tree-optimization/110298 - CFG cleanup and stale nb_iterations

When unrolling we eventually kill nb_iterations info since it may
refer to removed SSA names.  But we do this only after cleaning
up the CFG which in turn can end up accessing it.  Fixed by
swapping the two.

	PR tree-optimization/110298
	* tree-ssa-loop-ivcanon.cc (tree_unroll_loops_completely):
	Clear number of iterations info before cleaning up the CFG.

	* gcc.dg/torture/pr110298.c: New testcase.

(cherry picked from commit 916add3bf6e46467e4391e358b11ecfbc4daa275)

gcc/testsuite/gcc.dg/torture/pr110298.c

@@ -0,0 +1,20 @@
+/* { dg-do compile } */
+
+int a, b, c, d, e;
+int f() {
+  c = 0;
+  for (; c >= 0; c--) {
+    d = 0;
+    for (; d <= 0; d++) {
+      e = 0;
+      for (; d + c + e >= 0; e--)
+        ;
+      a = 1;
+      b = 0;
+      for (; a; ++b)
+        a *= 2;
+      for (; b + d >= 0;)
+        return 0;
+    }
+  }
+}

gcc/tree-ssa-loop-ivcanon.cc

@@ -1486,15 +1486,16 @@ tree_unroll_loops_completely (bool may_increase_size, bool unroll_outer)
 	    }
 	  BITMAP_FREE (fathers);
 
+	  /* Clean up the information about numbers of iterations, since
+	     complete unrolling might have invalidated it.  */
+	  scev_reset ();
+
 	  /* This will take care of removing completely unrolled loops
 	     from the loop structures so we can continue unrolling now
 	     innermost loops.  */
 	  if (cleanup_tree_cfg ())
 	    update_ssa (TODO_update_ssa_only_virtuals);
 
-	  /* Clean up the information about numbers of iterations, since
-	     complete unrolling might have invalidated it.  */
-	  scev_reset ();
 	  if (flag_checking && loops_state_satisfies_p (LOOP_CLOSED_SSA))
 	    verify_loop_closed_ssa (true);
 	}