fix: check widths are supported by concrete-lib

and if not, explain to the user
refs #139

concrete/common/mlir/utils.py

@@ -9,9 +9,13 @@ from ..data_types.dtypes_helpers import (
     value_is_encrypted_tensor_integer,
     value_is_scalar_integer,
 )
+from ..debugging.custom_assert import assert_true
 from ..operator_graph import OPGraph
 from ..representation.intermediate import ArbitraryFunction
 
+# TODO: should come from compiler, through an API, #402
+ACCEPTABLE_MAXIMAL_BITWIDTH_FROM_CONCRETE_LIB = 7
+
 
 def is_graph_values_compatible_with_mlir(op_graph: OPGraph) -> bool:
     """Make sure the graph outputs are unsigned integers, which is what the compiler supports.
@@ -55,16 +59,36 @@ def update_bit_width_for_mlir(op_graph: OPGraph):
         op_graph: graph to update bit_width for
     """
     max_bit_width = 0
+    offending_list = []
     for node in op_graph.graph.nodes:
         for value_out in node.outputs:
             if value_is_clear_scalar_integer(value_out) or value_is_clear_tensor_integer(value_out):
-                max_bit_width = max(max_bit_width, value_out.data_type.bit_width - 1)
-            elif value_is_encrypted_scalar_integer(value_out) or value_is_encrypted_tensor_integer(
-                value_out
-            ):
-                max_bit_width = max(max_bit_width, value_out.data_type.bit_width)
+                current_node_out_bit_width = value_out.data_type.bit_width - 1
+            else:
+
+                assert_true(
+                    value_is_encrypted_scalar_integer(value_out)
+                    or value_is_encrypted_tensor_integer(value_out)
+                )
+
+                current_node_out_bit_width = value_out.data_type.bit_width
+
+            max_bit_width = max(max_bit_width, current_node_out_bit_width)
+
+            # Check that current_node_out_bit_width is supported by the compiler
+            if current_node_out_bit_width > ACCEPTABLE_MAXIMAL_BITWIDTH_FROM_CONCRETE_LIB:
+                offending_list.append((node, current_node_out_bit_width))
+
     _set_all_bit_width(op_graph, max_bit_width)
 
+    # Check that the max_bit_width is supported by the compiler
+    if len(offending_list) != 0:
+        raise RuntimeError(
+            f"max_bit_width of some nodes is too high for the current version of "
+            f"the compiler (maximum must be {ACCEPTABLE_MAXIMAL_BITWIDTH_FROM_CONCRETE_LIB} "
+            f"which is not compatible with {offending_list})"
+        )
+
 
 def extend_direct_lookup_tables(op_graph: OPGraph):
     """Extend direct lookup tables to the maximum length the input bit width can support.

tests/numpy/test_compile.py

@@ -330,3 +330,45 @@ def test_compile_with_show_mlir(function, input_ranges, list_of_arg_names):
         data_gen(tuple(range(x[0], x[1] + 1) for x in input_ranges)),
         show_mlir=True,
     )
+
+
+def test_compile_too_high_bitwidth():
+    """Check that the check of maximal bitwidth of intermediate data works fine."""
+
+    def function(x, y):
+        return x + y
+
+    def data_gen(args):
+        for prod in itertools.product(*args):
+            yield prod
+
+    function_parameters = {
+        "x": EncryptedScalar(Integer(64, False)),
+        "y": EncryptedScalar(Integer(64, False)),
+    }
+
+    # A bit too much
+    input_ranges = [(0, 100), (0, 28)]
+
+    with pytest.raises(RuntimeError) as excinfo:
+        compile_numpy_function(
+            function,
+            function_parameters,
+            data_gen(tuple(range(x[0], x[1] + 1) for x in input_ranges)),
+        )
+
+    assert (
+        "max_bit_width of some nodes is too high for the current version of the "
+        "compiler (maximum must be 7 which is not compatible with" in str(excinfo.value)
+    )
+
+    assert str(excinfo.value).endswith(", 8)])")
+
+    # Just ok
+    input_ranges = [(0, 99), (0, 28)]
+
+    compile_numpy_function(
+        function,
+        function_parameters,
+        data_gen(tuple(range(x[0], x[1] + 1) for x in input_ranges)),
+    )