Nodes: Improve node tree copy performance

When copying a full node tree, we can avoid an O(n^2) loop finding a
unique name for every node if we assume they already have unique names.
That is a reasonable assumption, since unique names are verified
elsewhere when adding a new node.

Copying a node tree with about 4000 nodes took 42 ms before,
now it takes 6 ms.

Differential Revision: https://developer.blender.org/D13644

source/blender/blenkernel/BKE_node.h

@@ -702,7 +702,8 @@ namespace blender::bke {
 
 /**
  * \note keeps socket list order identical, for copying links.
- * \note `unique_name` needs to be true. It's only disabled for speed when doing GPUnodetrees.
+ * \note `unique_name` should usually be true, unless the \a dst_tree is temporary,
+ * or the names can already be assumed valid.
  */
 bNode *node_copy_with_mapping(bNodeTree *dst_tree,
                               const bNode &node_src,

source/blender/blenkernel/intern/node.cc

@@ -158,8 +158,9 @@ static void ntree_copy_data(Main *UNUSED(bmain), ID *id_dst, const ID *id_src, c
 
   BLI_listbase_clear(&ntree_dst->nodes);
   LISTBASE_FOREACH (const bNode *, src_node, &ntree_src->nodes) {
+    /* Don't find a unique name for every node, since they should have valid names already. */
     bNode *new_node = blender::bke::node_copy_with_mapping(
-        ntree_dst, *src_node, flag_subdata, true, socket_map);
+        ntree_dst, *src_node, flag_subdata, false, socket_map);
     node_map.add(src_node, new_node);
   }