[GSoC Patch 3/3] commit: convert commit->graph_pos to a slab

[Abhishek Kumar <abhishekkumar8222@gmail.com>]

The member graph_pos refers to the integer position used to identify a
commit in commit-graph files. However, graph_pos is not useful in other
contexts and bloats the struct.

Let's move it to a commit-slab and shrink the struct by four bytes.

Existing references to graph_pos are replaced using
'contrib/coccinelle/graph_pos.cocci'.

Signed-off-by: Abhishek Kumar <abhishekkumar8222@gmail.com>
---
 alloc.c                            |  1 -
 bloom.c                            |  6 ++--
 commit-graph.c                     | 50 +++++++++++++++++++++++-------
 commit-graph.h                     |  3 ++
 commit.c                           |  2 +-
 commit.h                           |  2 --
 contrib/coccinelle/graph_pos.cocci | 12 +++++++
 7 files changed, 58 insertions(+), 18 deletions(-)
 create mode 100644 contrib/coccinelle/graph_pos.cocci

diff --git a/alloc.c b/alloc.c
index cbed187094..f37fb3b8b6 100644
--- a/alloc.c
+++ b/alloc.c
@@ -108,7 +108,6 @@ void init_commit_node(struct repository *r, struct commit *c)
 {
 	c->object.type = OBJ_COMMIT;
 	c->index = alloc_commit_index(r);
-	c->graph_pos = COMMIT_NOT_FROM_GRAPH;
 }
 
 void *alloc_commit_node(struct repository *r)
diff --git a/bloom.c b/bloom.c
index 9b86aa3f59..5bee5bb0c1 100644
--- a/bloom.c
+++ b/bloom.c
@@ -34,14 +34,14 @@ static int load_bloom_filter_from_graph(struct commit_graph *g,
 {
 	uint32_t lex_pos, start_index, end_index;
 
-	while (c->graph_pos < g->num_commits_in_base)
+	while (graph_pos(c) < g->num_commits_in_base)
 		g = g->base_graph;
 
 	/* The commit graph commit 'c' lives in doesn't carry bloom filters. */
 	if (!g->chunk_bloom_indexes)
 		return 0;
 
-	lex_pos = c->graph_pos - g->num_commits_in_base;
+	lex_pos = graph_pos(c) - g->num_commits_in_base;
 
 	end_index = get_be32(g->chunk_bloom_indexes + 4 * lex_pos);
 
@@ -188,7 +188,7 @@ struct bloom_filter *get_bloom_filter(struct repository *r,
 
 	if (!filter->data) {
 		load_commit_graph_info(r, c);
-		if (c->graph_pos != COMMIT_NOT_FROM_GRAPH &&
+		if (graph_pos(c) != COMMIT_NOT_FROM_GRAPH &&
 			r->objects->commit_graph->chunk_bloom_indexes) {
 			if (load_bloom_filter_from_graph(r->objects->commit_graph, filter, c))
 				return filter;
diff --git a/commit-graph.c b/commit-graph.c
index 9ce7d4acb1..7ff460b442 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -87,6 +87,34 @@ static int commit_pos_cmp(const void *va, const void *vb)
 	       commit_pos_at(&commit_pos, b);
 }
 
+define_commit_slab(graph_pos_slab, uint32_t);
+static struct graph_pos_slab graph_pos_slab = COMMIT_SLAB_INIT(1, graph_pos_slab);
+
+uint32_t graph_pos(const struct commit *c)
+{
+	uint32_t *pos = graph_pos_slab_peek(&graph_pos_slab, c);
+
+	return pos ? *pos : COMMIT_NOT_FROM_GRAPH;
+}
+
+static void set_graph_pos(const struct commit *c, const uint32_t position)
+{
+	unsigned int i = graph_pos_slab.slab_count;
+	uint32_t *pos = graph_pos_slab_at(&graph_pos_slab, c);
+
+	/*
+	 * commit-slab initializes with zero, overwrite this with
+	 * COMMIT_NOT_FROM_GRAPH
+	 */
+	for (; i < graph_pos_slab.slab_count; ++i)
+	{
+		memset(graph_pos_slab.slab[i], COMMIT_NOT_FROM_GRAPH,
+		       graph_pos_slab.slab_size * sizeof(uint32_t));
+	}
+
+	*pos = position;
+}
+
 define_commit_slab(generation_slab, uint32_t);
 static struct generation_slab generation_slab = COMMIT_SLAB_INIT(1, generation_slab);
 
