feat: Support fallback options in trtorchc

Signed-off-by: Dheeraj Peri <peri.dheeraj@gmail.com>

cpp/trtorchc/README.md

@@ -37,13 +37,17 @@ trtorchc [input_file_path] [output_file_path]
       --allow-gpu-fallback              (Only used when targeting DLA
                                         (device-type)) Lets engine run layers on
                                         GPU if they are not supported on DLA
+      --allow-torch-fallback            Enable layers to run in torch
+                                        if they are not supported in TensorRT
       -p[precision],
       --default-op-precision=[precision]
                                         Default operating precision for the
                                         engine (Int8 requires a
                                         calibration-cache argument) [ float |
                                         float32 | f32 | half | float16 | f16 |
                                         int8 | i8 ] (default: float)
+      --forced-fallback-ops             List of operators in the graph that
+                                        should be forced to fallback to Pytorch for execution
       -d[type], --device-type=[type]    The type of device the engine should be
                                         built for [ gpu | dla ] (default: gpu)
       --engine-capability=[capability]  The type of device the engine should be
@@ -84,4 +88,4 @@ trtorchc [input_file_path] [output_file_path]
 e.g.
 ```
 trtorchc tests/modules/ssd_traced.jit.pt ssd_trt.ts "[(1,3,300,300); (1,3,512,512); (1, 3, 1024, 1024)]" -p f16
-```
+```

cpp/trtorchc/main.cpp

@@ -163,6 +163,9 @@ int main(int argc, char** argv) {
       "(Only used when targeting DLA (device-type)) Lets engine run layers on GPU if they are not supported on DLA",
       {"allow-gpu-fallback"});
 
+  args::Flag allow_torch_fallback(
+      parser, "allow-torch-fallback", "Enable layers to run in torch if they are not supported in TensorRT", {"allow-torch-fallback"});
+
   args::Flag disable_tf32(
       parser, "disable-tf32", "Prevent Float32 layers from using the TF32 data format", {"disable-tf32"});
 
@@ -191,6 +194,11 @@ int main(int argc, char** argv) {
       "file_path",
       "Path to calibration cache file to use for post training quantization",
       {"calibration-cache-file"});
+  args::ValueFlag<std::string> forced_fallback_ops(
+      parser,
+      "forced_fallback_ops",
+      "List of operators in the graph that should be forced to fallback to Pytorch for execution.",
+      {"ffo", "forced-fallback-ops"});
   args::ValueFlag<int> num_min_timing_iters(
       parser, "num_iters", "Number of minimization timing iterations used to select kernels", {"num-min-timing-iter"});
   args::ValueFlag<int> num_avg_timing_iters(
@@ -266,6 +274,10 @@ int main(int argc, char** argv) {
     compile_settings.device.allow_gpu_fallback = true;
   }
 
+  if (allow_torch_fallback) {
+    compile_settings.torch_fallback = trtorch::CompileSpec::TorchFallback(true);
+  }
+
   if (disable_tf32) {
     compile_settings.disable_tf32 = true;
   }
@@ -277,6 +289,20 @@ int main(int argc, char** argv) {
 
   auto calibrator = trtorch::ptq::make_int8_cache_calibrator(calibration_cache_file_path);
 
+  if (forced_fallback_ops) {
+    std::string fallback_ops = args::get(forced_fallback_ops);
+    if (!allow_torch_fallback){
+      trtorch::logging::log(
+          trtorch::logging::Level::kERROR,
+          "Forced fallback ops provided but allow_torch_fallback is False. Please use --allow_torch_fallback to enable automatic fallback of operators.");
+    }
+    std::string op;
+    std::stringstream  ss(fallback_ops);
+    while (getline(ss, op, ',')) {
+      compile_settings.torch_fallback.forced_fallback_ops.push_back(op);
+    }
+  }
+
   if (op_precision) {
     auto precision = args::get(op_precision);
     std::transform(