[wip] ns for fx: add support for subgraph matching (#52130)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/52130
We have patterns like (F.linear, F.relu) which need to match
to (toq.linear_relu). So, we need to match subgraphs.
This PR does the following:
* defines a "subgraph" as (start_node, end_node). The current assumption
is that subgraphs are simple, there is always a path from start_node to
end_node, and we can ignore any non-input args/kwargs of these nodes
for the purposes of matching and copying things. An example one node
subgraph is (F.linear, F.linear). An example two node subgraph
is (F.linear, F.relu).
* changes the matching logic to iterate over subgraphs instead of nodes
* changes the NS core APIs to use subgraph pairs instead of node pairs:
1. for weights, we match on the start node
2. for unshadowed activations, we observe the end nodes
3. for shadowed activations, we copy the subgraph of a to graph c
TODO(before review) write up better, not ready for review yet
Test Plan:
TODO before land: better test plan
Imported from OSS
Reviewed By: raghuramank100
Differential Revision: D26403092
fbshipit-source-id: e49aaad4b02b8d60589435848bee422b8f41937a
