Prevent `local_sum_make_vector` from introducing internal `float64` (#659)

pytensor/tensor/rewriting/basic.py

@@ -28,7 +28,7 @@ from typing import Union
 import numpy as np
 
 import pytensor.scalar.basic as ps
-from pytensor import compile
+from pytensor import compile, config
 from pytensor.compile.ops import ViewOp
 from pytensor.graph import FunctionGraph
 from pytensor.graph.basic import Constant, Variable
@@ -941,6 +941,11 @@ def local_sum_make_vector(fgraph, node):
     elements = array.owner.inputs
     acc_dtype = node.op.acc_dtype
     out_dtype = node.op.dtype
+
+    # Skip rewrite if it would add unnecessary float64 to the graph
+    if acc_dtype == "float64" and out_dtype != "float64" and config.floatX != "float64":
+        return
+
     if len(elements) == 0:
         element_sum = zeros(dtype=out_dtype, shape=())
     elif len(elements) == 1:

tests/tensor/rewriting/test_basic.py

@@ -12,7 +12,7 @@ from pytensor.compile.function import function
 from pytensor.compile.mode import get_default_mode, get_mode
 from pytensor.compile.ops import DeepCopyOp, deep_copy_op
 from pytensor.configdefaults import config
-from pytensor.graph.basic import equal_computations, vars_between
+from pytensor.graph.basic import equal_computations
 from pytensor.graph.fg import FunctionGraph
 from pytensor.graph.rewriting.basic import check_stack_trace, out2in
 from pytensor.graph.rewriting.db import RewriteDatabaseQuery
@@ -26,12 +26,12 @@ from pytensor.tensor.basic import (
     ScalarFromTensor,
     Split,
     TensorFromScalar,
+    cast,
     join,
     tile,
 )
 from pytensor.tensor.elemwise import DimShuffle, Elemwise
 from pytensor.tensor.math import (
-    Sum,
     add,
     bitwise_and,
     bitwise_or,
@@ -1298,41 +1298,48 @@ def test_local_join_make_vector():
 
 
 def test_local_sum_make_vector():
+    # To check that rewrite is applied, we must enforce dtype to
+    # allow rewrite to occur even if floatX != "float64"
     a, b, c = scalars("abc")
     mv = MakeVector(config.floatX)
-    output = mv(a, b, c).sum()
-
-    output = rewrite_graph(output)
-    between = vars_between([a, b, c], [output])
-    for var in between:
-        assert (var.owner is None) or (not isinstance(var.owner.op, MakeVector))
+    output = mv(a, b, c).sum(dtype="float64")
+    rewrite_output = rewrite_graph(output)
+    expected_output = cast(
+        add(*[cast(value, "float64") for value in [a, b, c]]), dtype="float64"
+    )
+    assert equal_computations([expected_output], [rewrite_output])
 
-    # Check for empty sum
+    # Empty axes should return input vector since no sum is applied
     a, b, c = scalars("abc")
     mv = MakeVector(config.floatX)
     output = mv(a, b, c).sum(axis=[])
+    rewrite_output = rewrite_graph(output)
+    expected_output = mv(a, b, c)
+    assert equal_computations([expected_output], [rewrite_output])
 
-    output = rewrite_graph(output)
-    between = vars_between([a, b, c], [output])
-    for var in between:
-        assert (var.owner is None) or (not isinstance(var.owner.op, Sum))
-
-    # Check empty MakeVector
+    # Empty input should return 0
     mv = MakeVector(config.floatX)
     output = mv().sum()
+    rewrite_output = rewrite_graph(output)
+    expected_output = pt.as_tensor(0, dtype=config.floatX)
+    assert equal_computations([expected_output], [rewrite_output])
 
-    output = rewrite_graph(output)
-    between = vars_between([a, b, c], [output])
-    for var in between:
-        assert (var.owner is None) or (not isinstance(var.owner.op, Sum))
-
+    # Single element input should return element value
+    a = scalars("a")
     mv = MakeVector(config.floatX)
     output = mv(a).sum()
+    rewrite_output = rewrite_graph(output)
+    expected_output = cast(a, config.floatX)
+    assert equal_computations([expected_output], [rewrite_output])
 
-    output = rewrite_graph(output)
-    between = vars_between([a, b, c], [output])
-    for var in between:
-        assert (var.owner is None) or (not isinstance(var.owner.op, Sum))
+    # This is a regression test for #653. Ensure that rewrite is NOT
+    # applied when user requests float32
+    with config.change_flags(floatX="float32", warn_float64="raise"):
+        a, b, c = scalars("abc")
+        mv = MakeVector(config.floatX)
+        output = mv(a, b, c).sum()
+        rewrite_output = rewrite_graph(output)
+        assert equal_computations([output], [rewrite_output])
 
 
 @pytest.mark.parametrize(