regclass.c (regclass): Properly compute loop_cost.

        * regclass.c (regclass): Properly compute loop_cost.  Adjust
        comments.

From-SVN: r31192

gcc/ChangeLog

 Tue Jan  4 00:18:46 2000  Jeffrey A Law  (law@cygnus.com)
 
+	* regclass.c (regclass): Properly compute loop_cost.  Adjust
+	comments.
+
 	* regclass.c: Fix minor whitespace problems.
 
 2000-01-03  Anthony Green  <green@cygnus.com>

gcc/regclass.c

@@ -1100,13 +1100,17 @@ regclass (f, nregs, dump)
 	    basic_block bb = BASIC_BLOCK (index);
 
 	    /* Show that an insn inside a loop is likely to be executed three
-	       times more than insns outside a loop.  This is much more aggressive
-	       than the assumptions made elsewhere and is being tried as an
-	       experiment.  */
+	       times more than insns outside a loop.  This is much more
+	       aggressive than the assumptions made elsewhere and is being
+	       tried as an experiment. 
+
+	       Note that a block's loop depth starts at zero, not one!  We
+	       must not subract one from the loop depth as that could give
+	       a negative shift count below.  */
 	    if (optimize_size)
 	      loop_cost = 1;
 	    else
-	      loop_cost = 1 << (2 * MIN (bb->loop_depth - 1, 5));
+	      loop_cost = 1 << (2 * MIN (bb->loop_depth, 5));
 	    for (insn = bb->head; ; insn = NEXT_INSN (insn))
 	      {
 		insn = scan_one_insn (insn, pass);