Adding upstream version 1:2.43.0.upstream/1%2.43.0

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1721 insertions, 0 deletions

diff --git a/diffcore-rename.c b/diffcore-rename.c
new file mode 100644
index 0000000..5a6e2bc
--- /dev/null
+++ b/diffcore-rename.c
@@ -0,0 +1,1721 @@
+/*
+ *
+ * Copyright (C) 2005 Junio C Hamano
+ */
+#include "git-compat-util.h"
+#include "diff.h"
+#include "diffcore.h"
+#include "object-store-ll.h"
+#include "hashmap.h"
+#include "mem-pool.h"
+#include "oid-array.h"
+#include "progress.h"
+#include "promisor-remote.h"
+#include "string-list.h"
+#include "strmap.h"
+#include "trace2.h"
+
+/* Table of rename/copy destinations */
+
+static struct diff_rename_dst {
+	struct diff_filepair *p;
+	struct diff_filespec *filespec_to_free;
+	int is_rename; /* false -> just a create; true -> rename or copy */
+} *rename_dst;
+static int rename_dst_nr, rename_dst_alloc;
+/* Mapping from break source pathname to break destination index */
+static struct strintmap *break_idx = NULL;
+
+static struct diff_rename_dst *locate_rename_dst(struct diff_filepair *p)
+{
+	/* Lookup by p->ONE->path */
+	int idx = break_idx ? strintmap_get(break_idx, p->one->path) : -1;
+	return (idx == -1) ? NULL : &rename_dst[idx];
+}
+
+/*
+ * Returns 0 on success, -1 if we found a duplicate.
+ */
+static int add_rename_dst(struct diff_filepair *p)
+{
+	ALLOC_GROW(rename_dst, rename_dst_nr + 1, rename_dst_alloc);
+	rename_dst[rename_dst_nr].p = p;
+	rename_dst[rename_dst_nr].filespec_to_free = NULL;
+	rename_dst[rename_dst_nr].is_rename = 0;
+	rename_dst_nr++;
+	return 0;
+}
+
+/* Table of rename/copy src files */
+static struct diff_rename_src {
+	struct diff_filepair *p;
+	unsigned short score; /* to remember the break score */
+} *rename_src;
+static int rename_src_nr, rename_src_alloc;
+
+static void register_rename_src(struct diff_filepair *p)
+{
+	if (p->broken_pair) {
+		if (!break_idx) {
+			break_idx = xmalloc(sizeof(*break_idx));
+			strintmap_init_with_options(break_idx, -1, NULL, 0);
+		}
+		strintmap_set(break_idx, p->one->path, rename_dst_nr);
+	}
+
+	ALLOC_GROW(rename_src, rename_src_nr + 1, rename_src_alloc);
+	rename_src[rename_src_nr].p = p;
+	rename_src[rename_src_nr].score = p->score;
+	rename_src_nr++;
+}
+
+static int basename_same(struct diff_filespec *src, struct diff_filespec *dst)
+{
+	int src_len = strlen(src->path), dst_len = strlen(dst->path);
+	while (src_len && dst_len) {
+		char c1 = src->path[--src_len];
+		char c2 = dst->path[--dst_len];
+		if (c1 != c2)
+			return 0;
+		if (c1 == '/')
+			return 1;
+	}
+	return (!src_len || src->path[src_len - 1] == '/') &&
+		(!dst_len || dst->path[dst_len - 1] == '/');
+}
+
+struct diff_score {
+	int src; /* index in rename_src */
+	int dst; /* index in rename_dst */
+	unsigned short score;
+	short name_score;
+};
+
+struct inexact_prefetch_options {
+	struct repository *repo;
+	int skip_unmodified;
+};
+static void inexact_prefetch(void *prefetch_options)
+{
+	struct inexact_prefetch_options *options = prefetch_options;
+	int i;
+	struct oid_array to_fetch = OID_ARRAY_INIT;
+
+	for (i = 0; i < rename_dst_nr; i++) {
+		if (rename_dst[i].p->renamed_pair)
+			/*
+			 * The loop in diffcore_rename() will not need these
+			 * blobs, so skip prefetching.
+			 */
+			continue; /* already found exact match */
+		diff_add_if_missing(options->repo, &to_fetch,
+				    rename_dst[i].p->two);
+	}
+	for (i = 0; i < rename_src_nr; i++) {
+		if (options->skip_unmodified &&
+		    diff_unmodified_pair(rename_src[i].p))
+			/*
+			 * The loop in diffcore_rename() will not need these
+			 * blobs, so skip prefetching.
+			 */
+			continue;
+		diff_add_if_missing(options->repo, &to_fetch,
+				    rename_src[i].p->one);
+	}
+	promisor_remote_get_direct(options->repo, to_fetch.oid, to_fetch.nr);
+	oid_array_clear(&to_fetch);
+}
+
+static int estimate_similarity(struct repository *r,
+			       struct diff_filespec *src,
+			       struct diff_filespec *dst,
+			       int minimum_score,
+			       struct diff_populate_filespec_options *dpf_opt)
+{
+	/* src points at a file that existed in the original tree (or
+	 * optionally a file in the destination tree) and dst points
+	 * at a newly created file.  They may be quite similar, in which
+	 * case we want to say src is renamed to dst or src is copied into
+	 * dst, and then some edit has been applied to dst.
+	 *
+	 * Compare them and return how similar they are, representing
+	 * the score as an integer between 0 and MAX_SCORE.
+	 *
+	 * When there is an exact match, it is considered a better
+	 * match than anything else; the destination does not even
+	 * call into this function in that case.
+	 */
+	unsigned long max_size, delta_size, base_size, src_copied, literal_added;
+	int score;
+
+	/* We deal only with regular files.  Symlink renames are handled
+	 * only when they are exact matches --- in other words, no edits
+	 * after renaming.
+	 */
+	if (!S_ISREG(src->mode) || !S_ISREG(dst->mode))
+		return 0;
+
+	/*
+	 * Need to check that source and destination sizes are
+	 * filled in before comparing them.
+	 *
+	 * If we already have "cnt_data" filled in, we know it's
+	 * all good (avoid checking the size for zero, as that
+	 * is a possible size - we really should have a flag to
+	 * say whether the size is valid or not!)
+	 */
+	dpf_opt->check_size_only = 1;
+
+	if (!src->cnt_data &&
+	    diff_populate_filespec(r, src, dpf_opt))
+		return 0;
+	if (!dst->cnt_data &&
+	    diff_populate_filespec(r, dst, dpf_opt))
+		return 0;
+
+	max_size = ((src->size > dst->size) ? src->size : dst->size);
+	base_size = ((src->size < dst->size) ? src->size : dst->size);
+	delta_size = max_size - base_size;
+
+	/* We would not consider edits that change the file size so
+	 * drastically.  delta_size must be smaller than
+	 * (MAX_SCORE-minimum_score)/MAX_SCORE * min(src->size, dst->size).
+	 *
+	 * Note that base_size == 0 case is handled here already
+	 * and the final score computation below would not have a
+	 * divide-by-zero issue.
+	 */
+	if (max_size * (MAX_SCORE-minimum_score) < delta_size * MAX_SCORE)
+		return 0;
+
+	dpf_opt->check_size_only = 0;
+
+	if (!src->cnt_data && diff_populate_filespec(r, src, dpf_opt))
+		return 0;
+	if (!dst->cnt_data && diff_populate_filespec(r, dst, dpf_opt))
+		return 0;
+
+	if (diffcore_count_changes(r, src, dst,
+				   &src->cnt_data, &dst->cnt_data,
+				   &src_copied, &literal_added))
+		return 0;
+
+	/* How similar are they?
+	 * what percentage of material in dst are from source?
+	 */
+	if (!dst->size)
+		score = 0; /* should not happen */
+	else
+		score = (int)(src_copied * MAX_SCORE / max_size);
+	return score;
+}
+
+static void record_rename_pair(int dst_index, int src_index, int score)
+{
+	struct diff_filepair *src = rename_src[src_index].p;
+	struct diff_filepair *dst = rename_dst[dst_index].p;
+
+	if (dst->renamed_pair)
+		die("internal error: dst already matched.");
+
+	src->one->rename_used++;
+	src->one->count++;
+
+	rename_dst[dst_index].filespec_to_free = dst->one;
+	rename_dst[dst_index].is_rename = 1;
+
+	dst->one = src->one;
+	dst->renamed_pair = 1;
+	if (!strcmp(dst->one->path, dst->two->path))
+		dst->score = rename_src[src_index].score;
+	else
+		dst->score = score;
+}
+
+/*
+ * We sort the rename similarity matrix with the score, in descending
+ * order (the most similar first).
+ */
+static int score_compare(const void *a_, const void *b_)
+{
+	const struct diff_score *a = a_, *b = b_;
+
+	/* sink the unused ones to the bottom */
+	if (a->dst < 0)
+		return (0 <= b->dst);
+	else if (b->dst < 0)
+		return -1;
+
+	if (a->score == b->score)
+		return b->name_score - a->name_score;
+
+	return b->score - a->score;
+}
+
+struct file_similarity {
+	struct hashmap_entry entry;
+	int index;
+	struct diff_filespec *filespec;
+};
+
+static unsigned int hash_filespec(struct repository *r,
+				  struct diff_filespec *filespec)
+{
+	if (!filespec->oid_valid) {
+		if (diff_populate_filespec(r, filespec, NULL))
+			return 0;
+		hash_object_file(r->hash_algo, filespec->data, filespec->size,
+				 OBJ_BLOB, &filespec->oid);
+	}
+	return oidhash(&filespec->oid);
+}
+
+static int find_identical_files(struct hashmap *srcs,
+				int dst_index,
+				struct diff_options *options)
+{
+	int renames = 0;
+	struct diff_filespec *target = rename_dst[dst_index].p->two;
+	struct file_similarity *p, *best = NULL;
+	int i = 100, best_score = -1;
+	unsigned int hash = hash_filespec(options->repo, target);
+
+	/*
+	 * Find the best source match for specified destination.
+	 */
+	p = hashmap_get_entry_from_hash(srcs, hash, NULL,
+					struct file_similarity, entry);
+	hashmap_for_each_entry_from(srcs, p, entry) {
+		int score;
+		struct diff_filespec *source = p->filespec;
+
+		/* False hash collision? */
+		if (!oideq(&source->oid, &target->oid))
+			continue;
+		/* Non-regular files? If so, the modes must match! */
+		if (!S_ISREG(source->mode) || !S_ISREG(target->mode)) {
+			if (source->mode != target->mode)
+				continue;
+		}
+		/* Give higher scores to sources that haven't been used already */
+		score = !source->rename_used;
+		if (source->rename_used && options->detect_rename != DIFF_DETECT_COPY)
+			continue;
+		score += basename_same(source, target);
+		if (score > best_score) {
+			best = p;
+			best_score = score;
+			if (score == 2)
+				break;
+		}
+
+		/* Too many identical alternatives? Pick one */
+		if (!--i)
+			break;
+	}
+	if (best) {
+		record_rename_pair(dst_index, best->index, MAX_SCORE);
+		renames++;
+	}
+	return renames;
+}
+
+static void insert_file_table(struct repository *r,
+			      struct mem_pool *pool,
+			      struct hashmap *table, int index,
+			      struct diff_filespec *filespec)
+{
+	struct file_similarity *entry = mem_pool_alloc(pool, sizeof(*entry));
+
+	entry->index = index;
+	entry->filespec = filespec;
+
+	hashmap_entry_init(&entry->entry, hash_filespec(r, filespec));
+	hashmap_add(table, &entry->entry);
+}
+
+/*
+ * Find exact renames first.
+ *
+ * The first round matches up the up-to-date entries,
+ * and then during the second round we try to match
+ * cache-dirty entries as well.
+ */
+static int find_exact_renames(struct diff_options *options,
+			      struct mem_pool *pool)
+{
+	int i, renames = 0;
+	struct hashmap file_table;
+
+	/* Add all sources to the hash table in reverse order, because
+	 * later on they will be retrieved in LIFO order.
+	 */
+	hashmap_init(&file_table, NULL, NULL, rename_src_nr);
+	for (i = rename_src_nr-1; i >= 0; i--)
+		insert_file_table(options->repo, pool,
+				  &file_table, i,
+				  rename_src[i].p->one);
+
+	/* Walk the destinations and find best source match */
+	for (i = 0; i < rename_dst_nr; i++)
+		renames += find_identical_files(&file_table, i, options);
+
+	/* Free the hash data structure (entries will be freed with the pool) */
+	hashmap_clear(&file_table);
+
+	return renames;
+}
+
+struct dir_rename_info {
+	struct strintmap idx_map;
+	struct strmap dir_rename_guess;
+	struct strmap *dir_rename_count;
+	struct strintmap *relevant_source_dirs;
+	unsigned setup;
+};
+
+static char *get_dirname(const char *filename)
+{
+	char *slash = strrchr(filename, '/');
+	return slash ? xstrndup(filename, slash - filename) : xstrdup("");
+}
+
+static void dirname_munge(char *filename)
+{
+	char *slash = strrchr(filename, '/');
+	if (!slash)
+		slash = filename;
+	*slash = '\0';
+}
+
+static const char *get_highest_rename_path(struct strintmap *counts)
+{
+	int highest_count = 0;
+	const char *highest_destination_dir = NULL;
+	struct hashmap_iter iter;
+	struct strmap_entry *entry;
+
+	strintmap_for_each_entry(counts, &iter, entry) {
+		const char *destination_dir = entry->key;
+		intptr_t count = (intptr_t)entry->value;
+		if (count > highest_count) {
+			highest_count = count;
+			highest_destination_dir = destination_dir;
+		}
+	}
+	return highest_destination_dir;
+}
+
+static char *UNKNOWN_DIR = "/";  /* placeholder -- short, illegal directory */
+
+static int dir_rename_already_determinable(struct strintmap *counts)
+{
+	struct hashmap_iter iter;
+	struct strmap_entry *entry;
+	int first = 0, second = 0, unknown = 0;
+	strintmap_for_each_entry(counts, &iter, entry) {
+		const char *destination_dir = entry->key;
+		intptr_t count = (intptr_t)entry->value;
+		if (!strcmp(destination_dir, UNKNOWN_DIR)) {
+			unknown = count;
+		} else if (count >= first) {
+			second = first;
+			first = count;
+		} else if (count >= second) {
+			second = count;
+		}
+	}
+	return first > second + unknown;
+}
+
+static void increment_count(struct dir_rename_info *info,
+			    char *old_dir,
+			    char *new_dir)
+{
+	struct strintmap *counts;
+	struct strmap_entry *e;
+
+	/* Get the {new_dirs -> counts} mapping using old_dir */
+	e = strmap_get_entry(info->dir_rename_count, old_dir);
+	if (e) {
+		counts = e->value;
+	} else {
+		counts = xmalloc(sizeof(*counts));
+		strintmap_init_with_options(counts, 0, NULL, 1);
+		strmap_put(info->dir_rename_count, old_dir, counts);
+	}
+
+	/* Increment the count for new_dir */
+	strintmap_incr(counts, new_dir, 1);
+}
+
+static void update_dir_rename_counts(struct dir_rename_info *info,
+				     struct strintmap *dirs_removed,
+				     const char *oldname,
+				     const char *newname)
+{
+	char *old_dir;
+	char *new_dir;
+	const char new_dir_first_char = newname[0];
+	int first_time_in_loop = 1;
+
+	if (!info->setup)
+		/*
+		 * info->setup is 0 here in two cases: (1) all auxiliary
+		 * vars (like dirs_removed) were NULL so
+		 * initialize_dir_rename_info() returned early, or (2)
+		 * either break detection or copy detection are active so
+		 * that we never called initialize_dir_rename_info().  In
+		 * the former case, we don't have enough info to know if
+		 * directories were renamed (because dirs_removed lets us
+		 * know about a necessary prerequisite, namely if they were
+		 * removed), and in the latter, we don't care about
+		 * directory renames or find_basename_matches.
