commit.cocci: refactor code, avoid double rewrite

"maybe" pointer in 'struct commit' is tricky because it can be lazily
initialized to take advantage of commit-graph if available. This makes
it not safe to access directly.

This leads to a rule in commit.cocci to rewrite 'x->maybe_tree' to
'get_commit_tree(x)'. But that rule alone could lead to incorrectly
rewrite assignments, e.g. from

    x->maybe_tree = yes

to

    get_commit_tree(x) = yes

Because of this we have a second rule to revert this effect. Szeder
found out that we could do better by performing the assignment rewrite
rule first, then the remaining is read-only access and handled by the
current first rule.

For this to work, we need to transform "x->maybe_tree = y" to something
that does NOT contain "x->maybe_tree" to avoid the original first
rule. This is where set_commit_tree() comes in.

Helped-by: SZEDER Gábor <szeder.dev@gmail.com>
Helped-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Nguyễn Thái Ngọc Duy 2019-04-16 16:33:18 +07:00 коммит произвёл Junio C Hamano
Родитель 7fdff47432
Коммит a133c40b23
4 изменённых файлов: 35 добавлений и 14 удалений

Просмотреть файл

@ -343,6 +343,11 @@ static void fill_commit_graph_info(struct commit *item, struct commit_graph *g,
item->generation = get_be32(commit_data + g->hash_len + 8) >> 2;
}
static inline void set_commit_tree(struct commit *c, struct tree *t)
{
c->maybe_tree = t;
}
static int fill_commit_in_graph(struct repository *r,
struct commit *item,
struct commit_graph *g, uint32_t pos)
@ -356,7 +361,7 @@ static int fill_commit_in_graph(struct repository *r,
item->object.parsed = 1;
item->graph_pos = pos;
item->maybe_tree = NULL;
set_commit_tree(item, NULL);
date_high = get_be32(commit_data + g->hash_len + 8) & 0x3;
date_low = get_be32(commit_data + g->hash_len + 12);
@ -442,7 +447,7 @@ static struct tree *load_tree_for_commit(struct repository *r,
GRAPH_DATA_WIDTH * (c->graph_pos);
hashcpy(oid.hash, commit_data);
c->maybe_tree = lookup_tree(r, &oid);
set_commit_tree(c, lookup_tree(r, &oid));
return c->maybe_tree;
}

Просмотреть файл

@ -340,6 +340,11 @@ void free_commit_buffer(struct parsed_object_pool *pool, struct commit *commit)
}
}
static inline void set_commit_tree(struct commit *c, struct tree *t)
{
c->maybe_tree = t;
}
struct tree *get_commit_tree(const struct commit *commit)
{
if (commit->maybe_tree || !commit->object.parsed)
@ -358,7 +363,7 @@ struct object_id *get_commit_tree_oid(const struct commit *commit)
void release_commit_memory(struct parsed_object_pool *pool, struct commit *c)
{
c->maybe_tree = NULL;
set_commit_tree(c, NULL);
c->index = 0;
free_commit_buffer(pool, c);
free_commit_list(c->parents);
@ -406,7 +411,7 @@ int parse_commit_buffer(struct repository *r, struct commit *item, const void *b
if (get_oid_hex(bufptr + 5, &parent) < 0)
return error("bad tree pointer in commit %s",
oid_to_hex(&item->object.oid));
item->maybe_tree = lookup_tree(r, &parent);
set_commit_tree(item, lookup_tree(r, &parent));
bufptr += tree_entry_len + 1; /* "tree " + "hex sha1" + "\n" */
pptr = &item->parents;

Просмотреть файл

@ -10,19 +10,25 @@ expression c;
- c->maybe_tree->object.oid.hash
+ get_commit_tree_oid(c)->hash
// These excluded functions must access c->maybe_tree direcly.
@@
identifier f !~ "^(get_commit_tree|get_commit_tree_in_graph_one|load_tree_for_commit)$";
identifier f !~ "^set_commit_tree$";
expression c;
expression s;
@@
f(...) {<...
- c->maybe_tree = s
+ set_commit_tree(c, s)
...>}
// These excluded functions must access c->maybe_tree direcly.
// Note that if c->maybe_tree is written somewhere outside of these
// functions, then the recommended transformation will be bogus with
// get_commit_tree() on the LHS.
@@
identifier f !~ "^(get_commit_tree|get_commit_tree_in_graph_one|load_tree_for_commit|set_commit_tree)$";
expression c;
@@
f(...) {<...
- c->maybe_tree
+ get_commit_tree(c)
...>}
@@
expression c;
expression s;
@@
- get_commit_tree(c) = s
+ c->maybe_tree = s

Просмотреть файл

@ -163,6 +163,11 @@ static struct tree *shift_tree_object(struct repository *repo,
return lookup_tree(repo, &shifted);
}
static inline void set_commit_tree(struct commit *c, struct tree *t)
{
c->maybe_tree = t;
}
static struct commit *make_virtual_commit(struct repository *repo,
struct tree *tree,
const char *comment)
@ -170,7 +175,7 @@ static struct commit *make_virtual_commit(struct repository *repo,
struct commit *commit = alloc_commit_node(repo);
set_merge_remote_desc(commit, comment, (struct object *)commit);
commit->maybe_tree = tree;
set_commit_tree(commit, tree);
commit->object.parsed = 1;
return commit;
}