Re: [04/05] Fix PR 69032

[Alexander Monakov <amonakov@ispras.ru>]

On Mon, 14 Mar 2016, Andrey Belevantsev wrote:
> We fail to find the proper seqno for the fresh bookkeeping copy in this PR.
> The problem is that in get_seqno_by_preds we are iterating over bb from the
> given insn backwards up to the first bb insn.  We skip the initial insn when
> iterating over bb, yet we should take seqno from it.
> 
> The code in question originally didn't include bb head when iterating, and was
> patched to do so in 2011.  The patch was wrong and instead of including bb
> head managed to exclude the original insn itself.  By reading the original and
> patched code I've convinced myself that the right fix will be to do what the
> patch intended and include both the initial insn and the bb head in the
> iteration.
> 
> Ok for trunk?
> 
> gcc/
> 
> 2016-03-14  Andrey Belevantsev  <abel@ispras.ru>
> 
>     PR rtl-optimization/69032
>     * sel-sched-ir.c (get_seqno_by_preds): Include both tmp and head when 
> looping backwards over basic block insns.

"both 'insn' and 'head'" (not tmp).

> diff --git a/gcc/sel-sched-ir.c b/gcc/sel-sched-ir.c
> index ec59280..c1a9e55 100644
> --- a/gcc/sel-sched-ir.c
> +++ b/gcc/sel-sched-ir.c
> @@ -4103,11 +4103,14 @@ get_seqno_by_preds (rtx_insn *insn)
>    insn_t *preds;
>    int n, i, seqno;
>  
> -  while (tmp != head)
> +  /* Loop backwards from insn to head including both.  */

"from INSN to HEAD" (uppercase).

The following structure is equivalent, but would look a bit more canonical:

  for (rtx_insn *tmp = insn; ; tmp = PREV_INSN (tmp))
    {
      if (INSN_P (tmp))
	return INSN_SEQNO (tmp);
      if (tmp == head)
	break;
    }

> +  while (1)
>      {
> -      tmp = PREV_INSN (tmp);
>        if (INSN_P (tmp))
>          return INSN_SEQNO (tmp);
> +      if (tmp == head)
> +	break;
> +      tmp = PREV_INSN (tmp);
>      }
>  
>    cfg_preds (bb, &preds, &n);

OK with formatting nits fixed ('while'/'for' spelling change at your choice).

Thanks.
Alexander