Subject: [PATCH 1/2] blame: large-scale performance rewrite

From: David Kastrup <[email-masked]>
Date: Sat, 26 Apr 2014 01:56:49 +0200

The previous implementation used a single sorted linear list of blame
entries for organizing all partial or completed work.  Every subtask had
to scan the whole list, with most entries not being relevant to the
task.  The resulting run-time was quadratic to the number of separate
chunks.

This change gives every subtask its own data to work with.  Subtasks are
organized into "struct origin" chains hanging off particular commits.
Commits are organized into a priority queue, processing them in commit
date order in order to keep most of the work affecting a particular blob
collated even in the presence of an extensive merge history.

For large files with a diversified history, a speedup by a factor of 3
or more is not unusual.

Signed-off-by: David Kastrup <[email-masked]>
---
 builtin/blame.c | 865 +++++++++++++++++++++++++++++++++++++-------------------
 1 file changed, 567 insertions(+), 298 deletions(-)

diff --git a/builtin/blame.c b/builtin/blame.c
index 88cb799..224f0ff 100644
--- a/builtin/blame.c
+++ b/builtin/blame.c
@@ -1,7 +1,8 @@
 /*
  * Blame
  *
- * Copyright (c) 2006, Junio C Hamano
+ * Copyright (c) 2006, 2014 by its authors
+ * See COPYING for licensing conditions
  */
 
 #include "cache.h"
@@ -18,7 +19,9 @@
 #include "cache-tree.h"
 #include "string-list.h"
 #include "mailmap.h"
+#include "mergesort.h"
 #include "parse-options.h"
+#include "prio-queue.h"
 #include "utf8.h"
 #include "userdiff.h"
 #include "line-range.h"
@@ -83,11 +86,42 @@ static unsigned blame_copy_score;
  */
 struct origin {
 	int refcnt;
+	/* Record preceding blame record for this blob */
 	struct origin *previous;
+	/* origins are put in a list linked via `next' hanging off the
+	 * corresponding commit's util field in order to make finding
+	 * them fast.  The presence in this chain does not count
+	 * towards the origin's reference count.  It is tempting to
+	 * let it count as long as the commit is pending examination,
+	 * but even under circumstances where the commit will be
+	 * present multiple times in the priority queue of unexamined
+	 * commits, processing the first instance will not leave any
+	 * work requiring the origin data for the second instance.  An
+	 * interspersed commit changing that would have to be
+	 * preexisting with a different ancestry and with the same
+	 * commit date in order to wedge itself between two instances
+	 * of the same commit in the priority queue _and_ produce
+	 * blame entries relevant for it.  While we don't want to let
+	 * us get tripped up by this case, it certainly does not seem
+	 * worth optimizing for.
+	 */
+	struct origin *next;
 	struct commit *commit;
+	/* `suspects' contains blame entries that may be attributed to
+	 * this origin's commit or to parent commits.  When a commit
+	 * is being processed, all suspects will be moved, either by
+	 * assigning them to an origin in a different commit, or by
+	 * shipping them to the scoreboard's ent list because they
+	 * cannot be attributed to a different commit.
+	 */
+	struct blame_entry *suspects;
 	mmfile_t file;
 	unsigned char blob_sha1[20];
 	unsigned mode;
+	/* guilty gets set when shipping any suspects to the final
+	 * blame list instead of other commits
+	 */
+	char guilty;
 	char path[FLEX_ARRAY];
 };
 
@@ -176,10 +210,22 @@ static inline struct origin *origin_incref(struct origin *o)
 static void origin_decref(struct origin *o)
 {
 	if (o && --o->refcnt <= 0) {
+		struct origin *p, *l = NULL;
 		if (o->previous)
 			origin_decref(o->previous);
 		free(o->file.ptr);
-		free(o);
+		/* Should be present exactly once in commit chain */
+		for (p = o->commit->util; p; l = p, p = p->next) {
+			if (p == o) {
+				if (l)
+					l->next = p->next;
+				else
+					o->commit->util = p->next;
+				free(o);
+				return;
+			}
+		}
+		die("internal error in blame::origin_decref");
 	}
 }
 
@@ -193,8 +239,12 @@ static void drop_origin_blob(struct origin *o)
 
 /*
  * Each group of lines is described by a blame_entry; it can be split
- * as we pass blame to the parents.  They form a linked list in the
- * scoreboard structure, sorted by the target line number.
+ * as we pass blame to the parents.  They are arranged in linked lists
+ * kept as `suspects' of some unprocessed origin, or entered (when the
+ * blame origin has been finalized) into the scoreboard structure.
+ * While the scoreboard structure is only sorted at the end of
+ * processing (according to final image line number), the lists
+ * attached to an origin are sorted by the target line number.
  */
 struct blame_entry {
 	struct blame_entry *next;
@@ -210,15 +260,6 @@ struct blame_entry {
 	/* the commit that introduced this group into the final image */
 	struct origin *suspect;
 
-	/* true if the suspect is truly guilty; false while we have not
-	 * checked if the group came from one of its parents.
-	 */
-	char guilty;
-
-	/* true if the entry has been scanned for copies in the current parent
-	 */
-	char scanned;
-
 	/* the line number of the first line of this group in the
 	 * suspect's file; internally all line numbers are 0 based.
 	 */
@@ -231,11 +272,112 @@ struct blame_entry {
 };
 
