Hi,
Thanks for the reply. The torch.ones(1) does actually seems to work but only for non-quantized models:
class TestNNAPI(torch.nn.Module):
    def __init__(self):
        super(TestNNAPI, self).__init__()
        self.conv = torch.nn.Conv2d(1, 6,  kernel_size=3, padding=1, stride=1)
        self.quant = torch.quantization.QuantStub()
        self.dequant = torch.quantization.DeQuantStub()

    def forward(self, x):
        x = self.quant(x)
        x = self.conv(x)
        x = self.dequant(x)
        res = x + torch.ones(1)
        return res

Tracing and converting this to NNAPI seems to work smoothly, however if quantization (using ‘qnnpack’ backend at least) is done on the model I get the following error:
Traceback (most recent call last):
  File "./test-constant.py", line 36, in <module>
    traced_nnapi_model = torch.backends._nnapi.prepare.convert_model_to_nnapi(traced_nnapi_model, testinput)
  File "<install>/lib/python3.6/site-packages/torch/backends/_nnapi/prepare.py", line 85, in convert_model_to_nnapi
    ser_model, used_weights, inp_mem_fmts, out_mem_fmts, shape_compute_lines, retval_count = serialize_model(model, inputs)
  File "<install>/lib/python3.6/site-packages/torch/backends/_nnapi/serializer.py", line 1739, in serialize_model
    return _NnapiSerializer(config).serialize_model(module, inputs)
  File "<install>/lib/python3.6/site-packages/torch/backends/_nnapi/serializer.py", line 628, in serialize_model
    self.add_node(node)
  File "<install>/lib/python3.6/site-packages/torch/backends/_nnapi/serializer.py", line 793, in add_node
    adder(self, node)
  File "<install>/lib/python3.6/site-packages/torch/backends/_nnapi/serializer.py", line 750, in <lambda>
    self.add_add_sub_op(node, NNAPI_OperationCode.ADD, NNAPI_FuseCode.FUSED_NONE),
  File "<install>/lib/python3.6/site-packages/torch/backends/_nnapi/serializer.py", line 1119, in add_add_sub_op
    self._do_add_binary(node, opcode, fuse_code)
  File "<install>/.local/lib/python3.6/site-packages/torch/backends/_nnapi/serializer.py", line 1074, in _do_add_binary
    in1_id, in1_oper = self.get_tensor_operand_by_jitval(node.inputsAt(1))
  File "<install>/lib/python3.6/site-packages/torch/backends/_nnapi/serializer.py", line 456, in get_tensor_operand_by_jitval
    operand_id = self.jitval_operand_map[jitval]
KeyError: 31 defined in (%31 : Float(1, strides=[1], requires_grad=0, device=cpu) = prim::Constant[value={1}]()
)

Which I find a bit surprising since the ones is not even used in quantized context. (And if I try to have a quantized torch.ones, I get the error  Could not run 'aten::empty.memory_format' with arguments from the 'QuantizedCPU' backend.
Is this a known limitation?