[pt2e][xnnpack_quantizer] add util function to convert scalars to att…

…rs (pytorch#110427)

Jerry provided a notebook solution for converting scalars to attrs so that they may be properly quantized:

https://fburl.com/anp/kzz7tfn1

Adding this pass as a util function in xnnpack_quantizer_utils.py

Differential Revision: [D49850150](https://our.internmc.facebook.com/intern/diff/D49850150/)
Pull Request resolved: pytorch#110427
Approved by: https://github.com/jerryzh168

torch/ao/quantization/quantizer/xnnpack_quantizer_utils.py

@@ -5,6 +5,7 @@
 
 import torch
 import torch.nn.functional as F
+from torch.ao.quantization.fx.utils import get_new_attr_name_with_prefix
 from torch.ao.quantization.pt2e.graph_utils import find_sequential_partitions
 from torch.ao.quantization.quantizer import (
     QuantizationAnnotation,
@@ -866,3 +867,30 @@ def propagate_annotation(model: torch.fx.GraphModule) -> None:
             output_qspec=shared_qspec,
             _annotated=True,
         )
+
+
+def convert_scalars_to_attrs(model: torch.fx.GraphModule) -> torch.fx.GraphModule:
+    for n in model.graph.nodes:
+        if n.op != "call_function" or n.target not in [
+            torch.ops.aten.add.Tensor,
+            torch.ops.aten.mul.Tensor,
+        ]:
+            continue
+        args = list(n.args)
+        new_args = []
+        for i in range(len(args)):
+            if isinstance(args[i], torch.fx.Node):
+                new_args.append(args[i])
+                continue
+            prefix = "_tensor_constant_"
+            get_new_attr_name = get_new_attr_name_with_prefix(prefix)
+            tensor_constant_name = get_new_attr_name(model)
+            model.register_buffer(tensor_constant_name, torch.tensor(float(args[i])))
+            with model.graph.inserting_before(n):
+                get_attr_node = model.graph.create_node(
+                    "get_attr", tensor_constant_name, (), {}
+                )
+                new_args.append(get_attr_node)
+        n.args = tuple(new_args)
+    model.recompile()
+    return model