[fx] refactored the file structure of patched function and module (#1238)

* [fx] refactored the file structure of patched function and module

* polish code

colossalai/fx/tracer/meta_patch/patched_function/python_ops.py

@@ -0,0 +1,24 @@
+import operator
+import torch
+from ..registry import meta_patched_function
+
+
+@meta_patched_function.register(operator.getitem)
+def operator_getitem(a, b):
+    # copied from huggingface.utils.fx
+    def to_concrete(t):
+        if isinstance(t, torch.Tensor):
+            concrete = torch.ones_like(t, device="cpu")
+            if concrete.dtype in [torch.float16, torch.float32, torch.float64, torch.int32]:
+                concrete = concrete.to(torch.int64)
+            return concrete
+        return t
+
+    if isinstance(a, torch.Tensor):
+        # TODO: infer shape without performing the computation.
+        if isinstance(b, tuple):
+            b = tuple(map(to_concrete, b))
+        else:
+            b = to_concrete(b)
+        return operator.getitem(torch.empty_like(a, device="cpu"), b).to("meta")
+    return operator.getitem(a, b)