[dataflow] fix reversed logic in combine

[Kenneth Zadeck]

Paolo Bonzini wrote:
> combine is not really a local pass, it does some analysis on registers
> where the sole definition dominates all uses.  On trunk, it does so by
> looking at global_live_at_start having a pseudo for the entry basic
> block.  On dataflow-branch, it looks at the pseudo *not being in the
> DF_UR* problem.
>
> The logic in trunk's combine with respect to uninitialized variables is
> correct.  We have to look at DF_LR_IN for the entry basic block to
> find variables that are not used uninitialized, and that fixes the bug.
>
> In fact, the name of UR is misleading, as it is a forward problem that
> computes *initialized* registers.
>
> Ok?
I am going to fire this up on my 4 platforms and make sure nothing
explodes. 
but otherwise it looks ok.

Kenny

>
> Paolo
> ------------------------------------------------------------------------
>
> Index: combine.c
> ===================================================================
> --- combine.c	(revision 122195)
> +++ combine.c	(working copy)
> @@ -1351,8 +1351,8 @@ set_nonzero_bits_and_sign_copies (rtx x,
>        && REGNO (x) >= FIRST_PSEUDO_REGISTER
>        /* If this register is undefined at the start of the file, we can't
>  	 say what its contents were.  */
> -      && REGNO_REG_SET_P
> -         (DF_UR_IN (ENTRY_BLOCK_PTR->next_bb), REGNO (x))
> +      && ! REGNO_REG_SET_P
> +           (DF_LR_IN (ENTRY_BLOCK_PTR->next_bb), REGNO (x))
>        && GET_MODE_BITSIZE (GET_MODE (x)) <= HOST_BITS_PER_WIDE_INT)
>      {
>        if (set == 0 || GET_CODE (set) == CLOBBER)
> @@ -8648,8 +8648,8 @@ reg_nonzero_bits_for_combine (rtx x, enu
>                && DF_INSN_LUID (reg_stat[REGNO (x)].last_set) < subst_low_luid)
>  	  || (REGNO (x) >= FIRST_PSEUDO_REGISTER
>  	      && REG_N_SETS (REGNO (x)) == 1
> -	      && REGNO_REG_SET_P
> -	      (DF_UR_IN (ENTRY_BLOCK_PTR->next_bb), REGNO (x)))))
> +	      && !REGNO_REG_SET_P
> +	          (DF_LR_IN (ENTRY_BLOCK_PTR->next_bb), REGNO (x)))))
>      {
>        *nonzero &= reg_stat[REGNO (x)].last_set_nonzero_bits;
>        return NULL;
> @@ -8717,8 +8717,8 @@ reg_num_sign_bit_copies_for_combine (rtx
>                && DF_INSN_LUID (reg_stat[REGNO (x)].last_set) < subst_low_luid)
>  	  || (REGNO (x) >= FIRST_PSEUDO_REGISTER
>  	      && REG_N_SETS (REGNO (x)) == 1
> -	      && REGNO_REG_SET_P
> -	      (DF_UR_IN (ENTRY_BLOCK_PTR->next_bb), REGNO (x)))))
> +	      && !REGNO_REG_SET_P
> +	          (DF_LR_IN (ENTRY_BLOCK_PTR->next_bb), REGNO (x)))))
>      {
>        *result = reg_stat[REGNO (x)].last_set_sign_bit_copies;
>        return NULL;
> @@ -11613,8 +11613,8 @@ get_last_value_validate (rtx *loc, rtx i
>  	       live at the beginning of the function, it is always valid.  */
>  	    || (! (regno >= FIRST_PSEUDO_REGISTER
>  		   && REG_N_SETS (regno) == 1
> -		   && (REGNO_REG_SET_P
> -		       (DF_UR_IN (ENTRY_BLOCK_PTR->next_bb), regno)))
> +		   && !REGNO_REG_SET_P
> +		       (DF_LR_IN (ENTRY_BLOCK_PTR->next_bb), regno))
>  		&& reg_stat[j].last_set_label > tick))
>  	  {
>  	    if (replace)
> @@ -11723,8 +11723,8 @@ get_last_value (rtx x)
>        || (reg_stat[regno].last_set_label < label_tick_ebb_start
>  	  && (regno < FIRST_PSEUDO_REGISTER
>  	      || REG_N_SETS (regno) != 1
> -	      || ! (REGNO_REG_SET_P
> -		    (DF_UR_IN (ENTRY_BLOCK_PTR->next_bb), regno)))))
> +	      || REGNO_REG_SET_P
> +		 (DF_LR_IN (ENTRY_BLOCK_PTR->next_bb), regno))))
>      return 0;
>  
>    /* If the value was set in a later insn than the ones we are processing,
>