ENH: Micro-optimize where=True path for mean, var, any, and all

This removes a 20%-30% overhead, and thus the largest chunk of
slowdown incurred by adding the `where` argument. Most other places
have fast-paths for `where=True`, this one also should have it.

The additional argument does slow down the function versions a bit
more than this, but that is to be expected probably (it has to
build a new argument dict, at some point we might want to move this
to C, but that seems worth much more with FASTCALL logic).

1 files changed, 8 insertions, 2 deletions

diff --git a/numpy/core/_methods.py b/numpy/core/_methods.py
index 75fd32ec8..c730e2035 100644
--- a/numpy/core/_methods.py
+++ b/numpy/core/_methods.py
@@ -51,9 +51,15 @@ def _prod(a, axis=None, dtype=None, out=None, keepdims=False,
     return umr_prod(a, axis, dtype, out, keepdims, initial, where)
 
 def _any(a, axis=None, dtype=None, out=None, keepdims=False, *, where=True):
+    # Parsing keyword arguments is currently fairly slow, so avoid it for now
+    if where is True:
+        return umr_any(a, axis, dtype, out, keepdims)
     return umr_any(a, axis, dtype, out, keepdims, where=where)
 
 def _all(a, axis=None, dtype=None, out=None, keepdims=False, *, where=True):
+    # Parsing keyword arguments is currently fairly slow, so avoid it for now
+    if where is True:
+        return umr_all(a, axis, dtype, out, keepdims)
     return umr_all(a, axis, dtype, out, keepdims, where=where)
 
 def _count_reduce_items(arr, axis, keepdims=False, where=True):
@@ -158,7 +164,7 @@ def _mean(a, axis=None, dtype=None, out=None, keepdims=False, *, where=True):
     is_float16_result = False
 
     rcount = _count_reduce_items(arr, axis, keepdims=keepdims, where=where)
-    if umr_any(rcount == 0, axis=None):
+    if rcount == 0 if where is True else umr_any(rcount == 0):
         warnings.warn("Mean of empty slice.", RuntimeWarning, stacklevel=2)
 
     # Cast bool, unsigned int, and int to float64 by default
@@ -191,7 +197,7 @@ def _var(a, axis=None, dtype=None, out=None, ddof=0, keepdims=False, *,
 
     rcount = _count_reduce_items(arr, axis, keepdims=keepdims, where=where)
     # Make this warning show up on top.
-    if umr_any(ddof >= rcount, axis=None):
+    if ddof >= rcount if where is True else umr_any(ddof >= rcount):
         warnings.warn("Degrees of freedom <= 0 for slice", RuntimeWarning,
                       stacklevel=2)