make sure cpu-only still works

dalle2_pytorch/dalle2_pytorch.py

@@ -35,6 +35,10 @@ def default(val, d):
 def cast_tuple(val, length = 1):
     return val if isinstance(val, tuple) else ((val,) * length)
 
+@contextmanager
+def null_context(*args, **kwargs):
+    yield
+
 def eval_decorator(fn):
     def inner(model, *args, **kwargs):
         was_training = model.training
@@ -1382,7 +1386,10 @@ class Decoder(BaseGaussianDiffusion):
         img = None
 
         for unet, vae, channel, image_size, predict_x_start in tqdm(zip(self.unets, self.vaes, self.sample_channels, self.image_sizes, self.predict_x_start)):
-            with self.one_unet_in_gpu(unet = unet):
+
+            context = self.one_unet_in_gpu(unet = unet) if image_embed.is_cuda else null_context()
+
+            with context:
                 lowres_cond_img = None
                 shape = (batch_size, channel, image_size, image_size)