比較でnumeric_stdを使うと便利

cmp_test.vhd

library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;

entity cmp_test is
  port (
    Q0 : out std_logic;
    Q1 : out std_logic);
end entity cmp_test;

architecture rtl of cmp_test is
  constant A : std_logic_vector (31 downto 0) := x"f1010100";
  constant B : std_logic_vector (31 downto 0) := x"01010100";
begin  -- architecture rtl

  with signed (A) < signed (B) select
    Q0 <=
    '1' when true,
    '0' when others;

  with unsigned (A) < unsigned (B) select
    Q1 <=
    '1' when true,
    '0' when others;

end architecture rtl;