RE: Regression in target MIC compiler

["David Sherwood" <david dot sherwood at arm dot com>]

Hi Thomas,

If this looks like my fault I am happy to look into this and fix the bug
if you can tell me how to reproduce it. I recently changed GET_MODE_INNER (m)
to return 'm' itself if there is no inner mode and I thought I'd fixed up lto,
but it seems I got it wrong. It also sounds like there is another bug in this
area too - if I want to test this do I need to apply any other patches too?

Regards,
David.

> 
> Hi!
> 
> It seems as if David's Â[PATCH][1/N] Change GET_MODE_INNER to always
> return a non-void mode is relevant here:
> 
> On Tue, 4 Aug 2015 16:06:23 +0300, Ilya Verbin <iverbin@gmail.com> wrote:
> > On Tue, Aug 04, 2015 at 14:35:11 +0200, Thomas Schwinge wrote:
> > > On Fri, 31 Jul 2015 20:13:02 +0300, Ilya Verbin <iverbin@gmail.com> wrote:
> > > > On Fri, Jul 31, 2015 at 18:59:59 +0200, Jakub Jelinek wrote:
> > > > > > > On Wed, Feb 18, 2015 at 11:00:35 +0100, Jakub Jelinek wrote:
> > > > > > > +      /* First search just the GET_CLASS_NARROWEST_MODE to wider modes,
> > > > > > > +	 if not found, fallback to all modes.  */
> > > > > > > +      int pass;
> > > > > > > +      for (pass = 0; pass < 2; pass++)
> > > > > > > +	for (machine_mode mr = pass ? VOIDmode
> > > > > > > +				    : GET_CLASS_NARROWEST_MODE (mclass);
> > > > > > > +	     pass ? mr < MAX_MACHINE_MODE : mr != VOIDmode;
> > > > > > > +	     pass ? mr = (machine_mode) (m + 1)
> > > > > > > +		  : mr = GET_MODE_WIDER_MODE (mr))
> > > > > > > +	  if (GET_MODE_CLASS (mr) != mclass
> > > > > > > +	      || GET_MODE_SIZE (mr) != size
> > > > > > > +	      || GET_MODE_PRECISION (mr) != prec
> > > > > > > +	      || GET_MODE_INNER (mr) != inner
> > > > > > > +	      || GET_MODE_IBIT (mr) != ibit
> > > > > > > +	      || GET_MODE_FBIT (mr) != fbit
> > > > > > > +	      || GET_MODE_NUNITS (mr) != nunits)
> > > > > > > +	    continue;
> > > > > > >
> > > > > > > Given that gomp-4_1-branch works ok, the problem was introduced somewhere
> > > > > > > between 9 and 31 Jul.  I'll try to find the revision.
> > > > > >
> > > > > > Shouldn't 'mr' be here instead of 'm'?
> > > > >
> > > > > I think so.  If it works, patch preapproved.
> > > >
> > > > It fixes the infinite loop, but causes an error:
> > > > lto1: fatal error: unsupported mode QI
> > >
> > > Confirmed.
> > >
> > > > > But wonder what changed that we haven't been triggering it before.
> > > > > What mode do you think it on (mclass/size/prec/inner/ibit/fbit/nunits)?
> > > >
> > > > When in hangs, mr is HImode.
> > >
> > > Do you already have any further analysis, a workaround, or even a fix?
> >
> > Not yet.  I thought since Jakub is the author of this function, he could easily
> > point what is wrong here :)  Actually, intelmic doesn't require
> > lto_input_mode_table, so temporary workaround is just to disable it.
> 
> Well, avoiding lto_input_mode_table doesn't help us with nvptx
> offloading...  ;-)
> 
> Anyway, I found that if I revert r226328, Â[PATCH][1/N] Change
> GET_MODE_INNER to always return a non-void modeÂ,
> <https://gcc.gnu.org/ml/gcc-patches/2015-07/msg02350.html>, the problem
> goes away.  I'm trying, but I cannot claim yet to really understand this
> mode streaming code...  But, with the producer
> gcc/lto-streamer-out.c:lto_write_mode_table having been changed, does
> maybe the consumer gcc/lto-streamer-in.c:lto_input_mode_table also need
> to be updated accordingly?
> 
> For reference, David's change to
> gcc/lto-streamer-out.c:lto_write_mode_table:
> 
> @@ -2679,23 +2679,23 @@ lto_write_mode_table (void)
>    /* Ensure that for GET_MODE_INNER (m) != VOIDmode we have
>       also the inner mode marked.  */
>    for (int i = 0; i < (int) MAX_MACHINE_MODE; i++)
>      if (streamer_mode_table[i])
>        {
>  	machine_mode m = (machine_mode) i;
> -	if (GET_MODE_INNER (m) != VOIDmode)
> +	if (GET_MODE_INNER (m) != m)
>  	  streamer_mode_table[(int) GET_MODE_INNER (m)] = 1;
>        }
>    /* First stream modes that have GET_MODE_INNER (m) == VOIDmode,
>       so that we can refer to them afterwards.  */
>    for (int pass = 0; pass < 2; pass++)
>      for (int i = 0; i < (int) MAX_MACHINE_MODE; i++)
>        if (streamer_mode_table[i] && i != (int) VOIDmode && i != (int) BLKmode)
>  	{
>  	  machine_mode m = (machine_mode) i;
> -	  if ((GET_MODE_INNER (m) == VOIDmode) ^ (pass == 0))
> +	  if ((GET_MODE_INNER (m) == m) ^ (pass == 0))
>  	    continue;
>  	  bp_pack_value (&bp, m, 8);
>  	  bp_pack_enum (&bp, mode_class, MAX_MODE_CLASS, GET_MODE_CLASS (m));
>  	  bp_pack_value (&bp, GET_MODE_SIZE (m), 8);
>  	  bp_pack_value (&bp, GET_MODE_PRECISION (m), 16);
>  	  bp_pack_value (&bp, GET_MODE_INNER (m), 8);
> 
> (Also, the source code comments need to be updated?)
> 
> 
> GrÃÃe,
>  Thomas