SLPVectorizer: Speedup isConsecutive by manually checking GEPs with multiple indices.
This brings the compile time of the SLP-Vectorizer to about 2.5% of OPT for my testcase.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@186592 91177308-0d34-0410-b5e6-96231b3b80d8