Re: [PATCH 1/3] rev-list: allow bisect and first-parent flags

From: Junio C Hamano <gitster@pobox.com>
To: "Aaron Lipman via GitGitGadget" <gitgitgadget@gmail.com>
Cc: git@vger.kernel.org, Aaron Lipman <alipman88@gmail.com>
Subject: Re: [PATCH 1/3] rev-list: allow bisect and first-parent flags
Date: Tue, 28 Jul 2020 14:53:05 -0700	[thread overview]
Message-ID: <xmqqa6zjcnni.fsf@gitster.c.googlers.com> (raw)
In-Reply-To: <xmqq4kpre6cl.fsf@gitster.c.googlers.com> (Junio C. Hamano's message of "Tue, 28 Jul 2020 13:23:54 -0700")

Taking all the suggestions and speculations I made in the message I
am responding to, I think squashing the following changes into the
[PATCH 1/3] would make the code simpler and much easier to follow.

The first two hunks revert the changes made to count_distance(); the
third hunk makes sure that count_distance() is not called under the
first-parent mode, since the "single-strand-of-pearls" optimization
is the only counting method needed in the first-parent mode.  The
last hunk is to revert the changes to the single-strand-of-pearls
optimized counting and tweak the loop control to take only the first
parent into account.

Your new tests in 6000 and 6002 of course still pass with this
clean-up.

 bisect.c | 27 ++++++++++++---------------
 1 file changed, 12 insertions(+), 15 deletions(-)

diff --git a/bisect.c b/bisect.c
index 762f68c8e9..a11fdb1473 100644
--- a/bisect.c
+++ b/bisect.c
@@ -37,7 +37,7 @@ static const char *term_good;
  * We care just barely enough to avoid recursing for
  * non-merge entries.
  */
-static int count_distance(struct commit_list *entry, int first_parent_only)
+static int count_distance(struct commit_list *entry)
 {
 	int nr = 0;
 
@@ -52,10 +52,10 @@ static int count_distance(struct commit_list *entry, int first_parent_only)
 		commit->object.flags |= COUNTED;
 		p = commit->parents;
 		entry = p;
-		if (p && !first_parent_only) {
+		if (p) {
 			p = p->next;
 			while (p) {
-				nr += count_distance(p, first_parent_only);
+				nr += count_distance(p);
 				p = p->next;
 			}
 		}
@@ -315,7 +315,9 @@ static struct commit_list *do_find_bisection(struct commit_list *list,
 			continue;
 		if (weight(p) != -2)
 			continue;
-		weight_set(p, count_distance(p, first_parent_only));
+		if (first_parent_only)
+			BUG("shouldn't be calling count-distance in fp mode");
+		weight_set(p, count_distance(p));
 		clear_distance(list);
 
 		/* Does it happen to be at exactly half-way? */
@@ -331,21 +333,16 @@ static struct commit_list *do_find_bisection(struct commit_list *list,
 			struct commit_list *q;
 			unsigned flags = p->item->object.flags;
 
-			/* if commit p has already been weighted, continue. */
 			if (0 <= weight(p))
 				continue;
 
-			/*
-			 * otherwise, find the first interesting
-			 * already-weighted parent of p and store as q.
-			 */
-			for (q = p->item->parents; q; q = q->next) {
-				if (!(q->item->object.flags & UNINTERESTING) && 0 <= weight(q)) {
-					break;
-				} else if (first_parent_only) {
-					q = NULL;
+			for (q = p->item->parents;
+			     q;
+			     q = first_parent_only ? NULL : q->next) {
+				if (q->item->object.flags & UNINTERESTING)
+					continue;
+				if (0 <= weight(q))
 					break;
-				}
 			}
 			if (!q)
 				continue;


