Summary:
This diff fixes two issues in the backend that were causing Bad_footprint
errors when abducing pointsto facts for expressions that start in an array
access and follow up with another structured access, eg `x[0].some_field`:
1. array accesses were assumed to come last in these expressions
2. the type of the root exp passed to the function that walks down the list of
offsets to apply to it was wrong in the case of arrays: it was always the
type of the whole expression instead of the root expr (eg the type of
`x[0].some_field` instead of the type of `x`).
Reviewed By: sblackshear, jeremydubreil
Differential Revision: D3800566
fbshipit-source-id: 0511604
Jules Villard