 /*
+ * Any merge of blames happens on lists of blames that arrived via
+ * different parents in a single suspect.  In this case, we want to
+ * sort according to the suspect line numbers as opposed to the final
+ * image line numbers.  The function body is somewhat longish because
+ * it avoids unnecessary writes.
+ */
+
+static struct blame_entry *blame_merge(struct blame_entry *list1,
+				       struct blame_entry *list2)
+{
+	struct blame_entry *p1 = list1, *p2 = list2,
+		**tail = &list1;
+
+	if (!p1)
+		return p2;
+	if (!p2)
+		return p1;
+
+	if (p1->s_lno <= p2->s_lno) {
+		do {
+			tail = &p1->next;
+			if ((p1 = *tail) == NULL) {
+				*tail = p2;
+				return list1;
+			}
+		} while (p1->s_lno <= p2->s_lno);
+	}
+	for (;;) {
+		*tail = p2;
+		do {
+			tail = &p2->next;
+			if ((p2 = *tail) == NULL)  {
+				*tail = p1;
+				return list1;
+			}
+		} while (p1->s_lno > p2->s_lno);
+		*tail = p1;
+		do {
+			tail = &p1->next;
+			if ((p1 = *tail) == NULL) {
+				*tail = p2;
+				return list1;
+			}
+		} while (p1->s_lno <= p2->s_lno);
+	}
+}
+
+static void *get_next_blame(const void *p)
+{
+	return ((struct blame_entry *)p)->next;
+}
+
+static void set_next_blame(void *p1, void *p2)
+{
+	((struct blame_entry *)p1)->next = p2;
+}
+
+/*
+ * Final image line numbers are all different, so we don't need a
+ * three-way comparison here.
+ */
+
+static int compare_blame_final(const void *p1, const void *p2)
+{
+	return ((struct blame_entry *)p1)->lno > ((struct blame_entry *)p2)->lno
+		? 1 : -1;
+}
+
+static int compare_blame_suspect(const void *p1, const void *p2)
+{
+	const struct blame_entry *s1 = p1, *s2 = p2;
+	/*
+	 * to allow for collating suspects, we sort according to the
+	 * respective pointer value as the primary sorting criterion.
+	 * The actual relation is pretty unimportant as long as it
+	 * establishes a total order.  Comparing as integers gives us
+	 * that.
+	 */
+	if (s1->suspect != s2->suspect)
+		return (intptr_t)s1->suspect > (intptr_t)s2->suspect ? 1 : -1;
+	if (s1->s_lno == s2->s_lno)
+		return 0;
+	return s1->s_lno > s2->s_lno ? 1 : -1;
+}
+
+static struct blame_entry *blame_sort(struct blame_entry *head,
+				      int (*compare_fn)(const void *, const void *))
+{
+	return llist_mergesort (head, get_next_blame, set_next_blame, compare_fn);
+}
+
+static int compare_commits_by_reverse_commit_date(const void *a,
+						  const void *b,
+						  void *c)
+{
+	return -compare_commits_by_commit_date(a, b, c);
+}
+
+/*
  * The current state of the blame assignment.
  */
 struct scoreboard {
 	/* the final commit (i.e. where we started digging from) */
 	struct commit *final;
+	/* Priority queue for commits with unassigned blame records */
+	struct prio_queue commits;
 	struct rev_info *revs;
 	const char *path;
 
@@ -268,7 +410,6 @@ static void coalesce(struct scoreboard *sb)
 
 	for (ent = sb->ent; ent && (next = ent->next); ent = next) {
 		if (ent->suspect == next->suspect &&
-		    ent->guilty == next->guilty &&
 		    ent->s_lno + ent->num_lines == next->s_lno) {
 			ent->num_lines += next->num_lines;
 			ent->next = next->next;
@@ -284,6 +425,30 @@ static void coalesce(struct scoreboard *sb)
 }
 
 /*
+ * Merge the given sorted list of blames into a preexisting origin.
+ * If there were no previous blames to that commit, it is entered into
+ * the commit priority queue of the score board.
+ */
+
+static void queue_blames(struct scoreboard *sb, struct origin *porigin,
+			 struct blame_entry *sorted)
+{
+	if (porigin->suspects)
+		porigin->suspects = blame_merge(porigin->suspects, sorted);
+	else {
+		struct origin *o;
+		for (o = porigin->commit->util; o; o = o->next) {
+			if (o->suspects) {
+				porigin->suspects = sorted;
+				return;
+			}
+		}
+		porigin->suspects = sorted;
+		prio_queue_put(&sb->commits, porigin->commit);
+	}
+}
+
+/*
  * Given a commit and a path in it, create a new origin structure.
  * The callers that add blame to the scoreboard should use
  * get_origin() to obtain shared, refcounted copy instead of calling
@@ -295,23 +460,32 @@ static struct origin *make_origin(struct commit *commit, const char *path)
 	o = xcalloc(1, sizeof(*o) + strlen(path) + 1);
 	o->commit = commit;
 	o->refcnt = 1;
+	o->next = commit->util;
+	commit->util = o;
 	strcpy(o->path, path);
 	return o;
 }
 
 /*
  * Locate an existing origin or create a new one.
+ * This moves the origin to front position in the commit util list.
  */
 static struct origin *get_origin(struct scoreboard *sb,
 				 struct commit *commit,
 				 const char *path)
 {
-	struct blame_entry *e;
+	struct origin *o, *l;
 
-	for (e = sb->ent; e; e = e->next) {
-		if (e->suspect->commit == commit &&
-		    !strcmp(e->suspect->path, path))
-			return origin_incref(e->suspect);
+	for (o = commit->util, l = NULL; o; l = o, o = o->next) {
+		if (!strcmp(o->path, path)) {
+			/* bump to front */
+			if (l) {
+				l->next = o->next;
+				o->next = commit->util;
+				commit->util = o;
+			}
+			return origin_incref(o);
+		}
 	}
 	return make_origin(commit, path);
 }
@@ -350,41 +524,19 @@ static struct origin *find_origin(struct scoreboard *sb,
 				  struct commit *parent,
 				  struct origin *origin)
 {
-	struct origin *porigin = NULL;
+	struct origin *porigin;
 	struct diff_options diff_opts;
 	const char *paths[2];
 
