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 <a...@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
