[x86] convert masked load of exactly one element to scalar load

This is the load counterpart to the store optimization that was added in:
http://reviews.llvm.org/rL260145



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@260325 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed