(a) Improve the extract element code: there's no need to do gymnastics with
rotates into the preferred slot if a shuffle will do the same thing.
(b) Rename a couple of SPUISD pseudo-instructions for readability and better
semantic correspondence.
(c) Fix i64 sign/any/zero extension lowering.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@59965 91177308-0d34-0410-b5e6-96231b3b80d8
104de4390b