+		 *
+		 * This matters because both basename and inexact matching
+		 * will also call update_dir_rename_counts().  In either of
+		 * the above two cases info->dir_rename_counts will not
+		 * have been properly initialized which prevents us from
+		 * updating it, but in these two cases we don't care about
+		 * dir_rename_counts anyway, so we can just exit early.
+		 */
+		return;
+
+
+	old_dir = xstrdup(oldname);
+	new_dir = xstrdup(newname);
+
+	while (1) {
+		int drd_flag = NOT_RELEVANT;
+
+		/* Get old_dir, skip if its directory isn't relevant. */
+		dirname_munge(old_dir);
+		if (info->relevant_source_dirs &&
+		    !strintmap_contains(info->relevant_source_dirs, old_dir))
+			break;
+
+		/* Get new_dir */
+		dirname_munge(new_dir);
+
+		/*
+		 * When renaming
+		 *   "a/b/c/d/e/foo.c" -> "a/b/some/thing/else/e/foo.c"
+		 * then this suggests that both
+		 *   a/b/c/d/e/ => a/b/some/thing/else/e/
+		 *   a/b/c/d/   => a/b/some/thing/else/
+		 * so we want to increment counters for both.  We do NOT,
+		 * however, also want to suggest that there was the following
+		 * rename:
+		 *   a/b/c/ => a/b/some/thing/
+		 * so we need to quit at that point.
+		 *
+		 * Note the when first_time_in_loop, we only strip off the
+		 * basename, and we don't care if that's different.
+		 */
+		if (!first_time_in_loop) {
+			char *old_sub_dir = strchr(old_dir, '\0')+1;
+			char *new_sub_dir = strchr(new_dir, '\0')+1;
+			if (!*new_dir) {
+				/*
+				 * Special case when renaming to root directory,
+				 * i.e. when new_dir == "".  In this case, we had
+				 * something like
+				 *    a/b/subdir => subdir
+				 * and so dirname_munge() sets things up so that
+				 *    old_dir = "a/b\0subdir\0"
+				 *    new_dir = "\0ubdir\0"
+				 * We didn't have a '/' to overwrite a '\0' onto
+				 * in new_dir, so we have to compare differently.
+				 */
+				if (new_dir_first_char != old_sub_dir[0] ||
+				    strcmp(old_sub_dir+1, new_sub_dir))
+					break;
+			} else {
+				if (strcmp(old_sub_dir, new_sub_dir))
+					break;
+			}
+		}
+
+		/*
+		 * Above we suggested that we'd keep recording renames for
+		 * all ancestor directories where the trailing directories
+		 * matched, i.e. for
+		 *   "a/b/c/d/e/foo.c" -> "a/b/some/thing/else/e/foo.c"
+		 * we'd increment rename counts for each of
+		 *   a/b/c/d/e/ => a/b/some/thing/else/e/
+		 *   a/b/c/d/   => a/b/some/thing/else/
+		 * However, we only need the rename counts for directories
+		 * in dirs_removed whose value is RELEVANT_FOR_SELF.
+		 * However, we add one special case of also recording it for
+		 * first_time_in_loop because find_basename_matches() can
+		 * use that as a hint to find a good pairing.
+		 */
+		if (dirs_removed)
+			drd_flag = strintmap_get(dirs_removed, old_dir);
+		if (drd_flag == RELEVANT_FOR_SELF || first_time_in_loop)
+			increment_count(info, old_dir, new_dir);
+
+		first_time_in_loop = 0;
+		if (drd_flag == NOT_RELEVANT)
+			break;
+		/* If we hit toplevel directory ("") for old or new dir, quit */
+		if (!*old_dir || !*new_dir)
+			break;
+	}
+
+	/* Free resources we don't need anymore */
+	free(old_dir);
+	free(new_dir);
+}
+
+static void initialize_dir_rename_info(struct dir_rename_info *info,
+				       struct strintmap *relevant_sources,
+				       struct strintmap *dirs_removed,
+				       struct strmap *dir_rename_count,
+				       struct strmap *cached_pairs)
+{
+	struct hashmap_iter iter;
+	struct strmap_entry *entry;
+	int i;
+
+	if (!dirs_removed && !relevant_sources) {
+		info->setup = 0;
+		return;
+	}
+	info->setup = 1;
+
+	info->dir_rename_count = dir_rename_count;
+	if (!info->dir_rename_count) {
+		info->dir_rename_count = xmalloc(sizeof(*dir_rename_count));
+		strmap_init(info->dir_rename_count);
+	}
+	strintmap_init_with_options(&info->idx_map, -1, NULL, 0);
+	strmap_init_with_options(&info->dir_rename_guess, NULL, 0);
+
+	/* Setup info->relevant_source_dirs */
+	info->relevant_source_dirs = NULL;
+	if (dirs_removed || !relevant_sources) {
+		info->relevant_source_dirs = dirs_removed; /* might be NULL */
+	} else {
+		info->relevant_source_dirs = xmalloc(sizeof(struct strintmap));
+		strintmap_init(info->relevant_source_dirs, 0 /* unused */);
+		strintmap_for_each_entry(relevant_sources, &iter, entry) {
+			char *dirname = get_dirname(entry->key);
+			if (!dirs_removed ||
+			    strintmap_contains(dirs_removed, dirname))
+				strintmap_set(info->relevant_source_dirs,
+					      dirname, 0 /* value irrelevant */);
+			free(dirname);
+		}
+	}
+
+	/*
+	 * Loop setting up both info->idx_map, and doing setup of
+	 * info->dir_rename_count.
+	 */
+	for (i = 0; i < rename_dst_nr; ++i) {
+		/*
+		 * For non-renamed files, make idx_map contain mapping of
+		 *   filename -> index (index within rename_dst, that is)
+		 */
+		if (!rename_dst[i].is_rename) {
+			char *filename = rename_dst[i].p->two->path;
+			strintmap_set(&info->idx_map, filename, i);
+			continue;
+		}
+
+		/*
+		 * For everything else (i.e. renamed files), make
+		 * dir_rename_count contain a map of a map:
+		 *   old_directory -> {new_directory -> count}
+		 * In other words, for every pair look at the directories for
+		 * the old filename and the new filename and count how many
+		 * times that pairing occurs.
+		 */
+		update_dir_rename_counts(info, dirs_removed,
+					 rename_dst[i].p->one->path,
+					 rename_dst[i].p->two->path);
+	}
+
+	/* Add cached_pairs to counts */
+	strmap_for_each_entry(cached_pairs, &iter, entry) {
+		const char *old_name = entry->key;
+		const char *new_name = entry->value;
+		if (!new_name)
+			/* known delete; ignore it */
+			continue;
+
+		update_dir_rename_counts(info, dirs_removed, old_name, new_name);
+	}
+
+	/*
+	 * Now we collapse
+	 *    dir_rename_count: old_directory -> {new_directory -> count}
+	 * down to
+	 *    dir_rename_guess: old_directory -> best_new_directory
+	 * where best_new_directory is the one with the highest count.
