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).

2 files changed, 73 insertions, 19 deletions

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