Fix mm pad regresion - more conservative estimation of plannable inputs (#128909)

- More conservative estimation of plannable inputs
- Consider constant_pad_nd as pointwise node in concat lowering
- Use aten.cat instead of constant pad ndwhen padding just a single dimension because it can be memory-planned away

Pull Request resolved: https://github.com/pytorch/pytorch/pull/128909
Approved by: https://github.com/Chillee

torch/utils/_config_module.py

@@ -8,6 +8,7 @@ import io
 import pickle
 import tokenize
 import unittest
+import warnings
 from types import FunctionType, ModuleType
 from typing import Any, Dict, Optional, Set, Union
 from typing_extensions import deprecated
@@ -178,6 +179,8 @@ class ConfigModule(ModuleType):
         mod = self.__name__
         for k, v in self._config.items():
             if k in self._config.get("_save_config_ignore", ()):
+                if v != self._default[k]:
+                    warnings.warn(f"Skipping serialization of {k} value {v}")
                 continue
             if v == self._default[k]:
                 continue