Functions: make multi functions smaller and cheaper to construct in many cases

Previously, the signature of a `MultiFunction` was always embedded into the function.
There are two issues with that. First, `MFSignature` is relatively large, because it contains
multiple strings and vectors. Secondly, constructing it can add overhead that should not
be necessary, because often the same signature can be reused.

The solution is to only keep a pointer to a signature in `MultiFunction` that is set during
construction. Child classes are responsible for making sure that the signature lives
long enough. In most cases, the signature is either embedded into the child class or
it is allocated statically (and is only created once).

9 files changed, 168 insertions, 60 deletions

diff --git a/source/blender/functions/FN_multi_function.hh b/source/blender/functions/FN_multi_function.hh
index d8924b3cf23..2ce65426245 100644
--- a/source/blender/functions/FN_multi_function.hh
+++ b/source/blender/functions/FN_multi_function.hh
@@ -53,7 +53,7 @@ namespace blender::fn {
 
 class MultiFunction {
  private:
-  MFSignature signature_;
+  const MFSignature *signature_ref_ = nullptr;
 
  public:
   virtual ~MultiFunction()
@@ -74,44 +74,50 @@ class MultiFunction {
 
   int param_amount() const
   {
-    return signature_.param_types.size();
+    return signature_ref_->param_types.size();
   }
 
   IndexRange param_indices() const
   {
-    return signature_.param_types.index_range();
+    return signature_ref_->param_types.index_range();
   }
 
   MFParamType param_type(int param_index) const
   {
-    return signature_.param_types[param_index];
+    return signature_ref_->param_types[param_index];
   }
 
   StringRefNull param_name(int param_index) const
   {
-    return signature_.param_names[param_index];
+    return signature_ref_->param_names[param_index];
   }
 
   StringRefNull name() const
   {
-    return signature_.function_name;
+    return signature_ref_->function_name;
   }
 
   bool depends_on_context() const
   {
-    return signature_.depends_on_context;
+    return signature_ref_->depends_on_context;
   }
 
   const MFSignature &signature() const
   {
-    return signature_;
+    BLI_assert(signature_ref_ != nullptr);
+    return *signature_ref_;
   }
 
  protected:
-  MFSignatureBuilder get_builder(std::string function_name)
+  /* Make the function use the given signature. This should be called once in the constructor of
+   * child classes. No copy of the signature is made, so the caller has to make sure that the
+   * signature lives as long as the multi function. It is ok to embed the signature into the child
+   * class. */
+  void set_signature(const MFSignature *signature)
   {
-    signature_.function_name = std::move(function_name);
-    return MFSignatureBuilder(signature_);
+    /* Take a pointer as argument, so that it is more obvious that no copy is created. */
+    BLI_assert(signature != nullptr);
+    signature_ref_ = signature;
   }
 };
 
diff --git a/source/blender/functions/FN_multi_function_builder.hh b/source/blender/functions/FN_multi_function_builder.hh
index b73c41d3f59..389d0b14bb5 100644
--- a/source/blender/functions/FN_multi_function_builder.hh
+++ b/source/blender/functions/FN_multi_function_builder.hh
@@ -40,13 +40,16 @@ template<typename In1, typename Out1> class CustomMF_SI_SO : public MultiFunctio
  private:
   using FunctionT = std::function<void(IndexMask, const VArray<In1> &, MutableSpan<Out1>)>;
   FunctionT function_;
+  MFSignature signature_;
 
  public:
   CustomMF_SI_SO(StringRef name, FunctionT function) : function_(std::move(function))
   {
-    MFSignatureBuilder signature = this->get_builder(name);
+    MFSignatureBuilder signature{name};
     signature.single_input<In1>("In1");
     signature.single_output<Out1>("Out1");
+    signature_ = signature.build();
+    this->set_signature(&signature_);
   }
 
