Simplify topo-sort logic

.. by not using quite so much indirection.

This currently grows the "struct commit" a bit, which could be avoided by
using a union for "util" and "indegree" (the topo-sort used to use "util"
anyway, so you cannot use them together), but for now the goal of this was
to simplify, not optimize.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

4 files changed, 55 insertions, 126 deletions

diff --git a/commit.c b/commit.c
index 8262f6ac58..ab4eb8bdd1 100644
--- a/commit.c
+++ b/commit.c
@@ -9,22 +9,6 @@
 
 int save_commit_buffer = 1;
 
-struct sort_node
-{
-	/*
-	 * the number of children of the associated commit
-	 * that also occur in the list being sorted.
-	 */
-	unsigned int indegree;
-
-	/*
-	 * reference to original list item that we will re-use
-	 * on output.
-	 */
-	struct commit_list * list_item;
-
-};
-
 const char *commit_type = "commit";
 
 static struct cmt_fmt_map {
@@ -1149,69 +1133,38 @@ struct commit *pop_commit(struct commit_list **stack)
 	return item;
 }
 
-void topo_sort_default_setter(struct commit *c, void *data)
-{
-	c->util = data;
-}
-
-void *topo_sort_default_getter(struct commit *c)
-{
-	return c->util;
-}
-
 /*
  * Performs an in-place topological sort on the list supplied.
  */
 void sort_in_topological_order(struct commit_list ** list, int lifo)
 {
-	sort_in_topological_order_fn(list, lifo, topo_sort_default_setter,
-				     topo_sort_default_getter);
-}
-
-void sort_in_topological_order_fn(struct commit_list ** list, int lifo,
-				  topo_sort_set_fn_t setter,
-				  topo_sort_get_fn_t getter)
-{
-	struct commit_list * next = *list;
-	struct commit_list * work = NULL, **insert;
-	struct commit_list ** pptr = list;
-	struct sort_node * nodes;
-	struct sort_node * next_nodes;
-	int count = 0;
-
-	/* determine the size of the list */
-	while (next) {
-		next = next->next;
-		count++;
-	}
+	struct commit_list *next, *orig = *list;
+	struct commit_list *work, **insert;
+	struct commit_list **pptr;
 
-	if (!count)
+	if (!orig)
 		return;
-	/* allocate an array to help sort the list */
-	nodes = xcalloc(count, sizeof(*nodes));
-	/* link the list to the array */
-	next_nodes = nodes;
-	next=*list;
-	while (next) {
-		next_nodes->list_item = next;
-		setter(next->item, next_nodes);
-		next_nodes++;
-		next = next->next;
+	*list = NULL;
+
+	/* Mark them and clear the indegree */
+	for (next = orig; next; next = next->next) {
+		struct commit *commit = next->item;
+		commit->object.flags |= TOPOSORT;
+		commit->indegree = 0;
 	}
+
 	/* update the indegree */
-	next=*list;
-	while (next) {
+	for (next = orig; next; next = next->next) {
 		struct commit_list * parents = next->item->parents;
 		while (parents) {
-			struct commit * parent=parents->item;
-			struct sort_node * pn = (struct sort_node *) getter(parent);
+			struct commit *parent = parents->item;
 
-			if (pn)
-				pn->indegree++;
-			parents=parents->next;
+			if (parent->object.flags & TOPOSORT)
+				parent->indegree++;
+			parents = parents->next;
 		}
-		next=next->next;
 	}
+
 	/*
 	 * find the tips
 	 *
@@ -1219,55 +1172,56 @@ void sort_in_topological_order_fn(struct commit_list ** list, int lifo,
 	 *
 	 * the tips serve as a starting set for the work queue.
 	 */
-	next=*list;
+	work = NULL;
 	insert = &work;
-	while (next) {
-		struct sort_node * node = (struct sort_node *) getter(next->item);
+	for (next = orig; next; next = next->next) {
+		struct commit *commit = next->item;
 
-		if (node->indegree == 0) {
-			insert = &commit_list_insert(next->item, insert)->next;
-		}
-		next=next->next;
+		if (!commit->indegree)
+			insert = &commit_list_insert(commit, insert)->next;
 	}
 
 	/* process the list in topological order */
 	if (!lifo)
 		sort_by_date(&work);
+
+	pptr = list;
+	*list = NULL;
 	while (work) {
-		struct commit * work_item = pop_commit(&work);
-		struct sort_node * work_node = (struct sort_node *) getter(work_item);
-		struct commit_list * parents = work_item->parents;
+		struct commit *commit;
+		struct commit_list *parents, *work_item;
 
