Fixes a miscompile when the index of `index_addr` is a negative integer constant. In this case two access paths were considered overlapping while in reality they reference two different array elements.
The miscompile manifested in the dead-store-elimination pass, but could potentially also show up in other passes, which use this utility.
https://github.com/swiftlang/swift/issues/77558
rdar://176820188
* Fix the right shift operator which didn't work if the number of bits is exactly 64
* Detect overflow when combining indices
Such large indices usually don't appear in real code, except in internal String operations where (potentially large) integer values are treated as pointers.
Fixes a compiler crash
https://github.com/swiftlang/swift/issues/84372
rdar://160863199
Add a `vectorBase` field kind which corresponds to `vector_base_addr`.
Also, improve `mayOverlap`: it didn't catch the case that the first element of a vector cannot overlap with another element.
Erik Eckstein
Jakub Florek