+	 */
+	strmap_for_each_entry(info->dir_rename_count, &iter, entry) {
+		/* entry->key is source_dir */
+		struct strintmap *counts = entry->value;
+		char *best_newdir;
+
+		best_newdir = xstrdup(get_highest_rename_path(counts));
+		strmap_put(&info->dir_rename_guess, entry->key,
+			   best_newdir);
+	}
+}
+
+void partial_clear_dir_rename_count(struct strmap *dir_rename_count)
+{
+	struct hashmap_iter iter;
+	struct strmap_entry *entry;
+
+	strmap_for_each_entry(dir_rename_count, &iter, entry) {
+		struct strintmap *counts = entry->value;
+		strintmap_clear(counts);
+	}
+	strmap_partial_clear(dir_rename_count, 1);
+}
+
+static void cleanup_dir_rename_info(struct dir_rename_info *info,
+				    struct strintmap *dirs_removed,
+				    int keep_dir_rename_count)
+{
+	struct hashmap_iter iter;
+	struct strmap_entry *entry;
+	struct string_list to_remove = STRING_LIST_INIT_NODUP;
+	int i;
+
+	if (!info->setup)
+		return;
+
+	/* idx_map */
+	strintmap_clear(&info->idx_map);
+
+	/* dir_rename_guess */
+	strmap_clear(&info->dir_rename_guess, 1);
+
+	/* relevant_source_dirs */
+	if (info->relevant_source_dirs &&
+	    info->relevant_source_dirs != dirs_removed) {
+		strintmap_clear(info->relevant_source_dirs);
+		FREE_AND_NULL(info->relevant_source_dirs);
+	}
+
+	/* dir_rename_count */
+	if (!keep_dir_rename_count) {
+		partial_clear_dir_rename_count(info->dir_rename_count);
+		strmap_clear(info->dir_rename_count, 1);
+		FREE_AND_NULL(info->dir_rename_count);
+		return;
+	}
+
+	/*
+	 * Although dir_rename_count was passed in
+	 * diffcore_rename_extended() and we want to keep it around and
+	 * return it to that caller, we first want to remove any counts in
+	 * the maps associated with UNKNOWN_DIR entries and any data
+	 * associated with directories that weren't renamed.
+	 */
+	strmap_for_each_entry(info->dir_rename_count, &iter, entry) {
+		const char *source_dir = entry->key;
+		struct strintmap *counts = entry->value;
+
+		if (!strintmap_get(dirs_removed, source_dir)) {
+			string_list_append(&to_remove, source_dir);
+			strintmap_clear(counts);
+			continue;
+		}
+
+		if (strintmap_contains(counts, UNKNOWN_DIR))
+			strintmap_remove(counts, UNKNOWN_DIR);
+	}
+	for (i = 0; i < to_remove.nr; ++i)
+		strmap_remove(info->dir_rename_count,
+			      to_remove.items[i].string, 1);
+	string_list_clear(&to_remove, 0);
+}
+
+static const char *get_basename(const char *filename)
+{
+	/*
+	 * gitbasename() has to worry about special drives, multiple
+	 * directory separator characters, trailing slashes, NULL or
+	 * empty strings, etc.  We only work on filenames as stored in
+	 * git, and thus get to ignore all those complications.
+	 */
+	const char *base = strrchr(filename, '/');
+	return base ? base + 1 : filename;
+}
+
+static int idx_possible_rename(char *filename, struct dir_rename_info *info)
+{
+	/*
+	 * Our comparison of files with the same basename (see
+	 * find_basename_matches() below), is only helpful when after exact
+	 * rename detection we have exactly one file with a given basename
+	 * among the rename sources and also only exactly one file with
+	 * that basename among the rename destinations.  When we have
+	 * multiple files with the same basename in either set, we do not
+	 * know which to compare against.  However, there are some
+	 * filenames that occur in large numbers (particularly
+	 * build-related filenames such as 'Makefile', '.gitignore', or
+	 * 'build.gradle' that potentially exist within every single
+	 * subdirectory), and for performance we want to be able to quickly
+	 * find renames for these files too.
+	 *
+	 * The reason basename comparisons are a useful heuristic was that it
+	 * is common for people to move files across directories while keeping
+	 * their filename the same.  If we had a way of determining or even
+	 * making a good educated guess about which directory these non-unique
+	 * basename files had moved the file to, we could check it.
+	 * Luckily...
+	 *
+	 * When an entire directory is in fact renamed, we have two factors
+	 * helping us out:
+	 *   (a) the original directory disappeared giving us a hint
+	 *       about when we can apply an extra heuristic.
+	 *   (a) we often have several files within that directory and
+	 *       subdirectories that are renamed without changes
+	 * So, rules for a heuristic:
+	 *   (0) If there basename matches are non-unique (the condition under
+	 *       which this function is called) AND
+	 *   (1) the directory in which the file was found has disappeared
+	 *       (i.e. dirs_removed is non-NULL and has a relevant entry) THEN
+	 *   (2) use exact renames of files within the directory to determine
+	 *       where the directory is likely to have been renamed to.  IF
+	 *       there is at least one exact rename from within that
+	 *       directory, we can proceed.
+	 *   (3) If there are multiple places the directory could have been
+	 *       renamed to based on exact renames, ignore all but one of them.
+	 *       Just use the destination with the most renames going to it.
+	 *   (4) Check if applying that directory rename to the original file
+	 *       would result in a destination filename that is in the
+	 *       potential rename set.  If so, return the index of the
+	 *       destination file (the index within rename_dst).
+	 *   (5) Compare the original file and returned destination for
+	 *       similarity, and if they are sufficiently similar, record the
+	 *       rename.
+	 *
+	 * This function, idx_possible_rename(), is only responsible for (4).
+	 * The conditions/steps in (1)-(3) are handled via setting up
+	 * dir_rename_count and dir_rename_guess in
+	 * initialize_dir_rename_info().  Steps (0) and (5) are handled by
+	 * the caller of this function.
+	 */
+	char *old_dir, *new_dir;
+	struct strbuf new_path = STRBUF_INIT;
+	int idx;
+
+	if (!info->setup)
+		return -1;
+
+	old_dir = get_dirname(filename);
+	new_dir = strmap_get(&info->dir_rename_guess, old_dir);
+	free(old_dir);
+	if (!new_dir)
+		return -1;
+
+	strbuf_addstr(&new_path, new_dir);
+	strbuf_addch(&new_path, '/');
+	strbuf_addstr(&new_path, get_basename(filename));
+
+	idx = strintmap_get(&info->idx_map, new_path.buf);
+	strbuf_release(&new_path);
+	return idx;
+}
+
+struct basename_prefetch_options {
+	struct repository *repo;
+	struct strintmap *relevant_sources;
+	struct strintmap *sources;
+	struct strintmap *dests;
+	struct dir_rename_info *info;
+};
+static void basename_prefetch(void *prefetch_options)
+{
+	struct basename_prefetch_options *options = prefetch_options;
+	struct strintmap *relevant_sources = options->relevant_sources;
+	struct strintmap *sources = options->sources;
+	struct strintmap *dests = options->dests;
+	struct dir_rename_info *info = options->info;
+	int i;
+	struct oid_array to_fetch = OID_ARRAY_INIT;
+
+	/*
+	 * TODO: The following loops mirror the code/logic from
+	 * find_basename_matches(), though not quite exactly.  Maybe
+	 * abstract the iteration logic out somehow?
+	 */
+	for (i = 0; i < rename_src_nr; ++i) {
+		char *filename = rename_src[i].p->one->path;
+		const char *base = NULL;
+		intptr_t src_index;
+		intptr_t dst_index;
+
+		/* Skip irrelevant sources */
+		if (relevant_sources &&
+		    !strintmap_contains(relevant_sources, filename))
+			continue;
+
+		/*
+		 * If the basename is unique among remaining sources, then
+		 * src_index will equal 'i' and we can attempt to match it
+		 * to a unique basename in the destinations.  Otherwise,
+		 * use directory rename heuristics, if possible.
