Avoid combinatorial explosion problem in inline reduction helpers
Avoid combinatorial explosion problem in inline reduction helpers

There's a mutator that runs before CSE is done, so we need to do CSE
early.


Former-commit-id: 6a3849bd1825b3666af07e3505dd9dec404104b0
Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide