Jan Hubicka - Loop construction versus 0 frequency (original) (raw)

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• From: Jan Hubicka
• To: gcc-patches at gcc dot gnu dot org, rakdver at atrey dot karlin dot mff dot cuni dot cz
• Date: Sun, 4 Feb 2007 21:12:42 +0100
• Subject: Loop construction versus 0 frequency

Hi, while looking into some dumps I noticed that loop construction code makes interesting decisions when frequencies are 0. This patch fix the problem. The patch really just reindents and adds if (max_freq) guard for the whole profile driven code block.

Bootstrapped/regtested i686-linux, will commit it shortly.

Honza

* cfgloop.c (canonicalize_loop_headers): When frequencies are zero,
do not attempt to use them.

Index: cfgloop.c

--- cfgloop.c (revision 121572) +++ cfgloop.c (working copy) @@ -402,30 +404,33 @@ canonicalize_loop_headers (void) if (LATCH_EDGE (e) && EDGE_FREQUENCY (e) > max_freq) max_freq = EDGE_FREQUENCY (e);

•  FOR_EACH_EDGE (e, ei, header->preds)

• if (LATCH_EDGE (e) &&

•    EDGE_FREQUENCY (e) >= max_freq / HEAVY_EDGE_RATIO)

•  {

•    if (heavy)

•  if (max_freq)

• {

•  FOR_EACH_EDGE (e, ei, header->preds)

•    if (LATCH_EDGE (e) &&

•   EDGE_FREQUENCY (e) >= max_freq / HEAVY_EDGE_RATIO)
        {

•   is_heavy = 0;

•   break;

•   if (heavy)

•     {

•       is_heavy = 0;

•       break;

•     }

•   else

•     heavy = e;
        }

•    else

•      heavy = e;

•  }

•  if (is_heavy)

• {

•  /* Split out the heavy edge, and create inner loop for it.  */

•  mfb_kj_edge = heavy;

•  tmp_edge = make_forwarder_block (header, mfb_keep_just,

•               update_latch_info);

•  alloc_aux_for_block (tmp_edge->dest, sizeof (int));

•  HEADER_BLOCK (tmp_edge->dest) = 1;

•  alloc_aux_for_edge (tmp_edge, sizeof (int));

•  LATCH_EDGE (tmp_edge) = 0;

•  HEADER_BLOCK (header)--;

•  if (is_heavy)

•    {

•      /* Split out the heavy edge, and create inner loop for it.  */

•      mfb_kj_edge = heavy;

•      tmp_edge = make_forwarder_block (header, mfb_keep_just,

•                   update_latch_info);

•      alloc_aux_for_block (tmp_edge->dest, sizeof (int));

•      HEADER_BLOCK (tmp_edge->dest) = 1;

•      alloc_aux_for_edge (tmp_edge, sizeof (int));

•      LATCH_EDGE (tmp_edge) = 0;

•      HEADER_BLOCK (header)--;

•    }
  }
  
    if (HEADER_BLOCK (header) > 1)

• Follow-Ups:
  • Re: Loop construction versus 0 frequency
    * From: Zdenek Dvorak