On 17 April 2015 at 15:19, <paul_kon...@dell.com> wrote: > >> On Apr 17, 2015, at 9:14 AM, Peter Sewell <peter.sew...@cl.cam.ac.uk> wrote: >> >> Dear gcc list, >> >> we are trying to clarify what behaviour of C implementations is >> actually relied upon in modern practice, and what behaviour is >> guaranteed by current mainstream implementations (these are quite >> different from the ISO standards, and may differ in different >> contexts). > > I’m not sure what you mean by “guaranteed”. > > I suspect what the GCC team will say is guaranteed is “what the standard > says”.
If that's really true, that will be interesting, but there may be areas where (a) current implementation behaviour is stronger than what the ISO standards require, and (b) important code relies on that behaviour to such an extent that it becomes pragmatically infeasible to change it. Such cases are part of what we're trying to discover here. There are also cases where the ISO standards are unclear or internally inconsistent. > If by “guaranteed” you mean the behavior that happens to be implemented in a > particular version of the compiler, that may well be different, as you said. > But it’s also not particularly meaningful, because it is subject to change at > any time subject to the constraints of the standard, and is likely to be > different among different versions, and for that matter among different > target architectures and of course optimization settings. Some amount of variation has to be allowed, of course - in fact, what we'd like to clarify is really the envelope of allowable variation, and that will have to be parametric on at least some optimisation settings. > paul >
