Check if array base addresses are invariant

Array base addresses need to be invariant in the region considered. The base
address has to be computed outside the region, or, when it is computed inside,
the value must not change with the iterations of the loops. For example, when a
two-dimensional array is represented as a pointer to pointers the base address
A[i] in an access A[i][j] changes with i; therefore, such regions have to be
rejected.

Contributed by:  Armin Größlinger <armin.groesslinger@uni-passau.de>

git-svn-id: https://llvm.org/svn/llvm-project/polly/trunk@200314 91177308-0d34-0410-b5e6-96231b3b80d8
Do not verify the base addresses

Verification of base addresses is difficult as the independent blocks pass may
introduce aliasing that was not there during scop detection. As a midterm
solution -polly-codegen-scev will remove the need for the independent blocks
pass. For now, we do not verify at compile time that the independent blocks pass
does not make the base addresses loop invariant. Disabling this just removes
one of the multiple safety layers we have. We still can check for correctness
in our regression tests.

git-svn-id: https://llvm.org/svn/llvm-project/polly/trunk@200315 91177308-0d34-0410-b5e6-96231b3b80d8