+0 It looks like there is a small net win.  Conceptually, constant folding is better done upstream where more semantic information is available (rather than downstream when the meaning has to be deduced from the opcodes).  The only drawback is that if unfolded tuples ever leak out of the AST step or get created by the peephole optimization step, then they won't get fixed-up downstream (as functionality gets moved out of peephole.c, it creates more obligations on the AST code generation step to always produce the best possible code because the finally neatening-up step no longer occurs).