[graph] Use a hb_map_t to keep parents, instead of hb_vector_t

In some fonts, for example Noto Duployan-Regular, nodes can
have over a thousand parents... Speeds up 10% subsetting.

src/graph/classdef-graph.hh

@@ -72,7 +72,7 @@ struct ClassDef : public OT::ClassDef
     class_def_link->width = SmallTypes::size;
     class_def_link->objidx = class_def_prime_id;
     class_def_link->position = link_position;
-    class_def_prime_vertex.parents.push (parent_id);
+    class_def_prime_vertex.add_parent (parent_id);
 
     return true;
   }

src/graph/coverage-graph.hh

@@ -96,7 +96,7 @@ struct Coverage : public OT::Layout::Common::Coverage
     coverage_link->width = SmallTypes::size;
     coverage_link->objidx = coverage_prime_id;
     coverage_link->position = link_position;
-    coverage_prime_vertex.parents.push (parent_id);
+    coverage_prime_vertex.add_parent (parent_id);
 
     return (Coverage*) coverage_prime_vertex.obj.head;
   }

src/graph/graph.hh

@@ -44,10 +44,11 @@ struct graph_t
     hb_serialize_context_t::object_t obj;
     int64_t distance = 0 ;
     int64_t space = 0 ;
-    hb_vector_t<unsigned> parents;
     unsigned start = 0;
     unsigned end = 0;
     unsigned priority = 0;
+    unsigned incoming_edges_ = 0;
+    hb_hashmap_t<unsigned, unsigned> parents;
 
 
     bool link_positions_valid (unsigned num_objects, bool removed_nil)
@@ -144,6 +145,7 @@ struct graph_t
       hb_swap (a.distance, b.distance);
       hb_swap (a.space, b.space);
       hb_swap (a.parents, b.parents);
+      hb_swap (a.incoming_edges_, b.incoming_edges_);
       hb_swap (a.start, b.start);
       hb_swap (a.end, b.end);
       hb_swap (a.priority, b.priority);
@@ -164,22 +166,36 @@ struct graph_t
 
     bool is_shared () const
     {
-      return parents.length > 1;
+      return parents.get_population () > 1;
     }
 
     unsigned incoming_edges () const
     {
-      return parents.length;
+      return incoming_edges_;
+    }
+
+    void reset_parents ()
+    {
+      incoming_edges_ = 0;
+      parents.reset ();
+    }
+
+    void add_parent (unsigned parent_index)
+    {
+      incoming_edges_++;
+      parents.set (parent_index, parents[parent_index] + 1);
     }
 
     void remove_parent (unsigned parent_index)
     {
-      unsigned count = parents.length;
-      for (unsigned i = 0; i < count; i++)
+      unsigned *v;
+      if (parents.has (parent_index, &v))
       {
-        if (parents.arrayZ[i] != parent_index) continue;
-        parents.remove_unordered (i);
-        break;
+	incoming_edges_--;
+	if (*v > 1)
+	  *v -= 1;
+	else
+	  parents.del (parent_index);
       }
     }
 
@@ -202,21 +218,35 @@ struct graph_t
 
     void remap_parents (const hb_vector_t<unsigned>& id_map)
     {
-      unsigned count = parents.length;
-      for (unsigned i = 0; i < count; i++)
-        parents.arrayZ[i] = id_map[parents.arrayZ[i]];
+      if (parents.get_population () == 1)
+      {
+        // Fast path for the common case.
+        const auto &_ = *parents.iter_ref ();
+        unsigned old_index = _.first;
+	unsigned new_index = id_map[old_index];
+	if (old_index != new_index)
+	{
+	  unsigned v = _.second;
+	  parents.del (old_index);
+	  parents.set (new_index, v);
+	}
+	return;
+      }
+
+      hb_map_t new_parents;
+      new_parents.alloc (parents.get_population ());
+      for (auto _ : parents)
+        new_parents.set (id_map[_.first], _.second);
+
+      parents = std::move (new_parents);
     }
 
     void remap_parent (unsigned old_index, unsigned new_index)
     {
-      unsigned count = parents.length;
-      for (unsigned i = 0; i < count; i++)
+      if (parents.has (old_index))
       {
-        if (parents.arrayZ[i] == old_index)
-	{
-	  parents.arrayZ[i] = new_index;
-	  break;
-	}
+	remove_parent (old_index);
+	add_parent (new_index);
       }
     }
 
@@ -423,7 +453,7 @@ struct graph_t
     link->width = 2;
     link->objidx = child_id;
     link->position = (char*) offset - (char*) v.obj.head;
-    vertices_[child_id].parents.push (parent_id);
+    vertices_[child_id].add_parent (parent_id);
   }
 
