[analyzer] Don't use shape=record in .dot output

[analyzer] Don't use shape=record in .dot output

[David Malcolm]

Recent versions of graphviz reject the .dot files emitted by the
analyzer, with messages such as:

  Warning: flat edge between adjacent nodes one of which has a record shape - replace records with HTML-like labels
    Edge node_9 -> node_8

The above warning seems to have been added to graphviz on 2014-07-25 in:
  https://gitlab.com/graphviz/graphviz/commit/763f02ef3cb7fbb62336f372b42279bd63266727

This patch reworks the .dot output from the analyzer so that it works
with newer graphviz (tested with graphviz-2.40.1-46.fc30.x86_64), and
adds DejaGnu test coverage that the .dot files can be parsed by "dot",
if installed on the host.

Successfully bootstrapped & regrtested on x86_64-pc-linux-gnu.

Pushed to branch "dmalcolm/analyzer" on the GCC git mirror.

gcc/ChangeLog:
	* analyzer/engine.cc (exploded_node::dump_dot): Replace
	'shape=record' with 'shape=none,margin=0' and eliminate outermost
	braces.
	(viz_callgraph_node::dump_dot): Replace 'shape=record' with
	'shape=none,margin=0' and use an HTML-like TABLE label.
	* analyzer/graphviz.cc (graphviz_out::begin_tr): New function.
	(graphviz_out::end_tr): New function.
	* analyzer/graphviz.h (graphviz_out::begin_tr): New decl.
	(graphviz_out::end_tr): New decl.
	* analyzer/region-model.cc (region::dump_dot_to_pp): Replace
	'shape=record' with 'shape=none,margin=0', and switch to
	non-record escaping.
	* analyzer/state-purge.cc
	(state_purge_annotator::add_node_annotations): Pass in a
	graphviz_out * rather than a pretty_printer *.  Replace
	'shape=record' with 'shape=none,margin=0' and eliminate outermost
	braces.
	(print_vec_of_names): Pass in a graphviz_out * rather than a
	pretty_printer *.  Wrap the output in a <TR><TD>.
	(state_purge_annotator::add_stmt_annotations): Pass in a
	graphviz_out * rather than a pretty_printer *.
	* analyzer/state-purge.h
	(state_purge_annotator::add_node_annotations): Pass in a
	graphviz_out * rather than a pretty_printer *.
	(state_purge_annotator::add_stmt_annotations): Likewise.
	* analyzer/supergraph.cc (supernode::dump_dot): Update for above
	annotator changes.  Replace 'shape=record' with
	'shape=none,margin=0' and convert label to an HTML-like TABLE.
	* analyzer/supergraph.h (dot_annotator::add_node_annotations):
	Pass in a graphviz_out * rather than a pretty_printer *.
	(dot_annotator::add_stmt_annotations): Likewise.
	* pretty-print.c (pp_write_text_as_html_like_dot_to_stream): New
	function.
	* pretty-print.h (pp_write_text_as_html_like_dot_to_stream): New decl.

gcc/testsuite/ChangeLog:
	* gcc.dg/analyzer/dot-output.c: New test.
	* lib/gcc-defs.exp (dg-check-dot): New procedure.
	* lib/target-supports-dg.exp (dg-require-dot): New procedure.
	* lib/target-supports.exp (check_dot_available): New procedure.
---
 gcc/analyzer/engine.cc                     | 30 +++++++++-----
 gcc/analyzer/graphviz.cc                   | 20 +++++++++
 gcc/analyzer/graphviz.h                    |  3 ++
 gcc/analyzer/region-model.cc               |  6 +--
 gcc/analyzer/state-purge.cc                | 29 +++++++------
 gcc/analyzer/state-purge.h                 |  4 +-
 gcc/analyzer/supergraph.cc                 | 44 +++++++++++++-------
 gcc/analyzer/supergraph.h                  |  4 +-
 gcc/pretty-print.c                         | 48 ++++++++++++++++++++++
 gcc/pretty-print.h                         |  3 ++
 gcc/testsuite/gcc.dg/analyzer/dot-output.c | 33 +++++++++++++++
 gcc/testsuite/lib/gcc-defs.exp             | 21 ++++++++++
 gcc/testsuite/lib/target-supports-dg.exp   | 10 +++++
 gcc/testsuite/lib/target-supports.exp      | 13 ++++++
 14 files changed, 224 insertions(+), 44 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/analyzer/dot-output.c

diff --git a/gcc/analyzer/engine.cc b/gcc/analyzer/engine.cc
index aa4a3590574d..e02ac7de6577 100644
--- a/gcc/analyzer/engine.cc
+++ b/gcc/analyzer/engine.cc
@@ -702,10 +702,8 @@ exploded_node::dump_dot (graphviz_out *gv, const dump_args_t &args) const
   pretty_printer *pp = gv->get_pp ();
 
   dump_dot_id (pp);
-  pp_printf (pp, " [shape=%s,style=filled,fillcolor=%s,label=\"",
-	     "record",
+  pp_printf (pp, " [shape=none,margin=0,style=filled,fillcolor=%s,label=\"",
 	     get_dot_fillcolor ());
-  pp_left_brace (pp);
   pp_write_text_to_stream (pp);
 
   pp_printf (pp, "EN: %i", m_index);
@@ -735,7 +733,6 @@ exploded_node::dump_dot (graphviz_out *gv, const dump_args_t &args) const
 
   pp_write_text_as_dot_label_to_stream (pp, /*for_record=*/true);
 
-  pp_right_brace (pp);
   pp_string (pp, "\"];\n\n");
   pp_flush (pp);
 }
@@ -3125,17 +3122,24 @@ public:
     pretty_printer *pp = gv->get_pp ();
 
     dump_dot_id (pp);
-    pp_printf (pp, " [shape=%s,style=filled,fillcolor=%s,label=\"",
-	       "record", "lightgrey");
-    pp_left_brace (pp);
+    pp_printf (pp, " [shape=none,margin=0,style=filled,fillcolor=%s,label=<",
+	       "lightgrey");
+    pp_string (pp, "<TABLE BORDER=\"0\">");
     pp_write_text_to_stream (pp);
 
+    gv->begin_tr ();
     pp_printf (pp, "VCG: %i: %s", m_index, function_name (m_fun));
+    gv->end_tr ();
     pp_newline (pp);
 
+    gv->begin_tr ();
     pp_printf (pp, "supernodes: %i\n", m_num_supernodes);
+    gv->end_tr ();
     pp_newline (pp);
+
+    gv->begin_tr ();
     pp_printf (pp, "superedges: %i\n", m_num_superedges);
+    gv->end_tr ();
     pp_newline (pp);
 
     if (args.m_eg)
@@ -3148,7 +3152,9 @@ public:
 	    if (enode->get_point ().get_function () == m_fun)
 	      num_enodes++;
 	  }
+	gv->begin_tr ();
 	pp_printf (pp, "enodes: %i\n", num_enodes);
+	gv->end_tr ();
 	pp_newline (pp);
 
 	// TODO: also show the per-callstring breakdown
@@ -3170,8 +3176,11 @@ public:
 	      }
 	    if (num_enodes > 0)
 	      {
+		gv->begin_tr ();
 		cs->print (pp);
 		pp_printf (pp, ": %i\n", num_enodes);
+		pp_write_text_as_html_like_dot_to_stream (pp);
+		gv->end_tr ();
 	      }
 	  }
 
@@ -3180,13 +3189,14 @@ public:
 	if (data)
 	  {
 	    pp_newline (pp);
+	    gv->begin_tr ();
 	    pp_printf (pp, "summaries: %i\n", data->m_summaries.length ());
+	    pp_write_text_as_html_like_dot_to_stream (pp);
+	    gv->end_tr ();
 	  }
       }
 
