The output of halide_log, exp, erf, etc needs CSE applied.
The output of halide_log, exp, erf, etc needs CSE applied.

This used to happen at func definition time, but then these
intrinsics were deferred until codegen. This caused very
slow codegen for anything taking exp(nasty_expression)


Former-commit-id: eb08720eca5e0931ef02331d33cfa043d0871d07
darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide