Extend Pattern Matcher to allow handling split-cat style patterns (#97726)
Summary:
This diff extends pattern matcher, by adding a few features which allows it to handle split-getitem-cat style patterns.
3 problems I encountered were:
1. In the handler, I only need one Arg() (the one which is the first input to split). None of the other args are relevant to replacement graph. So, we add a new Ignored() pattern to have ignored args
2. The pattern matching was visiting the split node again and again during the DFS. By propogating the patterns with _users>1 or Any into the child MatchContext, we avoid this problem.
3. To avoid the unbundling issue, I switched to using KeywordArg() instead of Arg() - as for this pattern, we need a flat list of Arg() in the end
Example pattern: https://www.internalfb.com/intern/anp/view/?id=3325856
```
pass_patterns.append(defaultdict(list))
register_replacement_pattern(
CallFunction(
aten.cat,
ListOf( CallFunction(operator.getitem, CallFunction(aten.split_with_sizes, KeywordArg("input_"), Ignored(), Ignored(), _users=Any),
Ignored()
),),
Ignored()
),
pass_number=3
)
def split_cat_replace(input_):
return input_
```
Test Plan: https://www.internalfb.com/intern/anp/view/?kernel=default&id=3317105
Reviewed By: jansel
Differential Revision: D44282499
Pull Request resolved: https://github.com/pytorch/pytorch/pull/97726
Approved by: https://github.com/jansel