   template<typename ElementFuncT>
@@ -83,14 +86,17 @@ class CustomMF_SI_SI_SO : public MultiFunction {
   using FunctionT =
       std::function<void(IndexMask, const VArray<In1> &, const VArray<In2> &, MutableSpan<Out1>)>;
   FunctionT function_;
+  MFSignature signature_;
 
  public:
   CustomMF_SI_SI_SO(StringRef name, FunctionT function) : function_(std::move(function))
   {
-    MFSignatureBuilder signature = this->get_builder(name);
+    MFSignatureBuilder signature{name};
     signature.single_input<In1>("In1");
     signature.single_input<In2>("In2");
     signature.single_output<Out1>("Out1");
+    signature_ = signature.build();
+    this->set_signature(&signature_);
   }
 
   template<typename ElementFuncT>
@@ -135,15 +141,18 @@ class CustomMF_SI_SI_SI_SO : public MultiFunction {
                                        const VArray<In3> &,
                                        MutableSpan<Out1>)>;
   FunctionT function_;
+  MFSignature signature_;
 
  public:
   CustomMF_SI_SI_SI_SO(StringRef name, FunctionT function) : function_(std::move(function))
   {
-    MFSignatureBuilder signature = this->get_builder(name);
+    MFSignatureBuilder signature{name};
     signature.single_input<In1>("In1");
     signature.single_input<In2>("In2");
     signature.single_input<In3>("In3");
     signature.single_output<Out1>("Out1");
+    signature_ = signature.build();
+    this->set_signature(&signature_);
   }
 
   template<typename ElementFuncT>
@@ -193,16 +202,19 @@ class CustomMF_SI_SI_SI_SI_SO : public MultiFunction {
                                        const VArray<In4> &,
                                        MutableSpan<Out1>)>;
   FunctionT function_;
+  MFSignature signature_;
 
  public:
   CustomMF_SI_SI_SI_SI_SO(StringRef name, FunctionT function) : function_(std::move(function))
   {
-    MFSignatureBuilder signature = this->get_builder(name);
+    MFSignatureBuilder signature{name};
     signature.single_input<In1>("In1");
     signature.single_input<In2>("In2");
     signature.single_input<In3>("In3");
     signature.single_input<In4>("In4");
     signature.single_output<Out1>("Out1");
+    signature_ = signature.build();
+    this->set_signature(&signature_);
   }
 
   template<typename ElementFuncT>
@@ -244,12 +256,15 @@ template<typename Mut1> class CustomMF_SM : public MultiFunction {
  private:
   using FunctionT = std::function<void(IndexMask, MutableSpan<Mut1>)>;
   FunctionT function_;
+  MFSignature signature_;
 
  public:
   CustomMF_SM(StringRef name, FunctionT function) : function_(std::move(function))
   {
-    MFSignatureBuilder signature = this->get_builder(name);
+    MFSignatureBuilder signature{name};
     signature.single_mutable<Mut1>("Mut1");
+    signature_ = signature.build();
+    this->set_signature(&signature_);
   }
 
   template<typename ElementFuncT>
@@ -279,10 +294,17 @@ template<typename From, typename To> class CustomMF_Convert : public MultiFuncti
  public:
   CustomMF_Convert()
   {
+    static MFSignature signature = create_signature();
+    this->set_signature(&signature);
+  }
+
+  static MFSignature create_signature()
+  {
     std::string name = CPPType::get<From>().name() + " to " + CPPType::get<To>().name();
-    MFSignatureBuilder signature = this->get_builder(std::move(name));
+    MFSignatureBuilder signature{std::move(name)};
     signature.single_input<From>("Input");
     signature.single_output<To>("Output");
+    return signature.build();
   }
 
   void call(IndexMask mask, MFParams params, MFContext UNUSED(context)) const override
@@ -304,6 +326,7 @@ class CustomMF_GenericConstant : public MultiFunction {
  private:
   const CPPType &type_;
   const void *value_;
+  MFSignature signature_;
 
   template<typename T> friend class CustomMF_Constant;
 
