torch.empty() for speed improvements (#9025)

`torch.empty()` for speed improvement

Signed-off-by: Glenn Jocher <glenn.jocher@ultralytics.com>

models/common.py

@@ -531,7 +531,7 @@ class DetectMultiBackend(nn.Module):
         # Warmup model by running inference once
         warmup_types = self.pt, self.jit, self.onnx, self.engine, self.saved_model, self.pb
         if any(warmup_types) and self.device.type != 'cpu':
-            im = torch.zeros(*imgsz, dtype=torch.half if self.fp16 else torch.float, device=self.device)  # input
+            im = torch.empty(*imgsz, dtype=torch.half if self.fp16 else torch.float, device=self.device)  # input
             for _ in range(2 if self.jit else 1):  #
                 self.forward(im)  # warmup
 
@@ -600,7 +600,7 @@ class AutoShape(nn.Module):
 
         dt = (Profile(), Profile(), Profile())
         with dt[0]:
-            p = next(self.model.parameters()) if self.pt else torch.zeros(1, device=self.model.device)  # param
+            p = next(self.model.parameters()) if self.pt else torch.empty(1, device=self.model.device)  # param
             autocast = self.amp and (p.device.type != 'cpu')  # Automatic Mixed Precision (AMP) inference
             if isinstance(ims, torch.Tensor):  # torch
                 with amp.autocast(autocast):

models/yolo.py

@@ -46,8 +46,8 @@ class Detect(nn.Module):
         self.no = nc + 5  # number of outputs per anchor
         self.nl = len(anchors)  # number of detection layers
         self.na = len(anchors[0]) // 2  # number of anchors
-        self.grid = [torch.zeros(1)] * self.nl  # init grid
+        self.grid = [torch.empty(1)] * self.nl  # init grid
-        self.anchor_grid = [torch.zeros(1)] * self.nl  # init anchor grid
+        self.anchor_grid = [torch.empty(1)] * self.nl  # init anchor grid
         self.register_buffer('anchors', torch.tensor(anchors).float().view(self.nl, -1, 2))  # shape(nl,na,2)
         self.m = nn.ModuleList(nn.Conv2d(x, self.no * self.na, 1) for x in ch)  # output conv
         self.inplace = inplace  # use inplace ops (e.g. slice assignment)
@@ -175,7 +175,7 @@ class DetectionModel(BaseModel):
         if isinstance(m, Detect):
             s = 256  # 2x min stride
             m.inplace = self.inplace
-            m.stride = torch.tensor([s / x.shape[-2] for x in self.forward(torch.zeros(1, ch, s, s))])  # forward
+            m.stride = torch.tensor([s / x.shape[-2] for x in self.forward(torch.empty(1, ch, s, s))])  # forward
             check_anchor_order(m)  # must be in pixel-space (not grid-space)
             m.anchors /= m.stride.view(-1, 1, 1)
             self.stride = m.stride

utils/autobatch.py

@@ -47,7 +47,7 @@ def autobatch(model, imgsz=640, fraction=0.9, batch_size=16):
     # Profile batch sizes
     batch_sizes = [1, 2, 4, 8, 16]
     try:
-        img = [torch.zeros(b, 3, imgsz, imgsz) for b in batch_sizes]
+        img = [torch.empty(b, 3, imgsz, imgsz) for b in batch_sizes]
         results = profile(img, model, n=3, device=device)
     except Exception as e:
         LOGGER.warning(f'{prefix}{e}')

utils/loggers/__init__.py

@@ -300,7 +300,7 @@ def log_tensorboard_graph(tb, model, imgsz=(640, 640)):
     try:
         p = next(model.parameters())  # for device, type
         imgsz = (imgsz, imgsz) if isinstance(imgsz, int) else imgsz  # expand
-        im = torch.zeros((1, 3, *imgsz)).to(p.device).type_as(p)  # input image
+        im = torch.empty((1, 3, *imgsz)).to(p.device).type_as(p)  # input image
         with warnings.catch_warnings():
             warnings.simplefilter('ignore')  # suppress jit trace warning
             tb.add_graph(torch.jit.trace(de_parallel(model), im, strict=False), [])

utils/torch_utils.py

@@ -282,7 +282,7 @@ def model_info(model, verbose=False, imgsz=640):
     try:  # FLOPs
         p = next(model.parameters())
         stride = max(int(model.stride.max()), 32) if hasattr(model, 'stride') else 32  # max stride
-        im = torch.zeros((1, p.shape[1], stride, stride), device=p.device)  # input image in BCHW format
+        im = torch.empty((1, p.shape[1], stride, stride), device=p.device)  # input image in BCHW format
         flops = thop.profile(deepcopy(model), inputs=(im,), verbose=False)[0] / 1E9 * 2  # stride GFLOPs
         imgsz = imgsz if isinstance(imgsz, list) else [imgsz, imgsz]  # expand if int/float
         fs = f', {flops * imgsz[0] / stride * imgsz[1] / stride:.1f} GFLOPs'  # 640x640 GFLOPs