-    pp_write_text_as_dot_label_to_stream (pp, /*for_record=*/true);
-    pp_right_brace (pp);
-    pp_string (pp, "\"];\n\n");
+    pp_string (pp, "</TABLE>>];\n\n");
     pp_flush (pp);
   }
 
diff --git a/gcc/analyzer/graphviz.cc b/gcc/analyzer/graphviz.cc
index 46e719447d67..4ba9330cd8c8 100644
--- a/gcc/analyzer/graphviz.cc
+++ b/gcc/analyzer/graphviz.cc
@@ -79,3 +79,23 @@ graphviz_out::write_indent ()
   for (int i = 0; i < m_indent * 2; ++i)
     pp_space (m_pp);
 }
+
+/* Write the start of an HTML-like row via <TR><TD>, writing to the stream
+   so that followup text can be escaped.  */
+
+void
+graphviz_out::begin_tr ()
+{
+  pp_string (m_pp, "<TR><TD ALIGN=\"LEFT\">");
+  pp_write_text_to_stream (m_pp);
+}
+
+/* Write the end of an HTML-like row via </TD></TR>, writing to the stream
+   so that followup text can be escaped.  */
+
+void
+graphviz_out::end_tr ()
+{
+  pp_string (m_pp, "</TD></TR>");
+  pp_write_text_to_stream (m_pp);
+}
diff --git a/gcc/analyzer/graphviz.h b/gcc/analyzer/graphviz.h
index d097834502ad..7ddd4ce36c15 100644
--- a/gcc/analyzer/graphviz.h
+++ b/gcc/analyzer/graphviz.h
@@ -40,6 +40,9 @@ class graphviz_out {
 
   void write_indent ();
 
+  void begin_tr ();
+  void end_tr ();
+
   pretty_printer *get_pp () const { return m_pp; }
 
  private:
diff --git a/gcc/analyzer/region-model.cc b/gcc/analyzer/region-model.cc
index 197f1be23746..56aa44dae142 100644
--- a/gcc/analyzer/region-model.cc
+++ b/gcc/analyzer/region-model.cc
@@ -1210,11 +1210,11 @@ region::dump_dot_to_pp (const region_model &model,
 			pretty_printer *pp) const
 {
   this_rid.dump_node_name_to_pp (pp);
-  pp_printf (pp, " [shape=%s,style=filled,fillcolor=%s,label=\"",
-	     "record", "lightgrey");
+  pp_printf (pp, " [shape=none,margin=0,style=filled,fillcolor=%s,label=\"",
+	     "lightgrey");
   pp_write_text_to_stream (pp);
   print (model, this_rid, pp);
-  pp_write_text_as_dot_label_to_stream (pp, /*for_record=*/true);
+  pp_write_text_as_dot_label_to_stream (pp, /*for_record=*/false);
   pp_string (pp, "\"];");
   pp_newline (pp);
 
diff --git a/gcc/analyzer/state-purge.cc b/gcc/analyzer/state-purge.cc
index caaa94650e99..79eb5549197c 100644
--- a/gcc/analyzer/state-purge.cc
+++ b/gcc/analyzer/state-purge.cc
@@ -408,16 +408,17 @@ state_purge_per_ssa_name::process_point (const function_point &point,
    to the supernode N.  */
 
 void
-state_purge_annotator::add_node_annotations (pretty_printer *pp,
+state_purge_annotator::add_node_annotations (graphviz_out *gv,
 					     const supernode &n) const
 {
   if (m_map == NULL)
     return;
 
+  pretty_printer *pp = gv->get_pp ();
+
    pp_printf (pp, "annotation_for_node_%i", n.m_index);
-   pp_printf (pp, " [shape=%s,style=filled,fillcolor=%s,label=\"",
-       "record", "lightblue");
-   pp_left_brace (pp);
+   pp_printf (pp, " [shape=none,margin=0,style=filled,fillcolor=%s,label=\"",
+	      "lightblue");
    pp_write_text_to_stream (pp);
 
    // FIXME: passing in a NULL in-edge means we get no hits
@@ -442,23 +443,23 @@ POP_IGNORE_WFORMAT
        pp_newline (pp);
      }
 
-   pp_right_brace (pp);
-
    pp_string (pp, "\"];\n\n");
    pp_flush (pp);
 }
 
-/* Print V to PP as a comma-separated list in braces, titling it
-   with TITLE.
+/* Print V to GV as a comma-separated list in braces within a <TR>,
+   titling it with TITLE.
 
