http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59890
--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> --- typedef unsigned long int mp_limb_t; typedef mp_limb_t * mp_ptr; typedef const mp_limb_t * mp_srcptr; typedef long int mp_size_t; mp_limb_t __quadmath_mpn_add_n (mp_ptr, mp_srcptr, mp_srcptr, mp_size_t); mp_limb_t __quadmath_mpn_addmul_1 (mp_ptr, mp_srcptr, mp_size_t, mp_limb_t); void __quadmath_mpn_impn_mul_n_basecase (mp_ptr prodp, mp_srcptr up, mp_srcptr vp, mp_size_t size) { mp_size_t i; mp_limb_t cy_limb; mp_limb_t v_limb = vp[0]; for (i = 1; i < size; i++) { if (v_limb <= 1) { cy_limb = 0; if (v_limb == 1) cy_limb = __quadmath_mpn_add_n (prodp, prodp, up, size); } else cy_limb = __quadmath_mpn_addmul_1 (prodp, up, size, v_limb); prodp[size] = cy_limb; } } fails to converge at -O2 -g -m32 with the patch applied.