MLBEDSW-7343: MLCE: Unsupported STRIDED_SLICE with negative index and shrinking an axis
- The problem was that the end values of STRIDED_SLICE operators
were not taking the shrink_axis_mask into account
- The fix is simply to ignore the end value set on the operator
and calculate one based upon shrinking the axis
Change-Id: I2e5f2d3c9b08035dfd9b1629c775408f2356d1cf
Signed-off-by: Tim Hall <tim.hall@arm.com>
diff --git a/ethosu/vela/tflite_model_semantic.py b/ethosu/vela/tflite_model_semantic.py
index 2851ab1..0c2086c 100644
--- a/ethosu/vela/tflite_model_semantic.py
+++ b/ethosu/vela/tflite_model_semantic.py
@@ -23,7 +23,6 @@
from .data_type import BaseType
from .data_type import DataType
from .numeric_util import is_integer
-from .operation import get_slice_offsets
from .operation import Op
from .supported_operators_util import docstring_format_args
from .supported_operators_util import list_formatter
@@ -551,15 +550,42 @@
valid = (new_axis == 0) or (shrink_axis == 0)
return valid, f"Op has new_axis_mask={new_axis} and shrink_axis_mask={shrink_axis}"
+ def _get_slice_offsets(input_shape, offset_tens, offset_mask, is_begin=True):
+ # For strided slice operator: get start or end offsets
+ # input_shape: List[int], offset_tens: Tensor, offset_mask: int, is_begin: bool = True
+ offsets = len(input_shape) * [0] if is_begin else input_shape[:]
+ for idx in range(len(input_shape)):
+ # If the i:th bit in the mask is not set then the value in offset_tens[i] should be used, otherwise it
+ # should be ignored
+ if (offset_mask & (1 << idx)) == 0:
+ offsets[idx] = offset_tens.values[idx]
+ if offsets[idx] < 0:
+ # Convert negative indexing to positive ones
+ offsets[idx] += input_shape[idx]
+ return offsets
+
@staticmethod
def constraint_slice_ranges(op):
"Slice 'end' values must be greater than 'begin' values"
ifm, begin, end, _ = op.inputs
+ shrink_axis_mask = op.attrs["shrink_axis_mask"]
# Calculate offset begin/end
- offset_begin = get_slice_offsets(ifm.shape, begin, op.attrs["begin_mask"], is_begin=True)
- offset_end = get_slice_offsets(ifm.shape, end, op.attrs["end_mask"], is_begin=False)
+ offset_begin = TFLiteSemantic._get_slice_offsets(ifm.shape, begin, op.attrs["begin_mask"], is_begin=True)
+ offset_end = TFLiteSemantic._get_slice_offsets(ifm.shape, end, op.attrs["end_mask"], is_begin=False)
# Check "end - begin" doesn't result in any zero or negative elements
- valid = all((e - b) > 0 for b, e in zip(offset_begin, offset_end))
+ valid = True
+ # if a shrink mask bit is set then the end position provided by the operation should be ignored, and instead a
+ # new end position should be calculated so that calculations in the graph optimiser, such as (end - start),
+ # result in the correct value. otherwise, we just need to check that the begin and end values are valid
+ for i in range(len(ifm.shape)):
+ if (shrink_axis_mask & (1 << i)) != 0:
+ offset_end[i] = offset_begin[i] + 1
+ else:
+ if offset_end[i] <= offset_begin[i]:
+ valid = False
+
+ op.attrs["offset_begin"] = offset_begin
+ op.attrs["offset_end"] = offset_end
return valid, f"Op has begin_values={begin.values} and end_values={end.values}"
@staticmethod