SLPVectorizer: Ignore users that are insertelements we can reschedule them

Patch by Arch D. Robison!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205018 91177308-0d34-0410-b5e6-96231b3b80d8
SLPVectorizer: Fix typos

Patch by Arch D. Robison!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205019 91177308-0d34-0410-b5e6-96231b3b80d8
SLPVectorizer: Take credit for free extractelement instructions

Extract element instructions that will be removed when vectorzing lower the
cost.

Patch by Arch D. Robison!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205020 91177308-0d34-0410-b5e6-96231b3b80d8