From 8dc6267bc0fdcc4786b374295d92b0634d983294 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Tue, 17 Mar 2026 19:07:41 +0000
Subject: [PATCH] Fix race condition: make reduction bound temporaries use
 PRIVATE address space

Co-authored-by: inducer <352067+inducer@users.noreply.github.com>

Potential fix for pull request finding

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
---
 doc/conf.py                    |  1 +
 pytato/target/loopy/codegen.py | 18 ++++++++++++------
 test/test_codegen.py           | 34 ++++++++++++++++++++++++++++++++++
 3 files changed, 47 insertions(+), 6 deletions(-)

diff --git a/doc/conf.py b/doc/conf.py
index cbf7dc94c..6d0f7a95e 100644
--- a/doc/conf.py
+++ b/doc/conf.py
@@ -72,6 +72,7 @@
     "ArithmeticExpression": "obj:pymbolic.ArithmeticExpression",
     # pytools
     "lp.TemporaryVariable": "class:loopy.TemporaryVariable",
+    "lp.AddressSpace": "class:loopy.AddressSpace",
 }
 
 
diff --git a/pytato/target/loopy/codegen.py b/pytato/target/loopy/codegen.py
index abf92e96a..22edf06e3 100644
--- a/pytato/target/loopy/codegen.py
+++ b/pytato/target/loopy/codegen.py
@@ -586,7 +586,8 @@ def map_index_lambda(self, expr: IndexLambda,
                                     bound_name, (), np.dtype(np.int64), bound_result,
                                     state, self, output_to_temporary=True,
                                     store_inames=(),
-                                    result_inames=inames, add_domain=False)]))
+                                    result_inames=inames, add_domain=False,
+                                    address_space=lp.AddressSpace.PRIVATE)]))
                         redn_bound_temps[bound_name] = bound_result
                         new_bound = prim.Variable(bound_name)
                     else:
@@ -1098,7 +1099,8 @@ def add_store(
         state: CodeGenState, cgen_mapper: CodeGenMapper, *,
         tags: frozenset[Tag] | None = None, axes: AxesT | None = None,
         output_to_temporary: bool = False, result_inames: tuple[str, ...] | None = None,
-        store_inames: tuple[str, ...] | None = None, add_domain: bool = True) -> str:
+        store_inames: tuple[str, ...] | None = None, add_domain: bool = True,
+        address_space: lp.AddressSpace = lp.AddressSpace.GLOBAL) -> str:
     """Add an instruction that stores to a variable in the kernel.
 
     :param name: name of the output array, which is created
@@ -1114,6 +1116,9 @@ def add_store(
         must be a subset of *result_inames*
     :param result_inames: the index inames of the right hand side of the assignment
     :param add_domain: add a new domain to the kernel for these inames/shape.
+    :param address_space: the address space for the temporary variable, when
+        *output_to_temporary* is ``True``. Defaults to
+        :attr:`loopy.AddressSpace.GLOBAL`.
 
     :returns: the id of the generated instruction
     """
@@ -1171,7 +1176,8 @@ def add_store(
     kernel = state.kernel
 
     if output_to_temporary:
-        tvar = get_loopy_temporary(name, shape, dtype, cgen_mapper, state, tags=tags)
+        tvar = get_loopy_temporary(name, shape, dtype, cgen_mapper, state, tags=tags,
+                                   address_space=address_space)
         temporary_variables = dict(kernel.temporary_variables)
         temporary_variables[name] = tvar
         kernel = kernel.copy(temporary_variables=temporary_variables,
@@ -1235,11 +1241,11 @@ def add_substitution(subst_name: str, ndim: int, result: ImplementedResult,
 def get_loopy_temporary(
         name: str, shape: ShapeType, dtype: np.dtype[Any],
         cgen_mapper: CodeGenMapper, state: CodeGenState, *,
-        tags: frozenset[Tag] | None = None) -> lp.TemporaryVariable:
+        tags: frozenset[Tag] | None = None,
+        address_space: lp.AddressSpace = lp.AddressSpace.GLOBAL
+        ) -> lp.TemporaryVariable:
     if tags is None:
         tags = frozenset()
-    # always allocating to global address space to avoid stack overflow
-    address_space = lp.AddressSpace.GLOBAL
     return lp.TemporaryVariable(name,
             shape=shape_to_scalar_expression(shape, cgen_mapper, state),
             dtype=dtype,
diff --git a/test/test_codegen.py b/test/test_codegen.py
index 073b80eca..ffba83bfd 100755
--- a/test/test_codegen.py
+++ b/test/test_codegen.py
@@ -601,6 +601,40 @@ def test_only_deps_as_knl_args():
     assert "y" not in knl.arg_dict
 
 
+def test_reduction_bound_temps_are_private():
+    # Regression test for https://github.com/inducer/pytato/issues/648
+    # (Temporaries for bounds should not be global)
+    # Reduction bound temporaries (for non-affine bounds) should use
+    # PRIVATE address space to avoid race conditions in parallel kernels.
+    n = 5
+    row_starts = pt.make_placeholder("row_starts", (n+1,), np.int64)
+    col_indices = pt.make_placeholder("col_indices", (n*3,), np.int64)
+    values = pt.make_placeholder("values", (n*3,), np.float64)
+    x = pt.make_placeholder("x", (n,), np.float64)
+
+    csr = pt.make_csr_matrix(
+        shape=(n, n),
+        elem_values=values,
+        elem_col_indices=col_indices,
+        row_starts=row_starts
+    )
+
+    result = csr @ x
+    knl = pt.generate_loopy(result).kernel
+
+    found_bound_temp = False
+    for name, tv in knl.temporary_variables.items():
+        if name.endswith(("_lbound", "_ubound")):
+            found_bound_temp = True
+            assert tv.address_space == lp.AddressSpace.PRIVATE, (
+                f"Reduction bound temporary '{name}' should be PRIVATE, "
+                f"got {tv.address_space}")
+
+    assert found_bound_temp, (
+        "Expected at least one reduction bound temporary whose name ends in "
+        "'_lbound' or '_ubound', but none were found.")
+
+
 @pytest.mark.parametrize("dtype", (np.float32, np.float64, np.complex128))
 @pytest.mark.parametrize("function_name", ("abs", "sin", "cos", "tan", "arcsin",
     "arccos", "arctan", "sinh", "cosh", "tanh", "exp", "log", "log10", "sqrt",