Functions: devirtualize virtual arrays in simple functions

In some multi-functions (such as a simple add function), the virtual method
call overhead to access array elements adds significant overhead. For these
simple functions it makes sense to generate optimized versions for different
types of virtual arrays. This is done by giving the compiler all the information
it needs to devirtualize virtual arrays.

In my benchmark this speeds up processing a lot of data with small function 2-3x.

This devirtualization should not be done for larger functions, because it increases
compile time and binary size, while providing a negilible performance benefit.

1 files changed, 10 insertions, 4 deletions

diff --git a/source/blender/functions/FN_multi_function_builder.hh b/source/blender/functions/FN_multi_function_builder.hh
index 389d0b14bb5..95a9f52e29e 100644
--- a/source/blender/functions/FN_multi_function_builder.hh
+++ b/source/blender/functions/FN_multi_function_builder.hh
@@ -61,8 +61,11 @@ template<typename In1, typename Out1> class CustomMF_SI_SO : public MultiFunctio
   template<typename ElementFuncT> static FunctionT create_function(ElementFuncT element_fn)
   {
     return [=](IndexMask mask, const VArray<In1> &in1, MutableSpan<Out1> out1) {
-      mask.foreach_index(
-          [&](int i) { new (static_cast<void *>(&out1[i])) Out1(element_fn(in1[i])); });
+      /* Devirtualization results in a 2-3x speedup for some simple functions. */
+      devirtualize_varray(in1, [&](const auto &in1) {
+        mask.foreach_index(
+            [&](int i) { new (static_cast<void *>(&out1[i])) Out1(element_fn(in1[i])); });
+      });
     };
   }
 
@@ -111,8 +114,11 @@ class CustomMF_SI_SI_SO : public MultiFunction {
                const VArray<In1> &in1,
                const VArray<In2> &in2,
                MutableSpan<Out1> out1) {
-      mask.foreach_index(
-          [&](int i) { new (static_cast<void *>(&out1[i])) Out1(element_fn(in1[i], in2[i])); });
+      /* Devirtualization results in a 2-3x speedup for some simple functions. */
+      devirtualize_varray2(in1, in2, [&](const auto &in1, const auto &in2) {
+        mask.foreach_index(
+            [&](int i) { new (static_cast<void *>(&out1[i])) Out1(element_fn(in1[i], in2[i])); });
+      });
     };
   }