    Subroutine of state_purge_annotator::add_stmt_annotations.  */
 
 static void
-print_vec_of_names (pretty_printer *pp, const char *title,
+print_vec_of_names (graphviz_out *gv, const char *title,
 		    const auto_vec<tree> &v)
 {
+  pretty_printer *pp = gv->get_pp ();
   tree name;
   unsigned i;
+  gv->begin_tr ();
   pp_printf (pp, "%s: {", title);
   FOR_EACH_VEC_ELT (v, i, name)
     {
@@ -469,6 +470,8 @@ PUSH_IGNORE_WFORMAT
 POP_IGNORE_WFORMAT
     }
   pp_printf (pp, "}");
+  pp_write_text_as_html_like_dot_to_stream (pp);
+  gv->end_tr ();
   pp_newline (pp);
 }
 
@@ -478,7 +481,7 @@ POP_IGNORE_WFORMAT
    Add text showing which names are purged at STMT.  */
 
 void
-state_purge_annotator::add_stmt_annotations (pretty_printer *pp,
+state_purge_annotator::add_stmt_annotations (graphviz_out *gv,
 					     const gimple *stmt) const
 {
   if (m_map == NULL)
@@ -487,6 +490,8 @@ state_purge_annotator::add_stmt_annotations (pretty_printer *pp,
   if (stmt->code == GIMPLE_PHI)
     return;
 
+  pretty_printer *pp = gv->get_pp ();
+
   pp_newline (pp);
 
   const supernode *supernode = m_map->get_sg ().get_supernode_for_stmt (stmt);
@@ -511,6 +516,6 @@ state_purge_annotator::add_stmt_annotations (pretty_printer *pp,
 	}
     }
 
-  print_vec_of_names (pp, "needed here", needed);
-  print_vec_of_names (pp, "not needed here", not_needed);
+  print_vec_of_names (gv, "needed here", needed);
+  print_vec_of_names (gv, "not needed here", not_needed);
 }
diff --git a/gcc/analyzer/state-purge.h b/gcc/analyzer/state-purge.h
index a86afc28ccb9..f50c239503ea 100644
--- a/gcc/analyzer/state-purge.h
+++ b/gcc/analyzer/state-purge.h
@@ -157,10 +157,10 @@ class state_purge_annotator : public dot_annotator
 public:
   state_purge_annotator (const state_purge_map *map) : m_map (map) {}
 
-  void add_node_annotations (pretty_printer *pp, const supernode &n)
+  void add_node_annotations (graphviz_out *gv, const supernode &n)
     const FINAL OVERRIDE;
 
-  void add_stmt_annotations (pretty_printer *pp,const gimple *stmt)
+  void add_stmt_annotations (graphviz_out *gv, const gimple *stmt)
     const FINAL OVERRIDE;
 
 private:
diff --git a/gcc/analyzer/supergraph.cc b/gcc/analyzer/supergraph.cc
index da5b13a316ef..17cfe5d5f2d7 100644
--- a/gcc/analyzer/supergraph.cc
+++ b/gcc/analyzer/supergraph.cc
@@ -412,7 +412,7 @@ supergraph::add_return_superedge (supernode *src, supernode *dest,
 
 /* Implementation of dnode::dump_dot vfunc for supernodes.
 
