[NNC] add hazard analysis to Bounds Inference (#47684)
Summary:
Adds a helper function to Bounds Inference / Memory Analaysis infrastructure which returns the kind of hazard found between two Stmts (e.g. Blocks or Loops). E.g.
```
for (int i = 0; i < 10; ++i) {
A[x] = i * 2;
}
for (int j = 0; j < 10; ++j) {
B[x] = A[x] / 2;
}
```
The two loops have a `ReadAfterWrite` hazard, while in this example:
```
for (int i = 0; i < 10; ++i) {
A[x] = i * 2;
}
for (int j = 0; j < 10; ++j) {
A[x] = B[x] / 2;
}
```
The loops have a `WriteAfterWrite` hazard.
This isn't 100% of what we need for loop fusion, for example we don't check the strides of the loop to see if they match.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/47684
Reviewed By: malfet
Differential Revision: D24873587
Pulled By: nickgg
fbshipit-source-id: 991149e5942e769612298ada855687469a219d62