   /*
@@ -609,7 +639,7 @@ struct graph_t
   {
     unsigned child_idx = index_for_offset (node_idx, offset);
     auto& child = vertices_[child_idx];
-    for (unsigned p : child.parents)
+    for (unsigned p : child.parents.keys ())
     {
       if (p != node_idx) {
         return duplicate (node_idx, child_idx);
@@ -828,7 +858,7 @@ struct graph_t
     new_link->position = (const char*) new_offset - (const char*) new_v.obj.head;
 
     auto& child = vertices_[child_id];
-    child.parents.push (new_parent_idx);
+    child.add_parent (new_parent_idx);
 
     old_v.remove_real_link (child_id, old_offset);
     child.remove_parent (old_parent_idx);
@@ -872,18 +902,18 @@ struct graph_t
     clone->obj.tail = child.obj.tail;
     clone->distance = child.distance;
     clone->space = child.space;
-    clone->parents.reset ();
+    clone->reset_parents ();
 
     unsigned clone_idx = vertices_.length - 2;
     for (const auto& l : child.obj.real_links)
     {
       clone->obj.real_links.push (l);
-      vertices_[l.objidx].parents.push (clone_idx);
+      vertices_[l.objidx].add_parent (clone_idx);
     }
     for (const auto& l : child.obj.virtual_links)
     {
       clone->obj.virtual_links.push (l);
-      vertices_[l.objidx].parents.push (clone_idx);
+      vertices_[l.objidx].add_parent (clone_idx);
     }
 
     check_success (!clone->obj.real_links.in_error ());
@@ -1136,7 +1166,7 @@ struct graph_t
       return 0;
     }
 
-    return space_for (node.parents[0], root);
+    return space_for (*node.parents.keys (), root);
   }
 
   void err_other_error () { this->successful = false; }
@@ -1160,12 +1190,8 @@ struct graph_t
   unsigned wide_parents (unsigned node_idx, hb_set_t& parents) const
   {
     unsigned count = 0;
-    hb_set_t visited;
-    for (unsigned p : vertices_[node_idx].parents)
+    for (unsigned p : vertices_[node_idx].parents.keys ())
     {
-      if (visited.has (p)) continue;
-      visited.add (p);
-
       // Only real links can be wide
       for (const auto& l : vertices_[p].obj.real_links)
       {
@@ -1195,13 +1221,13 @@ struct graph_t
     unsigned count = vertices_.length;
 
     for (unsigned i = 0; i < count; i++)
-      vertices_.arrayZ[i].parents.reset ();
+      vertices_.arrayZ[i].reset_parents ();
 
     for (unsigned p = 0; p < count; p++)
     {
       for (auto& l : vertices_.arrayZ[p].obj.all_links ())
       {
-        vertices_[l.objidx].parents.push (p);
+        vertices_[l.objidx].add_parent (p);
       }
     }
 
@@ -1309,7 +1335,7 @@ struct graph_t
     unsigned old_idx = link.objidx;
     link.objidx = new_idx;
     vertices_[old_idx].remove_parent (parent_idx);
-    vertices_[new_idx].parents.push (parent_idx);
+    vertices_[new_idx].add_parent (parent_idx);
   }
 
   /*
@@ -1379,7 +1405,7 @@ struct graph_t
     for (const auto& l : v.obj.all_links ())
       find_connected_nodes (l.objidx, targets, visited, connected);
 
-    for (unsigned p : v.parents)
+    for (unsigned p : v.parents.keys ())
       find_connected_nodes (p, targets, visited, connected);
   }
 

src/graph/gsubgpos-graph.hh

@@ -225,7 +225,7 @@ struct Lookup : public OT::Lookup
         if (is_ext)
         {
           unsigned ext_id = create_extension_subtable (c, subtable_id, type);
-          c.graph.vertices_[subtable_id].parents.push (ext_id);
+          c.graph.vertices_[subtable_id].add_parent (ext_id);
           subtable_id = ext_id;
         }
 
@@ -234,7 +234,7 @@ struct Lookup : public OT::Lookup
         link->objidx = subtable_id;
         link->position = (char*) &new_lookup->subTable[offset_index++] -
                          (char*) new_lookup;
-        c.graph.vertices_[subtable_id].parents.push (this_index);
+        c.graph.vertices_[subtable_id].add_parent (this_index);
       }
     }
 
@@ -315,7 +315,7 @@ struct Lookup : public OT::Lookup
     // Make extension point at the subtable.
     auto& ext_vertex = c.graph.vertices_[ext_index];
     auto& subtable_vertex = c.graph.vertices_[subtable_index];
-    ext_vertex.parents.push (lookup_index);
+    ext_vertex.add_parent (lookup_index);
     subtable_vertex.remap_parent (lookup_index, ext_index);
 
     return true;

src/graph/pairpos-graph.hh

@@ -419,7 +419,7 @@ struct PairPosFormat2 : public OT::Layout::GPOS_impl::PairPosFormat2_4<SmallType
     class_def_link->width = SmallTypes::size;
     class_def_link->objidx = class_def_2_id;
     class_def_link->position = 10;
-    graph.vertices_[class_def_2_id].parents.push (pair_pos_prime_id);
+    graph.vertices_[class_def_2_id].add_parent (pair_pos_prime_id);
     graph.duplicate (pair_pos_prime_id, class_def_2_id);
 
     return pair_pos_prime_id;