[PATCH] Adjust nb_iterations_upper_bound in loop header copying

[Richard Biener]

This patch decrements nb_iterations_upper_bound by one after we copied
the loop header.  This allows niter + 1 to more often not overflow.

Bootstrapped and tested on x86_64-unknown-linux-gnu, installed to trunk.

Richard.

2013-11-21  Richard Biener  <rguent...@suse.de>

        * tree-ssa-loop-ch.c (copy_loop_headers): Decrement
        nb_iterations_upper_bound by one.

Index: gcc/tree-ssa-loop-ch.c
===================================================================
--- gcc/tree-ssa-loop-ch.c      (revision 205097)
+++ gcc/tree-ssa-loop-ch.c      (working copy)
@@ -243,6 +243,16 @@ copy_loop_headers (void)
         are not now, since there was the loop exit condition.  */
       split_edge (loop_preheader_edge (loop));
       split_edge (loop_latch_edge (loop));
+
+      /* We peeled off one iteration of the loop thus we can lower
+        the maximum number of iterations if we have a previously
+        recorded value for that.  */
+      double_int max;
+      if (get_max_loop_iterations (loop, &max))
+       {
+         max -= double_int_one;
+         loop->nb_iterations_upper_bound = max;
+       }
     }
 
   update_ssa (TODO_update_ssa);