@@ -321,6 +344,7 @@ class CustomMF_GenericConstant : public MultiFunction {
 class CustomMF_GenericConstantArray : public MultiFunction {
  private:
   GSpan array_;
+  MFSignature signature_;
 
  public:
   CustomMF_GenericConstantArray(GSpan array);
@@ -333,14 +357,17 @@ class CustomMF_GenericConstantArray : public MultiFunction {
 template<typename T> class CustomMF_Constant : public MultiFunction {
  private:
   T value_;
+  MFSignature signature_;
 
  public:
   template<typename U> CustomMF_Constant(U &&value) : value_(std::forward<U>(value))
   {
-    MFSignatureBuilder signature = this->get_builder("Constant");
+    MFSignatureBuilder signature{"Constant"};
     std::stringstream ss;
     ss << value_;
     signature.single_output<T>(ss.str());
+    signature_ = signature.build();
+    this->set_signature(&signature_);
   }
 
   void call(IndexMask mask, MFParams params, MFContext UNUSED(context)) const override
@@ -375,6 +402,7 @@ template<typename T> class CustomMF_Constant : public MultiFunction {
 class CustomMF_DefaultOutput : public MultiFunction {
  private:
   int output_amount_;
+  MFSignature signature_;
 
  public:
   CustomMF_DefaultOutput(StringRef name,
diff --git a/source/blender/functions/FN_multi_function_network_evaluation.hh b/source/blender/functions/FN_multi_function_network_evaluation.hh
index 2c0d94615b0..17cffa406f7 100644
--- a/source/blender/functions/FN_multi_function_network_evaluation.hh
+++ b/source/blender/functions/FN_multi_function_network_evaluation.hh
@@ -28,6 +28,7 @@ class MFNetworkEvaluationStorage;
 
 class MFNetworkEvaluator : public MultiFunction {
  private:
+  MFSignature signature_;
   Vector<const MFOutputSocket *> inputs_;
   Vector<const MFInputSocket *> outputs_;
 
diff --git a/source/blender/functions/FN_multi_function_signature.hh b/source/blender/functions/FN_multi_function_signature.hh
index e05ea1c2578..23309c9a5e6 100644
--- a/source/blender/functions/FN_multi_function_signature.hh
+++ b/source/blender/functions/FN_multi_function_signature.hh
@@ -44,18 +44,21 @@ struct MFSignature {
 
 class MFSignatureBuilder {
  private:
-  MFSignature &data_;
+  MFSignature signature_;
   int span_count_ = 0;
   int virtual_array_count_ = 0;
   int virtual_vector_array_count_ = 0;
   int vector_array_count_ = 0;
 
  public:
-  MFSignatureBuilder(MFSignature &data) : data_(data)
+  MFSignatureBuilder(std::string function_name)
   {
-    BLI_assert(data.param_names.is_empty());
-    BLI_assert(data.param_types.is_empty());
-    BLI_assert(data.param_data_indices.is_empty());
+    signature_.function_name = std::move(function_name);
+  }
+
+  MFSignature build() const
+  {
+    return std::move(signature_);
   }
 
   /* Input Parameter Types */
@@ -78,15 +81,15 @@ class MFSignatureBuilder {
   }
   void input(StringRef name, MFDataType data_type)
   {
-    data_.param_names.append(name);
-    data_.param_types.append(MFParamType(MFParamType::Input, data_type));
+    signature_.param_names.append(name);
+    signature_.param_types.append(MFParamType(MFParamType::Input, data_type));
 
     switch (data_type.category()) {
       case MFDataType::Single:
-        data_.param_data_indices.append(virtual_array_count_++);
+        signature_.param_data_indices.append(virtual_array_count_++);
         break;
       case MFDataType::Vector:
-        data_.param_data_indices.append(virtual_vector_array_count_++);
+        signature_.param_data_indices.append(virtual_vector_array_count_++);
         break;
     }
   }
@@ -111,15 +114,15 @@ class MFSignatureBuilder {
   }
   void output(StringRef name, MFDataType data_type)
   {
-    data_.param_names.append(name);
-    data_.param_types.append(MFParamType(MFParamType::Output, data_type));
+    signature_.param_names.append(name);
+    signature_.param_types.append(MFParamType(MFParamType::Output, data_type));
 