-   Write a cluster for the node, and within it a record showing
+   Write a cluster for the node, and within it a .dot node showing
    the phi nodes and stmts.  Call into any node annotator from ARGS to
    potentially add other records to the cluster.  */
 
@@ -431,34 +431,41 @@ supernode::dump_dot (graphviz_out *gv, const dump_args_t &args) const
   pretty_printer *pp = gv->get_pp ();
 
   if (args.m_node_annotator)
-    args.m_node_annotator->add_node_annotations (pp, *this);
+    args.m_node_annotator->add_node_annotations (gv, *this);
 
   gv->write_indent ();
   dump_dot_id (pp);
-  pp_printf (pp, " [shape=%s,style=filled,fillcolor=%s,label=\"",
-	     "record", "lightgrey");
-  pp_left_brace (pp);
+  pp_printf (pp,
+	     " [shape=none,margin=0,style=filled,fillcolor=%s,label=<",
+	     "lightgrey");
+  pp_string (pp, "<TABLE BORDER=\"0\">");
   pp_write_text_to_stream (pp);
 
   if (m_returning_call)
     {
+      gv->begin_tr ();
       pp_string (pp, "returning call: ");
+      gv->end_tr ();
+
+      gv->begin_tr ();
       pp_gimple_stmt_1 (pp, m_returning_call, 0, (dump_flags_t)0);
+      pp_write_text_as_html_like_dot_to_stream (pp);
+      gv->end_tr ();
+
       if (args.m_node_annotator)
-	args.m_node_annotator->add_stmt_annotations (pp, m_returning_call);
-      pp_write_text_as_dot_label_to_stream (pp, /*for_record=*/true);
+	args.m_node_annotator->add_stmt_annotations (gv, m_returning_call);
       pp_newline (pp);
     }
 
   if (entry_p ())
     {
-      pp_string (pp, "ENTRY");
+      pp_string (pp, "<TR><TD>ENTRY</TD></TR>");
       pp_newline (pp);
     }
 
   if (return_p ())
     {
-      pp_string (pp, "EXIT");
+      pp_string (pp, "<TR><TD>EXIT</TD></TR>");
       pp_newline (pp);
     }
 
@@ -467,10 +474,14 @@ supernode::dump_dot (graphviz_out *gv, const dump_args_t &args) const
        !gsi_end_p (gpi); gsi_next (&gpi))
     {
       const gimple *stmt = gsi_stmt (gpi);
+      gv->begin_tr ();
       pp_gimple_stmt_1 (pp, stmt, 0, (dump_flags_t)0);
+      pp_write_text_as_html_like_dot_to_stream (pp);
+      gv->end_tr ();
+
       if (args.m_node_annotator)
-	args.m_node_annotator->add_stmt_annotations (pp, stmt);
-      pp_write_text_as_dot_label_to_stream (pp, /*for_record=*/true);
+	args.m_node_annotator->add_stmt_annotations (gv, stmt);
+
       pp_newline (pp);
     }
 
@@ -479,15 +490,18 @@ supernode::dump_dot (graphviz_out *gv, const dump_args_t &args) const
   gimple *stmt;
   FOR_EACH_VEC_ELT (m_stmts, i, stmt)
     {
+      gv->begin_tr ();
       pp_gimple_stmt_1 (pp, stmt, 0, (dump_flags_t)0);
+      pp_write_text_as_html_like_dot_to_stream (pp);
+      gv->end_tr ();
+
       if (args.m_node_annotator)
-	args.m_node_annotator->add_stmt_annotations (pp, stmt);
-      pp_write_text_as_dot_label_to_stream (pp, /*for_record=*/true);
+	args.m_node_annotator->add_stmt_annotations (gv, stmt);
+
       pp_newline (pp);
     }
 
-  pp_right_brace (pp);
-  pp_string (pp, "\"];\n\n");
+  pp_string (pp, "</TABLE>>];\n\n");
   pp_flush (pp);
 
