refactor _replace_linear_8da4w (#451)

* refactor _replace_linear_8da4w

* clean up version

---------

Author: Hanxian97

torchao/quantization/GPTQ.py

@@ -893,10 +893,15 @@ def _replace_linear_8da4w(
     linear_class: Type[torch.nn.Module],
     copy_weights: bool = False,
 ):
-    for name, child in module.named_children():
-        if isinstance(child, nn.Linear):
-            if _check_linear_int4_k(child.in_features, groupsize) or padding_allowed:
-                new_linear = linear_class(
+    
+    #import the util function here to avoid circular dependency
+    from torchao.quantization.quant_api import _replace_with_custom_fn_if_matches_filter
+
+    def filter_fn(child: torch.nn.Module, cur_fqn:str) -> bool:
+        return isinstance(child, nn.Linear) and (_check_linear_int4_k(child.in_features, groupsize) or padding_allowed)
+
+    def replacement_fn(child: torch.nn.Module) -> torch.nn.Module:
+        new_linear = linear_class(
                     child.in_features,
                     child.out_features,
                     bias=False,
@@ -905,22 +910,14 @@ def _replace_linear_8da4w(
                     precision=precision,
                     scales_precision=scales_precision,
                 )
-                # In distributed training, the model may be instantiated
-                # on the meta device, in which case there is no need to
-                # copy the weights, and doing so will result in an error
-                if copy_weights and child.weight.device != torch.device("meta"):
-                    new_linear.weight = child.weight
-                setattr(module, name, new_linear)
-        else:
-            _replace_linear_8da4w(
-                child,
-                groupsize,
-                padding_allowed,
-                precision,
-                scales_precision,
-                linear_class,
-                copy_weights,
-            )
+        # In distributed training, the model may be instantiated
+        # on the meta device, in which case there is no need to
+        # copy the weights, and doing so will result in an error
+        if copy_weights and child.weight.device != torch.device("meta"):
+            new_linear.weight = child.weight
+        return new_linear
+
+    _replace_with_custom_fn_if_matches_filter(module, replacement_fn, filter_fn)
 
 def replace_linear_8da4w(
     module: torch.nn.Module,