     switch (data_type.category()) {
       case MFDataType::Single:
-        data_.param_data_indices.append(span_count_++);
+        signature_.param_data_indices.append(span_count_++);
         break;
       case MFDataType::Vector:
-        data_.param_data_indices.append(vector_array_count_++);
+        signature_.param_data_indices.append(vector_array_count_++);
         break;
     }
   }
@@ -144,15 +147,15 @@ class MFSignatureBuilder {
   }
   void mutable_(StringRef name, MFDataType data_type)
   {
-    data_.param_names.append(name);
-    data_.param_types.append(MFParamType(MFParamType::Mutable, data_type));
+    signature_.param_names.append(name);
+    signature_.param_types.append(MFParamType(MFParamType::Mutable, data_type));
 
     switch (data_type.category()) {
       case MFDataType::Single:
-        data_.param_data_indices.append(span_count_++);
+        signature_.param_data_indices.append(span_count_++);
         break;
       case MFDataType::Vector:
-        data_.param_data_indices.append(vector_array_count_++);
+        signature_.param_data_indices.append(vector_array_count_++);
         break;
     }
   }
@@ -163,7 +166,7 @@ class MFSignatureBuilder {
    * depend on the fact that the function always performers the same operation. */
   void depends_on_context()
   {
-    data_.depends_on_context = true;
+    signature_.depends_on_context = true;
   }
 };
 
diff --git a/source/blender/functions/intern/multi_function.cc b/source/blender/functions/intern/multi_function.cc
index a41c6bdf3cd..bb657f321ec 100644
--- a/source/blender/functions/intern/multi_function.cc
+++ b/source/blender/functions/intern/multi_function.cc
@@ -22,7 +22,14 @@ class DummyMultiFunction : public MultiFunction {
  public:
   DummyMultiFunction()
   {
-    this->get_builder("Dummy");
+    static MFSignature signature = create_signature();
+    this->set_signature(&signature);
+  }
+
+  static MFSignature create_signature()
+  {
+    MFSignatureBuilder signature{"Dummy"};
+    return signature.build();
   }
 
   void call(IndexMask UNUSED(mask),
diff --git a/source/blender/functions/intern/multi_function_builder.cc b/source/blender/functions/intern/multi_function_builder.cc
index c9e8b88ba03..3567f4f9167 100644
--- a/source/blender/functions/intern/multi_function_builder.cc
+++ b/source/blender/functions/intern/multi_function_builder.cc
@@ -23,10 +23,12 @@ namespace blender::fn {
 CustomMF_GenericConstant::CustomMF_GenericConstant(const CPPType &type, const void *value)
     : type_(type), value_(value)
 {
-  MFSignatureBuilder signature = this->get_builder("Constant " + type.name());
+  MFSignatureBuilder signature{"Constant " + type.name()};
   std::stringstream ss;
   type.debug_print(value, ss);
   signature.single_output(ss.str(), type);
+  signature_ = signature.build();
+  this->set_signature(&signature_);
 }
 
 void CustomMF_GenericConstant::call(IndexMask mask,
@@ -73,8 +75,10 @@ static std::string gspan_to_string(GSpan array)
 CustomMF_GenericConstantArray::CustomMF_GenericConstantArray(GSpan array) : array_(array)
 {
   const CPPType &type = array.type();
-  MFSignatureBuilder signature = this->get_builder("Constant " + type.name() + " Vector");
+  MFSignatureBuilder signature{"Constant " + type.name() + " Vector"};
   signature.vector_output(gspan_to_string(array), type);
+  signature_ = signature.build();
+  this->set_signature(&signature_);
 }
 
