Geometry: Avoid unnecessary initialization when resizing data arrays

When resizing mesh and curves attribute storage, avoid initializing the
new memory for basic types. Also, avoid skipping "no free" layers; all
layers should be reallocated to the new size since they may be accessed.

The semantics introduced in 25237d2625078c6d1 are essential for this
change, because otherwise we don't have a way to construct non-trivial
types in the new memory.

In a basic test of the extrude node, I observed a performance
improvement of about 30%, from 55ms to 42ms.

Differential Revision: https://developer.blender.org/D15818

1 files changed, 4 insertions, 6 deletions

diff --git a/source/blender/blenkernel/BKE_customdata.h b/source/blender/blenkernel/BKE_customdata.h
index 09d37682b3c..24fa5f0e87a 100644
--- a/source/blender/blenkernel/BKE_customdata.h
+++ b/source/blender/blenkernel/BKE_customdata.h
@@ -178,13 +178,11 @@ bool CustomData_merge_mesh_to_bmesh(const struct CustomData *source,
                                     int totelem);
 
 /**
- * Reallocate custom data to a new element count.
- * Only affects on data layers which are owned by the CustomData itself,
- * referenced data is kept unchanged,
- *
- * \note Take care of referenced layers by yourself!
+ * Reallocate custom data to a new element count. If the new size is larger, the new values use
+ * the #CD_CONSTRUCT behavior, so trivial types must be initialized by the caller. After being
+ * resized, the #CustomData does not contain any referenced layers.
  */
-void CustomData_realloc(struct CustomData *data, int totelem);
+void CustomData_realloc(struct CustomData *data, int old_size, int new_size);
 
 /**
  * BMesh version of CustomData_merge; merges the layouts of source and `dest`,