https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93156
--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> --- (In reply to jim from comment #3) > Hi Andrew, thank you for the prompt investigation. > I'm probably just being dense, but how can the compiler ever generate code > for that null_ptr function that results in -1? It is not that null_ptr can result in -1 directly but rather if it is inlined and then later on passed to a non-null function, it will change it to be the non-null case. > > Your comment shows you know this already, but for others, here's a comment > from the sources in gnulib: > > /* If you want to know why this always returns NULL, read > https://en.wikipedia.org/wiki/Quadratic_residue#Prime_power_modulus . */ > I am saying that is not the best way of getting the compiler not to notice it as being a choice between a non-null and a null pointer. Using a volatile variable makes the compiler NOT do any optimization and will not see the non-null pointer choice. > Note that at least some versions of canonicalize_file_name *can* take a NULL > argument, so the use of the nonnull attribute in that declaration is wrong. The question comes, where is the nonnull attribute coming from? But I don't think it matters here. Using: static void * null_ptr (void) { typedef void *voidptr; volatile voidptr n = 0; return n; } Will allow all compilers not to optimize anything to be known about null_ptr() function even with inlining being involved.
