Fix #726 grad checkpointing + dynamo work in newer torch, but w/ ddp,…

… ddp optimizer must be disabled

src/open_clip_train/main.py

@@ -422,6 +422,12 @@ def main(args):
     original_model = model
     if args.torchcompile:
         logging.info('Compiling model...')
+
+        if args.grad_checkpointing and args.distributed:
+            logging.info('Disabling DDP dynamo optimizer when grad checkpointing enabled.')
+            # As of now (~PyTorch 2.4/2.5), compile + checkpointing but DDP optimizer must be disabled
+            torch._dynamo.config.optimize_ddp = False
+
         model = torch.compile(original_model)
 
     if 'train' not in data: