unpack_trees(): skip trees that are the same in all input

[thirdparty/git.git] / unpack-trees.c

diff --git a/unpack-trees.c b/unpack-trees.c
index aa585be1b01f21e3a94e3982b184cf4145e16c00..e1b4e996aed862da872c5e8d5a318d2b5d73127d 100644 (file)
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -436,6 +436,10 @@ static int switch_cache_bottom(struct traverse_info *info)
        return ret;
 }
 
+static int fast_forward_merge(int n, unsigned long dirmask,
+                             struct name_entry *names,
+                             struct traverse_info *info);
+
 static int traverse_trees_recursive(int n, unsigned long dirmask,
                                    unsigned long df_conflicts,
                                    struct name_entry *names,
@@ -447,6 +451,11 @@ static int traverse_trees_recursive(int n, unsigned long dirmask,
        struct traverse_info newinfo;
        struct name_entry *p;
 
+       if (!df_conflicts) {
+               int status = fast_forward_merge(n, dirmask, names, info);
+               if (status)
+                       return status;
+       }
        p = names;
        while (!p->mode)
                p++;
@@ -694,6 +703,53 @@ static struct cache_entry *find_cache_entry(struct traverse_info *info,
                return NULL;
 }
 
+static int fast_forward_merge(int n, unsigned long dirmask,
+                             struct name_entry *names,
+                             struct traverse_info *info)
+{
+       int i;
+       struct cache_entry *src[MAX_UNPACK_TREES + 1] = { NULL, };
+       struct unpack_trees_options *o = info->data;
+
+       /* merging two or more trees with an identical subdirectory? */
+       if ((n < 2) || ((1UL << n) - 1) != dirmask ||
+           !o->merge || o->reset || o->initial_checkout)
+               return 0;
+       for (i = 1; i < n; i++)
+               if (hashcmp(names[i-1].sha1, names[i].sha1))
+                       return 0;
+
+       /*
+        * Instead of descending into the directory, keep the contents
+        * of the current index.
+        */
+       while (1) {
+               struct cache_entry *ce;
+               ce = next_cache_entry(o);
+               if (!ce)
+                       break;
+               /* Is the entry still in that directory? */
+               if (do_compare_entry(ce, info, names))
+                       break;
+               /*
+                * Note: we do not just run unpack_index_entry() here,
+                * as the callback may want to compare what is in the
+                * index with what are from the HEAD and the other tree
+                * and reject the merge.  We pretend that ancestors, the
+                * HEAD and the other tree all have the same contents as
+                * the current index, which is a lie, but it works.
+                */
+               for (i = 0; i < n + 1; i++)
+                       src[i] = ce;
+               mark_ce_used(ce, o);
+               if (call_unpack_fn(src, o) < 0)
+                       return unpack_failed(o, NULL);
+               if (ce_stage(ce))
+                       mark_ce_used_same_name(ce, o);
+       }
+       return dirmask;
+}
+
 static void debug_path(struct traverse_info *info)
 {
        if (info->prev) {