https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95556
--- Comment #8 from Jakub Jelinek <jakub at gcc dot gnu.org> --- (In reply to Jeff Davis from comment #7) > "...built-in functions are optimized into the normal string functions like > memcpy if the last argument is (size_t) -1..." > > My reading of the document lead me to believe that a last argument of -1 > *would* be a normal library call. And certainly should be with > -fno-builtin-memcpy, right? No. Because -fno-builtin-memcpy only disables the special behavior if one uses memcpy, when one uses __builtin_memcpy, it behaves always as builtin. And you are using __builtin___memcpy_chk which is also a builtin and thus not affected by -fno-builtin*. You can use -fno-builtin-__memcpy_chk but then you'll get __memcpy_chk calls if you call it that way. As I wrote, if you for whatever reason want to use the library call, e.g. always, you can just use -mmemcpy-strategy=libcall:-1:1 or so, but then even very small ones will not be done inline, which is not really beneficial.
