reduce VRAM memory usage by half during model loading

* This moves the call to half() before model.to(device) to avoid GPU
copy of full model. Improves speed and reduces memory usage dramatically

* This fix contributed by @mh-dm (Mihai)

Author: lstein

ldm/generate.py

@@ -536,9 +536,6 @@ def _load_model_from_config(self, config, ckpt):
         sd = pl_sd['state_dict']
         model = instantiate_from_config(config.model)
         m, u = model.load_state_dict(sd, strict=False)
-        model.to(self.device)
-        model.eval()
-
 
         if self.full_precision:
             print(
@@ -549,6 +546,8 @@ def _load_model_from_config(self, config, ckpt):
                 '>> Using half precision math. Call with --full_precision to use more accurate but VRAM-intensive full precision.'
             )
             model.half()
+        model.to(self.device)
+        model.eval()
 
         # usage statistics
         toc = time.time()