https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111268
--- Comment #10 from Richard Biener <rguenth at gcc dot gnu.org> ---
Btw, we have
(gdb) p debug (node)
t.c:3:6: note: node 0x3f341d0 (max_nunits=1, refcnt=1) vector(2) long unsigned
int
t.c:3:6: note: op: VEC_PERM_EXPR
t.c:3:6: note: stmt 0 _1 = BIT_FIELD_REF <values_7(D), 64, 0>;
t.c:3:6: note: stmt 1 _4 = BIT_FIELD_REF <values_7(D), 64, 64>;
t.c:3:6: note: lane permutation { 0[0] 0[1] }
t.c:3:6: note: children 0x3f34260
$1 = void
(gdb) p vtype
$2 = <vector_type 0x7ffff6ca6bd0 svuint64_t>
it looks like "compatibility" somehow requires/allows us to V_C_E the
permuted argument to a fixed length vector? Otherwise vect_build_slp_tree_1
of course could check the BIT_FIELD_REF args are fixed length.
