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

        comments.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@31192 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 8 insertions, 4 deletions

diff --git a/gcc/regclass.c b/gcc/regclass.c
index d25af735f02..667250c7cc6 100644
--- a/gcc/regclass.c
+++ b/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);