-	if (parent->util) {
-		/*
-		 * Each commit object can cache one origin in that
-		 * commit.  This is a freestanding copy of origin and
-		 * not refcounted.
-		 */
-		struct origin *cached = parent->util;
-		if (!strcmp(cached->path, origin->path)) {
+	/* First check any existing origins */
+	for (porigin = parent->util; porigin; porigin = porigin->next)
+		if (!strcmp(porigin->path, origin->path)) {
 			/*
 			 * The same path between origin and its parent
 			 * without renaming -- the most common case.
 			 */
-			porigin = get_origin(sb, parent, cached->path);
-
-			/*
-			 * If the origin was newly created (i.e. get_origin
-			 * would call make_origin if none is found in the
-			 * scoreboard), it does not know the blob_sha1/mode,
-			 * so copy it.  Otherwise porigin was in the
-			 * scoreboard and already knows blob_sha1/mode.
-			 */
-			if (porigin->refcnt == 1) {
-				hashcpy(porigin->blob_sha1, cached->blob_sha1);
-				porigin->mode = cached->mode;
-			}
-			return porigin;
+			return origin_incref (porigin);
 		}
-		/* otherwise it was not very useful; free it */
-		free(parent->util);
-		parent->util = NULL;
-	}
 
 	/* See if the origin->path is different between parent
 	 * and origin first.  Most of the time they are the
@@ -450,19 +602,6 @@ static struct origin *find_origin(struct scoreboard *sb,
 	}
 	diff_flush(&diff_opts);
 	free_pathspec(&diff_opts.pathspec);
-	if (porigin) {
-		/*
-		 * Create a freestanding copy that is not part of
-		 * the refcounted origin found in the scoreboard, and
-		 * cache it in the commit.
-		 */
-		struct origin *cached;
-
-		cached = make_origin(porigin->commit, porigin->path);
-		hashcpy(cached->blob_sha1, porigin->blob_sha1);
-		cached->mode = porigin->mode;
-		parent->util = cached;
-	}
 	return porigin;
 }
 
@@ -509,46 +648,31 @@ static struct origin *find_rename(struct scoreboard *sb,
 }
 
 /*
- * Link in a new blame entry to the scoreboard.  Entries that cover the
- * same line range have been removed from the scoreboard previously.
+ * Append a new blame entry to a given output queue.
  */
-static void add_blame_entry(struct scoreboard *sb, struct blame_entry *e)
+static void add_blame_entry(struct blame_entry ***queue, struct blame_entry *e)
 {
-	struct blame_entry *ent, *prev = NULL;
-
 	origin_incref(e->suspect);
 
-	for (ent = sb->ent; ent && ent->lno < e->lno; ent = ent->next)
-		prev = ent;
-
-	/* prev, if not NULL, is the last one that is below e */
-
-	if (prev) {
-		e->next = prev->next;
-		prev->next = e;
-	}
-	else {
-		e->next = sb->ent;
-		sb->ent = e;
-	}
+	e->next = **queue;
+	**queue = e;
+	*queue = &e->next;
 }
 
 /*
  * src typically is on-stack; we want to copy the information in it to
- * a malloced blame_entry that is already on the linked list of the
- * scoreboard.  The origin of dst loses a refcnt while the origin of src
- * gains one.
+ * a malloced blame_entry that gets added to the given queue.  The
+ * origin of dst loses a refcnt.
  */
-static void dup_entry(struct blame_entry *dst, struct blame_entry *src)
+static void dup_entry(struct blame_entry ***queue,
+		      struct blame_entry *dst, struct blame_entry *src)
 {
-	struct blame_entry *n;
-
-	n = dst->next;
 	origin_incref(src->suspect);
 	origin_decref(dst->suspect);
 	memcpy(dst, src, sizeof(*src));
-	dst->next = n;
-	dst->score = 0;
+	dst->next = **queue;
+	**queue = dst;
+	*queue = &dst->next;
 }
 
 static const char *nth_line(struct scoreboard *sb, long lno)
@@ -620,10 +744,11 @@ static void split_overlap(struct blame_entry *split,
 
 /*
  * split_overlap() divided an existing blame e into up to three parts
- * in split.  Adjust the linked list of blames in the scoreboard to
+ * in split.  Any assigned blame is moved to queue to
  * reflect the split.
  */
-static void split_blame(struct scoreboard *sb,
+static void split_blame(struct blame_entry ***blamed,
+			struct blame_entry ***unblamed,
 			struct blame_entry *split,
 			struct blame_entry *e)
 {
@@ -631,61 +756,39 @@ static void split_blame(struct scoreboard *sb,
 
 	if (split[0].suspect && split[2].suspect) {
 		/* The first part (reuse storage for the existing entry e) */
-		dup_entry(e, &split[0]);
+		dup_entry(unblamed, e, &split[0]);
 
 		/* The last part -- me */
 		new_entry = xmalloc(sizeof(*new_entry));
 		memcpy(new_entry, &(split[2]), sizeof(struct blame_entry));
-		add_blame_entry(sb, new_entry);
+		add_blame_entry(unblamed, new_entry);
 
 		/* ... and the middle part -- parent */
 		new_entry = xmalloc(sizeof(*new_entry));
 		memcpy(new_entry, &(split[1]), sizeof(struct blame_entry));
-		add_blame_entry(sb, new_entry);
+		add_blame_entry(blamed, new_entry);
 	}
 	else if (!split[0].suspect && !split[2].suspect)
 		/*
 		 * The parent covers the entire area; reuse storage for
 		 * e and replace it with the parent.
 		 */
-		dup_entry(e, &split[1]);
+		dup_entry(blamed, e, &split[1]);
 	else if (split[0].suspect) {
 		/* me and then parent */
-		dup_entry(e, &split[0]);
+		dup_entry(unblamed, e, &split[0]);
 
 		new_entry = xmalloc(sizeof(*new_entry));
 		memcpy(new_entry, &(split[1]), sizeof(struct blame_entry));
-		add_blame_entry(sb, new_entry);
+		add_blame_entry(blamed, new_entry);
 	}
 	else {
 		/* parent and then me */
-		dup_entry(e, &split[1]);
+		dup_entry(blamed, e, &split[1]);
 
