[X86][SSE] Canonicalize scalar fp arithmetic shuffle patterns

As discussed on PR38197, this canonicalizes MOVS*(N0, OP(N0, N1)) --> MOVS*(N0, SCALAR_TO_VECTOR(OP(N0[0], N1[0])))

This returns the scalar-fp codegen lost by rL336971.

Additionally it handles the OP(N1, N0)) case for commutable (FADD/FMUL) ops.

Differential Revision: https://reviews.llvm.org/D49474

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@337419 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed