[Bug middle-end/121322] UBSAN error in find_bswap_or_nop (shift exponent 64 is too large for 64-bit type 'long unsigned int')

[jakub at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121322

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Reduced testcase:
unsigned long long
foo (unsigned long long *p)
{
  unsigned long long a = *p;
  unsigned long long b = __builtin_bswap64 (a);
  return ((b << 32)
          | ((b >> 8) & 0xff000000ULL)
          | ((b >> 24) & 0xff0000ULL)
          | ((b >> 40) & 0xff00ULL));
}
tmp_n is 0x403020105060700, the zero LSB byte is ignored and because the next
one is 7, (7 + 1) % 8 is 0.  We've already tried that and that didn't work, so
we should just punt.