From: René Scharfe <l.s.r@web.de>
Date: Thu, 14 Nov 2019 16:41:21 GMT
Subject: Re: coccinelle: adjustments for array.cocci?
Message-ID: <53346d52-e096-c651-f70a-ce6ca4d82ff9@web.de>
In-Reply-To: <ba5d609a-16ea-d7e9-66e6-19aab94b2acd@web.de>

Am 14.11.19 um 14:15 schrieb Markus Elfring:
> You mentioned “failures”. - I became curious then if corresponding software
> development challenges can be clarified a bit more.

Let's try to restore/repeat the pertinent paragraph, with context and
attribution:

Am 13.11.19 um 03:11 schrieb Junio C Hamano:
> René Scharfe <l.s.r@web.de> writes:
>> Am 12.11.19 um 16:08 schrieb Markus Elfring:
>>>
>>> Do you find the following code variant (for the semantic patch language) also useful?
>>>
>>>  memcpy(
>>> (       ptr, E, n *
>>> -       sizeof(*(ptr))
>>> +       sizeof(T)
>>> |       arr, E, n *
>>> -       sizeof(*(arr))
>>> +       sizeof(T)
>>> |       E, ptr, n *
>>> -       sizeof(*(ptr))
>>> +       sizeof(T)
>>> |       E, arr, n *
>>> -       sizeof(*(arr))
>>> +       sizeof(T)
>>> )
>>>        )
>
>> This reduces duplication in the semantic patch, which is nice.  I think
>> I tried something like that at the time, but found that it failed to
>> produce some of the cases in 921d49be86 ("use COPY_ARRAY for copying
>> arrays", 2019-06-15) for some reason.
> Thanks for mentioning.
>
> I too recall that seemingly redundant entries were noticed during
> the review and at least back then removing the seemingly redundant
> ones caused failures in rewriting.

You can see for yourself by:

 1. applying the patch at the bottom to implement your suggested change,
 2. running "git show 921d49be86 | patch -p1 -R" to undo 921d49be86,
 3. running "make contrib/coccinelle/array.cocci.patch",
 4. running "patch -p1 <contrib/coccinelle/array.cocci.patch",
 5. running "git diff".

If the new version of array.cocci is equivalent to the current one then
that last step should show no difference.  For me, "git diff --stat"
reports, however:

 contrib/coccinelle/array.cocci | 30 ++++++++++++++----------------
 fast-import.c                  |  2 +-
 packfile.c                     |  4 ++--
 pretty.c                       |  4 ++--
 4 files changed, 19 insertions(+), 21 deletions(-)

The changes in array.cocci are expected of course, but the others
indicate that the new version missed transformations that the current
version generated.

René


-- >8 --
diff --git a/contrib/coccinelle/array.cocci b/contrib/coccinelle/array.cocci
index 46b8d2ee11..e7bcbefcc1 100644
--- a/contrib/coccinelle/array.cocci
+++ b/contrib/coccinelle/array.cocci
@@ -12,27 +12,25 @@ T *ptr;
 T[] arr;
 expression E, n;
 @@
+  memcpy(
 (
-  memcpy(ptr, E,
-- n * sizeof(*(ptr))
-+ n * sizeof(T)
-  )
+  ptr, E, n *
+- sizeof(*(ptr))
++ sizeof(T)
 |
-  memcpy(arr, E,
-- n * sizeof(*(arr))
-+ n * sizeof(T)
-  )
+  arr, E, n *
+- sizeof(*(arr))
++ sizeof(T)
 |
-  memcpy(E, ptr,
-- n * sizeof(*(ptr))
-+ n * sizeof(T)
-  )
+  E, ptr, n *
+- sizeof(*(ptr))
++ sizeof(T)
 |
-  memcpy(E, arr,
-- n * sizeof(*(arr))
-+ n * sizeof(T)
-  )
+  E, arr, n *
+- sizeof(*(arr))
++ sizeof(T)
 )
+  )

 @@
 type T;