Jakub Jelinek <ja...@redhat.com> wrote: >On Mon, Dec 30, 2013 at 05:56:04PM +0100, Richard Biener wrote: >> Jakub Jelinek <ja...@redhat.com> wrote: >> >Setting gimple_call_set_fndecl of a random method call to >> >__bultin_unreachable can't work properly, the method call probably >> >passes in arguments that __builtin_unreachable doesn't expect, and >if >> >the method call has LHS, we'll ICE, because __builtin_unreachable >> >doesn't >> >have a LHS. Fixed by not doing anything for fold_stmt_inplace and >> >for fold_stmt just adding a new __buitin_unreachable () call before >the >> >method call, DCE will DTRT then and we don't have to bother with >adding >> >some dummy stmt to set up the lhs etc. >> > >> >Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk? >> >> You could re-set the number of arguments and the LHS though. > >While we have gimple_set_num_ops, I'd find that very ugly and >apparently >nothing in the compiler does that for calls right now. > >> But with a LHS and a not dead consumer both approaches will probably >ice. >> You'd need to replace all uses with a default def. > >Also, I think it could be quite surprising if fold_stmt changed other >stmts >(users of lhs), plus the lhs doesn't have to be in SSA form yet.
Yes. Also affecting other statements isn't allowed. >One would need to also unlink vdefs and release the vdef SSA_NAME, and >not >sure if fold_stmt_inplace callers would be even prepared for the stmt >to >become noreturn, and no longer throwing, etc. That I think they have to. Vdef handling is done by the caller which is required to update_stmt and to remove eh side effects if required. >What would be the advantages of doing all that over the posted patch? Not sure why this transform is in fold at all rather than in a pass that expects this kind of control flow changes. That said, your patch still requires all callers of statement folding to run control flow graph cleanup. That's undesired I think, so moving the transform elsewhere is better IMHO. I suggest dce. Richard. > Jakub
