fix cudagraphs without tensor inputs (#1324)

thunder/tests/test_transforms.py

@@ -596,3 +596,18 @@ def forward(x):
             break
     else:
         raise RuntimeError("Failed to find `add` symbol in trace")
+
+
+@requiresCUDA
+def test_cudagraph_empty_inputs():
+    def fn():
+        a = torch.ones(5, 5, device="cuda")
+        b = a * 2
+        return b
+
+    from thunder.transforms.cudagraph import CUDAGraphTransform
+
+    jfn = thunder.jit(fn, transforms=(CUDAGraphTransform(),), executors=())
+    assert_close(jfn(), fn())
+
+    assert any(("CUDAGraph" in bsym.sym.name) for bsym in thunder.last_traces(jfn)[-1].bound_symbols)

thunder/transforms/cudagraph.py

@@ -33,7 +33,10 @@ def extract_descriptor(arg):
         else:
             return type(arg), None, None, arg
 
-    dtypes, sizes, strides, non_tensor_args = zip(*map(extract_descriptor, args))
+    if args:
+        dtypes, sizes, strides, non_tensor_args = zip(*map(extract_descriptor, args))
+    else:
+        dtypes = sizes = strides = non_tensor_args = None
     return ArgsDescriptor(dtypes, sizes, strides, non_tensor_args)