Recognize code for doing vector gather/scatter index calculations with

Recognize code for doing vector gather/scatter index calculations with
32-bit indices. Instead of shuffling each element out of the index vector,
when all indices are needed, just store the input vector to the stack and
load the elements out.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@98588 91177308-0d34-0410-b5e6-96231b3b80d8