No matter whether gep merging takes effect or not, it is better for the analysis not to depend on having only one level GEP, just as DecomposeGEPExpression does right now.
The patch extends consecutive analysis in LoopVectorizer pass to handle multiple level GEPs. This is a following patch for http://reviews.llvm.org/D9865.
I also tried other way to solve the problem more generally by generating a temporarily merged GEP everytime when analyzing a GEP and removing it after the analysis, but it failed. A lot of existing analysis requires GEP to be a valid inst inserted in the function. We need to insert the temporarily combined GEP into the original BB, do the analysis, then delete it -- making a dangling GEP insn just for the analysis doesn't work. But it makes the IR during the analysis messy this way. Another way is to make the combined GEP kind of meta data just for analysis, but I am not sure how much effort it will cost because the meta data needs to be updated from time to time.