Replace torch.library.impl_abstract with torch.library.register_fake (pytorch#126606)

To remove the disrupting warning
```
      warnings.warn("torch.library.impl_abstract was renamed to "
                    "torch.library.register_fake. Please use that instead; "
                    "we will remove torch.library.impl_abstract in a future "
                    "version of PyTorch.",
                    DeprecationWarning, stacklevel=2)
```

Pull Request resolved: pytorch#126606
Approved by: https://github.com/ezyang

Author: cyyever

torch/_custom_ops.py

@@ -250,7 +250,7 @@ def impl_abstract(qualname, *, func=None):
     """
     import torch.library
 
-    return torch.library.impl_abstract(qualname, func, _stacklevel=2)
+    return torch.library.register_fake(qualname, func, _stacklevel=2)
 
 
 def impl_save_for_backward(qualname, *, func=None):

torch/distributed/pipelining/_IR.py

@@ -304,7 +304,7 @@ def _pipe_split():
     return None
 
 
-@torch.library.impl_abstract("pippy::_pipe_split")  # type: ignore[no-redef]
+@torch.library.register_fake("pippy::_pipe_split")  # type: ignore[no-redef]
 def _pipe_split():  # noqa: F811
     return None
 

torch/onnx/_internal/fx/decomposition_skip.py

@@ -71,7 +71,7 @@ def register_custom_op(cls):
         new_op_qualname = f"{_NEW_OP_NAMESPACE}::{cls.new_op_name}"
         torch.library.define(new_op_qualname, cls.new_op_schema)
         torch.library.impl(new_op_qualname, "default", cls.replacement)
-        torch.library.impl_abstract(new_op_qualname, cls.abstract)
+        torch.library.register_fake(new_op_qualname, cls.abstract)
 
     @classmethod
     def replacement(cls, *args, **kwargs):

torch/testing/_internal/custom_op_db.py

@@ -458,7 +458,7 @@ def source1_fake(x):
 
 lib.define("source2(Tensor x) -> Tensor")
 
-@torch.library.impl_abstract("_torch_testing::source2", lib=lib)
+@torch.library.register_fake("_torch_testing::source2", lib=lib)
 def _(x):
     return x.clone()
 
@@ -467,7 +467,7 @@ def _(x):
 def source3_fake(x):
     return x.clone()
 
-torch.library.impl_abstract("_torch_testing::source3", source3_fake, lib=lib)
+torch.library.register_fake("_torch_testing::source3", source3_fake, lib=lib)
 
 
 @torch.library.custom_op("_torch_testing::source4", mutates_args=())

torch/testing/_internal/hop_db.py

@@ -82,7 +82,7 @@ def foo_impl_cuda(x, z):
     return x, z, x + z
 
 
-@torch.library.impl_abstract("testlib::mutating_custom_op")
+@torch.library.register_fake("testlib::mutating_custom_op")
 def foo_impl_abstract(x, z):
     return x, z, x + z