   /* Terminate "subgraph" */
diff --git a/gcc/analyzer/supergraph.h b/gcc/analyzer/supergraph.h
index 78ae93aa95d1..a13d6730b3ca 100644
--- a/gcc/analyzer/supergraph.h
+++ b/gcc/analyzer/supergraph.h
@@ -547,10 +547,10 @@ class dot_annotator
 {
  public:
   virtual ~dot_annotator () {}
-  virtual void add_node_annotations (pretty_printer *pp ATTRIBUTE_UNUSED,
+  virtual void add_node_annotations (graphviz_out *gv ATTRIBUTE_UNUSED,
 				     const supernode &n ATTRIBUTE_UNUSED)
     const {}
-  virtual void add_stmt_annotations (pretty_printer *pp ATTRIBUTE_UNUSED,
+  virtual void add_stmt_annotations (graphviz_out *gv ATTRIBUTE_UNUSED,
 				     const gimple *stmt ATTRIBUTE_UNUSED)
     const {}
 };
diff --git a/gcc/pretty-print.c b/gcc/pretty-print.c
index d5aa451c1453..4ab70c9470e0 100644
--- a/gcc/pretty-print.c
+++ b/gcc/pretty-print.c
@@ -906,6 +906,54 @@ pp_write_text_as_dot_label_to_stream (pretty_printer *pp, bool for_record)
   pp_clear_output_area (pp);
 }
 
+/* As pp_write_text_to_stream, but for GraphViz HTML-like strings.
+
+   Flush the formatted text of pretty-printer PP onto the attached stream,
+   escaping these characters
+     " & < >
+   using XML escape sequences.
+
+   http://www.graphviz.org/doc/info/lang.html#html states:
+      special XML escape sequences for ", &, <, and > may be necessary in
+      order to embed these characters in attribute values or raw text
+   This doesn't list "'" (which would normally be escaped in XML
+   as "&apos;" or in HTML as "&#39;");.
+
+   Experiments show that escaping "'" doesn't seem to be necessary.  */
+
+void
+pp_write_text_as_html_like_dot_to_stream (pretty_printer *pp)
+{
+  const char *text = pp_formatted_text (pp);
+  const char *p = text;
+  FILE *fp = pp_buffer (pp)->stream;
+
+  for (;*p; p++)
+    {
+      switch (*p)
+	{
+	case '"':
+	  fputs ("&quot;", fp);
+	  break;
+	case '&':
+	  fputs ("&amp;", fp);
+	  break;
+	case '<':
+	  fputs ("&lt;", fp);
+	  break;
+	case '>':
+	  fputs ("&gt;",fp);
+	  break;
+
+	default:
+	  fputc (*p, fp);
+	  break;
+	}
+    }
+
+  pp_clear_output_area (pp);
+}
+
 /* Wrap a text delimited by START and END into PRETTY-PRINTER.  */
 static void
 pp_wrap_text (pretty_printer *pp, const char *start, const char *end)
diff --git a/gcc/pretty-print.h b/gcc/pretty-print.h
index 493507d41419..86b9e869eeb7 100644
--- a/gcc/pretty-print.h
+++ b/gcc/pretty-print.h
@@ -393,8 +393,11 @@ extern void pp_indent (pretty_printer *);
 extern void pp_newline (pretty_printer *);
 extern void pp_character (pretty_printer *, int);
 extern void pp_string (pretty_printer *, const char *);
+
 extern void pp_write_text_to_stream (pretty_printer *);
 extern void pp_write_text_as_dot_label_to_stream (pretty_printer *, bool);
+extern void pp_write_text_as_html_like_dot_to_stream (pretty_printer *pp);
+
 extern void pp_maybe_space (pretty_printer *);
 