-		while (parents) {
-			struct commit * parent=parents->item;
-			struct sort_node * pn = (struct sort_node *) getter(parent);
-
-			if (pn) {
-				/*
-				 * parents are only enqueued for emission
-				 * when all their children have been emitted thereby
-				 * guaranteeing topological order.
-				 */
-				pn->indegree--;
-				if (!pn->indegree) {
-					if (!lifo)
-						insert_by_date(parent, &work);
-					else
-						commit_list_insert(parent, &work);
-				}
+		work_item = work;
+		work = work_item->next;
+		work_item->next = NULL;
+
+		commit = work_item->item;
+		for (parents = commit->parents; parents ; parents = parents->next) {
+			struct commit *parent=parents->item;
+
+			if (!(parent->object.flags & TOPOSORT))
+				continue;
+
+			/*
+			 * parents are only enqueued for emission
+			 * when all their children have been emitted thereby
+			 * guaranteeing topological order.
+			 */
+			if (!--parent->indegree) {
+				if (!lifo)
+					insert_by_date(parent, &work);
+				else
+					commit_list_insert(parent, &work);
 			}
-			parents=parents->next;
 		}
 		/*
 		 * work_item is a commit all of whose children
 		 * have already been emitted. we can emit it now.
 		 */
-		*pptr = work_node->list_item;
-		pptr = &(*pptr)->next;
-		*pptr = NULL;
-		setter(work_item, NULL);
+		commit->object.flags &= ~TOPOSORT;
+		*pptr = work_item;
+		pptr = &work_item->next;
 	}
-	free(nodes);
 }
 
 /* merge-base stuff */
diff --git a/commit.h b/commit.h
index 13b537293d..4ed0c1cf7f 100644
--- a/commit.h
+++ b/commit.h
@@ -14,6 +14,7 @@ struct commit_list {
 struct commit {
 	struct object object;
 	void *util;
+	unsigned int indegree;
 	unsigned long date;
 	struct commit_list *parents;
 	struct tree *tree;
@@ -84,31 +85,12 @@ void clear_commit_marks(struct commit *commit, unsigned int mark);
 /*
  * Performs an in-place topological sort of list supplied.
  *
- * Pre-conditions for sort_in_topological_order:
- *   all commits in input list and all parents of those
- *   commits must have object.util == NULL
- *
- * Pre-conditions for sort_in_topological_order_fn:
- *   all commits in input list and all parents of those
- *   commits must have getter(commit) == NULL
- *
- * Post-conditions:
  *   invariant of resulting list is:
  *      a reachable from b => ord(b) < ord(a)
  *   in addition, when lifo == 0, commits on parallel tracks are
  *   sorted in the dates order.
  */
-
-typedef void (*topo_sort_set_fn_t)(struct commit*, void *data);
-typedef void* (*topo_sort_get_fn_t)(struct commit*);
-
-void topo_sort_default_setter(struct commit *c, void *data);
-void *topo_sort_default_getter(struct commit *c);
-
 void sort_in_topological_order(struct commit_list ** list, int lifo);
-void sort_in_topological_order_fn(struct commit_list ** list, int lifo,
-				  topo_sort_set_fn_t setter,
-				  topo_sort_get_fn_t getter);
 
 struct commit_graft {
 	unsigned char sha1[20];
diff --git a/revision.c b/revision.c
index e76da0d448..e85b4af392 100644
--- a/revision.c
+++ b/revision.c
@@ -677,9 +677,6 @@ void init_revisions(struct rev_info *revs, const char *prefix)
 	revs->prune_fn = NULL;
 	revs->prune_data = NULL;
 
-	revs->topo_setter = topo_sort_default_setter;
-	revs->topo_getter = topo_sort_default_getter;
-
 	revs->commit_format = CMIT_FMT_DEFAULT;
 
 	diff_setup(&revs->diffopt);
@@ -1303,9 +1300,7 @@ int prepare_revision_walk(struct rev_info *revs)
 		if (limit_list(revs) < 0)
 			return -1;
 	if (revs->topo_order)
-		sort_in_topological_order_fn(&revs->commits, revs->lifo,
-					     revs->topo_setter,
-					     revs->topo_getter);
+		sort_in_topological_order(&revs->commits, revs->lifo);
 	return 0;
 }
 
diff --git a/revision.h b/revision.h
index 98a0a8f3fa..1f645764a5 100644
--- a/revision.h
+++ b/revision.h
@@ -10,6 +10,7 @@
 #define CHILD_SHOWN	(1u<<6)
 #define ADDED		(1u<<7)	/* Parents already parsed and added? */
 #define SYMMETRIC_LEFT	(1u<<8)
+#define TOPOSORT	(1u<<9)	/* In the active toposort list.. */
 
 struct rev_info;
 struct log_info;
@@ -96,9 +97,6 @@ struct rev_info {
 	struct diff_options diffopt;
 	struct diff_options pruning;
 
-	topo_sort_set_fn_t topo_setter;
-	topo_sort_get_fn_t topo_getter;
-
 	struct reflog_walk_info *reflog_info;
 };