@@ -90,3 +83,1 @@
-  Array<int> vert_group_map; /* Maps the vertex group offset from the target vert index. */
-  Array<int> vert_groups_offs;
-  Array<int> vert_groups_buffer;
+  Vector<int> double_verts;

@@ -164,3 +149,3 @@
     }
   }
-  BLI_assert(kills == supposed_kill_len);
+  BLI_assert(kills == expected_kill_len);

@@ -446,3 +363,1 @@
-
-      if (we.vert_a == we.vert_b) {
-        we.flag = ELEM_COLLAPSED;
+      const int vert_a = (v_dest_1 != OUT_OF_CONTEXT) ? v_dest_1 : v1;

@@ -478,2 +389,3 @@
+ * \return r_edge_double_kill_len: Number of edges to be destroyed by merging or collapsing.
  */
-static void weld_edge_find_doubles(int remain_edge_ctx_len,
+static void weld_edge_find_doubles(Span<WeldEdge> wedge,

@@ -620,3 +475,1 @@
-        r_edge_groups_verts[wgroups_len] = {we->vert_a, we->vert_b};
-        r_edge_groups_map[i] = wgroups_len;
-        wgroups_len++;
+        const WeldEdge &we_b = wedge[e_ctx_b];

@@ -1449,0 +1274,4 @@
+ * \param double_elems: Affected elements in `dest_map` that will compose groups.
+ *                      Used for performance only.
+ *
+ * \return r_groups_map: Map that points out the group of elements that an element belongs to.

@@ -1449,0 +1282,4 @@
+                                Span<int> double_elems,
+                                Array<int> &r_groups_map,
+                                Array<int> &r_groups_buffer,
+                                Array<int> &r_groups_offs)

@@ -1449,0 +1305,4 @@
+  }
+
+  /* Add +1 to allow calculation of the length of the last group. */
+  r_groups_offs.reinitialize(wgroups_len + 1);

@@ -1449,0 +1308,4 @@
+  r_groups_offs.reinitialize(wgroups_len + 1);
+  r_groups_offs.fill(0);
+
+  for (const int elem_orig : double_elems) {

@@ -1449,0 +1315,4 @@
+  }
+
+  int offs = 0;
+  for (const int i : IndexRange(wgroups_len)) {

@@ -1449,0 +1324,4 @@
+  r_groups_buffer.reinitialize(offs);
+  BLI_assert(r_groups_buffer.size() == double_elems.size());
+
+  /* Use a reverse for loop to ensure that indexes are assigned in ascending order. */

@@ -1544,0 +1434,4 @@
+                                 Span<int> double_elems,
+                                 const int dest_size,
+                                 const bool do_mix_data,
+                                 Array<int> &r_final_map)

@@ -1544,0 +1476,4 @@
+      if (do_mix_data) {
+        const int grp_index = groups_map[i];
+        const int grp_buffer_offs = groups_offs[grp_index];
+        const int grp_buffer_len = groups_offs[grp_index + 1] - grp_buffer_offs;

@@ -1544,0 +1506,4 @@
+  }
+
+  if (finalize_map) {
+    for (int i : r_final_map.index_range()) {