> On Feb 6, 2017, at 10:04 AM, Joe Groff <jgr...@apple.com> wrote: > > >> On Feb 6, 2017, at 9:48 AM, Michael Gottesman via swift-dev >> <swift-dev@swift.org> wrote: >> >> One thing that is an issue that has come up with ownership is that at the >> SIL level we do not distinguish in between exceptional noreturn functions >> and exceptional return functions. >> >> This is important since in the non-exceptional case, we would like to clean >> up all of the values used in the current function before calling the >> no-return function. An example of such a function is dispatch_main from >> libdispatch. In the exceptional case though, we are ok with leaking since >> the program will be exiting. Beyond reducing code size (I guess?), the >> argument I have heard for this is that this will allow for people to examine >> values in the debugger since we will not have cleaned things up before the >> abort is called. >> >> From what I can tell, if we are going to distinguish in between these cases, >> then we need a distinction in between the two baked into the compiler. >> Thoughts? I have code written that will enable either case to be handled as >> long as I can distinguish in between them at the SIL level. > > The interesting distinction here to me strikes me as being the temporal > rather than exceptional nature of the exit. _exit(2) isn't an "exceptional" > noreturn per se, but you'd still want to leak cleanups before it since the > program's termination comes immediately after the call. If it's a profitable > distinction to be made, I think there are few enough immediate-exit > primitives like exit, abort, fatalError, etc. that we could probably > whitelist them with a @_semantics attribute for now, and maybe use an early > SIL pass to propagate the attribute in obvious cases where a function is a > simple wrapper around one of those functions.
I am fine with either approach as long as we make a decision. But just to bring it up in the discussion, Alexis brought up in chat an interesting point, namely what about higher level functions? I guess we don't care about that case? Michael > > -Joe _______________________________________________ swift-dev mailing list swift-dev@swift.org https://lists.swift.org/mailman/listinfo/swift-dev
