Add a pass to convert rank-0 tensor to rank-1 tensor (#8298)

Summary:


Test with following code, and no long see the error/warning to complain rank-0 tensor
```

class Model(torch.nn.Module):
    def forward(self, x, y):
        return x + y

model = Model()
model.eval()

example_inputs = (torch.tensor(1.0), torch.tensor(2.0))
exported_program_manager_aten = torch.export.export(model, example_inputs)
exported_program_manager_edge = executorch.exir.to_edge(
    exported_program_manager_aten
).transform([Rank0ToRank1Pass()])

delegated_module = to_backend(
    CoreMLBackend.__name__, exported_program_manager_edge.exported_program(), []
)
```

Differential Revision: D69281867

Author: cccclai

backends/transforms/rank_0_to_rank_1.py

@@ -0,0 +1,18 @@
+import torch
+from executorch.exir.pass_base import ExportPass, PassResult
+
+
+class Rank0ToRank1Pass(ExportPass):
+    """
+    Replace Rank-0 Tensor to Rank-1 Tensor for all the inputs.
+    """
+
+    def __init__(self) -> None:
+        super().__init__()
+
+    def call(self, graph_module: torch.fx.GraphModule) -> PassResult:
+        for node in graph_module.graph.nodes:
+            if node.op == "placeholder" and node.meta["val"].shape == ():
+                node.meta["val"] = node.meta["val"].reshape(1, 1)
+        graph_module.recompile()
+        return PassResult(graph_module, True)

backends/transforms/targets.bzl

@@ -187,6 +187,20 @@ def define_common_targets():
         ],
     )
 
+    runtime.python_library(
+        name = "rank_0_to_rank_1",
+        srcs = [
+            "rank_0_to_rank_1.py",
+        ],
+        visibility = [
+            "//executorch/backends/...",
+        ],
+        deps = [
+            "//caffe2:torch",
+            "//executorch/exir:pass_base",
+        ],
+    )
+
     runtime.python_test(
         name = "test_duplicate_dynamic_quant_chain",
         srcs = [
@@ -200,3 +214,16 @@ def define_common_targets():
             "//executorch/exir:lib",
         ],
     )
+
+
+    runtime.python_test(
+        name = "test_rank_0_to_rank_1",
+        srcs = [
+            "test/test_rank_0_to_rank_1.py",
+        ],
+        deps = [
+            "//caffe2:torch",
+            "//executorch/exir:lib",
+            ":rank_0_to_rank_1",
+        ],
+    )

backends/transforms/test/test_rank_0_to_rank_1.py

@@ -0,0 +1,32 @@
+import unittest
+
+import torch
+from executorch.backends.transforms.rank_0_to_rank_1 import Rank0ToRank1Pass
+from executorch.exir import to_edge
+class TestRank0ToRank1Pass(unittest.TestCase):
+    def test_pass(
+        self,
+    ):
+        class Model(torch.nn.Module):
+            def forward(self, x, y):
+                return x + y
+
+        model = Model()
+        model.eval()
+
+        example_inputs = (torch.tensor(1.0), torch.tensor(2.0))
+        aten = torch.export.export(model, example_inputs)
+
+        # Check that the input rank is 0
+        for node in aten.graph.nodes:
+            if node.op == "placeholder":
+                self.assertTrue(node.meta["val"].shape == ())
+
+        edge = to_edge(
+            aten
+        ).transform([Rank0ToRank1Pass()])
+
+        # Check that the input rank is 1
+        for node in edge.exported_program().graph.nodes:
+            if node.op == "placeholder":
+                self.assertTrue(node.meta["val"].shape == (1, 1))