linux-kernel - Re: [PATCH] coccinelle: misc: add swap script

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Date:   Thu, 18 Feb 2021 14:03:56 +0300
From:   Denis Efremov <efremov@...ux.com>
To:     Julia Lawall <julia.lawall@...ia.fr>
Cc:     cocci@...teme.lip6.fr, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] coccinelle: misc: add swap script



On 2/18/21 1:17 PM, Julia Lawall wrote:
> 
> 
> On Thu, 18 Feb 2021, Denis Efremov wrote:
> 
>>
>>
>> On 2/18/21 12:31 AM, Julia Lawall wrote:
>>>> +@...ends on patch@
>>>> +identifier tmp;
>>>> +expression a, b;
>>>> +type T;
>>>> +@@
>>>> +
>>>> +(
>>>> +- T tmp;
>>>> +|
>>>> +- T tmp = 0;
>>>> +|
>>>> +- T *tmp = NULL;
>>>> +)
>>>> +... when != tmp
>>>> +- tmp = a;
>>>> +- a = b;
>>>> +- b = tmp;
>>>> ++ swap(a, b);
>>>> +... when != tmp
>>>
>>> In this rule and the next one, if you remove the final ; from the b = tmp
>>> line and from the swap line, and put it into context code afterwards, them
>>> the generated code looks better on cases like fs/xfs/xfs_inode.c in the
>>> function xfs_lock_two_inodes where two successive swap calls are
>>> generated.
>>>
>>> There are also some cases such as drivers/net/wireless/ath/ath5k/phy.c in
>>> the function ath5k_hw_get_median_noise_floor where the swap code makes up
>>> a whole if branch.
>>
>>> In this cases it would be good to remove the {}.
>>
>> How this can be handled?
>>
>> If I use this pattern:
>> @depends on patch@
>> identifier tmp;
>> expression a, b;
>> @@
>>
>> (
>>   if (...)
>> - {
>> -       tmp = a;
>> -       a = b;
>> -       b = tmp
>> +       swap(a, b)
>>         ;
>> - }
>> |
>> -       tmp = a;
>> -       a = b;
>> -       b = tmp
>> +       swap(a, b)
>>         ;
>> )
>>
>> The tool fails with error:
>>
>> EXN: Failure("rule starting on line 58: already tagged token:\nC code
>> context\nFile \"drivers/net/wireless/ath/ath5k/phy.c\", line 1574,
>> column 4, charpos = 41650\n around = 'sort',\n whole content =
>> \t\t\t\tsort[j - 1] = tmp;") in drivers/net/wireless/ath/ath5k/phy.c
> 
> A disjunction basically says "at this node in the cfg, can I match the
> first patter, or can I match the second pattern, etc."  Unfortunately in
> this case the two branches start matching at different nodes, so the short
> circuit aspect of a disjunction isn't used, and it matches both patterns.
> 
> The solution is to just make two rules.  The first for the if case and the
> second for everything else.
> 

  if (...)
- {
-       tmp = a;
-       a = b;
-       b = tmp
+       swap(a, b)
        ;
- }


This produces "single-line ifs".
Maybe generated patches can be improved somehow?
Moving -+; doesn't help in this case.

diff -u -p a/drivers/net/wireless/ath/ath9k/calib.c b/drivers/net/wireless/ath/ath9k/calib.c
--- a/drivers/net/wireless/ath/ath9k/calib.c
+++ b/drivers/net/wireless/ath/ath9k/calib.c
@@ -32,11 +32,7 @@ static int16_t ath9k_hw_get_nf_hist_mid(
 
        for (i = 0; i < ATH9K_NF_CAL_HIST_MAX - 1; i++) {
                for (j = 1; j < ATH9K_NF_CAL_HIST_MAX - i; j++) {
-                       if (sort[j] > sort[j - 1]) {
-                               nfval = sort[j];
-                               sort[j] = sort[j - 1];
-                               sort[j - 1] = nfval;
-                       }
+                       if (sort[j] > sort[j - 1]) swap(sort[j], sort[j - 1]);
                }
        }
        nfval = sort[(ATH9K_NF_CAL_HIST_MAX - 1) >> 1];
diff -u -p a/drivers/net/wireless/ath/ath9k/ar9003_calib.c b/drivers/net/wireless/ath/ath9k/ar9003_calib.c
--- a/drivers/net/wireless/ath/ath9k/ar9003_calib.c
+++ b/drivers/net/wireless/ath/ath9k/ar9003_calib.c
@@ -1011,19 +1011,11 @@ static void __ar955x_tx_iq_cal_sort(stru
                for (ix = 0; ix < MAXIQCAL - 1; ix++) {
                        for (iy = ix + 1; iy <= MAXIQCAL - 1; iy++) {
                                if (coeff->mag_coeff[i][im][iy] <
-                                   coeff->mag_coeff[i][im][ix]) {
-                                       temp = coeff->mag_coeff[i][im][ix];
-                                       coeff->mag_coeff[i][im][ix] =
-                                               coeff->mag_coeff[i][im][iy];
-                                       coeff->mag_coeff[i][im][iy] = temp;
-                               }
+                                   coeff->mag_coeff[i][im][ix]) swap(coeff->mag_coeff[i][im][ix],
+                                                                     coeff->mag_coeff[i][im][iy]);
                                if (coeff->phs_coeff[i][im][iy] <
-                                   coeff->phs_coeff[i][im][ix]) {
-                                       temp = coeff->phs_coeff[i][im][ix];
-                                       coeff->phs_coeff[i][im][ix] =
-                                               coeff->phs_coeff[i][im][iy];
-                                       coeff->phs_coeff[i][im][iy] = temp;
-                               }
+                                   coeff->phs_coeff[i][im][ix]) swap(coeff->phs_coeff[i][im][ix],
+                                                                     coeff->phs_coeff[i][im][iy]);

Thanks,
Denis