 extern void pp_begin_quote (pretty_printer *, bool);
diff --git a/gcc/testsuite/gcc.dg/analyzer/dot-output.c b/gcc/testsuite/gcc.dg/analyzer/dot-output.c
new file mode 100644
index 000000000000..586e14421e0e
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/analyzer/dot-output.c
@@ -0,0 +1,33 @@
+/* Verify that the various .dot output files from the analyzer are readable
+   by .dot.  */
+
+/* { dg-require-dot "" } */
+/* { dg-additional-options "-fdump-analyzer-callgraph -fdump-analyzer-exploded-graph -fdump-analyzer-state-purge -fdump-analyzer-supergraph" } */
+
+#include <stdlib.h>
+
+int some_call (int i, char ch)
+{
+  return i * i;
+}
+
+int *test (int *buf, int n, int *out)
+{
+  int i;
+  int *result = malloc (sizeof (int) * n);
+  
+  /* A loop, to ensure we have phi nodes.  */
+  for (i = 0; i < n; i++)
+    result[i] = buf[i] + i; /* { dg-warning "possibly-NULL" "" { xfail *-*-* } } */
+  /* TODO(xfail): why isn't the warning appearing? */
+
+  /* Example of a "'" (to test quoting).  */
+  *out = some_call (i, 'a');
+  
+  return result;
+}
+
+/* { dg-final { dg-check-dot "dot-output.c.callgraph.dot" } } */
+/* { dg-final { dg-check-dot "dot-output.c.eg.dot" } } */
+/* { dg-final { dg-check-dot "dot-output.c.state-purge.dot" } } */
+/* { dg-final { dg-check-dot "dot-output.c.supergraph.dot" } } */
diff --git a/gcc/testsuite/lib/gcc-defs.exp b/gcc/testsuite/lib/gcc-defs.exp
index 945b48afa398..44e583aba064 100644
--- a/gcc/testsuite/lib/gcc-defs.exp
+++ b/gcc/testsuite/lib/gcc-defs.exp
@@ -403,3 +403,24 @@ proc handle-dg-regexps { text } {
 
     return $text
 }
+
+# Verify that the initial arg is a valid .dot file
+# (by running dot -Tpng on it, and verifying the exit code is 0).
+
+proc dg-check-dot { args } {
+    verbose "dg-check-dot: args: $args" 2
+
+    set testcase [testname-for-summary]
+
+    set dotfile [lindex $args 0]
+    verbose "  dotfile: $dotfile" 2
+
+    set status [remote_exec host "dot" "-O -Tpng $dotfile"]
+    verbose "  status: $status" 2
+    if { [lindex $status 0] != 0 } {
+	fail "$testcase dg-check-dot $dotfile"
+	return 0
+    }
+
+    pass "$testcase dg-check-dot $dotfile"
+}
diff --git a/gcc/testsuite/lib/target-supports-dg.exp b/gcc/testsuite/lib/target-supports-dg.exp
index e1da57abcf7b..88c6bd9d7db8 100644
--- a/gcc/testsuite/lib/target-supports-dg.exp
+++ b/gcc/testsuite/lib/target-supports-dg.exp
@@ -180,6 +180,16 @@ proc dg-require-iconv { args } {
     }
 }
 
+# If this host does not have "dot", skip this test.
+
+proc dg-require-dot { args } {
+    verbose "dg-require-dot" 2
+    if { ![ check_dot_available ] } {
+	upvar dg-do-what dg-do-what
+        set dg-do-what [list [lindex ${dg-do-what} 0] "N" "P"]
+    }
+}
+
 # If this target does not have sufficient stack size, skip this test.
 
 proc dg-require-stack-size { args } {
diff --git a/gcc/testsuite/lib/target-supports.exp b/gcc/testsuite/lib/target-supports.exp
index 2ac2f08cb968..59e0540ee237 100644
--- a/gcc/testsuite/lib/target-supports.exp
+++ b/gcc/testsuite/lib/target-supports.exp
@@ -514,6 +514,19 @@ proc check_gc_sections_available { } {
     }]
 }
 
+# Returns 1 if "dot" is supported on the host.
+
+proc check_dot_available { } {
+    verbose "check_dot_available" 2
+
+    set status [remote_exec host "dot" "-V"]
+    verbose "  status: $status" 2
+    if { [lindex $status 0] != 0 } {
+	return 0
+    }
+    return 1
+}
+
 # Return 1 if according to target_info struct and explicit target list
 # target is supposed to support trampolines.
  
-- 
2.21.0