+		 */
+		base = get_basename(filename);
+		src_index = strintmap_get(sources, base);
+		assert(src_index == -1 || src_index == i);
+
+		if (strintmap_contains(dests, base)) {
+			struct diff_filespec *one, *two;
+
+			/* Find a matching destination, if possible */
+			dst_index = strintmap_get(dests, base);
+			if (src_index == -1 || dst_index == -1) {
+				src_index = i;
+				dst_index = idx_possible_rename(filename, info);
+			}
+			if (dst_index == -1)
+				continue;
+
+			/* Ignore this dest if already used in a rename */
+			if (rename_dst[dst_index].is_rename)
+				continue; /* already used previously */
+
+			one = rename_src[src_index].p->one;
+			two = rename_dst[dst_index].p->two;
+
+			/* Add the pairs */
+			diff_add_if_missing(options->repo, &to_fetch, two);
+			diff_add_if_missing(options->repo, &to_fetch, one);
+		}
+	}
+
+	promisor_remote_get_direct(options->repo, to_fetch.oid, to_fetch.nr);
+	oid_array_clear(&to_fetch);
+}
+
+static int find_basename_matches(struct diff_options *options,
+				 int minimum_score,
+				 struct dir_rename_info *info,
+				 struct strintmap *relevant_sources,
+				 struct strintmap *dirs_removed)
+{
+	/*
+	 * When I checked in early 2020, over 76% of file renames in linux
+	 * just moved files to a different directory but kept the same
+	 * basename.  gcc did that with over 64% of renames, gecko did it
+	 * with over 79%, and WebKit did it with over 89%.
+	 *
+	 * Therefore we can bypass the normal exhaustive NxM matrix
+	 * comparison of similarities between all potential rename sources
+	 * and destinations by instead using file basename as a hint (i.e.
+	 * the portion of the filename after the last '/'), checking for
+	 * similarity between files with the same basename, and if we find
+	 * a pair that are sufficiently similar, record the rename pair and
+	 * exclude those two from the NxM matrix.
+	 *
+	 * This *might* cause us to find a less than optimal pairing (if
+	 * there is another file that we are even more similar to but has a
+	 * different basename).  Given the huge performance advantage
+	 * basename matching provides, and given the frequency with which
+	 * people use the same basename in real world projects, that's a
+	 * trade-off we are willing to accept when doing just rename
+	 * detection.
+	 *
+	 * If someone wants copy detection that implies they are willing to
+	 * spend more cycles to find similarities between files, so it may
+	 * be less likely that this heuristic is wanted.  If someone is
+	 * doing break detection, that means they do not want filename
+	 * similarity to imply any form of content similiarity, and thus
+	 * this heuristic would definitely be incompatible.
+	 */
+
+	int i, renames = 0;
+	struct strintmap sources;
+	struct strintmap dests;
+	struct diff_populate_filespec_options dpf_options = {
+		.check_binary = 0,
+		.missing_object_cb = NULL,
+		.missing_object_data = NULL
+	};
+	struct basename_prefetch_options prefetch_options = {
+		.repo = options->repo,
+		.relevant_sources = relevant_sources,
+		.sources = &sources,
+		.dests = &dests,
+		.info = info
+	};
+
+	/*
+	 * Create maps of basename -> fullname(s) for remaining sources and
+	 * dests.
+	 */
+	strintmap_init_with_options(&sources, -1, NULL, 0);
+	strintmap_init_with_options(&dests, -1, NULL, 0);
+	for (i = 0; i < rename_src_nr; ++i) {
+		char *filename = rename_src[i].p->one->path;
+		const char *base;
+
+		/* exact renames removed in remove_unneeded_paths_from_src() */
+		assert(!rename_src[i].p->one->rename_used);
+
+		/* Record index within rename_src (i) if basename is unique */
+		base = get_basename(filename);
+		if (strintmap_contains(&sources, base))
+			strintmap_set(&sources, base, -1);
+		else
+			strintmap_set(&sources, base, i);
+	}
+	for (i = 0; i < rename_dst_nr; ++i) {
+		char *filename = rename_dst[i].p->two->path;
+		const char *base;
+
+		if (rename_dst[i].is_rename)
+			continue; /* involved in exact match already. */
+
+		/* Record index within rename_dst (i) if basename is unique */
+		base = get_basename(filename);
+		if (strintmap_contains(&dests, base))
+			strintmap_set(&dests, base, -1);
+		else
+			strintmap_set(&dests, base, i);
+	}
+
+	if (options->repo == the_repository && repo_has_promisor_remote(the_repository)) {
+		dpf_options.missing_object_cb = basename_prefetch;
+		dpf_options.missing_object_data = &prefetch_options;
+	}
+
+	/* Now look for basename matchups and do similarity estimation */
+	for (i = 0; i < rename_src_nr; ++i) {
+		char *filename = rename_src[i].p->one->path;
+		const char *base = NULL;
+		intptr_t src_index;
+		intptr_t dst_index;
+
+		/* Skip irrelevant sources */
+		if (relevant_sources &&
+		    !strintmap_contains(relevant_sources, filename))
+			continue;
+
+		/*
+		 * If the basename is unique among remaining sources, then
+		 * src_index will equal 'i' and we can attempt to match it
+		 * to a unique basename in the destinations.  Otherwise,
+		 * use directory rename heuristics, if possible.
+		 */
+		base = get_basename(filename);
+		src_index = strintmap_get(&sources, base);
+		assert(src_index == -1 || src_index == i);
+
+		if (strintmap_contains(&dests, base)) {
+			struct diff_filespec *one, *two;
+			int score;
+
+			/* Find a matching destination, if possible */
+			dst_index = strintmap_get(&dests, base);
+			if (src_index == -1 || dst_index == -1) {
+				src_index = i;
+				dst_index = idx_possible_rename(filename, info);
+			}
+			if (dst_index == -1)
+				continue;
+
+			/* Ignore this dest if already used in a rename */
+			if (rename_dst[dst_index].is_rename)
+				continue; /* already used previously */
+
+			/* Estimate the similarity */
+			one = rename_src[src_index].p->one;
+			two = rename_dst[dst_index].p->two;
+			score = estimate_similarity(options->repo, one, two,
+						    minimum_score, &dpf_options);
+
+			/* If sufficiently similar, record as rename pair */
+			if (score < minimum_score)
+				continue;
+			record_rename_pair(dst_index, src_index, score);
+			renames++;
+			update_dir_rename_counts(info, dirs_removed,
+						 one->path, two->path);
+
+			/*
+			 * Found a rename so don't need text anymore; if we
+			 * didn't find a rename, the filespec_blob would get
+			 * re-used when doing the matrix of comparisons.
+			 */
+			diff_free_filespec_blob(one);
+			diff_free_filespec_blob(two);
+		}
+	}
+
+	strintmap_clear(&sources);
+	strintmap_clear(&dests);
+
+	return renames;
+}
+
+#define NUM_CANDIDATE_PER_DST 4
+static void record_if_better(struct diff_score m[], struct diff_score *o)
+{
+	int i, worst;
+
+	/* find the worst one */
+	worst = 0;
+	for (i = 1; i < NUM_CANDIDATE_PER_DST; i++)
+		if (score_compare(&m[i], &m[worst]) > 0)
+			worst = i;
+
+	/* is it better than the worst one? */
+	if (score_compare(&m[worst], o) > 0)
+		m[worst] = *o;
+}
+
+/*
+ * Returns:
+ * 0 if we are under the limit;
+ * 1 if we need to disable inexact rename detection;
+ * 2 if we would be under the limit if we were given -C instead of -C -C.
