PERF: Skip probing `__array_ufunc__` for NumPy builtin scalars (#21470)

The method `PyUFuncOverride_GetNonDefaultArrayUfunc` is expensive on numpy scalars because these objects do not have a `__array_ufunc__` set and for a missing attribute lookup cpython generates an exception that is later cleared by numpy. This is a performance bottleneck, see #21455.

An issue has been submitted to cpython (https://github.com/python/cpython/issues/92216). But even if this is addressed in cpython, it will take untill python 3.12+ before this will be useable by numpy.

As an alternative solution, this PR adds a fast path to `PyUFuncOverride_GetNonDefaultArrayUfunc` to determine whether an object is a numpy scalar.

2 files changed, 7 insertions, 1 deletions

diff --git a/numpy/core/src/common/get_attr_string.h b/numpy/core/src/common/get_attr_string.h
index a3e5d5ec8..90eca5ee6 100644
--- a/numpy/core/src/common/get_attr_string.h
+++ b/numpy/core/src/common/get_attr_string.h
@@ -42,7 +42,7 @@ _is_basic_python_type(PyTypeObject *tp)
  * on the type object, rather than on the instance itself.
  *
  * Assumes that the special method is a numpy-specific one, so does not look
- * at builtin types, nor does it look at a base ndarray.
+ * at builtin types. It does check base ndarray and numpy scalar types.
  *
  * In future, could be made more like _Py_LookupSpecial
  */
diff --git a/numpy/core/src/common/ufunc_override.c b/numpy/core/src/common/ufunc_override.c
index 2c3dc5cb3..4fb4d4b3e 100644
--- a/numpy/core/src/common/ufunc_override.c
+++ b/numpy/core/src/common/ufunc_override.c
@@ -5,6 +5,7 @@
 #include "get_attr_string.h"
 #include "npy_import.h"
 #include "ufunc_override.h"
+#include "scalartypes.h"
 
 /*
  * Check whether an object has __array_ufunc__ defined on its class and it
@@ -30,6 +31,11 @@ PyUFuncOverride_GetNonDefaultArrayUfunc(PyObject *obj)
     if (PyArray_CheckExact(obj)) {
         return NULL;
     }
+   /* Fast return for numpy scalar types */
+    if (is_anyscalar_exact(obj)) {
+        return NULL;
+    }
+
     /*
      * Does the class define __array_ufunc__? (Note that LookupSpecial has fast
      * return for basic python types, so no need to worry about those here)