Added an assert to guarantee that we don't drop a non-trivial update step.
Added an assert to guarantee that we don't drop a non-trivial update step.


Former-commit-id: 055f0f16fddf11f1eb6bb2a8c564fa59b8edbac1
Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide