Optimize redundant vcombine/lo/hi sequences.
Optimize redundant vcombine/lo/hi sequences.

jiawen/Halide,ronen/Halide,ronen/Halide,jiawen/Halide,jiawen/Halide,ronen/Halide,ronen/Halide,jiawen/Halide,kgnk/Halide,psuriana/Halide,ronen/Halide,ronen/Halide,psuriana/Halide,psuriana/Halide,kgnk/Halide,kgnk/Halide,ronen/Halide,ronen/Halide,psuriana/Halide,psuriana/Halide,kgnk/Halide,psuriana/Halide,kgnk/Halide,jiawen/Halide,psuriana/Halide,kgnk/Halide,jiawen/Halide,kgnk/Halide,jiawen/Halide,kgnk/Halide