loop.c (check_dbra_loop): Use a vanilla loop reversal if the biv is used to…

loop.c (check_dbra_loop): Use a vanilla loop reversal if the biv is used to compute a giv or as some...

        * loop.c (check_dbra_loop): Use a vanilla loop reversal if the biv is
        used to compute a giv or as some other non-counting use.

From-SVN: r22684

gcc/ChangeLog

+Wed Sep 30 18:29:26 1998  Jeffrey A Law  (law@cygnus.com)
+
+	* loop.c (check_dbra_loop): Use a vanilla loop reversal if the biv is
+	used to compute a giv or as some other non-counting use.
+
 Wed Sep 30 18:19:27 1998  Michael Hayes  <m.hayes@elec.canterbury.ac.nz>
 
 	* regs.h (HARD_REGNO_CALLER_SAVE_MODE): New macro.

gcc/loop.c

@@ -6992,9 +6992,13 @@ check_dbra_loop (loop_end, insn_count, loop_start)
 	      if (initial_value == const0_rtx
 		  /* If we have a decrement_and_branch_on_count, prefer
 		     the NE test, since this will allow that instruction to
-		     be generated.  */
+		     be generated.  Note that we must use a vanilla loop
+		     reversal if the biv is used to calculate a giv or has
+		     a non-counting use.  */
 #if ! defined (HAVE_decrement_and_branch_until_zero) && defined (HAVE_decrement_and_branch_on_count)
-		  && (add_val != 1 || ! vtop)
+		  && (! (add_val == 1 && vtop
+		         && (bl->biv_count == 0
+			     || no_use_except_counting)))
 #endif
 		  && GET_CODE (comparison_value) == CONST_INT
 		     /* Now do postponed overflow checks on COMPARISON_VAL.  */
@@ -7007,7 +7011,9 @@ check_dbra_loop (loop_end, insn_count, loop_start)
 		  nonneg = 1;
 		  cmp_code = GE;
 		}
-	      else if (add_val == 1 && vtop)
+	      else if (add_val == 1 && vtop
+		       && (bl->biv_count == 0
+			   || no_use_except_counting))
 		{
 		  add_adjust = 0;
 		  cmp_code = NE;