 		new_entry = xmalloc(sizeof(*new_entry));
 		memcpy(new_entry, &(split[2]), sizeof(struct blame_entry));
-		add_blame_entry(sb, new_entry);
-	}
-
-	if (DEBUG) { /* sanity */
-		struct blame_entry *ent;
-		int lno = sb->ent->lno, corrupt = 0;
-
-		for (ent = sb->ent; ent; ent = ent->next) {
-			if (lno != ent->lno)
-				corrupt = 1;
-			if (ent->s_lno < 0)
-				corrupt = 1;
-			lno += ent->num_lines;
-		}
-		if (corrupt) {
-			lno = sb->ent->lno;
-			for (ent = sb->ent; ent; ent = ent->next) {
-				printf("L %8d l %8d n %8d\n",
-				       lno, ent->lno, ent->num_lines);
-				lno = ent->lno + ent->num_lines;
-			}
-			die("oops");
-		}
+		add_blame_entry(unblamed, new_entry);
 	}
 }
 
@@ -702,74 +805,146 @@ static void decref_split(struct blame_entry *split)
 }
 
 /*
- * Helper for blame_chunk().  blame_entry e is known to overlap with
- * the patch hunk; split it and pass blame to the parent.
+ * reverse_blame reverses the list given in head, appending tail.
+ * That allows us to build lists in reverse order, then reverse them
+ * afterwards.  This can be faster than building the list in proper
+ * order right away.  The reason is that building in proper order
+ * requires writing a link in the _previous_ element, while building
+ * in reverse order just requires placing the list head into the
+ * _current_ element.
  */
-static void blame_overlap(struct scoreboard *sb, struct blame_entry *e,
-			  int tlno, int plno, int same,
-			  struct origin *parent)
-{
-	struct blame_entry split[3];
-
-	split_overlap(split, e, tlno, plno, same, parent);
-	if (split[1].suspect)
-		split_blame(sb, split, e);
-	decref_split(split);
-}
 
-/*
- * Find the line number of the last line the target is suspected for.
- */
-static int find_last_in_target(struct scoreboard *sb, struct origin *target)
+static struct blame_entry *reverse_blame(struct blame_entry *head,
+					 struct blame_entry *tail)
 {
-	struct blame_entry *e;
-	int last_in_target = -1;
-
-	for (e = sb->ent; e; e = e->next) {
-		if (e->guilty || e->suspect != target)
-			continue;
-		if (last_in_target < e->s_lno + e->num_lines)
-			last_in_target = e->s_lno + e->num_lines;
+	while (head) {
+		struct blame_entry *next = head->next;
+		head->next = tail;
+		tail = head;
+		head = next;
 	}
-	return last_in_target;
+	return tail;
 }
 
 /*
  * Process one hunk from the patch between the current suspect for
- * blame_entry e and its parent.  Find and split the overlap, and
- * pass blame to the overlapping part to the parent.
+ * blame_entry e and its parent.  This first blames any unfinished
+ * entries before the chunk (which is where target and parent start
+ * differing) on the parent, and then splits blame entries at the
+ * start and at the end of the difference region.  Since use of -M and
+ * -C options may lead to overlapping/duplicate source line number
+ * ranges, all we can rely on from sorting/merging is the order of the
+ * first suspect line number.
  */
-static void blame_chunk(struct scoreboard *sb,
-			int tlno, int plno, int same,
-			struct origin *target, struct origin *parent)
+static void blame_chunk(struct blame_entry ***dstq, struct blame_entry ***srcq,
+			int tlno, int offset, int same,
+			struct origin *parent)
 {
-	struct blame_entry *e;
+	struct blame_entry *e = **srcq;
+	struct blame_entry *samep = NULL, *diffp = NULL;
 
-	for (e = sb->ent; e; e = e->next) {
-		if (e->guilty || e->suspect != target)
-			continue;
-		if (same <= e->s_lno)
-			continue;
-		if (tlno < e->s_lno + e->num_lines)
-			blame_overlap(sb, e, tlno, plno, same, parent);
+	while (e && e->s_lno < tlno) {
+		struct blame_entry *next = e->next;
+		/*
+		 * current record starts before differing portion.  If
+		 * it reaches into it, we need to split it up and
+		 * examine the second part separately.
+		 */
+		if (e->s_lno + e->num_lines > tlno) {
+			/* Move second half to a new record */
+			int len = tlno - e->s_lno;
+			struct blame_entry *n = xcalloc(1, sizeof (struct blame_entry));
+			n->suspect = e->suspect;
+			n->lno = e->lno + len;
+			n->s_lno = e->s_lno + len;
+			n->num_lines = e->num_lines - len;
+			e->num_lines = len;
+			e->score = 0;
+			/* Push new record to diffp */
+			n->next = diffp;
+			diffp = n;
+		} else
+			origin_decref(e->suspect);
+		/* Pass blame for everything before the differing
+		 * chunk to the parent */
+		e->suspect = origin_incref(parent);
+		e->s_lno += offset;
+		e->next = samep;
+		samep = e;
+		e = next;
+	}
+	/*
+	 * As we don't know how much of a common stretch after this
+	 * diff will occur, the currently blamed parts are all that we
+	 * can assign to the parent for now.
+	 */
+
+	if (samep) {
+		**dstq = reverse_blame(samep, **dstq);
+		*dstq = &samep->next;
 	}
+	/*
+	 * Prepend the split off portions: everything after e starts
+	 * after the blameable portion.
+	 */
+	e = reverse_blame(diffp, e);
+
+	/*
+	 * Now retain records on the target while parts are different
+	 * from the parent.
+	 */
+	samep = NULL;
+	diffp = NULL;
+	while (e && e->s_lno < same) {
+		struct blame_entry *next = e->next;
+
+		/*
+		 * If current record extends into sameness, need to split.
+		 */
+		if (e->s_lno + e->num_lines > same) {
+			/*
+			 * Move second half to a new record to be
+			 * processed by later chunks
+			 */
+			int len = same - e->s_lno;
+			struct blame_entry *n = xcalloc(1, sizeof (struct blame_entry));
+			n->suspect = origin_incref(e->suspect);
+			n->lno = e->lno + len;
+			n->s_lno = e->s_lno + len;
+			n->num_lines = e->num_lines - len;
+			e->num_lines = len;
+			e->score = 0;
+			/* Push new record to samep */
+			n->next = samep;
+			samep = n;
+		}
+		e->next = diffp;
+		diffp = e;
+		e = next;
+	}
+	**srcq = reverse_blame(diffp, reverse_blame(samep, e));
+	/* Move across elements that are in the unblamable portion */
+	if (diffp)
+		*srcq = &diffp->next;
 }
 
