Author Name: Jeremy Bennett (@jeremybennett)
Original Redmine Issue: 555 from https://www.veripool.org
Original Date: 2012-08-27
Original Assignee: Jeremy Bennett (@jeremybennett)

I've been working on some utilities to analyze the DOT files generated by Verilator, using the GraphViz cgraph library (more about this shortly). Verilator labels its graphs by creating a custom node, nTITLE, formatted with a black box around it. However this is mildly inconvenient - it creates a "special" node, which has to be found to determine the title.

I've modified V3Graph.cpp to generate instead a "label" attribute for the graph title, along with labelloc and labeljust to position it at the top left of the graph. This is not quite as powerful visually as a custom node (you can't specify a box around it), but it avoids having a "special" node, and allows the graph title to be easily found. Details of the permitted attributes can be found at http://www.graphviz.org/doc/info/attrs.html

It seems from cgraph that GraphViz prefers DOT graph attributes to be specified as attributes of the graph entity, rather than just within the graph itself. I.e. rather than:

digraph v3graph {
         label="obj_dir/t_unopt_array/Vt_unopt_array_58_gate_opt.dot";
         labelloc=t;
         labeljust=l;
         //size="7.5,10";
         rankdir=TB;

Use

digraph v3graph {
         graph   [label="obj_dir/t_unopt_array/Vt_unopt_array_58_gate_opt.dot",
                  labelloc=t, labeljust=l,
                  //size="7.5,10",
                  rankdir=TB];

This patch also makes this change. Please pull the patch from the graphviz-fix branch at git://github.com/jeremybennett/verilator.git.