Replace ScalarEvolution based domain generation

This patch replaces the last legacy part of the domain generation, namely the
ScalarEvolution part that was used to obtain loop bounds. We now iterate over
the loops in the region and propagate the back edge condition to the header
blocks. Afterwards we propagate the new information once through the whole
region. In this process we simply ignore unbounded parts of the domain and
thereby assume the absence of infinite loops.

  + This patch already identified a couple of broken unit tests we had for
    years.
  + We allow more loops already and the step to multiple exit and multiple back
    edges is minimal.
  + It allows to model the overflow checks properly as we actually visit
    every block in the SCoP and know where which condition is evaluated.
  - It is currently not compatible with modulo constraints in the
    domain.

Differential Revision: http://reviews.llvm.org/D12499

llvm-svn: 247279