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mark_parents_uninteresting(): avoid most allocation

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Commit 941ba8db57 (Eliminate recursion in setting/clearing
marks in commit list, 2012-01-14) used a clever double-loop
to avoid allocations for single-parent chains of history.
However, it did so only when following parents of parents
(which was an uncommon case), and _always_ incurred at least
one allocation to populate the list of pending parents in
the first place.

We can turn this into zero-allocation in the common case by
iterating directly over the initial parent list, and then
following up on any pending items we might have discovered.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Jeff King 2018-05-11 14:03:15 -04:00 committed by Junio C Hamano
parent 43fc643b75
commit 8702b30fd7
1 changed files with 25 additions and 19 deletions
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44
revision.c
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@ -114,32 +114,38 @@ static void commit_stack_clear(struct commit_stack *stack)
stack->nr = stack->alloc = 0;
}
static void mark_one_parent_uninteresting(struct commit *commit,
struct commit_stack *pending)
{
struct commit_list *l;
if (commit->object.flags & UNINTERESTING)
return;
commit->object.flags |= UNINTERESTING;
/*
* Normally we haven't parsed the parent
* yet, so we won't have a parent of a parent
* here. However, it may turn out that we've
* reached this commit some other way (where it
* wasn't uninteresting), in which case we need
* to mark its parents recursively too..
*/
for (l = commit->parents; l; l = l->next)
commit_stack_push(pending, l->item);
}
void mark_parents_uninteresting(struct commit *commit)
{
struct commit_stack pending = COMMIT_STACK_INIT;
struct commit_list *l;
for (l = commit->parents; l; l = l->next)
commit_stack_push(&pending, l->item);
mark_one_parent_uninteresting(l->item, &pending);
while (pending.nr > 0) {
struct commit *commit = commit_stack_pop(&pending);
if (commit->object.flags & UNINTERESTING)
return;
commit->object.flags |= UNINTERESTING;
/*
* Normally we haven't parsed the parent
* yet, so we won't have a parent of a parent
* here. However, it may turn out that we've
* reached this commit some other way (where it
* wasn't uninteresting), in which case we need
* to mark its parents recursively too..
*/
for (l = commit->parents; l; l = l->next)
commit_stack_push(&pending, l->item);
}
while (pending.nr > 0)
mark_one_parent_uninteresting(commit_stack_pop(&pending),
&pending);
commit_stack_clear(&pending);
}