https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89490
--- Comment #1 from Alan Modra <amodra at gmail dot com> --- Reduced C testcase, compile at -O1. static const unsigned char utf8_bom[3] = { 0xEF, 0xBB, 0xBF }; void plonk (unsigned char *p) { __builtin_memcpy (p, utf8_bom, 3); }