[PATCH] middle-end: Add debug function to dump dominator tree in dot format

[Alex Coplan]

Hi,

This adds a debug function to dump the dominator tree in dot/graphviz
format.  The idea is that the function can be called in GDB, the output
copy/pasted into a .dot file and then rendered using graphviz.

Bootstrapped/regtested on aarch64-linux-gnu, OK for trunk?

Thanks,
Alex

gcc/ChangeLog:

        * dominance.cc (debug_dominance_tree_dot): New.

diff --git a/gcc/dominance.cc b/gcc/dominance.cc
index 0357210ed27..b536f193abc 100644
--- a/gcc/dominance.cc
+++ b/gcc/dominance.cc
@@ -1658,6 +1658,20 @@ debug_dominance_info (enum cdi_direction dir)
       fprintf (stderr, "%i %i\n", bb->index, bb2->index);
 }
 
+/* Print the dominance tree (in direction DIR) in dot form.  This allows easily
+   visualizing the tree using graphviz.  */
+
+DEBUG_FUNCTION void
+debug_dominance_tree_dot (enum cdi_direction dir)
+{
+  fprintf (stderr, "digraph {\n");
+  basic_block bb, idom;
+  FOR_EACH_BB_FN (bb, cfun)
+    if ((idom = get_immediate_dominator (dir, bb)))
+      fprintf (stderr, "%i -> %i;\n", idom->index, bb->index);
+  fprintf (stderr, "}\n");
+}
+
 /* Prints to stderr representation of the dominance tree (for direction DIR)
    rooted in ROOT, indented by INDENT tabulators.  If INDENT_FIRST is false,
    the first line of the output is not indented.  */