not create new symbol with immutable shape convolution. (#1867)

Author: fukatani

coremltools/converters/mil/mil/ops/defs/_utils.py

@@ -252,7 +252,10 @@ def spatial_dimensions_out_shape(
         # * `effective_ks` (effective kernel size, determined from kernel size + dilations) cannot be symbolic
         # * strides cannot be symbolic
         if is_symbolic(input_shape[r]):
-            out_shape.append(get_new_symbol())
+            if not is_symbolic(pad[r]) and pad[r] - effective_ks[r] == -1 and strides[r] == 1:
+                out_shape.append(input_shape[r])
+            else:
+                out_shape.append(get_new_symbol())
         else:
             out_dim = 0
             if not ceil_mode:

coremltools/converters/mil/mil/ops/tests/test_utils.py

@@ -4,6 +4,7 @@
 #  found in the LICENSE.txt file or at https://opensource.org/licenses/BSD-3-Clause
 
 import numpy as np
+from coremltools.converters.mil import get_new_symbol
 
 from coremltools.converters.mil.mil.ops.defs._utils import (
     aggregated_pad, effective_kernel, spatial_dimensions_out_shape)
@@ -260,3 +261,15 @@ def test_same_padding_shape_dilation_2(self):
 
         expected = [5, 5]
         np.testing.assert_equal(actual, expected)
+
+    def test_symbolic_custom_pad(self):
+        input_shape = (get_new_symbol(), get_new_symbol())
+        actual = spatial_dimensions_out_shape(
+            pad_type="custom",
+            input_shape=input_shape,
+            kernel_shape=(1, 1),
+            strides=(1, 1),
+            dilations=(1, 1),
+            custom_pad=(0, 0, 0, 0),
+        )
+        np.testing.assert_equal(actual, input_shape)