TensorRT 7 anchor_grid compatibility fix (#6185)

* fix: TensorRT 7 incompatiable

* Add comment

* Add if: else and comment

Co-authored-by: Glenn Jocher <glenn.jocher@ultralytics.com>

export.py

@@ -175,7 +175,13 @@ def export_engine(model, im, file, train, half, simplify, workspace=4, verbose=F
         import tensorrt as trt
 
         opset = (12, 13)[trt.__version__[0] == '8']  # test on TensorRT 7.x and 8.x
-        export_onnx(model, im, file, opset, train, False, simplify)
+        if opset == 12:  # TensorRT 7 handling https://github.com/ultralytics/yolov5/issues/6012
+            grid = model.model[-1].anchor_grid
+            model.model[-1].anchor_grid = [a[..., :1, :1, :] for a in grid]
+            export_onnx(model, im, file, opset, train, False, simplify)
+            model.model[-1].anchor_grid = grid
+        else:  # TensorRT >= 8
+            export_onnx(model, im, file, opset, train, False, simplify)
         onnx = file.with_suffix('.onnx')
         assert onnx.exists(), f'failed to export ONNX file: {onnx}'
 
@@ -418,12 +424,12 @@ def run(data=ROOT / 'data/coco128.yaml',  # 'dataset.yaml path'
     # Exports
     if 'torchscript' in include:
         export_torchscript(model, im, file, optimize)
+    if 'engine' in include:  # TensorRT required before ONNX
+        export_engine(model, im, file, train, half, simplify, workspace, verbose)
     if ('onnx' in include) or ('openvino' in include):  # OpenVINO requires ONNX
         export_onnx(model, im, file, opset, train, dynamic, simplify)
     if 'openvino' in include:
         export_openvino(model, im, file)
-    if 'engine' in include:
-        export_engine(model, im, file, train, half, simplify, workspace, verbose)
     if 'coreml' in include:
         export_coreml(model, im, file)