…ating to part of the DAG (pytorch#1775)

`MaxInfoPropagator` is renamed to `MaxInfoSpanningTree`, it now only does path-finding, and the propagation is in a separate class `MaxInfoSpanningTree::Propagator`. Same for `MaxRootDomainInfoPropagator`.

`MaxInfoSpanningTree` and `MaxRootDomainInfoSpanningTree`  now allow specifying a selector, which controls which subgraph should be included in path-finding.

`MaxRootDomainInfoSpanningTree` also gets a few new constructors for convenience to use.

`TransormPropagator` is now a subclass of `MaxInfoSpanningTree::Propagator`, so the way to use it has changed.

Now `MaxInfoSpanningTree` and `MaxRootDomainInfoSpanningTree` will store the path after generation so that the same path can be traversed multiple times. This will be useful to support use cases like new `computeAt`. Pseudo-code:
```C++
void TensorView::computeAt(TensorView tv, int pos) {
  auto ComputeAtSubgraphSelector selector(this, tv);
  MaxRootDomainInfoSpanningTree path(tv, pos, &selector);
  TransformPropagator propagator(tv, pos);
  path.traverse(&propagator);
  ComputeAtPosPropagator ca_propagator(tv, pos);
  path.traverse(&ca_propagator);
}
```

Syncing nvfuser devel branch to upstream master. https://github.com/csarofeen/pytorch/

Code changes includes:

- TransformPropagator refactor: switched to Dijkstra instead of exhaustive enumeration on all possible paths to reduce compilation time on transform propagation;
- Indexing refactor: remove reference tensor creation in all tensor indexing logic (#1690)
- (more) generic grouped grid reduction kernel;
- Minor parser/fuser patches:
  1. zero-dim tensor reduction support
  3. no-op binary removal within fused graph
  4. expand supported in fusion

Squashed commits to WAR github API
Commits that's actually in this PR from the devel branch:

```
a054b3e Refactor TransormPropagator to allow specifying a position and propagating to part of the DAG (#1775)
d67e1cd Indexing refactor stage 1: remove reference tensor creation in all tensor indexing logic (#1690)
1b65299 Issue 1770 (#1774)
35b0427 Avoid compilation errors like below: (#1773)
452c773 Ignore reductions of zero-dim tensors per PyTorch conventions (#1771)
31d6c56 TransformPropagator refactor (#1769)
570c5a8 Merge pull request #1767 from csarofeen/upstream_merge_0621
9d6c3d8 merging upstream 61305cd
0ed815f New TransformPropagator algorithm (#1763)
6c19520 no-op binary removal (#1764)
ec7fa41 Proper propagation of IterType (#1762)
b263562 Fix dimensionality check (#1759)
2d6343f More generic grouped grid reduction kernel (#1740)
64e2b56 [nvfuser] prevent spamming warning message (#77777) (#1758)
0c43162 [nvFuser] Improving bitwise ops support (#77158) (#1757)
b93a147 Parser expand (#1754)
```

RUN_TORCHBENCH: nvfuser
Pull Request resolved: #80355
Approved by: https://github.com/davidberard98

Summary:
Syncing nvfuser devel branch to upstream master. https://github.com/csarofeen/pytorch/

Code changes includes:

- TransformPropagator refactor: switched to Dijkstra instead of exhaustive enumeration on all possible paths to reduce compilation time on transform propagation;
- Indexing refactor: remove reference tensor creation in all tensor indexing logic (#1690)
- (more) generic grouped grid reduction kernel;
- Minor parser/fuser patches:
  1. zero-dim tensor reduction support
  3. no-op binary removal within fused graph
  4. expand supported in fusion

Squashed commits to WAR github API
Commits that's actually in this PR from the devel branch:

```
a054b3e Refactor TransormPropagator to allow specifying a position and propagating to part of the DAG (#1775)
d67e1cd Indexing refactor stage 1: remove reference tensor creation in all tensor indexing logic (#1690)
1b65299 Issue 1770 (#1774)
35b0427 Avoid compilation errors like below: (#1773)
452c773 Ignore reductions of zero-dim tensors per PyTorch conventions (#1771)
31d6c56 TransformPropagator refactor (#1769)
570c5a8 Merge pull request #1767 from csarofeen/upstream_merge_0621
9d6c3d8 merging upstream 61305cd
0ed815f New TransformPropagator algorithm (#1763)
6c19520 no-op binary removal (#1764)
ec7fa41 Proper propagation of IterType (#1762)
b263562 Fix dimensionality check (#1759)
2d6343f More generic grouped grid reduction kernel (#1740)
64e2b56 [nvfuser] prevent spamming warning message (#77777) (#1758)
0c43162 [nvFuser] Improving bitwise ops support (#77158) (#1757)
b93a147 Parser expand (#1754)
```

RUN_TORCHBENCH: nvfuser

Pull Request resolved: #80355

Reviewed By: qihqi

Differential Revision: D37573400

Pulled By: davidberard98

fbshipit-source-id: 52ab68d89ec01ef61f69f5abeb18c9d3a312aa64