tree-diff: reuse base str(buf) memory on sub-tree recursion

Instead of allocating it all the time for every subtree in
ll_diff_tree_sha1, let's allocate it once in diff_tree_sha1, and then
all callee just use it in stacking style, without memory allocations.

This should be faster, and for me this change gives the following
slight speedups for

git log --raw --no-abbrev --no-renames --format='%H'

navy.git    linux.git v3.10..v3.11

before      0.618s      1.903s
after       0.611s      1.889s
speedup     1.1%        0.7%

Signed-off-by: Kirill Smelkov <kirr@mns.spb.ru>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/tree-diff.c b/tree-diff.c
index 80527c046472d41a03299b84ec9cc7fb1f0cd575..278acc807a3564f363a1f6e4ad689f0b6823e899 100644 (file)
--- a/tree-diff.c
+++ b/tree-diff.c
@@ -8,7 +8,7 @@
 
 
 static int ll_diff_tree_sha1(const unsigned char *old, const unsigned char *new,
-                            const char *base_str, struct diff_options *opt);
+                            struct strbuf *base, struct diff_options *opt);
 
 /*
  * Compare two tree entries, taking into account only path/S_ISDIR(mode),
@@ -123,7 +123,7 @@ static void show_path(struct strbuf *base, struct diff_options *opt,
        if (recurse) {
                strbuf_addch(base, '/');
                ll_diff_tree_sha1(t1 ? t1->entry.sha1 : NULL,
-                                 t2 ? t2->entry.sha1 : NULL, base->buf, opt);
+                                 t2 ? t2->entry.sha1 : NULL, base, opt);
        }
 
        strbuf_setlen(base, old_baselen);
@@ -146,12 +146,10 @@ static void skip_uninteresting(struct tree_desc *t, struct strbuf *base,
 }
 
 static int ll_diff_tree_sha1(const unsigned char *old, const unsigned char *new,
-                            const char *base_str, struct diff_options *opt)
+                            struct strbuf *base, struct diff_options *opt)
 {
        struct tree_desc t1, t2;
        void *t1tree, *t2tree;
-       struct strbuf base;
-       int baselen = strlen(base_str);
 
        t1tree = fill_tree_descriptor(&t1, old);
        t2tree = fill_tree_descriptor(&t2, new);
@@ -159,17 +157,14 @@ static int ll_diff_tree_sha1(const unsigned char *old, const unsigned char *new,
        /* Enable recursion indefinitely */
        opt->pathspec.recursive = DIFF_OPT_TST(opt, RECURSIVE);
 
-       strbuf_init(&base, PATH_MAX);
-       strbuf_add(&base, base_str, baselen);
-
        for (;;) {
                int cmp;
 
                if (diff_can_quit_early(opt))
                        break;
                if (opt->pathspec.nr) {
-                       skip_uninteresting(&t1, &base, opt);
-                       skip_uninteresting(&t2, &base, opt);
+                       skip_uninteresting(&t1, base, opt);
+                       skip_uninteresting(&t2, base, opt);
                }
                if (!t1.size && !t2.size)
                        break;
@@ -181,7 +176,7 @@ static int ll_diff_tree_sha1(const unsigned char *old, const unsigned char *new,
                        if (DIFF_OPT_TST(opt, FIND_COPIES_HARDER) ||
                            hashcmp(t1.entry.sha1, t2.entry.sha1) ||
                            (t1.entry.mode != t2.entry.mode))
-                               show_path(&base, opt, &t1, &t2);
+                               show_path(base, opt, &t1, &t2);
 
                        update_tree_entry(&t1);
                        update_tree_entry(&t2);
@@ -189,18 +184,17 @@ static int ll_diff_tree_sha1(const unsigned char *old, const unsigned char *new,
 
                /* t1 < t2 */
                else if (cmp < 0) {
-                       show_path(&base, opt, &t1, /*t2=*/NULL);
+                       show_path(base, opt, &t1, /*t2=*/NULL);
                        update_tree_entry(&t1);
                }
 
                /* t1 > t2 */
                else {
-                       show_path(&base, opt, /*t1=*/NULL, &t2);
+                       show_path(base, opt, /*t1=*/NULL, &t2);
                        update_tree_entry(&t2);
                }
        }
 
-       strbuf_release(&base);
        free(t2tree);
        free(t1tree);
        return 0;
@@ -217,7 +211,7 @@ static inline int diff_might_be_rename(void)
                !DIFF_FILE_VALID(diff_queued_diff.queue[0]->one);
 }
 
-static void try_to_follow_renames(const unsigned char *old, const unsigned char *new, const char *base, struct diff_options *opt)
+static void try_to_follow_renames(const unsigned char *old, const unsigned char *new, struct strbuf *base, struct diff_options *opt)
 {
        struct diff_options diff_opts;
        struct diff_queue_struct *q = &diff_queued_diff;
@@ -314,13 +308,19 @@ static void try_to_follow_renames(const unsigned char *old, const unsigned char
        q->nr = 1;
 }
 
-int diff_tree_sha1(const unsigned char *old, const unsigned char *new, const char *base, struct diff_options *opt)
+int diff_tree_sha1(const unsigned char *old, const unsigned char *new, const char *base_str, struct diff_options *opt)
 {
+       struct strbuf base;
        int retval;
 
-       retval = ll_diff_tree_sha1(old, new, base, opt);
-       if (!*base && DIFF_OPT_TST(opt, FOLLOW_RENAMES) && diff_might_be_rename())
-               try_to_follow_renames(old, new, base, opt);
+       strbuf_init(&base, PATH_MAX);
+       strbuf_addstr(&base, base_str);
+
+       retval = ll_diff_tree_sha1(old, new, &base, opt);
+       if (!*base_str && DIFF_OPT_TST(opt, FOLLOW_RENAMES) && diff_might_be_rename())
+               try_to_follow_renames(old, new, &base, opt);
+
+       strbuf_release(&base);
 
        return retval;
 }