Hold the ref_cache instance for the main repository in a dedicated,
statically-allocated instance to avoid the need for a function call
and a linked-list traversal when it is needed.

Suggested by: Heiko Voigt <hvo...@hvoigt.net>

Signed-off-by: Michael Haggerty <mhag...@alum.mit.edu>
---
 refs.c | 60 +++++++++++++++++++++++++++++++-----------------------------
 1 file changed, 31 insertions(+), 29 deletions(-)

diff --git a/refs.c b/refs.c
index f246b77..d17931a 100644
--- a/refs.c
+++ b/refs.c
@@ -810,9 +810,13 @@ static struct ref_cache {
        struct ref_cache *next;
        struct ref_entry *loose;
        struct ref_entry *packed;
-       /* The submodule name, or "" for the main repo. */
-       char name[FLEX_ARRAY];
-} *ref_cache;
+       /*
+        * The submodule name, or "" for the main repo.  We allocate
+        * length 1 rather than FLEX_ARRAY so that the main ref_cache
+        * is initialized correctly.
+        */
+       char name[1];
+} ref_cache, *submodule_ref_caches;
 
 static void clear_packed_ref_cache(struct ref_cache *refs)
 {
@@ -850,18 +854,18 @@ static struct ref_cache *create_ref_cache(const char 
*submodule)
  */
 static struct ref_cache *get_ref_cache(const char *submodule)
 {
-       struct ref_cache *refs = ref_cache;
-       if (!submodule)
-               submodule = "";
-       while (refs) {
+       struct ref_cache *refs;
+
+       if (!submodule || !*submodule)
+               return &ref_cache;
+
+       for (refs = submodule_ref_caches; refs; refs = refs->next)
                if (!strcmp(submodule, refs->name))
                        return refs;
-               refs = refs->next;
-       }
 
        refs = create_ref_cache(submodule);
-       refs->next = ref_cache;
-       ref_cache = refs;
+       refs->next = submodule_ref_caches;
+       submodule_ref_caches = refs;
        return refs;
 }
 
@@ -1010,8 +1014,8 @@ static struct ref_dir *get_packed_refs(struct ref_cache 
*refs)
 
 void add_packed_ref(const char *refname, const unsigned char *sha1)
 {
-       add_ref(get_packed_refs(get_ref_cache(NULL)),
-                       create_ref_entry(refname, sha1, REF_ISPACKED, 1));
+       add_ref(get_packed_refs(&ref_cache),
+               create_ref_entry(refname, sha1, REF_ISPACKED, 1));
 }
 
 /*
@@ -1186,7 +1190,7 @@ int resolve_gitlink_ref(const char *path, const char 
*refname, unsigned char *sh
  */
 static struct ref_entry *get_packed_ref(const char *refname)
 {
-       return find_ref(get_packed_refs(get_ref_cache(NULL)), refname);
+       return find_ref(get_packed_refs(&ref_cache), refname);
 }
 
 const char *resolve_ref_unsafe(const char *refname, unsigned char *sha1, int 
reading, int *flag)
@@ -1591,7 +1595,7 @@ int head_ref_submodule(const char *submodule, each_ref_fn 
fn, void *cb_data)
 
 int for_each_ref(each_ref_fn fn, void *cb_data)
 {
-       return do_for_each_ref(get_ref_cache(NULL), "", fn, 0, 0, cb_data);
+       return do_for_each_ref(&ref_cache, "", fn, 0, 0, cb_data);
 }
 
 int for_each_ref_submodule(const char *submodule, each_ref_fn fn, void 
*cb_data)
@@ -1601,7 +1605,7 @@ int for_each_ref_submodule(const char *submodule, 
each_ref_fn fn, void *cb_data)
 
 int for_each_ref_in(const char *prefix, each_ref_fn fn, void *cb_data)
 {
-       return do_for_each_ref(get_ref_cache(NULL), prefix, fn, strlen(prefix), 
0, cb_data);
+       return do_for_each_ref(&ref_cache, prefix, fn, strlen(prefix), 0, 
cb_data);
 }
 
 int for_each_ref_in_submodule(const char *submodule, const char *prefix,
@@ -1642,7 +1646,7 @@ int for_each_remote_ref_submodule(const char *submodule, 
each_ref_fn fn, void *c
 
 int for_each_replace_ref(each_ref_fn fn, void *cb_data)
 {
-       return do_for_each_ref(get_ref_cache(NULL), "refs/replace/", fn, 13, 0, 
cb_data);
+       return do_for_each_ref(&ref_cache, "refs/replace/", fn, 13, 0, cb_data);
 }
 
