https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116016
--- Comment #16 from qinzhao at gcc dot gnu.org --- (In reply to Siddhesh Poyarekar from comment #15) > (In reply to qinzhao from comment #14) > > If we go with the category B (as I mentioned in Comment #9), define the new > > builtin as a regular builtin, > > Then, arbitrary pointer for the 1st parameter is fine. > > If we go with the category A, i.e, define the new builtin as a C language > > extension as a key word, then I think that > > The 1st parameter is better to be a FAM_exp. > > > > I think for our purpose of using this new builtin, defining it as a > > RID_BUITLIN should be enough. > > > > However, I am open to define it as a regular builtin and implement it in the > > middle-end. > > If there are no actual problems with associating a size expression with an > object then I'd lean towards making it arbitrary. > > Either way though, one thing the compiler would have to guard against (and > document) is the possibility of an object changing after this association is > made. This could either be due to reallocation or the pointer pointing to a > different object. The compiler can probably make out if this happens within > the function where this builtin is called, but if the object gets modified > in a different function which the compiler cannot see into, or in a > different thread in parallel, then it will be the responsibility of the user > to make sure that the modification gets reflected in the size expression > somehow. > > Also, I reckon this expression will have to become a barrier to code > reordering, similar to the .ACCESS_WITH_SIZE internal builtin. I guess that all the above is the complication if we implement this builtin as a regular builtin in middle-end. If we just simply define it as a C RID_BUILTIN (Please see gcc/c-family/c-common.), then this is just a language extension, user just use it as a simple C statement. In C FE, when see __builtin_set_counted_by (p->fam, count_exp) if has_counted_by_attribute (p->fam) p->count = count_exp; else ; then that's it. The compiler's responsibility is:
