From a2792785fe02e28de17dd74a7541accb990602b2 Mon Sep 17 00:00:00 2001
From: Geza Lore <gezalore@gmail.com>
Date: Mon, 2 May 2022 09:42:12 +0100
Subject: [PATCH] Add V3GraphVertex::dotRank to add GraphViz ranks to graph
 dumps

This is a simple debugging aid to allow constraining the graph layout
via GraphViz rank directives. Note this is not related in any way to the
vertex 'rank' attribute used by some of the graph algorithms.

No functional change.
---
 src/V3Graph.cpp | 33 ++++++++++++++++++++++++++++++++-
 src/V3Graph.h   |  1 +
 2 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/src/V3Graph.cpp b/src/V3Graph.cpp
index d47b786a6..1b5bc1ae4 100644
--- a/src/V3Graph.cpp
+++ b/src/V3Graph.cpp
@@ -23,6 +23,8 @@
 
 #include <map>
 #include <memory>
+#include <unordered_map>
+#include <unordered_set>
 #include <vector>
 
 int V3Graph::s_debug = 0;
@@ -325,11 +327,19 @@ void V3Graph::dumpDotFile(const string& filename, bool colorAsSubgraph) const {
     *logp << "\t\t rankdir=" << dotRankDir() << "];\n";
 
     // List of all possible subgraphs
+    // Collections of explicit ranks
+    std::unordered_set<std::string> ranks;
+    std::unordered_multimap<std::string, V3GraphVertex*> rankSets;
     std::multimap<std::string, V3GraphVertex*> subgraphs;
     for (V3GraphVertex* vertexp = verticesBeginp(); vertexp; vertexp = vertexp->verticesNextp()) {
         const string vertexSubgraph
             = (colorAsSubgraph && vertexp->color()) ? cvtToStr(vertexp->color()) : "";
         subgraphs.emplace(vertexSubgraph, vertexp);
+        const string& dotRank = vertexp->dotRank();
+        if (!dotRank.empty()) {
+            ranks.emplace(dotRank);
+            rankSets.emplace(dotRank, vertexp);
+        }
     }
 
     // We use a map here, as we don't want to corrupt anything (userp) in the graph,
@@ -346,7 +356,10 @@ void V3Graph::dumpDotFile(const string& filename, bool colorAsSubgraph) const {
         if (subgr != vertexSubgraph) {
             if (subgr != "") *logp << "\t};\n";
             subgr = vertexSubgraph;
-            if (subgr != "") *logp << "\tsubgraph cluster_" << subgr << " {\n";
+            if (subgr != "") {
+                *logp << "\tsubgraph cluster_" << subgr << " {\n";
+                *logp << "\tlabel=\"" << subgr << "\"\n";
+            }
         }
         if (subgr != "") *logp << "\t";
         *logp << "\tn" << vertexp->dotName() << (n++) << "\t[fontsize=8 "
@@ -382,6 +395,24 @@ void V3Graph::dumpDotFile(const string& filename, bool colorAsSubgraph) const {
             }
         }
     }
+
+    // Print ranks
+    for (auto dotRank : ranks) {
+        *logp << "\t{ rank=";
+        if (dotRank != "sink" && dotRank != "source" && dotRank != "min" && dotRank != "max") {
+            *logp << "same";
+        } else {
+            *logp << dotRank;
+        }
+        *logp << "; ";
+        auto bounds = rankSets.equal_range(dotRank);
+        for (auto it{bounds.first}; it != bounds.second; ++it) {
+            if (it != bounds.first) *logp << ", ";
+            *logp << 'n' << numMap[it->second] << "";
+        }
+        *logp << " }\n";
+    }
+
     // Vertex::m_user end, now unused
 
     // Trailer
diff --git a/src/V3Graph.h b/src/V3Graph.h
index c8319f5a8..ae59fe4a4 100644
--- a/src/V3Graph.h
+++ b/src/V3Graph.h
@@ -218,6 +218,7 @@ public:
     virtual string dotShape() const { return ""; }
     virtual string dotStyle() const { return ""; }
     virtual string dotName() const { return ""; }
+    virtual string dotRank() const { return ""; }
     virtual uint32_t rankAdder() const { return 1; }
     virtual FileLine* fileline() const { return nullptr; }  // nullptr for unknown
     virtual int sortCmp(const V3GraphVertex* rhsp) const {