 struct blame_chunk_cb_data {
-	struct scoreboard *sb;
-	struct origin *target;
 	struct origin *parent;
-	long plno;
-	long tlno;
+	long offset;
+	struct blame_entry **dstq;
+	struct blame_entry **srcq;
 };
 
+/* diff chunks are from parent to target */
 static int blame_chunk_cb(long start_a, long count_a,
 			  long start_b, long count_b, void *data)
 {
 	struct blame_chunk_cb_data *d = data;
-	blame_chunk(d->sb, d->tlno, d->plno, start_b, d->target, d->parent);
-	d->plno = start_a + count_a;
-	d->tlno = start_b + count_b;
+	if (start_a - start_b != d->offset)
+		die("internal error in blame::blame_chunk_cb");
+	blame_chunk(&d->dstq, &d->srcq, start_b, start_a - start_b,
+		    start_b + count_b, d->parent);
+	d->offset = start_a + count_a - (start_b + count_b);
 	return 0;
 }
 
@@ -778,29 +953,32 @@ static int blame_chunk_cb(long start_a, long count_a,
  * for the lines it is suspected to its parent.  Run diff to find
  * which lines came from parent and pass blame for them.
  */
-static int pass_blame_to_parent(struct scoreboard *sb,
-				struct origin *target,
-				struct origin *parent)
+static void pass_blame_to_parent(struct scoreboard *sb,
+				 struct origin *target,
+				 struct origin *parent)
 {
-	int last_in_target;
 	mmfile_t file_p, file_o;
 	struct blame_chunk_cb_data d;
+	struct blame_entry *newdest = NULL;
 
-	memset(&d, 0, sizeof(d));
-	d.sb = sb; d.target = target; d.parent = parent;
-	last_in_target = find_last_in_target(sb, target);
-	if (last_in_target < 0)
-		return 1; /* nothing remains for this target */
+	if (!target->suspects)
+		return; /* nothing remains for this target */
+
+	d.parent = parent;
+	d.offset = 0;
+	d.dstq = &newdest; d.srcq = &target->suspects;
 
 	fill_origin_blob(&sb->revs->diffopt, parent, &file_p);
 	fill_origin_blob(&sb->revs->diffopt, target, &file_o);
 	num_get_patch++;
 
 	diff_hunks(&file_p, &file_o, 0, blame_chunk_cb, &d);
-	/* The rest (i.e. anything after tlno) are the same as the parent */
-	blame_chunk(sb, d.tlno, d.plno, last_in_target, target, parent);
+	/* The rest are the same as the parent */
+	blame_chunk(&d.dstq, &d.srcq, INT_MAX, d.offset, INT_MAX, parent);
+	*d.dstq = NULL;
+	queue_blames(sb, parent, newdest);
 
-	return 0;
+	return;
 }
 
 /*
@@ -945,43 +1123,80 @@ static void find_copy_in_blob(struct scoreboard *sb,
 	handle_split(sb, ent, d.tlno, d.plno, ent->num_lines, parent, split);
 }
 
+/* Move all blame entries from list *source that have a score smaller
+ * than score_min to the front of list *small.
+ * Returns a pointer to the link pointing to the old head of the small list.
+ */
+
+static struct blame_entry **filter_small(struct scoreboard *sb,
+					 struct blame_entry **small,
+					 struct blame_entry **source,
+					 unsigned score_min)
+{
+	struct blame_entry *p = *source;
+	struct blame_entry *oldsmall = *small;
+	while (p) {
+		if (ent_score(sb, p) <= score_min) {
+			*small = p;
+			small = &p->next;
+			p = *small;
+		} else {
+			*source = p;
+			source = &p->next;
+			p = *source;
+		}
+	}
+	*small = oldsmall;
+	*source = NULL;
+	return small;
+}
+
 /*
  * See if lines currently target is suspected for can be attributed to
  * parent.
  */
-static int find_move_in_parent(struct scoreboard *sb,
-			       struct origin *target,
-			       struct origin *parent)
+static void find_move_in_parent(struct scoreboard *sb,
+				struct blame_entry ***blamed,
+				struct blame_entry **toosmall,
+				struct origin *target,
+				struct origin *parent)
 {
-	int last_in_target, made_progress;
 	struct blame_entry *e, split[3];
+	struct blame_entry *unblamed = target->suspects;
+	struct blame_entry *leftover = NULL;
 	mmfile_t file_p;
 
-	last_in_target = find_last_in_target(sb, target);
-	if (last_in_target < 0)
-		return 1; /* nothing remains for this target */
+	if (!unblamed)
+		return; /* nothing remains for this target */
 
 	fill_origin_blob(&sb->revs->diffopt, parent, &file_p);
 	if (!file_p.ptr)
-		return 0;
+		return;
 
