This enables the LLVM optimizer to view accesses to distinct struct
members as independent, also for array members. For example, the
following two stores no longer alias:

    struct S { int a[10]; int b; };
    void test(S *p, int i) {
      p->a[i] = ...;
      p->b = ...;
    }

Array members were already added to TBAA struct type nodes in commit
57493e29. Here, we extend a path tag for an array subscript expression.

Now that in the new TBAA format we allow access types to be of
any object types, including aggregate ones, it becomes critical
to specify types of all sub-objects such aggregates comprise as
their members. In order to meet this requirement, this patch
enables generation of field descriptors for members of array
types.

Differential Revision: https://reviews.llvm.org/D41399

llvm-svn: 321352

Resolves:
Fatal error: Offset not zero at the point of scalar access.
http://llvm.org/PR34992

Differential Revision: https://reviews.llvm.org/D39083

llvm-svn: 316211