From 122ef538b9e1bcc95eec6fb4f2ea8ffb22c04148 Mon Sep 17 00:00:00 2001
From: Sebastian Mossburger <sebastian.mossburger@helsing.ai>
Date: Wed, 6 Aug 2025 09:58:12 +0200
Subject: [PATCH 1/4] Add test case for reverse step rewrite

---
 onnxscript/rewriter/collapse_slices_test.py | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/onnxscript/rewriter/collapse_slices_test.py b/onnxscript/rewriter/collapse_slices_test.py
index ce803b8a4f..52b59f9037 100644
--- a/onnxscript/rewriter/collapse_slices_test.py
+++ b/onnxscript/rewriter/collapse_slices_test.py
@@ -100,3 +100,22 @@ def test_slice_equal_dynamic_shape(self):
         model = ir.serde.deserialize_model(model_proto)
         count = collapse_slices.rules.apply_to_model(model)
         self.assertEqual(count, 1)
+
+    def test_slice_equal_dynamic_shape_but_step_reverse(self):
+        model_proto = onnx.parser.parse_model(
+            f"""
+            <ir_version: 7, opset_import: [ "" : 17]>
+            agraph (float[L, M, N] data) => (float[L, M, N] output)
+            {{
+                starts = Constant<value: tensor = int64[1] {{0}}>()
+                ends = Constant<value: tensor = int64[1] {{{9}}}>()
+                axes = Constant<value: tensor = int64[1] {{0}}>()
+                steps = Constant<value: tensor = int64[1] {{-1}}>()
+                output = Slice (data, starts, ends, axes, steps)
+            }}
+        """
+        )
+        model = ir.serde.deserialize_model(model_proto)
+        count = collapse_slices.rules.apply_to_model(model)
+        # Should not change the output shape if we did not use the default step of 1
+        self.assertEqual(count, 0)

From 16ce711111fcd2d4832d5fef3ceccbd79cde4edc Mon Sep 17 00:00:00 2001
From: Sebastian Mossburger <sebastian.mossburger@helsing.ai>
Date: Wed, 6 Aug 2025 10:06:50 +0200
Subject: [PATCH 2/4] Add potential fix

---
 onnxscript/rewriter/collapse_slices.py | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/onnxscript/rewriter/collapse_slices.py b/onnxscript/rewriter/collapse_slices.py
index e38f0f443d..a83ac29f38 100644
--- a/onnxscript/rewriter/collapse_slices.py
+++ b/onnxscript/rewriter/collapse_slices.py
@@ -76,10 +76,14 @@ def _potential_redundant_slice(op, data, starts, ends, axes, steps):
     return op.Slice(data, starts, ends, axes, steps, _outputs=["slice_output"])
 
 
-def _same_shape(op, data: ir.Value, slice_output: ir.Value, **_):
+def _same_shape(op, data: ir.Value, slice_output: ir.Value, steps: ir.Value, **_):
     """Check if the shape of the slice output is the same as the data."""
     if data.shape is None or slice_output.shape is None:
         return False
+
+    if not (steps.const_value.numpy() == 1).all():
+        return False
+
     return data.shape == slice_output.shape
 
 

From 11b3648aeb791e05b226d30d613ff7b887112875 Mon Sep 17 00:00:00 2001
From: Sebastian Mossburger <sebastian.mossburger@helsing.ai>
Date: Thu, 7 Aug 2025 09:18:17 +0200
Subject: [PATCH 3/4] Use is_singleton_value for the check from
 onnxscript.rewriter

---
 onnxscript/rewriter/collapse_slices.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/onnxscript/rewriter/collapse_slices.py b/onnxscript/rewriter/collapse_slices.py
index a83ac29f38..d2fbf3ac43 100644
--- a/onnxscript/rewriter/collapse_slices.py
+++ b/onnxscript/rewriter/collapse_slices.py
@@ -6,6 +6,7 @@
 
 from onnxscript import ir
 from onnxscript.rewriter._rewrite_rule import RewriteRule, RewriteRuleSet
+from onnxscript.rewriter._ir_utils import is_singleton_value
 
 logger = logging.getLogger(__name__)
 _INT64_MAX = 9223372036854775807
@@ -81,7 +82,7 @@ def _same_shape(op, data: ir.Value, slice_output: ir.Value, steps: ir.Value, **_
     if data.shape is None or slice_output.shape is None:
         return False
 
-    if not (steps.const_value.numpy() == 1).all():
+    if not is_singleton_value(steps, 1):
         return False
 
     return data.shape == slice_output.shape

From 42bc95a9030ba19510c1b062ebd66d7a42245e95 Mon Sep 17 00:00:00 2001
From: Sebastian Mossburger <sebastian.mossburger@helsing.ai>
Date: Wed, 13 Aug 2025 11:46:45 +0200
Subject: [PATCH 4/4] Run lintrunner f

---
 onnxscript/rewriter/collapse_slices.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/onnxscript/rewriter/collapse_slices.py b/onnxscript/rewriter/collapse_slices.py
index d2fbf3ac43..291128157d 100644
--- a/onnxscript/rewriter/collapse_slices.py
+++ b/onnxscript/rewriter/collapse_slices.py
@@ -5,8 +5,8 @@
 import logging
 
 from onnxscript import ir
-from onnxscript.rewriter._rewrite_rule import RewriteRule, RewriteRuleSet
 from onnxscript.rewriter._ir_utils import is_singleton_value
+from onnxscript.rewriter._rewrite_rule import RewriteRule, RewriteRuleSet
 
 logger = logging.getLogger(__name__)
 _INT64_MAX = 9223372036854775807