[Bug target/100165] fmov could be used to zero out the upper bits instead of movi/zip or movi/ins with __builtin_shuffle and zero vector

["pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100165

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
For the ones which produce ins, it should be easy to modify the pattern to emit
fmov for those cases, that is `elt == 0`:

(define_insn "aarch64_simd_vec_set_zero<mode>"
  [(set (match_operand:VALLS_F16 0 "register_operand" "=w")
        (vec_merge:VALLS_F16
            (match_operand:VALLS_F16 1 "aarch64_simd_imm_zero" "")
            (match_operand:VALLS_F16 3 "register_operand" "0")
            (match_operand:SI 2 "immediate_operand" "i")))]
  "TARGET_SIMD && exact_log2 (INTVAL (operands[2])) >= 0"
  {
    int elt = ENDIAN_LANE_N (<nunits>, exact_log2 (INTVAL (operands[2])));
    operands[2] = GEN_INT ((HOST_WIDE_INT) 1 << elt);
    return "ins\\t%0.<Vetype>[%p2], <vwcore>zr";
  }
)