-	made_progress = 1;
-	while (made_progress) {
-		made_progress = 0;
-		for (e = sb->ent; e; e = e->next) {
-			if (e->guilty || e->suspect != target ||
-			    ent_score(sb, e) < blame_move_score)
-				continue;
+	/* At each iteration, unblamed has a NULL-terminated list of
+	 * entries that have not yet been tested for blame.  leftover
+	 * contains the reversed list of entries that have been tested
+	 * without being assignable to the parent.
+	 */
+	do {
+		struct blame_entry **unblamedtail = &unblamed;
+		struct blame_entry *next;
+		for (e = unblamed; e; e = next) {
+			next = e->next;
 			find_copy_in_blob(sb, e, parent, split, &file_p);
 			if (split[1].suspect &&
 			    blame_move_score < ent_score(sb, &split[1])) {
-				split_blame(sb, split, e);
-				made_progress = 1;
+				split_blame(blamed, &unblamedtail, split, e);
+			} else {
+				e->next = leftover;
+				leftover = e;
 			}
 			decref_split(split);
 		}
-	}
-	return 0;
+		*unblamedtail = NULL;
+		toosmall = filter_small(sb, toosmall, &unblamed, blame_move_score);
+	} while (unblamed);
+	target->suspects = reverse_blame(leftover, NULL);
 }
 
 struct blame_list {
@@ -993,62 +1208,46 @@ struct blame_list {
  * Count the number of entries the target is suspected for,
  * and prepare a list of entry and the best split.
  */
-static struct blame_list *setup_blame_list(struct scoreboard *sb,
-					   struct origin *target,
-					   int min_score,
+static struct blame_list *setup_blame_list(struct blame_entry *unblamed,
 					   int *num_ents_p)
 {
 	struct blame_entry *e;
 	int num_ents, i;
 	struct blame_list *blame_list = NULL;
 
-	for (e = sb->ent, num_ents = 0; e; e = e->next)
-		if (!e->scanned && !e->guilty &&
-		    e->suspect == target &&
-		    min_score < ent_score(sb, e))
-			num_ents++;
+	for (e = unblamed, num_ents = 0; e; e = e->next)
+		num_ents++;
 	if (num_ents) {
 		blame_list = xcalloc(num_ents, sizeof(struct blame_list));
-		for (e = sb->ent, i = 0; e; e = e->next)
-			if (!e->scanned && !e->guilty &&
-			    e->suspect == target &&
-			    min_score < ent_score(sb, e))
-				blame_list[i++].ent = e;
+		for (e = unblamed, i = 0; e; e = e->next)
+			blame_list[i++].ent = e;
 	}
 	*num_ents_p = num_ents;
 	return blame_list;
 }
 
 /*
- * Reset the scanned status on all entries.
- */
-static void reset_scanned_flag(struct scoreboard *sb)
-{
-	struct blame_entry *e;
-	for (e = sb->ent; e; e = e->next)
-		e->scanned = 0;
-}
-
-/*
  * For lines target is suspected for, see if we can find code movement
  * across file boundary from the parent commit.  porigin is the path
  * in the parent we already tried.
  */
-static int find_copy_in_parent(struct scoreboard *sb,
-			       struct origin *target,
-			       struct commit *parent,
-			       struct origin *porigin,
-			       int opt)
+static void find_copy_in_parent(struct scoreboard *sb,
+				struct blame_entry ***blamed,
+				struct blame_entry **toosmall,
+				struct origin *target,
+				struct commit *parent,
+				struct origin *porigin,
+				int opt)
 {
 	struct diff_options diff_opts;
 	int i, j;
-	int retval;
 	struct blame_list *blame_list;
 	int num_ents;
+	struct blame_entry *unblamed = target->suspects;
+	struct blame_entry *leftover = NULL;
 
-	blame_list = setup_blame_list(sb, target, blame_copy_score, &num_ents);
-	if (!blame_list)
-		return 1; /* nothing remains for this target */
+	if (!unblamed)
+		return; /* nothing remains for this target */
 
 	diff_setup(&diff_opts);
 	DIFF_OPT_SET(&diff_opts, RECURSIVE);
@@ -1078,9 +1277,9 @@ static int find_copy_in_parent(struct scoreboard *sb,
 	if (!DIFF_OPT_TST(&diff_opts, FIND_COPIES_HARDER))
 		diffcore_std(&diff_opts);
 
-	retval = 0;
-	while (1) {
-		int made_progress = 0;
+	do {
+		struct blame_entry **unblamedtail = &unblamed;
+		blame_list = setup_blame_list(unblamed, &num_ents);
 
 		for (i = 0; i < diff_queued_diff.nr; i++) {
 			struct diff_filepair *p = diff_queued_diff.queue[i];
@@ -1117,27 +1316,21 @@ static int find_copy_in_parent(struct scoreboard *sb,
 			struct blame_entry *split = blame_list[j].split;
 			if (split[1].suspect &&
 			    blame_copy_score < ent_score(sb, &split[1])) {
-				split_blame(sb, split, blame_list[j].ent);
-				made_progress = 1;
+				split_blame(blamed, &unblamedtail, split,
+					    blame_list[j].ent);
+			} else {
+				blame_list[j].ent->next = leftover;
+				leftover = blame_list[j].ent;
 			}
-			else
-				blame_list[j].ent->scanned = 1;
 			decref_split(split);
 		}
 		free(blame_list);
-
-		if (!made_progress)
-			break;
-		blame_list = setup_blame_list(sb, target, blame_copy_score, &num_ents);
-		if (!blame_list) {
-			retval = 1;
-			break;
-		}
-	}
-	reset_scanned_flag(sb);
+		*unblamedtail = NULL;
+		toosmall = filter_small(sb, toosmall, &unblamed, blame_copy_score);
+	} while (unblamed);
+	target->suspects = reverse_blame(leftover, NULL);
 	diff_flush(&diff_opts);
 	free_pathspec(&diff_opts.pathspec);
-	return retval;
 }
 
