[Bug middle-end/30904] [dataflow] No longer optimizes shifts with large count

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

------- Comment #3 from bonzini at gnu dot org  2007-02-21 16:03 -------
This unrelated patch fixes a very similar case for powerpc

unpatched:
<       or r0,r3,r28
<       rlwinm r0,r0,0,0xff
<       cmpwi cr7,r0,0
<       beq- cr7,L4929

patched: (r3 and r28 are both extended from QImode)
>       or. r0,r3,r28
>       beq- cr0,L4929


With some luck, it does the same for this testcase too?  It would be nice to
examine why though. :-)

Sorry for the lack of professionality exhibited in this comment...

Index: combine.c
===================================================================
--- combine.c   (revision 122195)
+++ combine.c   (working copy)
@@ -1016,6 +1016,7 @@ combine_instructions (rtx f, unsigned in
 #endif
   rtx links, nextlinks;
   rtx first;
+  basic_block prev_basic_block;

   int new_direct_jump_p = 0;

@@ -1057,15 +1058,20 @@ combine_instructions (rtx f, unsigned in
      for what bits are known to be set.  */

   label_tick = label_tick_ebb_start = 1;
+  prev_basic_block = NULL;

   setup_incoming_promotions (first);
-
   create_log_links ();
+
   FOR_EACH_BB (this_basic_block)
     {
       last_call_luid = 0;
       mem_last_set = -1;
       label_tick++;
+      if (!single_pred_p (this_basic_block)
+         || single_pred (this_basic_block) != prev_basic_block)
+       label_tick_ebb_start = label_tick;
+
       FOR_BB_INSNS (this_basic_block, insn)
         if (INSN_P (insn) && BLOCK_FOR_INSN (insn))
          {
@@ -1090,8 +1096,8 @@ combine_instructions (rtx f, unsigned in
              fprintf(dump_file, "insn_cost %d: %d\n",
                    INSN_UID (insn), INSN_COST (insn));
          }
-       else if (LABEL_P (insn))
-         label_tick_ebb_start = label_tick;
+
+      prev_basic_block = this_basic_block;
     }

   nonzero_sign_valid = 1;
@@ -1099,6 +1105,8 @@ combine_instructions (rtx f, unsigned in
   /* Now scan all the insns in forward order.  */

   label_tick = label_tick_ebb_start = 1;
+  prev_basic_block = NULL;
+
   init_reg_last ();
   setup_incoming_promotions (first);

@@ -1107,6 +1115,10 @@ combine_instructions (rtx f, unsigned in
       last_call_luid = 0;
       mem_last_set = -1;
       label_tick++;
+      if (!single_pred_p (this_basic_block)
+          || single_pred (this_basic_block) != prev_basic_block)
+        label_tick_ebb_start = label_tick;
+     
       for (insn = BB_HEAD (this_basic_block);
           insn != NEXT_INSN (BB_END (this_basic_block));
           insn = next ? next : NEXT_INSN (insn))
@@ -1253,9 +1265,9 @@ combine_instructions (rtx f, unsigned in
            retry:
              ;
            }
-         else if (LABEL_P (insn))
-           label_tick_ebb_start = label_tick;
        }
+
+      prev_basic_block = this_basic_block;
     }

   clear_log_links ();


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30904