Re: Question about gcse.c vs cc0

[Jeff Law <law at redhat dot com>]

On 05/29/2012 03:03 AM, Steven Bosscher wrote:
> Hello,
>
> In gcse.c:insert_insn_end_basic_block() I found the following code:
>
> #ifdef HAVE_cc0
>        /* FIXME: 'twould be nice to call prev_cc0_setter here but it aborts
>           if cc0 isn't set.  */
>        note = find_reg_note (insn, REG_CC_SETTER, NULL_RTX);
>        if (note)
>          insn = XEXP (note, 0);
>        else
>          {
>            rtx maybe_cc0_setter = prev_nonnote_insn (insn);
>            if (maybe_cc0_setter
>                &&  INSN_P (maybe_cc0_setter)
>                &&  sets_cc0_p (PATTERN (maybe_cc0_setter)))
>              insn = maybe_cc0_setter;
>          }
> #endif
>
> How can this work? As far as grep understands, only link_cc0_insns
> creates REG_CC_SETTER notes, but that function is only called from
> reorg.c (and even then, only if it makes a transformation). So NOTE
> will always be NULL.
>
> Are REG_CC_SETTER/REG_CC_USER notes supposed to exist before dbr_sched?
Well, we're talking about code that is 14 years old...  I really don't 
remember.

> P.S. The code goes on to use prev_nonnote_insn, which may cross basic
> block boundaries, so prev_nonnote_insn_bb should be used instead.
On a cc0 target, this is not true.

jeff