Extended Description

Currently the isl AST generator derives

for (long i = LB; i <= UB; i++)
A[i]

for most loops. An alternative would be to generate

for (long i = LB; i != UB + 1; i++)
A[i]

In the second version a value of LB that is strictly larger than UB + 1 will cause i to eventually overflow. As we know this is not valid (and we annotate i in Polly with NSW), the IR carries the information that such an overflow can never happen
and consequently that LB must be smaller or equal to UB + 1.

LLVM and its -indvars pass prefers the second alternative precisely for this reason.

We should consider to generate IR with the above type.