On Tue, 11 Oct 2005, Raymond Hettinger wrote: > [Tom Anderson]: > >> What puzzles me, though, are bytecodes 17, 39 and 42 - surely these >> aren't reachable? Does the compiler just throw in a default 'return >> None' epilogue, with routes there from every code path, even when it's >> not needed? If so, why? > > Since unreachable code is never executed, there is no performance payoff > for optimizing it away. It is not hard to write a dead-code elimination > routine, but why bother?
Fair enough - it wasn't a criticism, i was just wondering if those bytecodes were serving some crucial function i hadn't appreciated! > It would save a few bytes, slow down compilation time, save nothing at > runtime, and make the compiler more complex/fragile. I have this vague idea that a compiler could be written in such a way that, rather than dead code being weeded out by some extra-complexity-inducing component, it would simply never be generated in the first place; that could perhaps even be simpler than the situation at present. I have tree reduction and SSA graphs frolicking in soft focus in my imagination. But, that said, i have no experience of actually writing compilers, so maybe this SSA stuff is harder than it sounds! tom -- That's no moon! -- http://mail.python.org/mailman/listinfo/python-list
