Optimization for certain shufflevector by using insertps.

Summary:
If we're doing a v4f32/v4i32 shuffle on x86 with SSE4.1, we can lower
certain shufflevectors to an insertps instruction:
When most of the shufflevector result's elements come from one vector (and
keep their index), and one element comes from another vector or a memory
operand.

Added tests for insertps optimizations on shufflevector.
Added support and tests for v4i32 vector optimization.

Reviewers: nadav

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D3475

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207291 91177308-0d34-0410-b5e6-96231b3b80d8