Functions: use static names for multi-functions

Previously, the function names were stored in `std::string` and were often
created dynamically (especially when the function just output a constant).
This resulted in a lot of overhead.

Now the function name is just a `const char *` that should be statically
allocated. This is good enough for the majority of cases. If a multi-function
needs a more dynamic name, it can override the `MultiFunction::debug_name`
method.

In my test file with >400,000 simple math nodes, the execution time improves from
3s to 1s.

1 files changed, 4 insertions, 4 deletions

diff --git a/source/blender/nodes/intern/type_conversions.cc b/source/blender/nodes/intern/type_conversions.cc
index b1611679ced..d4cd7dc6bfe 100644
--- a/source/blender/nodes/intern/type_conversions.cc
+++ b/source/blender/nodes/intern/type_conversions.cc
@@ -29,11 +29,11 @@ using fn::MFDataType;
 template<typename From, typename To, To (*ConversionF)(const From &)>
 static void add_implicit_conversion(DataTypeConversions &conversions)
 {
-  const CPPType &from_type = CPPType::get<From>();
-  const CPPType &to_type = CPPType::get<To>();
-  const std::string conversion_name = from_type.name() + " to " + to_type.name();
+  static const CPPType &from_type = CPPType::get<From>();
+  static const CPPType &to_type = CPPType::get<To>();
+  static const std::string conversion_name = from_type.name() + " to " + to_type.name();
 
-  static fn::CustomMF_SI_SO<From, To> multi_function{conversion_name, ConversionF};
+  static fn::CustomMF_SI_SO<From, To> multi_function{conversion_name.c_str(), ConversionF};
   static auto convert_single_to_initialized = [](const void *src, void *dst) {
     *(To *)dst = ConversionF(*(const From *)src);
   };