LoopVectorize: Simplify code. No functionality change.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@182100 91177308-0d34-0410-b5e6-96231b3b80d8
FileCheckize test.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@182101 91177308-0d34-0410-b5e6-96231b3b80d8
X86: Make shuffle -> shift conversion more aggressive about undefs.

Shuffles that only move an element into position 0 of the vector are common in
the output of the loop vectorizer and often generate suboptimal code when SSSE3
is not available. Lower them to vector shifts if possible.

We still prefer palignr over psrldq because it has higher throughput on
sandybridge.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@182102 91177308-0d34-0410-b5e6-96231b3b80d8