use the canonical IV only when it exists

git-svn-id: https://llvm.org/svn/llvm-project/polly/trunk@177306 91177308-0d34-0410-b5e6-96231b3b80d8
ScopHelper: Remove some dead code

git-svn-id: https://llvm.org/svn/llvm-project/polly/trunk@177307 91177308-0d34-0410-b5e6-96231b3b80d8
ScopHelper: clang-format

git-svn-id: https://llvm.org/svn/llvm-project/polly/trunk@177309 91177308-0d34-0410-b5e6-96231b3b80d8
Correct function to decide if a SCEV can be ignored

When doing SCEV based code generation, we ignore instructions calculating values
that are fully defined by a SCEV expression. The values that are calculated by
this instructions are recalculated on demand.

This commit improves the check to verify if certain instructions can be ignored
and recalculated on demand.

git-svn-id: https://llvm.org/svn/llvm-project/polly/trunk@177313 91177308-0d34-0410-b5e6-96231b3b80d8