 void CustomMF_GenericConstantArray::call(IndexMask mask,
@@ -92,13 +96,15 @@ CustomMF_DefaultOutput::CustomMF_DefaultOutput(StringRef name,
                                                Span<MFDataType> output_types)
     : output_amount_(output_types.size())
 {
-  MFSignatureBuilder signature = this->get_builder(name);
+  MFSignatureBuilder signature{name};
   for (MFDataType data_type : input_types) {
     signature.input("Input", data_type);
   }
   for (MFDataType data_type : output_types) {
     signature.output("Output", data_type);
   }
+  signature_ = signature.build();
+  this->set_signature(&signature_);
 }
 void CustomMF_DefaultOutput::call(IndexMask mask, MFParams params, MFContext UNUSED(context)) const
 {
diff --git a/source/blender/functions/intern/multi_function_network_evaluation.cc b/source/blender/functions/intern/multi_function_network_evaluation.cc
index 98500a350ae..daa0a42963a 100644
--- a/source/blender/functions/intern/multi_function_network_evaluation.cc
+++ b/source/blender/functions/intern/multi_function_network_evaluation.cc
@@ -115,7 +115,7 @@ MFNetworkEvaluator::MFNetworkEvaluator(Vector<const MFOutputSocket *> inputs,
     : inputs_(std::move(inputs)), outputs_(std::move(outputs))
 {
   BLI_assert(outputs_.size() > 0);
-  MFSignatureBuilder signature = this->get_builder("Function Tree");
+  MFSignatureBuilder signature{"Function Tree"};
 
   for (const MFOutputSocket *socket : inputs_) {
     BLI_assert(socket->node().is_dummy());
@@ -144,6 +144,9 @@ MFNetworkEvaluator::MFNetworkEvaluator(Vector<const MFOutputSocket *> inputs,
         break;
     }
   }
+
+  signature_ = signature.build();
+  this->set_signature(&signature_);
 }
 
 void MFNetworkEvaluator::call(IndexMask mask, MFParams params, MFContext context) const
diff --git a/source/blender/functions/tests/FN_multi_function_network_test.cc b/source/blender/functions/tests/FN_multi_function_network_test.cc
index 70da0315b93..51e116b5983 100644
--- a/source/blender/functions/tests/FN_multi_function_network_test.cc
+++ b/source/blender/functions/tests/FN_multi_function_network_test.cc
@@ -69,9 +69,16 @@ class ConcatVectorsFunction : public MultiFunction {
  public:
   ConcatVectorsFunction()
   {
-    MFSignatureBuilder signature = this->get_builder("Concat Vectors");
+    static MFSignature signature = create_signature();
+    this->set_signature(&signature);
+  }
+
+  static MFSignature create_signature()
+  {
+    MFSignatureBuilder signature{"Concat Vectors"};
     signature.vector_mutable<int>("A");
     signature.vector_input<int>("B");
+    return signature.build();
   }
 
   void call(IndexMask mask, MFParams params, MFContext UNUSED(context)) const override
@@ -86,9 +93,16 @@ class AppendFunction : public MultiFunction {
  public:
   AppendFunction()
   {
-    MFSignatureBuilder signature = this->get_builder("Append");
+    static MFSignature signature = create_signature();
+    this->set_signature(&signature);
+  }
+
+  static MFSignature create_signature()
+  {
+    MFSignatureBuilder signature{"Append"};
     signature.vector_mutable<int>("Vector");
     signature.single_input<int>("Value");
+    return signature.build();
   }
 
   void call(IndexMask mask, MFParams params, MFContext UNUSED(context)) const override
@@ -106,9 +120,16 @@ class SumVectorFunction : public MultiFunction {
  public:
   SumVectorFunction()
   {
-    MFSignatureBuilder signature = this->get_builder("Sum Vector");
+    static MFSignature signature = create_signature();
+    this->set_signature(&signature);
+  }
+
+  static MFSignature create_signature()
+  {
+    MFSignatureBuilder signature{"Sum Vectors"};
     signature.vector_input<int>("Vector");
     signature.single_output<int>("Sum");
+    return signature.build();
   }
 