 int head_ref_namespaced(each_ref_fn fn, void *cb_data)
@@ -1665,7 +1669,7 @@ int for_each_namespaced_ref(each_ref_fn fn, void *cb_data)
        struct strbuf buf = STRBUF_INIT;
        int ret;
        strbuf_addf(&buf, "%srefs/", get_git_namespace());
-       ret = do_for_each_ref(get_ref_cache(NULL), buf.buf, fn, 0, 0, cb_data);
+       ret = do_for_each_ref(&ref_cache, buf.buf, fn, 0, 0, cb_data);
        strbuf_release(&buf);
        return ret;
 }
@@ -1707,7 +1711,7 @@ int for_each_glob_ref(each_ref_fn fn, const char 
*pattern, void *cb_data)
 
 int for_each_rawref(each_ref_fn fn, void *cb_data)
 {
-       return do_for_each_ref(get_ref_cache(NULL), "", fn, 0,
+       return do_for_each_ref(&ref_cache, "", fn, 0,
                               DO_FOR_EACH_INCLUDE_BROKEN, cb_data);
 }
 
@@ -1913,7 +1917,7 @@ static struct ref_lock *lock_ref_sha1_basic(const char 
*refname,
         * name is a proper prefix of our refname.
         */
        if (missing &&
-            !is_refname_available(refname, NULL, 
get_packed_refs(get_ref_cache(NULL)))) {
+            !is_refname_available(refname, NULL, get_packed_refs(&ref_cache))) 
{
                last_errno = ENOTDIR;
                goto error_return;
        }
@@ -2102,7 +2106,7 @@ int pack_refs(unsigned int flags)
 
        write_or_die(cbdata.fd, PACKED_REFS_HEADER, strlen(PACKED_REFS_HEADER));
 
-       do_for_each_entry(get_ref_cache(NULL), "", pack_one_ref, &cbdata);
+       do_for_each_entry(&ref_cache, "", pack_one_ref, &cbdata);
        if (commit_lock_file(&packlock) < 0)
                die_errno("unable to overwrite old ref-pack file");
        prune_refs(cbdata.ref_to_prune);
@@ -2160,7 +2164,6 @@ static int repack_ref_fn(struct ref_entry *entry, void 
*cb_data)
 static int repack_without_ref(const char *refname)
 {
        int fd;
-       struct ref_cache *refs = get_ref_cache(NULL);
        struct ref_dir *packed;
 
        if (!get_packed_ref(refname))
@@ -2171,8 +2174,8 @@ static int repack_without_ref(const char *refname)
                unable_to_lock_error(git_path("packed-refs"), errno);
                return error("cannot delete '%s' from packed refs", refname);
        }
-       clear_packed_ref_cache(refs);
-       packed = get_packed_refs(refs);
+       clear_packed_ref_cache(&ref_cache);
+       packed = get_packed_refs(&ref_cache);
        /* Remove refname from the cache. */
        if (remove_entry(packed, refname) == -1) {
                /*
@@ -2212,7 +2215,7 @@ int delete_ref(const char *refname, const unsigned char 
*sha1, int delopt)
        ret |= repack_without_ref(lock->ref_name);
 
        unlink_or_warn(git_path("logs/%s", lock->ref_name));
-       clear_loose_ref_cache(get_ref_cache(NULL));
+       clear_loose_ref_cache(&ref_cache);
        unlock_ref(lock);
        return ret;
 }
@@ -2234,7 +2237,6 @@ int rename_ref(const char *oldrefname, const char 
*newrefname, const char *logms
        struct stat loginfo;
        int log = !lstat(git_path("logs/%s", oldrefname), &loginfo);
        const char *symref = NULL;
-       struct ref_cache *refs = get_ref_cache(NULL);
 
        if (log && S_ISLNK(loginfo.st_mode))
                return error("reflog for %s is a symlink", oldrefname);
@@ -2246,10 +2248,10 @@ int rename_ref(const char *oldrefname, const char 
*newrefname, const char *logms
        if (!symref)
                return error("refname %s not found", oldrefname);
 
-       if (!is_refname_available(newrefname, oldrefname, 
get_packed_refs(refs)))
+       if (!is_refname_available(newrefname, oldrefname, 
get_packed_refs(&ref_cache)))
                return 1;
 
-       if (!is_refname_available(newrefname, oldrefname, get_loose_refs(refs)))
+       if (!is_refname_available(newrefname, oldrefname, 
get_loose_refs(&ref_cache)))
                return 1;
 
        if (log && rename(git_path("logs/%s", oldrefname), 
git_path(TMP_RENAMED_LOG)))
@@ -2505,7 +2507,7 @@ int write_ref_sha1(struct ref_lock *lock,
                unlock_ref(lock);
                return -1;
        }
-       clear_loose_ref_cache(get_ref_cache(NULL));
+       clear_loose_ref_cache(&ref_cache);
        if (log_ref_write(lock->ref_name, lock->old_sha1, sha1, logmsg) < 0 ||
            (strcmp(lock->ref_name, lock->orig_ref_name) &&
             log_ref_write(lock->orig_ref_name, lock->old_sha1, sha1, logmsg) < 
0)) {
-- 
1.8.2.1

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