[JIT] improve alias analysis for list constructs (#39111)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/39111
In our present alias analysis, we consider any Value that enter another container as entering the heap, and thus aliasing all other heap values of the same type. There are a number of advantages to this approach:
- it is not to hard to maintain the aliasDb implementation
- it is much easier from an op schema perspective - there are many composite list ops registered internally and externally that would be tricky to register and get right if we did something more complicated
- It limits the size of the AliasDb, because a container of size 10 only contains a single memory dag element instead of 10 elements.
The downside is that we have are unable to handle the simple and extremely common case of a list of tensors being used in an ATen op.
In an example like:
```
def foo(input):
x = torch.tensor([1, 2, 3, 4])
y = [x, x]
input.add_(1)
return torch.cat(y)
```
we will consider x to be written to. any write to any wildcard element (an element that enters a tuple, an element that is taken from a list) will mark x as written to. This can be limiting for our ability to create a functional subset and fuse graphs - as a result, 4 of TorchVision classification models could not be functionalized.
Test Plan: Imported from OSS
Reviewed By: SplitInfinity
Differential Revision: D23828003
Pulled By: eellison
fbshipit-source-id: 9109fcb6f2ca20ca897cae71683530285da9d537
