Geometry Nodes: speedup joining many geometries

Joining many geometries was O(n^2) because of deduplication of the same
components was not done using a map. My test file that generates 1000
stars in a repeat zone got 10x faster, but it's possible to create a file for any
speedup.

source/blender/blenkernel/BKE_geometry_set.hh

@@ -446,6 +446,12 @@ struct GeometrySet {
     return Span(a.components_) == Span(b.components_) && a.name == b.name;
   }
 
+  uint64_t hash() const
+  {
+    /* This should have the same data that's also taken into account in #operator==. */
+    return get_default_hash(Span(components_), this->name);
+  }
+
   void count_memory(MemoryCounter &memory) const;
 
  private:

source/blender/blenkernel/BKE_instances.hh

@@ -105,6 +105,8 @@ class InstanceReference {
   void count_memory(MemoryCounter &memory) const;
 
   friend bool operator==(const InstanceReference &a, const InstanceReference &b);
+
+  uint64_t hash() const;
 };
 
 class Instances {

source/blender/blenkernel/intern/instances.cc

@@ -131,6 +131,11 @@ bool operator==(const InstanceReference &a, const InstanceReference &b)
   return a.type_ == b.type_ && a.data_ == b.data_;
 }
 
+uint64_t InstanceReference::hash() const
+{
+  return get_default_hash(geometry_set_, type_, data_);
+}
+
 Instances::Instances()
 {
   CustomData_reset(&attributes_);

source/blender/geometry/intern/join_geometries.cc

@@ -110,6 +110,8 @@ static void join_instances(const Span<const GeometryComponent *> src_components,
 
   MutableSpan<int> all_handles = dst_instances->reference_handles_for_write();
 
+  Map<std::reference_wrapper<const bke::InstanceReference>, int> new_handle_by_src_reference;
+
   for (const int i : src_components.index_range()) {
     const auto &src_component = static_cast<const bke::InstancesComponent &>(*src_components[i]);
     const bke::Instances &src_instances = *src_component.get();
@@ -117,7 +119,9 @@ static void join_instances(const Span<const GeometryComponent *> src_components,
     const Span<bke::InstanceReference> src_references = src_instances.references();
     Array<int> handle_map(src_references.size());
     for (const int src_handle : src_references.index_range()) {
-      handle_map[src_handle] = dst_instances->add_reference(src_references[src_handle]);
+      const bke::InstanceReference &src_reference = src_references[src_handle];
+      handle_map[src_handle] = new_handle_by_src_reference.lookup_or_add_cb(
+          src_reference, [&]() { return dst_instances->add_new_reference(src_reference); });
     }
 
     const IndexRange dst_range = offsets[i];
@@ -174,10 +178,14 @@ static void join_component_type(const bke::GeometryComponent::Type component_typ
   instances->resize(components.size());
   instances->transforms_for_write().fill(float4x4::identity());
   MutableSpan<int> handles = instances->reference_handles_for_write();
+  Map<const GeometryComponent *, int> handle_by_component;
   for (const int i : components.index_range()) {
-    GeometrySet tmp_geo;
-    tmp_geo.add(*components[i]);
-    handles[i] = instances->add_reference(bke::InstanceReference{tmp_geo});
+    const GeometryComponent *component = components[i];
+    handles[i] = handle_by_component.lookup_or_add_cb(component, [&]() {
+      GeometrySet tmp_geo;
+      tmp_geo.add(*components[i]);
+      return instances->add_new_reference(bke::InstanceReference{tmp_geo});
+    });
   }
 
   RealizeInstancesOptions options;