When a pattern contains only a single asterisk as wildcard,
e.g. "foo*bar", after literally comparing the leading part "foo" with
the string, we can compare the tail of the string and make sure it
matches "bar", instead of running fnmatch() on "*bar" against the
remainder of the string.

-O2 build on linux-2.6, without the patch:

$ time git rev-list --quiet HEAD -- '*.c'

real    0m40.770s
user    0m40.290s
sys     0m0.256s

With the patch

$ time ~/w/git/git rev-list --quiet HEAD -- '*.c'

real    0m34.288s
user    0m33.997s
sys     0m0.205s

The above command is not supposed to be widely popular. It's chosen
because it exercises pathspec matching a lot. The point is it cuts
down matching time for popular patterns like *.c, which could be used
as pathspec in other places.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclo...@gmail.com>
---
 The optimization's condition could be loosen to "only one asterisk"
 (iow, fixed-length wildcards are OK, e.g. "abc[de]gh*.[ch]") when we
 have a custom fnmatch implementation that supports dry-run, so it can
 parse the pattern and determine the actual string length of
 "abc[de]gh" and ".[ch]". We would have something similar to regcomp in
 addition to git_fnmatch().

 cache.h     |  3 +++
 dir.c       | 18 ++++++++++++++++--
 dir.h       |  1 +
 tree-walk.c |  6 ++++--
 4 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/cache.h b/cache.h
index bf031f1..babf9e5 100644
--- a/cache.h
+++ b/cache.h
@@ -473,6 +473,8 @@ extern int index_name_is_other(const struct index_state *, 
const char *, int);
 extern int ie_match_stat(const struct index_state *, struct cache_entry *, 
struct stat *, unsigned int);
 extern int ie_modified(const struct index_state *, struct cache_entry *, 
struct stat *, unsigned int);
 
+#define PATHSPEC_ONESTAR 1     /* the pathspec pattern sastisfies GFNM_ONESTAR 
*/
+
 struct pathspec {
        const char **raw; /* get_pathspec() result, not freed by 
free_pathspec() */
        int nr;
@@ -483,6 +485,7 @@ struct pathspec {
                const char *match;
                int len;
                int nowildcard_len;
+               int flags;
        } *items;
 };
 
diff --git a/dir.c b/dir.c
index f81e1d2..9afd388 100644
--- a/dir.c
+++ b/dir.c
@@ -46,6 +46,13 @@ inline int git_fnmatch(const char *pattern, const char 
*string,
                pattern += prefix;
                string += prefix;
        }
+       if (flags & GFNM_ONESTAR) {
+               int pattern_len = strlen(++pattern);
+               int string_len = strlen(string);
+               return string_len < pattern_len ||
+                      strcmp(pattern,
+                             string + string_len - pattern_len);
+       }
        return fnmatch(pattern, string, fnm_flags);
 }
 
@@ -246,7 +253,9 @@ static int match_pathspec_item(const struct pathspec_item 
*item, int prefix,
        }
 
        if (item->nowildcard_len < item->len &&
-           !git_fnmatch(match, name, 0, item->nowildcard_len - prefix))
+           !git_fnmatch(match, name,
+                        item->flags & PATHSPEC_ONESTAR ? GFNM_ONESTAR : 0,
+                        item->nowildcard_len - prefix))
                return MATCHED_FNMATCH;
 
        return 0;
@@ -1446,8 +1455,13 @@ int init_pathspec(struct pathspec *pathspec, const char 
**paths)
                item->match = path;
                item->len = strlen(path);
                item->nowildcard_len = simple_length(path);
-               if (item->nowildcard_len < item->len)
+               item->flags = 0;
+               if (item->nowildcard_len < item->len) {
                        pathspec->has_wildcard = 1;
+                       if (path[item->nowildcard_len] == '*' &&
+                           no_wildcard(path + item->nowildcard_len + 1))
+                               item->flags |= PATHSPEC_ONESTAR;
+               }
        }
 
        qsort(pathspec->items, pathspec->nr,
diff --git a/dir.h b/dir.h
index 0e8ae84..ab5af42 100644
--- a/dir.h
+++ b/dir.h
@@ -143,6 +143,7 @@ extern int fnmatch_icase(const char *pattern, const char 
*string, int flags);
  * The prefix part of pattern must not contains wildcards.
  */
 #define GFNM_PATHNAME 1                /* similar to FNM_PATHNAME */
+#define GFNM_ONESTAR  2                /* there is only _one_ wildcard, a star 
*/
 
 extern int git_fnmatch(const char *pattern, const char *string,
                       int flags, int prefix);
diff --git a/tree-walk.c b/tree-walk.c
index 2fcf3c0..585899e 100644
--- a/tree-walk.c
+++ b/tree-walk.c
@@ -628,7 +628,8 @@ enum interesting tree_entry_interesting(const struct 
name_entry *entry,
 
                        if (item->nowildcard_len < item->len) {
                                if (!git_fnmatch(match + baselen, entry->path,
-                                                0, item->nowildcard_len - 
baselen))
+                                                item->flags & PATHSPEC_ONESTAR 
? GFNM_ONESTAR : 0,
+                                                item->nowildcard_len - 
baselen))
                                        return entry_interesting;
 
                                /*
@@ -654,7 +655,8 @@ match_wildcards:
                strbuf_add(base, entry->path, pathlen);
 
                if (!git_fnmatch(match, base->buf + base_offset,
-                                0, item->nowildcard_len)) {
+                                item->flags & PATHSPEC_ONESTAR ? GFNM_ONESTAR 
: 0,
+                                item->nowildcard_len)) {
                        strbuf_setlen(base, base_offset + baselen);
                        return entry_interesting;
                }
-- 
1.8.0.rc2.23.g1fb49df

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