+ */
+static int too_many_rename_candidates(int num_destinations, int num_sources,
+				      struct diff_options *options)
+{
+	int rename_limit = options->rename_limit;
+	int i, limited_sources;
+
+	options->needed_rename_limit = 0;
+
+	/*
+	 * This basically does a test for the rename matrix not
+	 * growing larger than a "rename_limit" square matrix, ie:
+	 *
+	 *    num_destinations * num_sources > rename_limit * rename_limit
+	 *
+	 * We use st_mult() to check overflow conditions; in the
+	 * exceptional circumstance that size_t isn't large enough to hold
+	 * the multiplication, the system won't be able to allocate enough
+	 * memory for the matrix anyway.
+	 */
+	if (rename_limit <= 0)
+		return 0; /* treat as unlimited */
+	if (st_mult(num_destinations, num_sources)
+	    <= st_mult(rename_limit, rename_limit))
+		return 0;
+
+	options->needed_rename_limit =
+		num_sources > num_destinations ? num_sources : num_destinations;
+
+	/* Are we running under -C -C? */
+	if (!options->flags.find_copies_harder)
+		return 1;
+
+	/* Would we bust the limit if we were running under -C? */
+	for (limited_sources = i = 0; i < num_sources; i++) {
+		if (diff_unmodified_pair(rename_src[i].p))
+			continue;
+		limited_sources++;
+	}
+	if (st_mult(num_destinations, limited_sources)
+	    <= st_mult(rename_limit, rename_limit))
+		return 2;
+	return 1;
+}
+
+static int find_renames(struct diff_score *mx,
+			int dst_cnt,
+			int minimum_score,
+			int copies,
+			struct dir_rename_info *info,
+			struct strintmap *dirs_removed)
+{
+	int count = 0, i;
+
+	for (i = 0; i < dst_cnt * NUM_CANDIDATE_PER_DST; i++) {
+		struct diff_rename_dst *dst;
+
+		if ((mx[i].dst < 0) ||
+		    (mx[i].score < minimum_score))
+			break; /* there is no more usable pair. */
+		dst = &rename_dst[mx[i].dst];
+		if (dst->is_rename)
+			continue; /* already done, either exact or fuzzy. */
+		if (!copies && rename_src[mx[i].src].p->one->rename_used)
+			continue;
+		record_rename_pair(mx[i].dst, mx[i].src, mx[i].score);
+		count++;
+		update_dir_rename_counts(info, dirs_removed,
+					 rename_src[mx[i].src].p->one->path,
+					 rename_dst[mx[i].dst].p->two->path);
+	}
+	return count;
+}
+
+static void remove_unneeded_paths_from_src(int detecting_copies,
+					   struct strintmap *interesting)
+{
+	int i, new_num_src;
+
+	if (detecting_copies && !interesting)
+		return; /* nothing to remove */
+	if (break_idx)
+		return; /* culling incompatible with break detection */
+
+	/*
+	 * Note on reasons why we cull unneeded sources but not destinations:
+	 *   1) Pairings are stored in rename_dst (not rename_src), which we
+	 *      need to keep around.  So, we just can't cull rename_dst even
+	 *      if we wanted to.  But doing so wouldn't help because...
+	 *
+	 *   2) There is a matrix pairwise comparison that follows the
+	 *      "Performing inexact rename detection" progress message.
+	 *      Iterating over the destinations is done in the outer loop,
+	 *      hence we only iterate over each of those once and we can
+	 *      easily skip the outer loop early if the destination isn't
+	 *      relevant.  That's only one check per destination path to
+	 *      skip.
+	 *
+	 *      By contrast, the sources are iterated in the inner loop; if
+	 *      we check whether a source can be skipped, then we'll be
+	 *      checking it N separate times, once for each destination.
+	 *      We don't want to have to iterate over known-not-needed
+	 *      sources N times each, so avoid that by removing the sources
+	 *      from rename_src here.
+	 */
+	for (i = 0, new_num_src = 0; i < rename_src_nr; i++) {
+		struct diff_filespec *one = rename_src[i].p->one;
+
+		/*
+		 * renames are stored in rename_dst, so if a rename has
+		 * already been detected using this source, we can just
+		 * remove the source knowing rename_dst has its info.
+		 */
+		if (!detecting_copies && one->rename_used)
+			continue;
+
+		/* If we don't care about the source path, skip it */
+		if (interesting && !strintmap_contains(interesting, one->path))
+			continue;
+
+		if (new_num_src < i)
+			memcpy(&rename_src[new_num_src], &rename_src[i],
+			       sizeof(struct diff_rename_src));
+		new_num_src++;
+	}
+
+	rename_src_nr = new_num_src;
+}
+
+static void handle_early_known_dir_renames(struct dir_rename_info *info,
+					   struct strintmap *relevant_sources,
+					   struct strintmap *dirs_removed)
+{
+	/*
+	 * Directory renames are determined via an aggregate of all renames
+	 * under them and using a "majority wins" rule.  The fact that
+	 * "majority wins", though, means we don't need all the renames
+	 * under the given directory, we only need enough to ensure we have
+	 * a majority.
+	 */
+
+	int i, new_num_src;
+	struct hashmap_iter iter;
+	struct strmap_entry *entry;
+
+	if (!dirs_removed || !relevant_sources)
+		return; /* nothing to cull */
+	if (break_idx)
+		return; /* culling incompatbile with break detection */
+
+	/*
+	 * Supplement dir_rename_count with number of potential renames,
+	 * marking all potential rename sources as mapping to UNKNOWN_DIR.
+	 */
+	for (i = 0; i < rename_src_nr; i++) {
+		char *old_dir;
+		struct diff_filespec *one = rename_src[i].p->one;
+
+		/*
+		 * sources that are part of a rename will have already been
+		 * removed by a prior call to remove_unneeded_paths_from_src()
+		 */
+		assert(!one->rename_used);
+
+		old_dir = get_dirname(one->path);
+		while (*old_dir != '\0' &&
+		       NOT_RELEVANT != strintmap_get(dirs_removed, old_dir)) {
+			char *freeme = old_dir;
+
+			increment_count(info, old_dir, UNKNOWN_DIR);
+			old_dir = get_dirname(old_dir);
+
+			/* Free resources we don't need anymore */
+			free(freeme);
+		}
+		/*
+		 * old_dir and new_dir free'd in increment_count, but
+		 * get_dirname() gives us a new pointer we need to free for
+		 * old_dir.  Also, if the loop runs 0 times we need old_dir
+		 * to be freed.
+		 */
+		free(old_dir);
+	}
+
+	/*
+	 * For any directory which we need a potential rename detected for
+	 * (i.e. those marked as RELEVANT_FOR_SELF in dirs_removed), check
+	 * whether we have enough renames to satisfy the "majority rules"
+	 * requirement such that detecting any more renames of files under
+	 * it won't change the result.  For any such directory, mark that
+	 * we no longer need to detect a rename for it.  However, since we
+	 * might need to still detect renames for an ancestor of that
+	 * directory, use RELEVANT_FOR_ANCESTOR.
