"Godmar Back" <godmar@xxxxxxxxx> writes: > Thanks. I did see that gcc_unreachable() showed up as a symbol in the > assembly (consistent with it not meaning anything special); I suppose > I was misled by this comment in the gcc coding conventions at > http://gcc.gnu.org/codingconventions.html > > "Use gcc_unreachable() to mark places that should never be reachable > (such as an unreachable default case of a switch). Do not use > gcc_assert(0) for such purposes, as gcc_unreachable gives the compiler > more information." > > Apparently, this discussion refers to the (currently executing) > compiler, not the compiler used to compile the gcc code. Those coding convention are for people working on gcc itself, not for people using gcc. > I assume a corollary of that statement is that there is no way to > trick the compiler into omitting the default branch without incurring > runtime checks (or is there a clever way I'm not realizing)? In general, yes. There has been some discussion of implementing __builtin_unreachable() which would direct the optimizers to assume that the code path was never taken. Howver, as far as I know no actual woek has been done on this. Ian
