Describes the evolutions of indices of the memory reference. The indices
are indices of the ARRAY_REFs, indexes in artificial dimensions
added for member selection of records and the operands of MEM_REFs.
BASE_OBJECT is the part of the reference that is loop-invariant
(note that this reference does not have to cover the whole object
being accessed, in which case UNCONSTRAINED_BASE is set; hence it is
not recommended to use BASE_OBJECT in any code generation).
For the examples above,
base_object: a *(p + x + 4B * j_0)
indices: {j_0, +, 1}_2 {16, +, 4}_2
4
{i_0, +, 1}_1
{j_0, +, 1}_2