trivial df_analyse_1 fix

[Jan Hubicka]

Hi,
when dataflow is asked to compute only DU_CHAIN, it creates them empty,
because it forgets to create RU_CHAINS needed to compute RU needed to create
the DU_CHAIN.

This patch adds the missing flag.

Honza

Fri Sep 28 18:14:09 CEST 2001  Jan Hubicka  <jh@suse.cz>
	* df.c (df_analyse_1): Set DF_RU_CHAIN when DF_DU_CHAIN is set.
diff -Nrc3p /p2/cfg9/egcs/gcc/df.c gcc/df.c
*** /p2/cfg9/egcs/gcc/df.c	Thu Sep 20 18:33:13 2001
--- gcc/df.c	Thu Sep 27 14:03:31 2001
*************** df_analyse_1 (df, blocks, flags, update)
*** 2175,2185 ****
  
    dflags = 0;
    aflags = flags;
    if (flags & DF_UD_CHAIN)
      aflags |= DF_RD | DF_RD_CHAIN;
  
    if (flags & DF_DU_CHAIN)
!     aflags |= DF_RU;
  
    if (flags & DF_RU)
      aflags |= DF_RU_CHAIN;
--- 2164,2175 ----
  
    dflags = 0;
    aflags = flags;
+ 
    if (flags & DF_UD_CHAIN)
      aflags |= DF_RD | DF_RD_CHAIN;
  
    if (flags & DF_DU_CHAIN)
!     aflags |= DF_RU | DF_RU_CHAIN;
  
    if (flags & DF_RU)
      aflags |= DF_RU_CHAIN;