tree-optimization/114787 - more careful loop update with CFG cleanup

When CFG cleanup removes a backedge we have to be more careful with
loop update.  In particular we need to clear niter info and estimates
and if we remove the last backedge of a loop we have to also mark
it for removal to prevent a following basic block merging to associate
loop info with an unrelated header.

	PR tree-optimization/114787
	* tree-cfg.cc (remove_edge_and_dominated_blocks): When
	removing a loop backedge clear niter info and when removing
	the last backedge of a loop mark that loop for removal.

	* gcc.dg/torture/pr114787.c: New testcase.

gcc/testsuite/gcc.dg/torture/pr114787.c

@@ -0,0 +1,27 @@
+/* { dg-do run } */
+
+int a, b, c, d, e = -1, f, g, h, j, k, n, o, p;
+int main() {
+  int i, l = 2, m;
+  for (b = 0; b < 1; b++)
+    l = 0;
+  for (; a >= 0; a--)
+    for (m = 3; m; m--) {
+      k = g;
+      i = 0;
+      for (; i < 1; i++)
+        for (; f < 1; f++)
+          h = g;
+      n = 2 & ((e ^ d) | 1) * j;
+      o = ~(e & n);
+    q:
+      if (c <= e)
+        return 0;
+      e = o;
+    }
+  p = l;
+  l = 0;
+  if (p)
+    goto q;
+  return 0;
+}

gcc/tree-cfg.cc

@@ -9013,10 +9013,30 @@ remove_edge_and_dominated_blocks (edge e)
 
   /* If we are removing a path inside a non-root loop that may change
      loop ownership of blocks or remove loops.  Mark loops for fixup.  */
+  class loop *src_loop = e->src->loop_father;
   if (current_loops
-      && loop_outer (e->src->loop_father) != NULL
-      && e->src->loop_father == e->dest->loop_father)
-    loops_state_set (LOOPS_NEED_FIXUP);
+      && loop_outer (src_loop) != NULL
+      && src_loop == e->dest->loop_father)
+    {
+      loops_state_set (LOOPS_NEED_FIXUP);
+      /* If we are removing a backedge clear the number of iterations
+	 and estimates.  */
+      class loop *dest_loop = e->dest->loop_father;
+      if (e->dest == src_loop->header
+	  || (e->dest == dest_loop->header
+	      && flow_loop_nested_p (dest_loop, src_loop)))
+	{
+	  free_numbers_of_iterations_estimates (dest_loop);
+	  /* If we removed the last backedge mark the loop for removal.  */
+	  FOR_EACH_EDGE (f, ei, dest_loop->header->preds)
+	    if (f != e
+		&& (f->src->loop_father == dest_loop
+		    || flow_loop_nested_p (dest_loop, f->src->loop_father)))
+	      break;
+	  if (!f)
+	    mark_loop_for_removal (dest_loop);
+	}
+    }
 
   if (!dom_info_available_p (CDI_DOMINATORS))
     {