[PATCH v2 3/4] pathspec: apply "*.c" optimization from exclude

["Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>]

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 <pclouds@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