Subject: Re: [PATCH 1/3] commit-reach: use one walk in remove_redundant()

From: Derrick Stolee <[email-masked]>
Date: Sat, 30 Jan 2021 22:52:59 -0500

On 1/29/2021 12:11 PM, René Scharfe wrote:
> Am 28.01.21 um 21:51 schrieb Junio C Hamano:
>> "Derrick Stolee via GitGitGadget" <[email-masked]> writes:
>>> +	/* rearrange array */
>>> +	dup = xcalloc(cnt, sizeof(struct commit *));
>>> +	COPY_ARRAY(dup, array, cnt);
>>> +	for (i = 0; i < cnt; i++) {
>>> +		if (dup[i]->object.flags & STALE) {
>>> +			int insert = cnt - 1 - (i - count_non_stale);
>>> +			array[insert] = dup[i];
>>> +		} else {
>>> +			array[count_non_stale] = dup[i];
>>> +			count_non_stale++;
>>> +		}
>>> +	}
>>> +	free(dup);
>>
>> The "fill stale ones from the end, non-stale ones from the
>> beginning" in the loop looks unnecessarily complex to me.  I wonder
>> if we can do only the "fill non-stale ones from the beginning" half,
>> i.e.
>>
>> 	for (i = count_non_stale = 0; i < cnt; i++) {
>> 		if (dup[i] is not stale)
>> 			array[count_non_stale++] = dup[i];
>> 	}
>>
>> without the "keep the stale one at the end of array[]", and clear
>> marks using what is in dup[] as starting points before discarding
>> dup[]?
>>
>> Or do the callers still look at the entries beyond count_non_stale?
> 
> Had the same reaction.  Both callers ignore the stale entries.

Ok, I can update that logic accordingly. I wanted to keep consistent
with the comment at the start of the method:

	/*
	 * Some commit in the array may be an ancestor of
	 * another commit.  Move such commit to the end of
	 * the array, and return the number of commits that
	 * are independent from each other.
	 */

but if no caller actually needs that, then I can remove this
behavior. Anyone mind if it is a follow-up patch to change this
part of the behavior?

>> Other than that, nicely done.
>>
>>> +	/* clear marks */
>>> +	for (i = 0; i < cnt; i++) {
>>> +		struct commit_list *parents;
>>> +		parents = array[i]->parents;
>>> +
>>> +		while (parents) {
>>> +			clear_commit_marks(parents->item, STALE);
>>> +			parents = parents->next;
>>>  		}
> 
> This loop clears STALE from the parents of both the non-stale and
> stale entries.  OK.  Should it also clear it from the stale entries
> themselves?

clear_commit_marks() walks commits starting from the input commit
(parents->item in this case) and clears the STALE bit as long as
it is present. This way, the accumulated clear_commit_marks() will
walk each commit only once _and_ will visit any of the commits from
'array' that received the STALE bit during the above walk.

Thanks,
-Stolee