entity dummy is
end dummy;

architecture sig of dummy is
  signal trigger, sum: integer:=0;
  signal sig1: integer:=1;
  signal sig2: integer:=2;
  signal sig3: integer:=3;
begin
  process
  begin
    wait on trigger;
    sig1 <= sig2 + sig3;
    sig2 <= sig1;
    sig3 <= sig2;
    sum <= sig1 + sig2 + sig3;
  end process;
end sig;