Geometry Nodes: create local tree logger only when something is logged

Currently, we create a logger for every compute context that is evaluated,
even when we don't actually log anything in that context (due to other
optimizations). Now, the logger is not created eagerly anymore.

This can be especially benefitial when there are many compute contexts
that should not log anything, e.g. if there is a repeat zone with many iterations.
In an extrem case I measured a speedup for the modifier evaluation
from 24ms to 14ms.

source/blender/nodes/NOD_geometry_exec.hh

@@ -181,7 +181,7 @@ class GeoNodeExecParams {
 
   geo_eval_log::GeoTreeLogger *get_local_tree_logger() const
   {
-    return this->local_user_data()->tree_logger;
+    return this->local_user_data()->try_get_tree_logger();
   }
 
   /**

source/blender/nodes/NOD_geometry_nodes_lazy_function.hh

@@ -194,13 +194,31 @@ struct GeoNodesLFUserData : public lf::UserData {
 };
 
 struct GeoNodesLFLocalUserData : public lf::LocalUserData {
- public:
+ private:
+  GeoNodesLFUserData &user_data_;
   /**
-   * Thread-local logger for the current node tree in the current compute context.
+   * Thread-local logger for the current node tree in the current compute context. It is only
+   * instantiated when it is actually used and then cached for the current thread.
    */
-  geo_eval_log::GeoTreeLogger *tree_logger = nullptr;
+  mutable std::optional<geo_eval_log::GeoTreeLogger *> tree_logger_;
 
-  GeoNodesLFLocalUserData(GeoNodesLFUserData &user_data);
+ public:
+  GeoNodesLFLocalUserData(GeoNodesLFUserData &user_data) : user_data_(user_data) {}
+
+  /**
+   * Get the current tree logger. This method is not thread-safe, each thread is supposed to have
+   * a separate logger.
+   */
+  geo_eval_log::GeoTreeLogger *try_get_tree_logger() const
+  {
+    if (!tree_logger_.has_value()) {
+      this->ensure_tree_logger();
+    }
+    return *tree_logger_;
+  }
+
+ private:
+  void ensure_tree_logger() const;
 };
 
 /**

source/blender/nodes/intern/geometry_nodes_lazy_function.cc

@@ -328,9 +328,8 @@ class LazyFunctionForGeometryNode : public LazyFunction {
     node_.typeinfo->geometry_node_execute(geo_params);
     geo_eval_log::TimePoint end_time = geo_eval_log::Clock::now();
 
-    if (local_user_data.tree_logger) {
-      local_user_data.tree_logger->node_execution_times.append(
-          {node_.identifier, start_time, end_time});
+    if (geo_eval_log::GeoTreeLogger *tree_logger = local_user_data.try_get_tree_logger()) {
+      tree_logger->node_execution_times.append({node_.identifier, start_time, end_time});
     }
   }
 
@@ -779,7 +778,8 @@ class LazyFunctionForViewerNode : public LazyFunction {
   void execute_impl(lf::Params &params, const lf::Context &context) const override
   {
     const auto &local_user_data = *static_cast<GeoNodesLFLocalUserData *>(context.local_user_data);
-    if (local_user_data.tree_logger == nullptr) {
+    geo_eval_log::GeoTreeLogger *tree_logger = local_user_data.try_get_tree_logger();
+    if (tree_logger == nullptr) {
       return;
     }
 
@@ -828,7 +828,7 @@ class LazyFunctionForViewerNode : public LazyFunction {
       }
     }
 
-    local_user_data.tree_logger->log_viewer_node(bnode_, std::move(geometry));
+    tree_logger->log_viewer_node(bnode_, std::move(geometry));
   }
 };
 
@@ -3919,7 +3919,8 @@ void GeometryNodesLazyFunctionLogger::log_socket_value(
     return;
   }
   auto &local_user_data = *static_cast<GeoNodesLFLocalUserData *>(context.local_user_data);
-  if (local_user_data.tree_logger == nullptr) {
+  geo_eval_log::GeoTreeLogger *tree_logger = local_user_data.try_get_tree_logger();
+  if (tree_logger == nullptr) {
     return;
   }
 
@@ -3939,7 +3940,7 @@ void GeometryNodesLazyFunctionLogger::log_socket_value(
     if (bnode.is_reroute()) {
       continue;
     }
-    local_user_data.tree_logger->log_value(bsocket->owner_node(), *bsocket, value);
+    tree_logger->log_value(bsocket->owner_node(), *bsocket, value);
   }
 }
 
@@ -4000,7 +4001,8 @@ Vector<const lf::FunctionNode *> GeometryNodesLazyFunctionSideEffectProvider::
   static thread_local const std::string thread_id_str = "Thread: " + std::to_string(thread_id);
 
   const auto &local_user_data = *static_cast<GeoNodesLFLocalUserData *>(context.local_user_data);
-  if (local_user_data.tree_logger == nullptr) {
+  geo_eval_log::GeoTreeLogger *tree_logger = local_user_data.try_get_tree_logger();
+  if (tree_logger == nullptr) {
     return;
   }
 
@@ -4012,7 +4014,7 @@ Vector<const lf::FunctionNode *> GeometryNodesLazyFunctionSideEffectProvider::
       if (!bsockets.is_empty()) {
         const bNodeSocket &bsocket = *bsockets[0];
         const bNode &bnode = bsocket.owner_node();
-        local_user_data.tree_logger->debug_messages.append({bnode.identifier, thread_id_str});
+        tree_logger->debug_messages.append({bnode.identifier, thread_id_str});
         return true;
       }
     }
@@ -4040,16 +4042,18 @@ destruct_ptr<lf::LocalUserData> GeoNodesLFUserData::get_local(LinearAllocator<>
   return allocator.construct<GeoNodesLFLocalUserData>(*this);
 }
 
-GeoNodesLFLocalUserData::GeoNodesLFLocalUserData(GeoNodesLFUserData &user_data)
+void GeoNodesLFLocalUserData::ensure_tree_logger() const
 {
-  if (user_data.modifier_data == nullptr) {
-    this->tree_logger = nullptr;
+  if (user_data_.modifier_data == nullptr) {
+    tree_logger_.emplace(nullptr);
     return;
   }
-  if (user_data.modifier_data->eval_log != nullptr) {
-    this->tree_logger = &user_data.modifier_data->eval_log->get_local_tree_logger(
-        *user_data.compute_context);
+  if (user_data_.modifier_data->eval_log != nullptr) {
+    tree_logger_.emplace(
+        &user_data_.modifier_data->eval_log->get_local_tree_logger(*user_data_.compute_context));
+    return;
   }
+  this->tree_logger_.emplace(nullptr);
 }
 
 std::optional<FoundNestedNodeID> find_nested_node_id(const GeoNodesLFUserData &user_data,