@@ -697,7 +725,7 @@ static struct commit_list **insert_parent_or_die(struct repository *r,
 	c = lookup_commit(r, &oid);
 	if (!c)
 		die(_("could not find commit %s"), oid_to_hex(&oid));
-	c->graph_pos = pos;
+	set_graph_pos(c, pos);
 	return &commit_list_insert(c, pptr)->next;
 }
 
@@ -711,7 +739,7 @@ static void fill_commit_graph_info(struct commit *item, struct commit_graph *g,
 
 	lex_index = pos - g->num_commits_in_base;
 	commit_data = g->chunk_commit_data + GRAPH_DATA_WIDTH * lex_index;
-	item->graph_pos = pos;
+	set_graph_pos(item, pos);
 	set_generation(item, get_be32(commit_data + g->hash_len + 8) >> 2);
 }
 
@@ -741,7 +769,7 @@ static int fill_commit_in_graph(struct repository *r,
 	 * Store the "full" position, but then use the
 	 * "local" position for the rest of the calculation.
 	 */
-	item->graph_pos = pos;
+	set_graph_pos(item, pos);
 	lex_index = pos - g->num_commits_in_base;
 
 	commit_data = g->chunk_commit_data + (g->hash_len + 16) * lex_index;
@@ -786,8 +814,8 @@ static int fill_commit_in_graph(struct repository *r,
 
 static int find_commit_in_graph(struct commit *item, struct commit_graph *g, uint32_t *pos)
 {
-	if (item->graph_pos != COMMIT_NOT_FROM_GRAPH) {
-		*pos = item->graph_pos;
+	if (graph_pos(item) != COMMIT_NOT_FROM_GRAPH) {
+		*pos = graph_pos(item);
 		return 1;
 	} else {
 		struct commit_graph *cur_g = g;
@@ -843,11 +871,11 @@ static struct tree *load_tree_for_commit(struct repository *r,
 	struct object_id oid;
 	const unsigned char *commit_data;
 
-	while (c->graph_pos < g->num_commits_in_base)
+	while (graph_pos(c) < g->num_commits_in_base)
 		g = g->base_graph;
 
 	commit_data = g->chunk_commit_data +
-			GRAPH_DATA_WIDTH * (c->graph_pos - g->num_commits_in_base);
+			GRAPH_DATA_WIDTH * (graph_pos(c) - g->num_commits_in_base);
 
 	hashcpy(oid.hash, commit_data);
 	set_commit_tree(c, lookup_tree(r, &oid));
@@ -861,7 +889,7 @@ static struct tree *get_commit_tree_in_graph_one(struct repository *r,
 {
 	if (c->maybe_tree)
 		return c->maybe_tree;
-	if (c->graph_pos == COMMIT_NOT_FROM_GRAPH)
+	if (graph_pos(c) == COMMIT_NOT_FROM_GRAPH)
 		BUG("get_commit_tree_in_graph_one called from non-commit-graph commit");
 
 	return load_tree_for_commit(r, g, (struct commit *)c);
@@ -1247,7 +1275,7 @@ static void close_reachable(struct write_commit_graph_context *ctx)
 			continue;
 		if (ctx->split) {
 			if ((!parse_commit(commit) &&
-			     commit->graph_pos == COMMIT_NOT_FROM_GRAPH) ||
+			     graph_pos(commit) == COMMIT_NOT_FROM_GRAPH) ||
 			    flags == COMMIT_GRAPH_SPLIT_REPLACE)
 				add_missing_parents(ctx, commit);
 		} else if (!parse_commit_no_graph(commit))
@@ -1493,7 +1521,7 @@ static uint32_t count_distinct_commits(struct write_commit_graph_context *ctx)
 			if (ctx->split) {
 				struct commit *c = lookup_commit(ctx->r, &ctx->oids.list[i]);
 