 /*
@@ -1147,20 +1340,21 @@ static int find_copy_in_parent(struct scoreboard *sb,
 static void pass_whole_blame(struct scoreboard *sb,
 			     struct origin *origin, struct origin *porigin)
 {
-	struct blame_entry *e;
+	struct blame_entry *e, *suspects;
 
 	if (!porigin->file.ptr && origin->file.ptr) {
 		/* Steal its file */
 		porigin->file = origin->file;
 		origin->file.ptr = NULL;
 	}
-	for (e = sb->ent; e; e = e->next) {
-		if (e->suspect != origin)
-			continue;
+	suspects = origin->suspects;
+	origin->suspects = NULL;
+	for (e = suspects; e; e = e->next) {
 		origin_incref(porigin);
 		origin_decref(e->suspect);
 		e->suspect = porigin;
 	}
+	queue_blames(sb, porigin, suspects);
 }
 
 /*
@@ -1184,6 +1378,27 @@ static int num_scapegoats(struct rev_info *revs, struct commit *commit)
 	return cnt;
 }
 
+/* Distribute collected unsorted blames to the respected sorted lists
+ * in the various origins.
+ */
+static void distribute_blame(struct scoreboard *sb, struct blame_entry *blamed)
+{
+	blamed = blame_sort(blamed, compare_blame_suspect);
+	while (blamed)
+	{
+		struct origin *porigin = blamed->suspect;
+		struct blame_entry *suspects = NULL;
+		do {
+			struct blame_entry *next = blamed->next;
+			blamed->next = suspects;
+			suspects = blamed;
+			blamed = next;
+		} while (blamed && blamed->suspect == porigin);
+		suspects = reverse_blame(suspects, NULL);
+		queue_blames(sb, porigin, suspects);
+	}
+}
+
 #define MAXSG 16
 
 static void pass_blame(struct scoreboard *sb, struct origin *origin, int opt)
@@ -1194,6 +1409,8 @@ static void pass_blame(struct scoreboard *sb, struct origin *origin, int opt)
 	struct commit_list *sg;
 	struct origin *sg_buf[MAXSG];
 	struct origin *porigin, **sg_origin = sg_buf;
+	struct blame_entry *toosmall = NULL;
+	struct blame_entry *blames, **blametail = &blames;
 
 	num_sg = num_scapegoats(revs, commit);
 	if (!num_sg)
@@ -1255,38 +1472,71 @@ static void pass_blame(struct scoreboard *sb, struct origin *origin, int opt)
 			origin_incref(porigin);
 			origin->previous = porigin;
 		}
-		if (pass_blame_to_parent(sb, origin, porigin))
+		pass_blame_to_parent(sb, origin, porigin);
+		if (!origin->suspects)
 			goto finish;
 	}
 
 	/*
 	 * Optionally find moves in parents' files.
 	 */
-	if (opt & PICKAXE_BLAME_MOVE)
-		for (i = 0, sg = first_scapegoat(revs, commit);
-		     i < num_sg && sg;
-		     sg = sg->next, i++) {
-			struct origin *porigin = sg_origin[i];
-			if (!porigin)
-				continue;
-			if (find_move_in_parent(sb, origin, porigin))
-				goto finish;
+	if (opt & PICKAXE_BLAME_MOVE) {
+		filter_small(sb, &toosmall, &origin->suspects, blame_move_score);
+		if (origin->suspects) {
+			for (i = 0, sg = first_scapegoat(revs, commit);
+			     i < num_sg && sg;
+			     sg = sg->next, i++) {
+				struct origin *porigin = sg_origin[i];
+				if (!porigin)
+					continue;
+				find_move_in_parent(sb, &blametail, &toosmall, origin, porigin);
+				if (!origin->suspects)
+					break;
+			}
 		}
+	}
 
 	/*
 	 * Optionally find copies from parents' files.
 	 */
-	if (opt & PICKAXE_BLAME_COPY)
+	if (opt & PICKAXE_BLAME_COPY) {
+		if (blame_copy_score > blame_move_score)
+			filter_small(sb, &toosmall, &origin->suspects, blame_copy_score);
+		else if (blame_copy_score < blame_move_score) {
+			origin->suspects = blame_merge(origin->suspects, toosmall);
+			toosmall = NULL;
+			filter_small(sb, &toosmall, &origin->suspects, blame_copy_score);
+		}
+		if (!origin->suspects)
+			goto finish;
+
 		for (i = 0, sg = first_scapegoat(revs, commit);
 		     i < num_sg && sg;
 		     sg = sg->next, i++) {
 			struct origin *porigin = sg_origin[i];
-			if (find_copy_in_parent(sb, origin, sg->item,
-						porigin, opt))
+			find_copy_in_parent(sb, &blametail, &toosmall,
+					    origin, sg->item, porigin, opt);
+			if (!origin->suspects)
 				goto finish;
 		}
+	}
 
- finish:
+finish:
+	*blametail = NULL;
+	distribute_blame(sb, blames);
+	/*
+	 * prepend toosmall to origin->suspects
+	 *
+	 * There is no point in sorting: this ends up on a big
+	 * unsorted list in the caller anyway.
+	 */
+	if (toosmall) {
+		struct blame_entry **tail = &toosmall;
+		while (*tail)
+			tail = &(*tail)->next;
+		*tail = origin->suspects;
+		origin->suspects = toosmall;
+	}
 	for (i = 0; i < num_sg; i++) {
 		if (sg_origin[i]) {
 			drop_origin_blob(sg_origin[i]);
@@ -1481,14 +1731,11 @@ static int emit_one_suspect_detail(struct origin *suspect, int repeat)
 }
 
 /*
- * The blame_entry is found to be guilty for the range.  Mark it
- * as such, and show it in incremental output.
+ * The blame_entry is found to be guilty for the range.
+ * Show it in incremental output.
  */
 static void found_guilty_entry(struct blame_entry *ent)
 {
-	if (ent->guilty)
-		return;
-	ent->guilty = 1;
 	if (incremental) {
 		struct origin *suspect = ent->suspect;
 
