[Bug middle-end/32758] [4.3 Regression] ecj1 hangs

["jakub at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #26 from jakub at gcc dot gnu dot org  2007-08-29 13:56 -------
Apparently dce is the only user of df_simulate_* which at the start of the
basic block compares the resulting bitmap with DF_LR_IN.  All other users
of these interfaces don't do that (ifcvt, rtl-factoring, peephole2).
And df-problems.c which computes DF_LR_IN doesn't or in the regular or eh
artificial uses bitmap in every step.
So, if fast dce is to keep comparing the local_live bitmap with DF_LR_IN
(and it probably needs to, since if some insns are marked to be deleted,
it needs to update it), local_live has to be computed the same way as it is
now.

So either we just check either local_live or au bitmaps:

--- dce.c.jj    2007-08-13 15:11:18.000000000 +0200
+++ dce.c       2007-08-29 15:37:57.000000000 +0200
@@ -527,6 +527,7 @@ static bool
 dce_process_block (basic_block bb, bool redo_out)
 {
   bitmap local_live = BITMAP_ALLOC (&dce_tmp_bitmap_obstack);
+  bitmap au;
   rtx insn;
   bool block_changed;
   struct df_ref **def_rec, **use_rec;
@@ -569,6 +570,15 @@ dce_process_block (basic_block bb, bool 
        bitmap_set_bit (local_live, DF_REF_REGNO (use));
     }

+  /* These regs are considered always live so if they end up dying
+     because of some def, we need to bring the back again.
+     Calling df_simulate_fixup_sets has the disadvantage of calling
+     df_has_eh_preds once per insn, so we cache the information here.  */
+  if (df_has_eh_preds (bb))
+    au = df->eh_block_artificial_uses;
+  else
+    au = df->regular_block_artificial_uses;
+
   FOR_BB_INSNS_REVERSE (bb, insn)
     if (INSN_P (insn))
       {
@@ -580,7 +590,8 @@ dce_process_block (basic_block bb, bool 

            /* The insn is needed if there is someone who uses the output.  */
            for (def_rec = DF_INSN_DEFS (insn); *def_rec; def_rec++)
-             if (bitmap_bit_p (local_live, DF_REF_REGNO (*def_rec)))
+             if (bitmap_bit_p (local_live, DF_REF_REGNO (*def_rec))
+                 || bitmap_bit_p (au, DF_REG_REGNO (*def_rec)))
                {
                  needed = true;
                  break;

or add another bitmap:

--- dce.c.jj    2007-08-13 15:11:18.000000000 +0200
+++ dce.c       2007-08-29 15:41:48.000000000 +0200
@@ -527,6 +527,8 @@ static bool
 dce_process_block (basic_block bb, bool redo_out)
 {
   bitmap local_live = BITMAP_ALLOC (&dce_tmp_bitmap_obstack);
+  bitmap local_live_or_au = BITMAP_ALLOC (&dce_tmp_bitmap_obstack);
+  bitmap au;
   rtx insn;
   bool block_changed;
   struct df_ref **def_rec, **use_rec;
@@ -569,6 +571,16 @@ dce_process_block (basic_block bb, bool 
        bitmap_set_bit (local_live, DF_REF_REGNO (use));
     }

+  /* These regs are considered always live so if they end up dying
+     because of some def, we need to bring the back again.
+     Calling df_simulate_fixup_sets has the disadvantage of calling
+     df_has_eh_preds once per insn, so we cache the information here.  */
+  if (df_has_eh_preds (bb))
+    au = df->eh_block_artificial_uses;
+  else
+    au = df->regular_block_artificial_uses;
+  bitmap_ior (local_live_or_au, local_live, au);
+
   FOR_BB_INSNS_REVERSE (bb, insn)
     if (INSN_P (insn))
       {
@@ -580,7 +592,7 @@ dce_process_block (basic_block bb, bool 

            /* The insn is needed if there is someone who uses the output.  */
            for (def_rec = DF_INSN_DEFS (insn); *def_rec; def_rec++)
-             if (bitmap_bit_p (local_live, DF_REF_REGNO (*def_rec)))
+             if (bitmap_bit_p (local_live_or_au, DF_REF_REGNO (*def_rec)))
                {
                  needed = true;
                  break;
@@ -600,6 +612,7 @@ dce_process_block (basic_block bb, bool 
                    if (dump_file)
                      fprintf (dump_file, "needed libcall %d\n", INSN_UID
(insn));
                    mark_libcall (insn, true);
+                   BITMAP_FREE (local_live_or_au);
                    BITMAP_FREE (local_live);
                    return dce_process_block (bb, false);
                  }
@@ -616,6 +629,8 @@ dce_process_block (basic_block bb, bool 
           anything in local_live.  */
        if (marked_insn_p (insn))
          df_simulate_uses (insn, local_live);
+
+       bitmap_ior (local_live_or_au, local_live, au);
       }

   for (def_rec = df_get_artificial_defs (bb_index); *def_rec; def_rec++)
@@ -640,6 +655,7 @@ dce_process_block (basic_block bb, bool 
   if (block_changed)
     bitmap_copy (DF_LR_IN (bb), local_live);

+  BITMAP_FREE (local_live_or_au);
   BITMAP_FREE (local_live);
   return block_changed;
 }

The latter might be faster, but I'm not 100% sure about that.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32758