Locations and combing statements.
Which location to use?
Say we have:
```
if (a)
t = STMT(b);
else
t = STMT(c);
```
We combine this into:
```
if (a)
t = b;
else
t = c;
STMT(t)
```
What location should be used for the new STMT? So with PHIs we have one extra location of the phi and the phi arguments each have a location.
So at least the location of the new phi args will be the same as the stmt/stmt originally was. But what should be the new stmt. I chose it to be location of the phi and if that does not exist either location of the stmts (if one but not both have a location).