+	 */
+	strmap_for_each_entry(info->dir_rename_count, &iter, entry) {
+		/* entry->key is source_dir */
+		struct strintmap *counts = entry->value;
+
+		if (strintmap_get(dirs_removed, entry->key) ==
+		    RELEVANT_FOR_SELF &&
+		    dir_rename_already_determinable(counts)) {
+			strintmap_set(dirs_removed, entry->key,
+				      RELEVANT_FOR_ANCESTOR);
+		}
+	}
+
+	for (i = 0, new_num_src = 0; i < rename_src_nr; i++) {
+		struct diff_filespec *one = rename_src[i].p->one;
+		int val;
+
+		val = strintmap_get(relevant_sources, one->path);
+
+		/*
+		 * sources that were not found in relevant_sources should
+		 * have already been removed by a prior call to
+		 * remove_unneeded_paths_from_src()
+		 */
+		assert(val != -1);
+
+		if (val == RELEVANT_LOCATION) {
+			int removable = 1;
+			char *dir = get_dirname(one->path);
+			while (1) {
+				char *freeme = dir;
+				int res = strintmap_get(dirs_removed, dir);
+
+				/* Quit if not found or irrelevant */
+				if (res == NOT_RELEVANT)
+					break;
+				/* If RELEVANT_FOR_SELF, can't remove */
+				if (res == RELEVANT_FOR_SELF) {
+					removable = 0;
+					break;
+				}
+				/* Else continue searching upwards */
+				assert(res == RELEVANT_FOR_ANCESTOR);
+				dir = get_dirname(dir);
+				free(freeme);
+			}
+			free(dir);
+			if (removable) {
+				strintmap_set(relevant_sources, one->path,
+					      RELEVANT_NO_MORE);
+				continue;
+			}
+		}
+
+		if (new_num_src < i)
+			memcpy(&rename_src[new_num_src], &rename_src[i],
+			       sizeof(struct diff_rename_src));
+		new_num_src++;
+	}
+
+	rename_src_nr = new_num_src;
+}
+
+static void free_filespec_data(struct diff_filespec *spec)
+{
+	if (!--spec->count)
+		diff_free_filespec_data(spec);
+}
+
+static void pool_free_filespec(struct mem_pool *pool,
+			       struct diff_filespec *spec)
+{
+	if (!pool) {
+		free_filespec(spec);
+		return;
+	}
+
+	/*
+	 * Similar to free_filespec(), but only frees the data.  The spec
+	 * itself was allocated in the pool and should not be individually
+	 * freed.
+	 */
+	free_filespec_data(spec);
+}
+
+void pool_diff_free_filepair(struct mem_pool *pool,
+			     struct diff_filepair *p)
+{
+	if (!pool) {
+		diff_free_filepair(p);
+		return;
+	}
+
+	/*
+	 * Similar to diff_free_filepair() but only frees the data from the
+	 * filespecs; not the filespecs or the filepair which were
+	 * allocated from the pool.
+	 */
+	free_filespec_data(p->one);
+	free_filespec_data(p->two);
+}
+
+void diffcore_rename_extended(struct diff_options *options,
+			      struct mem_pool *pool,
+			      struct strintmap *relevant_sources,
+			      struct strintmap *dirs_removed,
+			      struct strmap *dir_rename_count,
+			      struct strmap *cached_pairs)
+{
+	int detect_rename = options->detect_rename;
+	int minimum_score = options->rename_score;
+	struct diff_queue_struct *q = &diff_queued_diff;
+	struct diff_queue_struct outq;
+	struct diff_score *mx;
+	int i, j, rename_count, skip_unmodified = 0;
+	int num_destinations, dst_cnt;
+	int num_sources, want_copies;
+	struct progress *progress = NULL;
+	struct mem_pool local_pool;
+	struct dir_rename_info info;
+	struct diff_populate_filespec_options dpf_options = {
+		.check_binary = 0,
+		.missing_object_cb = NULL,
+		.missing_object_data = NULL
+	};
+	struct inexact_prefetch_options prefetch_options = {
+		.repo = options->repo
+	};
+
+	trace2_region_enter("diff", "setup", options->repo);
+	info.setup = 0;
+	assert(!dir_rename_count || strmap_empty(dir_rename_count));
+	want_copies = (detect_rename == DIFF_DETECT_COPY);
+	if (dirs_removed && (break_idx || want_copies))
+		BUG("dirs_removed incompatible with break/copy detection");
+	if (break_idx && relevant_sources)
+		BUG("break detection incompatible with source specification");
+	if (!minimum_score)
+		minimum_score = DEFAULT_RENAME_SCORE;
+
+	for (i = 0; i < q->nr; i++) {
+		struct diff_filepair *p = q->queue[i];
+		if (!DIFF_FILE_VALID(p->one)) {
+			if (!DIFF_FILE_VALID(p->two))
+				continue; /* unmerged */
+			else if (options->single_follow &&
+				 strcmp(options->single_follow, p->two->path))
+				continue; /* not interested */
+			else if (!options->flags.rename_empty &&
+				 is_empty_blob_oid(&p->two->oid))
+				continue;
+			else if (add_rename_dst(p) < 0) {
+				warning("skipping rename detection, detected"
+					" duplicate destination '%s'",
+					p->two->path);
+				goto cleanup;
+			}
+		}
+		else if (!options->flags.rename_empty &&
+			 is_empty_blob_oid(&p->one->oid))
+			continue;
+		else if (!DIFF_PAIR_UNMERGED(p) && !DIFF_FILE_VALID(p->two)) {
+			/*
+			 * If the source is a broken "delete", and
+			 * they did not really want to get broken,
+			 * that means the source actually stays.
+			 * So we increment the "rename_used" score
+			 * by one, to indicate ourselves as a user
+			 */
+			if (p->broken_pair && !p->score)
+				p->one->rename_used++;
+			register_rename_src(p);
+		}
+		else if (want_copies) {
+			/*
+			 * Increment the "rename_used" score by
+			 * one, to indicate ourselves as a user.
+			 */
+			p->one->rename_used++;
+			register_rename_src(p);
+		}
+	}
+	trace2_region_leave("diff", "setup", options->repo);
+	if (rename_dst_nr == 0 || rename_src_nr == 0)
+		goto cleanup; /* nothing to do */
+
+	trace2_region_enter("diff", "exact renames", options->repo);
+	mem_pool_init(&local_pool, 32*1024);
+	/*
+	 * We really want to cull the candidates list early
+	 * with cheap tests in order to avoid doing deltas.
+	 */
+	rename_count = find_exact_renames(options, &local_pool);
+	/*
+	 * Discard local_pool immediately instead of at "cleanup:" in order
+	 * to reduce maximum memory usage; inexact rename detection uses up
+	 * a fair amount of memory, and mem_pools can too.
+	 */
+	mem_pool_discard(&local_pool, 0);
+	trace2_region_leave("diff", "exact renames", options->repo);
+
+	/* Did we only want exact renames? */
+	if (minimum_score == MAX_SCORE)
+		goto cleanup;
+
+	num_sources = rename_src_nr;
+
+	if (want_copies || break_idx) {
+		/*
+		 * Cull sources:
+		 *   - remove ones corresponding to exact renames
+		 *   - remove ones not found in relevant_sources
+		 */
+		trace2_region_enter("diff", "cull after exact", options->repo);
+		remove_unneeded_paths_from_src(want_copies, relevant_sources);
+		trace2_region_leave("diff", "cull after exact", options->repo);
+	} else {
+		/* Determine minimum score to match basenames */
+		double factor = 0.5;
+		char *basename_factor = getenv("GIT_BASENAME_FACTOR");
+		int min_basename_score;
+
+		if (basename_factor)
+			factor = strtol(basename_factor, NULL, 10)/100.0;
+		assert(factor >= 0.0 && factor <= 1.0);
+		min_basename_score = minimum_score +
+			(int)(factor * (MAX_SCORE - minimum_score));
+
+		/*
+		 * Cull sources:
+		 *   - remove ones involved in renames (found via exact match)
+		 */
+		trace2_region_enter("diff", "cull after exact", options->repo);
+		remove_unneeded_paths_from_src(want_copies, NULL);
+		trace2_region_leave("diff", "cull after exact", options->repo);
+
+		/* Preparation for basename-driven matching. */
+		trace2_region_enter("diff", "dir rename setup", options->repo);
+		initialize_dir_rename_info(&info, relevant_sources,
+					   dirs_removed, dir_rename_count,
+					   cached_pairs);
+		trace2_region_leave("diff", "dir rename setup", options->repo);
+
+		/* Utilize file basenames to quickly find renames. */
+		trace2_region_enter("diff", "basename matches", options->repo);
+		rename_count += find_basename_matches(options,
+						      min_basename_score,
+						      &info,
+						      relevant_sources,
+						      dirs_removed);
+		trace2_region_leave("diff", "basename matches", options->repo);
+
+		/*
+		 * Cull sources, again:
+		 *   - remove ones involved in renames (found via basenames)
+		 *   - remove ones not found in relevant_sources
+		 * and
+		 *   - remove ones in relevant_sources which are needed only
+		 *     for directory renames IF no ancestory directory
+		 *     actually needs to know any more individual path
+		 *     renames under them
+		 */
+		trace2_region_enter("diff", "cull basename", options->repo);
+		remove_unneeded_paths_from_src(want_copies, relevant_sources);
+		handle_early_known_dir_renames(&info, relevant_sources,
+					       dirs_removed);
+		trace2_region_leave("diff", "cull basename", options->repo);
+	}
+
+	/* Calculate how many rename destinations are left */
+	num_destinations = (rename_dst_nr - rename_count);
+	num_sources = rename_src_nr; /* rename_src_nr reflects lower number */
+
+	/* All done? */
+	if (!num_destinations || !num_sources)
+		goto cleanup;
+
+	switch (too_many_rename_candidates(num_destinations, num_sources,
+					   options)) {
+	case 1:
+		goto cleanup;
+	case 2:
+		options->degraded_cc_to_c = 1;
+		skip_unmodified = 1;
+		break;
+	default:
+		break;
+	}
+
+	trace2_region_enter("diff", "inexact renames", options->repo);
+	if (options->show_rename_progress) {
+		progress = start_delayed_progress(
+				_("Performing inexact rename detection"),
+				(uint64_t)num_destinations * (uint64_t)num_sources);
+	}
+
+	/* Finish setting up dpf_options */
+	prefetch_options.skip_unmodified = skip_unmodified;
+	if (options->repo == the_repository && repo_has_promisor_remote(the_repository)) {
+		dpf_options.missing_object_cb = inexact_prefetch;
+		dpf_options.missing_object_data = &prefetch_options;
+	}
+
+	CALLOC_ARRAY(mx, st_mult(NUM_CANDIDATE_PER_DST, num_destinations));
+	for (dst_cnt = i = 0; i < rename_dst_nr; i++) {
+		struct diff_filespec *two = rename_dst[i].p->two;
+		struct diff_score *m;
+
+		if (rename_dst[i].is_rename)
+			continue; /* exact or basename match already handled */
+
+		m = &mx[dst_cnt * NUM_CANDIDATE_PER_DST];
+		for (j = 0; j < NUM_CANDIDATE_PER_DST; j++)
+			m[j].dst = -1;
+
+		for (j = 0; j < rename_src_nr; j++) {
+			struct diff_filespec *one = rename_src[j].p->one;
+			struct diff_score this_src;
+
+			assert(!one->rename_used || want_copies || break_idx);
+
+			if (skip_unmodified &&
+			    diff_unmodified_pair(rename_src[j].p))
+				continue;
+
+			this_src.score = estimate_similarity(options->repo,
+							     one, two,
+							     minimum_score,
+							     &dpf_options);
+			this_src.name_score = basename_same(one, two);
+			this_src.dst = i;
+			this_src.src = j;
+			record_if_better(m, &this_src);
+			/*
+			 * Once we run estimate_similarity,
+			 * We do not need the text anymore.
+			 */
+			diff_free_filespec_blob(one);
+			diff_free_filespec_blob(two);
+		}
+		dst_cnt++;
+		display_progress(progress,
+				 (uint64_t)dst_cnt * (uint64_t)num_sources);
+	}
+	stop_progress(&progress);
+
+	/* cost matrix sorted by most to least similar pair */
+	STABLE_QSORT(mx, dst_cnt * NUM_CANDIDATE_PER_DST, score_compare);
+
+	rename_count += find_renames(mx, dst_cnt, minimum_score, 0,
+				     &info, dirs_removed);
+	if (want_copies)
+		rename_count += find_renames(mx, dst_cnt, minimum_score, 1,
+					     &info, dirs_removed);
+	free(mx);
+	trace2_region_leave("diff", "inexact renames", options->repo);
+
+ cleanup:
+	/* At this point, we have found some renames and copies and they
+	 * are recorded in rename_dst.  The original list is still in *q.
+	 */
+	trace2_region_enter("diff", "write back to queue", options->repo);
+	DIFF_QUEUE_CLEAR(&outq);
+	for (i = 0; i < q->nr; i++) {
+		struct diff_filepair *p = q->queue[i];
+		struct diff_filepair *pair_to_free = NULL;
+
+		if (DIFF_PAIR_UNMERGED(p)) {
+			diff_q(&outq, p);
+		}
+		else if (!DIFF_FILE_VALID(p->one) && DIFF_FILE_VALID(p->two)) {
+			/* Creation */
+			diff_q(&outq, p);
+		}
+		else if (DIFF_FILE_VALID(p->one) && !DIFF_FILE_VALID(p->two)) {
+			/*
+			 * Deletion
+			 *
+			 * We would output this delete record if:
+			 *
+			 * (1) this is a broken delete and the counterpart
+			 *     broken create remains in the output; or
+			 * (2) this is not a broken delete, and rename_dst
+			 *     does not have a rename/copy to move p->one->path
+			 *     out of existence.
+			 *
+			 * Otherwise, the counterpart broken create
+			 * has been turned into a rename-edit; or
+			 * delete did not have a matching create to
+			 * begin with.
+			 */
+			if (DIFF_PAIR_BROKEN(p)) {
+				/* broken delete */
+				struct diff_rename_dst *dst = locate_rename_dst(p);
+				if (!dst)
+					BUG("tracking failed somehow; failed to find associated dst for broken pair");
+				if (dst->is_rename)
+					/* counterpart is now rename/copy */
+					pair_to_free = p;
+			}
+			else {
+				if (p->one->rename_used)
+					/* this path remains */
+					pair_to_free = p;
+			}
+
+			if (!pair_to_free)
+				diff_q(&outq, p);
+		}
+		else if (!diff_unmodified_pair(p))
+			/* all the usual ones need to be kept */
+			diff_q(&outq, p);
+		else
+			/* no need to keep unmodified pairs */
+			pair_to_free = p;
+
+		if (pair_to_free)
+			pool_diff_free_filepair(pool, pair_to_free);
+	}
+	diff_debug_queue("done copying original", &outq);
+
+	free(q->queue);
+	*q = outq;
+	diff_debug_queue("done collapsing", q);
+
+	for (i = 0; i < rename_dst_nr; i++)
+		if (rename_dst[i].filespec_to_free)
+			pool_free_filespec(pool, rename_dst[i].filespec_to_free);
+
+	cleanup_dir_rename_info(&info, dirs_removed, dir_rename_count != NULL);
+	FREE_AND_NULL(rename_dst);
+	rename_dst_nr = rename_dst_alloc = 0;
+	FREE_AND_NULL(rename_src);
+	rename_src_nr = rename_src_alloc = 0;
+	if (break_idx) {
+		strintmap_clear(break_idx);
+		FREE_AND_NULL(break_idx);
+	}
+	trace2_region_leave("diff", "write back to queue", options->repo);
+	return;
+}
+
+void diffcore_rename(struct diff_options *options)
+{
+	diffcore_rename_extended(options, NULL, NULL, NULL, NULL, NULL);
+}