Creating a custom plugin for ctc_beam_search_decoder

Description

Hi,

I’m trying to create a custom TensorRT plugin with the eventual goal of supporting TensorFlow’s tf.nn.ctc_beam_search_decoder function. For now all i am trying to do is create a dummy plugin that passes-through all inputs (so no operations) to test converting a TensorFlow model with ctc_beam_search_decoder function to onnx, then to a tensorrt engine.

The Tensorflow → ONNX conversion produces the following error:

Tensorflow op [LprNet/decode_layer/CTCBeamSearchDecoder: CTCBeamSearchDecoder] is not supported

Which is expected.

The custom TensorRT plugin produces this error when returning from CtcBeamSearchCustom::getOutputDimensions():

IndexError: vector::_M_range_check: __n (which is 1) >= this->size() (which is 1)

The plugin is based on the example in the Developer Guide. With:

DimsExprs CtcBeamSearchCustom::getOutputDimensions (int32_t outputIndex, const DimsExprs *inputs, int32_t nbInputs, IExprBuilder &exprBuilder)
{
    std::cout << "CtcBeamSearchCustom::getOutputDimensions()" << std::endl;
    std::cout << "CtcBeamSearchCustom::getOutputDimensions(); nbDims:" << inputs->nbDims << std::endl;

    switch (outputIndex)
    {
    case 0: 
    {
        // First dimension of output is sum of input 
        // first dimensions.
        DimsExprs output(inputs[0]);
        output.d[0] = 
            exprBuilder.operation(DimensionOperation::kSUM, 
                *inputs[0].d[0], *inputs[1].d[0]);
	   return output;
    }
    case 1:
        return inputs[0];
    default:
         throw std::invalid_argument("invalid output");
    }
}

Is there an obvious error here? Or an example plugin with a similar goal?

Thanks

Environment

TensorRT Version: 7.2.2.3
TensorRT OSS Version: 21.02
GPU Type: TITAN RTX
Nvidia Driver Version: 460
CUDA Version: 11.2 (libnvinfer for 11.1)
CUDNN Version: 8.1
Operating System + Version: Ubuntu bionic
Python Version: 3.8
TensorFlow Version: 2.5.0
Baremetal or Container: Custom container

Relevant Files

ctcBeamSearchDecoderCustom.cpp (7.1 KB)
ctcBeamSearchDecoderCustom.h (3.4 KB)

Hi,
Please refer to below links related custom plugin implementation and sample:

Thanks!