@@ -1502,32 +1749,34 @@ static void found_guilty_entry(struct blame_entry *ent)
 }
 
 /*
- * The main loop -- while the scoreboard has lines whose true origin
- * is still unknown, pick one blame_entry, and allow its current
- * suspect to pass blames to its parents.
- */
+ * The main loop -- while we have blobs with lines whose true origin
+ * is still unknown, pick one blob, and allow its lines to pass blames
+ * to its parents. */
 static void assign_blame(struct scoreboard *sb, int opt)
 {
 	struct rev_info *revs = sb->revs;
+	struct commit *commit = prio_queue_get(&sb->commits);
 
-	while (1) {
+	while (commit) {
 		struct blame_entry *ent;
-		struct commit *commit;
-		struct origin *suspect = NULL;
+		struct origin *suspect = commit->util;
 
 		/* find one suspect to break down */
-		for (ent = sb->ent; !suspect && ent; ent = ent->next)
-			if (!ent->guilty)
-				suspect = ent->suspect;
-		if (!suspect)
-			return; /* all done */
+		while (suspect && !suspect->suspects)
+			suspect = suspect->next;
+
+		if (!suspect) {
+			commit = prio_queue_get(&sb->commits);
+			continue;
+		}
+
+		assert(commit == suspect->commit);
 
 		/*
 		 * We will use this suspect later in the loop,
 		 * so hold onto it in the meantime.
 		 */
 		origin_incref(suspect);
-		commit = suspect->commit;
 		parse_commit(commit);
 		if (reverse ||
 		    (!(commit->object.flags & UNINTERESTING) &&
@@ -1543,9 +1792,22 @@ static void assign_blame(struct scoreboard *sb, int opt)
 			commit->object.flags |= UNINTERESTING;
 
 		/* Take responsibility for the remaining entries */
-		for (ent = sb->ent; ent; ent = ent->next)
-			if (ent->suspect == suspect)
+		ent = suspect->suspects;
+		if (ent) {
+			suspect->guilty = 1;
+			for (;;) {
+				struct blame_entry *next = ent->next;
 				found_guilty_entry(ent);
+				if (next) {
+					ent = next;
+					continue;
+				}
+				ent->next = sb->ent;
+				sb->ent = suspect->suspects;
+				suspect->suspects = NULL;
+				break;
+			}
+		}
 		origin_decref(suspect);
 
 		if (DEBUG) /* sanity */
@@ -1602,9 +1864,8 @@ static void emit_porcelain(struct scoreboard *sb, struct blame_entry *ent,
 	char hex[41];
 
 	strcpy(hex, sha1_to_hex(suspect->commit->object.sha1));
-	printf("%s%c%d %d %d\n",
+	printf("%s %d %d %d\n",
 	       hex,
-	       ent->guilty ? ' ' : '*', /* purely for debugging */
 	       ent->s_lno + 1,
 	       ent->lno + 1,
 	       ent->num_lines);
@@ -1717,17 +1978,16 @@ static void output(struct scoreboard *sb, int option)
 
 	if (option & OUTPUT_PORCELAIN) {
 		for (ent = sb->ent; ent; ent = ent->next) {
-			struct blame_entry *oth;
-			struct origin *suspect = ent->suspect;
-			struct commit *commit = suspect->commit;
+			int count = 0;
+			struct origin *suspect;
+			struct commit *commit = ent->suspect->commit;
 			if (commit->object.flags & MORE_THAN_ONE_PATH)
 				continue;
-			for (oth = ent->next; oth; oth = oth->next) {
-				if ((oth->suspect->commit != commit) ||
-				    !strcmp(oth->suspect->path, suspect->path))
-					continue;
-				commit->object.flags |= MORE_THAN_ONE_PATH;
-				break;
+			for (suspect = commit->util; suspect; suspect = suspect->next) {
+				if (suspect->guilty && count++) {
+					commit->object.flags |= MORE_THAN_ONE_PATH;
+					break;
+				}
 			}
 		}
 	}
@@ -2092,7 +2352,6 @@ static struct commit *fake_working_tree_commit(struct diff_options *opt,
 	origin->file.ptr = buf.buf;
 	origin->file.size = buf.len;
 	pretend_sha1_file(buf.buf, buf.len, OBJ_BLOB, origin->blob_sha1);
-	commit->util = origin;
 
 	/*
 	 * Read the current index, replace the path entry with
@@ -2403,12 +2662,16 @@ parse_done:
 	memset(&sb, 0, sizeof(sb));
 
 	sb.revs = &revs;
-	if (!reverse)
+	if (!reverse) {
 		final_commit_name = prepare_final(&sb);
+		sb.commits.compare = compare_commits_by_commit_date;
+	}
 	else if (contents_from)
 		die("--contents and --children do not blend well.");
-	else
+	else {
 		final_commit_name = prepare_initial(&sb);
+		sb.commits.compare = compare_commits_by_reverse_commit_date;
+	}
 
 	if (!sb.final) {
 		/*
@@ -2497,12 +2760,16 @@ parse_done:
 		ent->next = next;
 		origin_incref(o);
 	}
+
+	o->suspects = ent;
+	prio_queue_put(&sb.commits, o->commit);
+
 	origin_decref(o);
 
 	range_set_release(&ranges);
 	string_list_clear(&range_list, 0);
 
-	sb.ent = ent;
+	sb.ent = NULL;
 	sb.path = path;
 
 	read_mailmap(&mailmap, NULL);
@@ -2515,6 +2782,8 @@ parse_done:
 	if (incremental)
 		return 0;
 
+	sb.ent = blame_sort(sb.ent, compare_blame_final);
+
 	coalesce(&sb);
 
 	if (!(output_option & OUTPUT_PORCELAIN))
-- 
1.9.1