Simplify raises an exception on LoopRegion

The simplify pass throws the exception below in the GT4Py SDFGs containing LoopRegion nodes. This error goes away if I run sdutils.inline_loop_blocks(sdfg) before simplify().

Traceback (most recent call last):
  File "/opt/homebrew/Caskroom/miniconda/base/envs/edopao-gt4py/lib/python3.10/site-packages/networkx/classes/graph.py", line 2010, in bunch_iter
    for n in nlist:
TypeError: 'AccessNode' object is not iterable

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/Users/epaone/repo/dace/dace/sdfg/sdfg.py", line 2384, in simplify
    return SimplifyPass(validate=validate, validate_all=validate_all, verbose=verbose).apply_pass(self, {})
  File "/Users/epaone/repo/dace/dace/transformation/passes/simplify.py", line 113, in apply_pass
    result = super().apply_pass(sdfg, pipeline_results)
  File "/Users/epaone/repo/dace/dace/transformation/pass_pipeline.py", line 547, in apply_pass
    newret = super().apply_pass(sdfg, state)
  File "/Users/epaone/repo/dace/dace/transformation/pass_pipeline.py", line 502, in apply_pass
    r = self.apply_subpass(sdfg, p, state)
  File "/Users/epaone/repo/dace/dace/transformation/passes/simplify.py", line 90, in apply_subpass
    ret = p.apply_pass(sdfg, state)
  File "/Users/epaone/repo/dace/dace/transformation/passes/analysis.py", line 162, in apply_pass
    if state.in_degree(anode) > 0:
  File "/Users/epaone/repo/dace/dace/sdfg/graph.py", line 696, in in_degree
    return self._nx.in_degree(node)
  File "/opt/homebrew/Caskroom/miniconda/base/envs/edopao-gt4py/lib/python3.10/site-packages/networkx/classes/reportviews.py", line 436, in __call__
    return self.__class__(self._graph, nbunch, weight)
  File "/opt/homebrew/Caskroom/miniconda/base/envs/edopao-gt4py/lib/python3.10/site-packages/networkx/classes/reportviews.py", line 421, in __init__
    self._nodes = self._succ if nbunch is None else list(G.nbunch_iter(nbunch))
  File "/opt/homebrew/Caskroom/miniconda/base/envs/edopao-gt4py/lib/python3.10/site-packages/networkx/classes/graph.py", line 2025, in bunch_iter
    raise exc
networkx.exception.NetworkXError: nbunch is not a node or a sequence of nodes.

Here is a test case to reproduce the issue.

import dace

M = 4
N = 10
dtype = dace.float64

def build_reduce_sdfg() -> dace.SDFG:
    acc_var = "__acc"
    neighbor_idx = "__idx"

    sdfg = dace.SDFG("reduce")
    sdfg.add_scalar(acc_var, dtype, transient=True)
    sdfg.add_array("A", (N,), dtype)
    sdfg.add_array("B", (1,), dtype)

    reduce_loop = dace.sdfg.state.LoopRegion(
        label="reduce",
        loop_var=neighbor_idx,
        initialize_expr=f"{neighbor_idx} = 0",
        condition_expr=f"{neighbor_idx} < {N}",
        update_expr=f"{neighbor_idx} = {neighbor_idx} + 1",
        inverted=False,
    )
    sdfg.add_node(reduce_loop)
    reduce_state = reduce_loop.add_state("loop")

    reduce_tasklet = reduce_state.add_tasklet(
        "reduce",
        {"x", "y"},
        {"res"},
        "res = x + y",
    )
    reduce_state.add_edge(
        reduce_state.add_access(acc_var),
        None,
        reduce_tasklet,
        "x",
        dace.Memlet(data=acc_var, subset="0"),
    )
    reduce_state.add_edge(
        reduce_state.add_access("A"),
        None,
        reduce_tasklet,
        "y",
        dace.Memlet(data="A", subset=neighbor_idx),
    )
    reduce_state.add_edge(
        reduce_tasklet,
        "res",
        reduce_state.add_access(acc_var),
        None,
        dace.Memlet(data=acc_var, subset="0"),
    )

    init_state = sdfg.add_state("init", is_start_block=True)
    sdfg.add_edge(init_state, reduce_loop, dace.InterstateEdge())
    init_state.add_edge(
        init_state.add_tasklet("write", {}, {"val"}, "val = 0"),
        "val",
        init_state.add_access(acc_var),
        None,
        dace.Memlet(f"{acc_var}[0]")
    )

    exit_state = sdfg.add_state("exit")
    sdfg.add_edge(reduce_loop, exit_state, dace.InterstateEdge())
    exit_state.add_nedge(
        exit_state.add_access(acc_var),
        exit_state.add_access("B"),
        dace.Memlet(data=acc_var, subset="0", other_subset="0"),
    )

    return sdfg

def test_gt_loop():
    reduce_sdfg = build_reduce_sdfg()

    sdfg = dace.SDFG("gt_loop")
    sdfg.add_array("inp", (M, N), dtype)
    sdfg.add_array("out", (M,), dtype)

    state = sdfg.add_state()
    me, mx = state.add_map("row_loop", dict(i=f"0:{M}"))
    nsdfg = state.add_nested_sdfg(reduce_sdfg, sdfg, {"A"}, {"B"})
    state.add_memlet_path(state.add_access("inp"), me, nsdfg, dst_conn="A", memlet=dace.Memlet(f"inp[i, 0:{N}]"))
    state.add_memlet_path(nsdfg, mx, state.add_access("out"), src_conn="B", memlet=dace.Memlet(f"out[i]"))

    sdfg.validate()
    sdfg.simplify()

spcl / dace

Simplify raises an exception on LoopRegion #1592