On Wed, 1 Mar 2023 22:58:59 +0100 Bernhard Reutner-Fischer <rep.dot....@gmail.com> wrote:
> On Wed, 1 Mar 2023 22:28:56 +0100 > Bernhard Reutner-Fischer <rep.dot....@gmail.com> wrote: > > > Remarks: > > 1) We should do this in if-conversion (?) on our own. > > I suppose. Independently of -fdelete-null-pointer-checks > > and iff we can prove that ptr was NULL when passed to free(ptr) then we > can elide the call, of course. Likewise for realloc(ptr, 0), obviously. > [or reallocarray -- yikes -- if nmemb == 0 || size == 0] > > But that would probably be a ranger call in DCE, i guess. Didn't look. > thanks, And, if under C, we rule out validity of a life ptr as a return value of malloc(0), ---8<--- If size is 0, either: A null pointer shall be returned [CX] [Option Start] and errno may be set to an implementation-defined value, [Option End] or A pointer to the allocated space shall be returned. The application shall ensure that the pointer is not used to access an object. ---8<--- Where CX == "Extension to the ISO C standard" https://pubs.opengroup.org/onlinepubs/9699919799/help/codes.html#CX then one might be baffled that malloc(0) still is underspecified or at least unpleasantly specified WRT realloc(NULL,0) after all these years in the wild. The exact quote from CX is ---8<--- [CX] [Option Start] Extension to the ISO C standard [Option End] The functionality described is an extension to the ISO C standard. Application developers may make use of an extension as it is supported on all POSIX.1-2017-conforming systems. With each function or header from the ISO C standard, a statement to the effect that "any conflict is unintentional" is included. That is intended to refer to a direct conflict. POSIX.1-2017 acts in part as a profile of the ISO C standard, and it may choose to further constrain behaviors allowed to vary by the ISO C standard. Such limitations and other compatible differences are not considered conflicts, even if a CX mark is missing. The markings are for information only. Where additional semantics apply to a function or header, the material is identified by use of the CX margin legend. ---8<--- So, what in the end this all gives is IMHO that natural stuff like valid C or C++ can only borderline elide any of these calls which hinders everyone and helps nobody for real IMHO. Doesn't it. That's how conceptually devirt does it's thing for just a very particular flavour of the family and rightfully leaves the rest alone, which really is a pity IMHO. But that's enough as far as an unfounded rant goes for today and should probably be addressed elsewhere either way. So, please remind me, why, again, does C do it's life ptr thing, short of an optimisation barrier? thanks,
