[legacy] clean up legacy code (#4743)

* [legacy] remove outdated codes of pipeline (#4692)

* [legacy] remove cli of benchmark and update optim (#4690)

* [legacy] remove cli of benchmark and update optim

* [doc] fix cli doc test

* [legacy] fix engine clip grad norm

* [legacy] remove outdated colo tensor (#4694)

* [legacy] remove outdated colo tensor

* [test] fix test import

* [legacy] move outdated zero to legacy (#4696)

* [legacy] clean up utils (#4700)

* [legacy] clean up utils

* [example] update examples

* [legacy] clean up amp

* [legacy] fix amp module

* [legacy] clean up gpc (#4742)

* [legacy] clean up context

* [legacy] clean core, constants and global vars

* [legacy] refactor initialize

* [example] fix examples ci

* [example] fix examples ci

* [legacy] fix tests

* [example] fix gpt example

* [example] fix examples ci

* [devops] fix ci installation

* [example] fix examples ci

colossalai/legacy/pipeline/layer_spec.py

@@ -0,0 +1,57 @@
+import torch
+
+from colossalai.utils.model.utils import call_to_str
+
+
+class LayerSpec:
+    """
+
+    """
+
+    def __init__(self, typename, *module_args, **module_kwargs):
+        self.typename = typename
+        self.module_args = module_args
+        self.module_kwargs = module_kwargs
+        self.children = None
+        self._param_count = 0
+
+        if not issubclass(typename, torch.nn.Module):
+            raise RuntimeError('LayerSpec only supports torch.nn.Module types.')
+
+    def __repr__(self):
+        return call_to_str(self.typename.__name__, self.module_args, self.module_kwargs)
+
+    @property
+    def param_count(self):
+        return self._param_count
+
+    def build(self):
+        """Build the stored specification."""
+
+        recovered_args = []
+        for obj in self.module_args:
+            if isinstance(obj, LayerSpec):
+                obj = obj.build()
+            recovered_args.append(obj)
+        recovered_args = tuple(recovered_args)
+
+        recovered_kwargs = {}
+        for k, v in self.module_kwargs.items():
+            if isinstance(v, LayerSpec):
+                v = v.build()
+            recovered_kwargs[k] = v
+
+        return self.typename(*recovered_args, **recovered_kwargs)
+
+    def set_children(self, children):
+        self.children = children
+
+    def count_params(self):
+        self._param_count = 0
+        layer = self.build()
+        for param in layer.parameters():
+            self._param_count += param.numel()
+        return self._param_count
+
+    def reset_param_count(self):
+        self._param_count = 0