-				if (!c || c->graph_pos != COMMIT_NOT_FROM_GRAPH)
+				if (!c || graph_pos(c) != COMMIT_NOT_FROM_GRAPH)
 					continue;
 			}
 
@@ -1527,7 +1555,7 @@ static void copy_oids_to_commits(struct write_commit_graph_context *ctx)
 		ctx->commits.list[ctx->commits.nr] = lookup_commit(ctx->r, &ctx->oids.list[i]);
 
 		if (ctx->split && flags != COMMIT_GRAPH_SPLIT_REPLACE &&
-		    ctx->commits.list[ctx->commits.nr]->graph_pos != COMMIT_NOT_FROM_GRAPH)
+		    graph_pos(ctx->commits.list[ctx->commits.nr]) != COMMIT_NOT_FROM_GRAPH)
 			continue;
 
 		if (ctx->split && flags == COMMIT_GRAPH_SPLIT_REPLACE)
diff --git a/commit-graph.h b/commit-graph.h
index 653bd041ad..3cb59ba336 100644
--- a/commit-graph.h
+++ b/commit-graph.h
@@ -8,6 +8,7 @@
 #include "object-store.h"
 #include "oidset.h"
 
+#define COMMIT_NOT_FROM_GRAPH 0xFFFFFFFF
 #define GENERATION_NUMBER_INFINITY 0xFFFFFFFF
 #define GENERATION_NUMBER_MAX 0x3FFFFFFF
 #define GENERATION_NUMBER_ZERO 0
@@ -142,4 +143,6 @@ void free_commit_graph(struct commit_graph *);
 void disable_commit_graph(struct repository *r);
 
 uint32_t generation(const struct commit *c);
+
+uint32_t graph_pos(const struct commit *c);
 #endif
diff --git a/commit.c b/commit.c
index 8dad0f8446..da6de08b2b 100644
--- a/commit.c
+++ b/commit.c
@@ -339,7 +339,7 @@ struct tree *repo_get_commit_tree(struct repository *r,
 	if (commit->maybe_tree || !commit->object.parsed)
 		return commit->maybe_tree;
 
-	if (commit->graph_pos != COMMIT_NOT_FROM_GRAPH)
+	if (graph_pos(commit) != COMMIT_NOT_FROM_GRAPH)
 		return get_commit_tree_in_graph(r, commit);
 
 	return NULL;
diff --git a/commit.h b/commit.h
index 01e1c4c3eb..0b10464a10 100644
--- a/commit.h
+++ b/commit.h
@@ -10,8 +10,6 @@
 #include "pretty.h"
 #include "commit-slab.h"
 
-#define COMMIT_NOT_FROM_GRAPH 0xFFFFFFFF
-
 struct commit_list {
 	struct commit *item;
 	struct commit_list *next;
diff --git a/contrib/coccinelle/graph_pos.cocci b/contrib/coccinelle/graph_pos.cocci
new file mode 100644
index 0000000000..0929164bdf
--- /dev/null
+++ b/contrib/coccinelle/graph_pos.cocci
@@ -0,0 +1,12 @@
+@@
+struct commit *c;
+expression E;
+@@
+- c->graph_pos = E
++ set_graph_pos(c, E)
+
+@@
+struct commit *c;
+@@
+- c->graph_pos
++ graph_pos(c)
-- 
2.27.0