[X86] When selecting sse_load_f32/f64 pattern, make sure there's only one use...

[X86] When selecting sse_load_f32/f64 pattern, make sure there's only one use of every node all the way back to the root of the match

Summary: With masked operations, its possible for the operation node like fadd, fsub, etc. to be used by multiple different vselects. Since the pattern matching will start at the vselect, we need to make sure the operation node itself is only used once before we can fold a load. Otherwise we'll end up folding the same load into multiple instructions.

Reviewers: RKSimon, spatel, zvi, igorb

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D36938

llvm-svn: 311342