[PATCH 2/2] name-rev: use mem_pool_strfmt()

["René Scharfe" <l.s.r@web.de>]

1c56fc2084 (name-rev: pre-size buffer in get_parent_name(), 2020-02-04)
got a big performance boost in an unusual repository by calculating the
name length in advance.  This is a bit awkward, as it references the
name components twice.

Use a memory pool to store the strings for the struct rev_name member
tip_name.  Using mem_pool_strfmt() allows efficient allocation without
explicit size calculation.  This simplifies the formatting part of the
code without giving up performance:

Benchmark 1: ./git_2.44.0 -C ../chromium/src name-rev --all
  Time (mean ± σ):      1.231 s ±  0.013 s    [User: 1.082 s, System: 0.136 s]
  Range (min … max):    1.214 s …  1.252 s    10 runs

Benchmark 2: ./git -C ../chromium/src name-rev --all
  Time (mean ± σ):      1.220 s ±  0.020 s    [User: 1.083 s, System: 0.130 s]
  Range (min … max):    1.197 s …  1.254 s    10 runs

Don't bother discarding the memory pool just before exiting.  The effort
for that would be very low, but actually measurable in the above
example, with no benefit to users.  At least UNLEAK it to calm down leak
checkers.  This addresses the leaks that 45a14f578e (Revert "name-rev:
release unused name strings", 2022-04-22) brought back.

Signed-off-by: René Scharfe <l.s.r@web.de>
---
This doesn't make any test script leak-free, though.

 builtin/name-rev.c | 39 ++++++++++++++++++++-------------------
 1 file changed, 20 insertions(+), 19 deletions(-)

diff --git a/builtin/name-rev.c b/builtin/name-rev.c
index 2dd1807c4e..ad9930c831 100644
--- a/builtin/name-rev.c
+++ b/builtin/name-rev.c
@@ -15,6 +15,7 @@
 #include "commit-slab.h"
 #include "commit-graph.h"
 #include "wildmatch.h"
+#include "mem-pool.h"

 /*
  * One day.  See the 'name a rev shortly after epoch' test in t6120 when
@@ -155,30 +156,25 @@ static struct rev_name *create_or_update_name(struct commit *commit,
 	return name;
 }

-static char *get_parent_name(const struct rev_name *name, int parent_number)
+static char *get_parent_name(const struct rev_name *name, int parent_number,
+			     struct mem_pool *string_pool)
 {
-	struct strbuf sb = STRBUF_INIT;
 	size_t len;

 	strip_suffix(name->tip_name, "^0", &len);
 	if (name->generation > 0) {
-		strbuf_grow(&sb, len +
-			    1 + decimal_width(name->generation) +
-			    1 + decimal_width(parent_number));
-		strbuf_addf(&sb, "%.*s~%d^%d", (int)len, name->tip_name,
-			    name->generation, parent_number);
+		return mem_pool_strfmt(string_pool, "%.*s~%d^%d",
+				       (int)len, name->tip_name,
+				       name->generation, parent_number);
 	} else {
-		strbuf_grow(&sb, len +
-			    1 + decimal_width(parent_number));
-		strbuf_addf(&sb, "%.*s^%d", (int)len, name->tip_name,
-			    parent_number);
+		return mem_pool_strfmt(string_pool, "%.*s^%d",
+				       (int)len, name->tip_name, parent_number);
 	}
-	return strbuf_detach(&sb, NULL);
 }

 static void name_rev(struct commit *start_commit,
 		const char *tip_name, timestamp_t taggerdate,
-		int from_tag, int deref)
+		int from_tag, int deref, struct mem_pool *string_pool)
 {
 	struct prio_queue queue;
 	struct commit *commit;
@@ -195,9 +191,10 @@ static void name_rev(struct commit *start_commit,
 	if (!start_name)
 		return;
 	if (deref)
-		start_name->tip_name = xstrfmt("%s^0", tip_name);
+		start_name->tip_name = mem_pool_strfmt(string_pool, "%s^0",
+						       tip_name);
 	else
-		start_name->tip_name = xstrdup(tip_name);
+		start_name->tip_name = mem_pool_strdup(string_pool, tip_name);

 	memset(&queue, 0, sizeof(queue)); /* Use the prio_queue as LIFO */
 	prio_queue_put(&queue, start_commit);
@@ -235,7 +232,8 @@ static void name_rev(struct commit *start_commit,
 				if (parent_number > 1)
 					parent_name->tip_name =
 						get_parent_name(name,
-								parent_number);
+								parent_number,
+								string_pool);
 				else
 					parent_name->tip_name = name->tip_name;
 				ALLOC_GROW(parents_to_queue,
@@ -415,7 +413,7 @@ static int name_ref(const char *path, const struct object_id *oid,
 	return 0;
 }

-static void name_tips(void)
+static void name_tips(struct mem_pool *string_pool)
 {
 	int i;

@@ -428,7 +426,7 @@ static void name_tips(void)
 		struct tip_table_entry *e = &tip_table.table[i];
 		if (e->commit) {
 			name_rev(e->commit, e->refname, e->taggerdate,
-				 e->from_tag, e->deref);
+				 e->from_tag, e->deref, string_pool);
 		}
 	}
 }
@@ -561,6 +559,7 @@ static void name_rev_line(char *p, struct name_ref_data *data)

 int cmd_name_rev(int argc, const char **argv, const char *prefix)
 {
+	struct mem_pool string_pool;
 	struct object_array revs = OBJECT_ARRAY_INIT;
 	int all = 0, annotate_stdin = 0, transform_stdin = 0, allow_undefined = 1, always = 0, peel_tag = 0;
 	struct name_ref_data data = { 0, 0, STRING_LIST_INIT_NODUP, STRING_LIST_INIT_NODUP };
@@ -587,6 +586,7 @@ int cmd_name_rev(int argc, const char **argv, const char *prefix)
 		OPT_END(),
 	};

+	mem_pool_init(&string_pool, 0);
 	init_commit_rev_name(&rev_names);
 	git_config(git_default_config, NULL);
 	argc = parse_options(argc, argv, prefix, opts, name_rev_usage, 0);
@@ -648,7 +648,7 @@ int cmd_name_rev(int argc, const char **argv, const char *prefix)
 	adjust_cutoff_timestamp_for_slop();

 	for_each_ref(name_ref, &data);
-	name_tips();
+	name_tips(&string_pool);

 	if (annotate_stdin) {
 		struct strbuf sb = STRBUF_INIT;
@@ -676,6 +676,7 @@ int cmd_name_rev(int argc, const char **argv, const char *prefix)
 				  always, allow_undefined, data.name_only);
 	}

+	UNLEAK(string_pool);
 	UNLEAK(revs);
 	return 0;
 }
--
2.44.0