Skip out-of-range broadcast axes instead of erroring

Broadcasting a dimension past the input's rank is a no-op, so match
broadcast_like and skip assigning the bitset when the converted slinky
dim falls outside the input, rather than validating and returning an
error. This also avoids the out-of-range axes_set index.

Author: aizu-m

ynnpack/subgraph/broadcast.cc

@@ -32,9 +32,12 @@ ynn_status ynn_define_broadcast(ynn_subgraph_t subgraph, size_t num_axes,
 
   ynn::axes_set axes_set;
   for (size_t i = 0; i < num_axes; ++i) {
-    YNN_RETURN_IF_ERROR(
-        validate_axis("broadcast", "input", input.rank(), axes[i]));
-    axes_set[axis_to_slinky_dim(input.rank(), axes[i])] = true;
+    const int axis = axis_to_slinky_dim(input.rank(), axes[i]);
+    if (axis < input.rank()) {
+      // Dimensions past the input's rank are implicit broadcasts; broadcasting
+      // a broadcast dimension is a no-op, so skip it.
+      axes_set[axis] = true;
+    }
   }
 
   ynn_node node;

ynnpack/subgraph/test/errors.cc

@@ -54,13 +54,16 @@ TEST(Errors, broadcast_axis_out_of_bounds) {
   SubgraphBuilder subgraph(1);
   subgraph.AddInput(ynn_type_fp32, 3, in_id);
 
-  // An axis far outside [-rank, rank) maps to a slinky dim past the end of the
-  // axes_set bitset; broadcast must reject it instead of indexing out of range.
+  // An axis far outside [-rank, rank) maps to a slinky dim past the input's
+  // dimensions. Such a dimension is an implicit broadcast, so broadcasting it
+  // is a no-op: it must be skipped rather than indexing the axes_set bitset out
+  // of range.
   const int32_t axes[] = {-100};
   uint32_t output_id = YNN_INVALID_VALUE_ID;
   EXPECT_EQ(ynn_define_broadcast(subgraph.GetSubgraph(), /*num_axes=*/1, axes,
                                  in_id, &output_id, /*flags=*/0),
-            ynn_status_invalid_parameter);
+            ynn_status_success);
+  EXPECT_EQ(output_id, in_id);
 }
 
 }  // namespace ynn