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commit.cocci: refactor code, avoid double rewrite

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"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
committed by Junio C Hamano
parent 7fdff47432
commit a133c40b23
4 changed files with 35 additions and 14 deletions
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9
commit.c
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@ -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;