>
>>>
>>>
>>> Here's an example where it got it "wrong" - notice how the blank line is
>>> missing the - :
>>>
>>> diff -u -p a/arch/frv/mm/pgalloc.c b/arch/frv/mm/pgalloc.c
>>> --- a/arch/frv/mm/pgalloc.c 2011-06-13 14:06:37.855954391 -0500
>>> +++ b/arch/frv/mm/pgalloc.c 2011-06-14 16:07:16.714954008 -0500
>>> @@ -136,8 +136,6 @@ pgd_t *pgd_alloc(struct mm_struct *mm)
>>> pgd_t *pgd;
>>>
>>> pgd = quicklist_alloc(0, GFP_KERNEL, pgd_ctor);
>>> - if (!pgd)
>>> - return pgd;
>>>
>>> return pgd;
>>> }
>
> OK, but it is going to be hard for Coccinelle to know that, although the
> programmer previously thought that return should be separated from the
> rest of the function by a blank line, that is now no longer the case.
> Perhaps it is due to the fact that there is now only one other line in the
> body of the function, but it seems like an opinion as to how to draw the
> line.
>

OK - I can see how that would be hard for Coccinelle to guess what we 
really want in this case.

> So your - return ret; + return ret; is probably the appropriate solution.
> You want to get rid of the whole pattern if (...) return ret; return ret;
> and replace it with just return ret;, which will then be inserted at the
> point of the beginning of the match to the pattern.

ok

> It would be nicer to put the - return ret; + return ret; inside the last
> line of the ( | ).  Then only those return ret's are rewritten rather than
> every return ret in the program.  It should improver performance and

except that 4 of the 5 ORs are cases where we want to do the -return 
ret; + return ret; So I suppose for performance, I should actually add 
the +/- to each of the 4 cases that we want cocci to generate a patch for?


thanks,
Greg

> reduce the risk of changing spacing.  The other ifs in the ( | ) don't
> need to be followed by return ret.  They are just ifs that you want to
> ignore completely.
>
> julia