Split now pushes evaluations upwards instead of downwards.
Split now pushes evaluations upwards instead of downwards.

Simplifies better.


Former-commit-id: a896ca7d0e927abaf767b315db398fa15a9a2c4c
darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,Trass3r/Halide