   void call(IndexMask mask, MFParams params, MFContext UNUSED(context)) const override
@@ -130,9 +151,16 @@ class CreateRangeFunction : public MultiFunction {
  public:
   CreateRangeFunction()
   {
-    MFSignatureBuilder builder = this->get_builder("Create Range");
-    builder.single_input<int>("Size");
-    builder.vector_output<int>("Range");
+    static MFSignature signature = create_signature();
+    this->set_signature(&signature);
+  }
+
+  static MFSignature create_signature()
+  {
+    MFSignatureBuilder signature{"Create Range"};
+    signature.single_input<int>("Size");
+    signature.vector_output<int>("Range");
+    return signature.build();
   }
 
   void call(IndexMask mask, MFParams params, MFContext UNUSED(context)) const override
diff --git a/source/blender/functions/tests/FN_multi_function_test.cc b/source/blender/functions/tests/FN_multi_function_test.cc
index 3ed60665149..3d73e020eb2 100644
--- a/source/blender/functions/tests/FN_multi_function_test.cc
+++ b/source/blender/functions/tests/FN_multi_function_test.cc
@@ -12,10 +12,17 @@ class AddFunction : public MultiFunction {
  public:
   AddFunction()
   {
-    MFSignatureBuilder builder = this->get_builder("Add");
-    builder.single_input<int>("A");
-    builder.single_input<int>("B");
-    builder.single_output<int>("Result");
+    static MFSignature signature = create_signature();
+    this->set_signature(&signature);
+  }
+
+  static MFSignature create_signature()
+  {
+    MFSignatureBuilder signature("Add");
+    signature.single_input<int>("A");
+    signature.single_input<int>("B");
+    signature.single_output<int>("Result");
+    return signature.build();
   }
 
   void call(IndexMask mask, MFParams params, MFContext UNUSED(context)) const override
@@ -56,9 +63,16 @@ class AddPrefixFunction : public MultiFunction {
  public:
   AddPrefixFunction()
   {
-    MFSignatureBuilder builder = this->get_builder("Add Prefix");
-    builder.single_input<std::string>("Prefix");
-    builder.single_mutable<std::string>("Strings");
+    static MFSignature signature = create_signature();
+    this->set_signature(&signature);
+  }
+
+  static MFSignature create_signature()
+  {
+    MFSignatureBuilder signature{"Add Prefix"};
+    signature.single_input<std::string>("Prefix");
+    signature.single_mutable<std::string>("Strings");
+    return signature.build();
   }
 
   void call(IndexMask mask, MFParams params, MFContext UNUSED(context)) const override
@@ -103,9 +117,16 @@ class CreateRangeFunction : public MultiFunction {
  public:
   CreateRangeFunction()
   {
-    MFSignatureBuilder builder = this->get_builder("Create Range");
-    builder.single_input<uint>("Size");
-    builder.vector_output<uint>("Range");
+    static MFSignature signature = create_signature();
+    this->set_signature(&signature);
+  }
+
+  static MFSignature create_signature()
+  {
+    MFSignatureBuilder signature{"Create Range"};
+    signature.single_input<uint>("Size");
+    signature.vector_output<uint>("Range");
+    return signature.build();
   }
 
   void call(IndexMask mask, MFParams params, MFContext UNUSED(context)) const override
@@ -152,12 +173,17 @@ TEST(multi_function, CreateRangeFunction)
 }
 
 class GenericAppendFunction : public MultiFunction {
+ private:
+  MFSignature signature_;
+
  public:
   GenericAppendFunction(const CPPType &type)
   {
-    MFSignatureBuilder builder = this->get_builder("Append");
-    builder.vector_mutable("Vector", type);
-    builder.single_input("Value", type);
+    MFSignatureBuilder signature{"Append"};
+    signature.vector_mutable("Vector", type);
+    signature.single_input("Value", type);
+    signature_ = signature.build();
+    this->set_signature(&signature_);
   }
 
   void call(IndexMask mask, MFParams params, MFContext UNUSED(context)) const override