Modifiers: Bring back custom data referencing logic

Brings dependency graph evaluation time to similar time than 2.79
for file reported in T55228.

1 files changed, 13 insertions, 7 deletions

diff --git a/source/blender/modifiers/intern/MOD_normal_edit.c b/source/blender/modifiers/intern/MOD_normal_edit.c
index 5ac6569ea1f..bbb4608ee71 100644
--- a/source/blender/modifiers/intern/MOD_normal_edit.c
+++ b/source/blender/modifiers/intern/MOD_normal_edit.c
@@ -405,13 +405,19 @@ static Mesh *normalEditModifier_do(NormalEditModifierData *enmd, Object *ob, Mes
 	}
 
 	Mesh *result;
-	BKE_id_copy_ex(
-	        NULL, &mesh->id, (ID **)&result,
-	        LIB_ID_CREATE_NO_MAIN |
-	        LIB_ID_CREATE_NO_USER_REFCOUNT |
-	        LIB_ID_CREATE_NO_DEG_TAG |
-	        LIB_ID_COPY_NO_PREVIEW,
-	        false);
+	if (mesh->medge == ((Mesh *)ob->data)->medge) {
+		/* We need to duplicate data here, otherwise setting custom normals (which may also affect sharp edges) could
+		 * modify org mesh, see T43671. */
+		BKE_id_copy_ex(
+		        NULL, &mesh->id, (ID **)&result,
+		        LIB_ID_CREATE_NO_MAIN |
+		        LIB_ID_CREATE_NO_USER_REFCOUNT |
+		        LIB_ID_CREATE_NO_DEG_TAG |
+		        LIB_ID_COPY_NO_PREVIEW,
+		        false);
+	} else {
+		result = mesh;
+	}
 
 	const int num_verts = result->totvert;
 	const int num_edges = result->totedge;