Support 3 argument variant of the getattr() call where the third arg is the default return value (#61599)
Summary:
Issue: https://github.com/pytorch/pytorch/issues/56909
Note the emitted code for such a call will either be a) getattr() call with first two args if the
attribute name (which must be a string literal) is determined to be valid based on the hasAttr() result,
or b) just the AST node for the default value (the 3rd arg) alone with no getattr call at all.
Test code:
```
import torch
import numpy as np
class Shape:
def __init__(self):
self.center = 1.0
def f(x):
s = Shape()
return getattr(s, "missing", [])
y = torch.jit.script(f)
print(y.graph)
```
Output:
```
graph(%x : Tensor):
%s.1 : __torch__.Shape = prim::CreateObject()
%2 : NoneType = prim::CallMethod[name="__init__"](%s.1) # ts.py:10:8
%4 : Tensor[] = prim::ListConstruct()
return (%4)
```
Another example:
```
import torch
class Shape:
def __init__(self):
self.center = 1.0
def f(x):
s = Shape()
y = getattr(s, "center")
w : list[float] = [1.0]
z = getattr(s, "missing", w)
z.append(y)
return z
y = torch.jit.script(f)
print(y.graph)
--- output ---
graph(%x : Tensor):
%5 : float = prim::Constant[value=1.]() # ts.py:12:23
%s.1 : __torch__.Shape = prim::CreateObject()
%2 : NoneType = prim::CallMethod[name="__init__"](%s.1) # ts.py:10:8
%center : float = prim::GetAttr[name="center"](%s.1)
%w.1 : float[] = prim::ListConstruct(%5)
%11 : float[] = aten::append(%w.1, %center) # ts.py:14:4
return (%w.1)
```
Fixes #{56969}
Pull Request resolved: https://github.com/pytorch/pytorch/pull/61599
Reviewed By: ZolotukhinM
Differential Revision: D29776058
Pulled By: jerryzhenleicai
fbshipit-source-id: 76333bd54002e08a064677c1f287115a80cc7c8e
