[SLP] Fix for PR32164: Improve vectorization of reverse order of extract operations.

Summary: Sometimes vectorization of insertelement instructions with extractelement operands may produce an extra shuffle operation, if these operands are in the reverse order. Patch tries to improve this situation by the reordering of the operands to remove this extra shuffle operation.

Reviewers: mkuper, hfinkel, RKSimon, spatel

Subscribers: mzolotukhin, llvm-commits

Differential Revision: https://reviews.llvm.org/D33954

llvm-svn: 322579