[polly] ICE with scev-codegen after removal of RegionSimplify

[Sebastian Pop]

Sebastian Pop wrote:
> Let's focus on removing independent blocks, as it creates too many problems.

I quickly removed the independent blocks pass and it does fix the compilation of
Isl/CodeGen/20110226-PHI-Node-removed.ll: the only fails that I see are

Failing Tests (2):
    Polly :: Isl/CodeGen/20100713_2.ll
    Polly :: Isl/CodeGen/20110226-Ignore-Dead-Code.ll

both of these fails are ICEing after codegen verification with:

Instruction does not dominate all uses!
  %tmp25 = add i64 undef, 1
  %exitcond26.old = icmp eq i64 undef, %tmp25

We most likely fail to copy the scalar dependences for %tmp25 that probably
still points to the original scop or so.

I think that the patch looks pretty good for a first shot at removing
independent blocks.

Sebastian
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