timing: Add topological sort from Yosys

Signed-off-by: gatecat <gatecat@ds0.me>

3 files changed, 130 insertions, 0 deletions

diff --git a/common/timing.cc b/common/timing.cc
index 785f9e7b..f642153f 100644
--- a/common/timing.cc
+++ b/common/timing.cc
@@ -34,6 +34,7 @@ void TimingAnalyser::setup()
 {
     init_ports();
     get_cell_delays();
+    topo_sort();
 }
 
 void TimingAnalyser::init_ports()
@@ -43,6 +44,7 @@ void TimingAnalyser::init_ports()
         CellInfo *ci = cell.second;
         for (auto port : sorted_ref(ci->ports)) {
             auto &data = ports[CellPortKey(ci->name, port.first)];
+            data.type = port.second.type;
             data.cell_port = CellPortKey(ci->name, port.first);
         }
     }
@@ -118,6 +120,44 @@ void TimingAnalyser::get_cell_delays()
     }
 }
 
+void TimingAnalyser::topo_sort()
+{
+    TopoSort<CellPortKey> topo;
+    for (auto &port : ports) {
+        auto &pd = port.second;
+        // All ports are nodes
+        topo.node(port.first);
+        if (pd.type == PORT_IN) {
+            // inputs: combinational arcs through the cell are edges
+            for (auto &arc : pd.cell_arcs) {
+                if (arc.type != CellArc::COMBINATIONAL)
+                    continue;
+                topo.edge(port.first, CellPortKey(port.first.cell, arc.other_port));
+            }
+        } else if (pd.type == PORT_OUT) {
+            // output: routing arcs are edges
+            const NetInfo *pn = port_info(port.first).net;
+            if (pn != nullptr) {
+                for (auto &usr : pn->users)
+                    topo.edge(port.first, CellPortKey(usr));
+            }
+        }
+    }
+    bool no_loops = topo.sort();
+    if (!no_loops) {
+        log_info("Found %d combinational loops:\n", int(topo.loops.size()));
+        int i = 0;
+        for (auto &loop : topo.loops) {
+            log_info("    loop %d:\n", ++i);
+            for (auto &port : loop) {
+                log_info("        %s.%s (%s)\n", ctx->nameOf(port.cell), ctx->nameOf(port.port),
+                         ctx->nameOf(port_info(port).net));
+            }
+        }
+    }
+    std::swap(topological_order, topo.sorted);
+}
+
 CellInfo *TimingAnalyser::cell_info(const CellPortKey &key) { return ctx->cells.at(key.cell).get(); }
 
 PortInfo &TimingAnalyser::port_info(const CellPortKey &key) { return ctx->cells.at(key.cell)->ports.at(key.port); }
diff --git a/common/timing.h b/common/timing.h
index 9c15911d..e07dc105 100644
--- a/common/timing.h
+++ b/common/timing.h
@@ -45,6 +45,10 @@ struct CellPortKey
         }
     };
     inline bool operator==(const CellPortKey &other) const { return (cell == other.cell) && (port == other.port); }
+    inline bool operator<(const CellPortKey &other) const
+    {
+        return cell == other.cell ? port < other.port : cell < other.cell;
+    }
 };
 
 struct NetPortKey
@@ -104,6 +108,7 @@ struct TimingAnalyser
   private:
     void init_ports();
     void get_cell_delays();
+    void topo_sort();
     // To avoid storing the domain tag structure (which could get large when considering more complex constrained tag
     // cases), assign each domain an ID and use that instead
     typedef int domain_id_t;
@@ -153,6 +158,7 @@ struct TimingAnalyser
     {
         CellPortKey cell_port;
         NetPortKey net_port;
+        PortType type;
         // per domain timings
         std::unordered_map<domain_id_t, PortDomainData> domains;
         // cell timing arcs to (outputs)/from (inputs)  from this port
@@ -168,6 +174,8 @@ struct TimingAnalyser
     std::unordered_map<ClockDomainKey, domain_id_t, ClockDomainKey::Hash> domain_to_id;
     std::vector<ClockDomainKey> id_to_domain;
 
+    std::vector<CellPortKey> topological_order;
+
     Context *ctx;
 };
 
diff --git a/common/util.h b/common/util.h
index 55718344..ce2b4da1 100644
--- a/common/util.h
+++ b/common/util.h
@@ -181,6 +181,88 @@ template <typename ForwardRange> inline auto get_only_value(ForwardRange r)
     return get_only_value(b, e);
 }
 
+// From Yosys
+// https://github.com/YosysHQ/yosys/blob/0fb4224ebca86156a1296b9210116d9a9cbebeed/kernel/utils.h#L131
+template <typename T, typename C = std::less<T>> struct TopoSort
+{
+    bool analyze_loops, found_loops;
+    std::map<T, std::set<T, C>, C> database;
+    std::set<std::set<T, C>> loops;
+    std::vector<T> sorted;
+
+    TopoSort()
+    {
+        analyze_loops = true;
+        found_loops = false;
+    }
+
+    void node(T n)
+    {
+        if (database.count(n) == 0)
+            database[n] = std::set<T, C>();
+    }
+
+    void edge(T left, T right)
+    {
+        node(left);
+        database[right].insert(left);
+    }
+
+    void sort_worker(const T &n, std::set<T, C> &marked_cells, std::set<T, C> &active_cells,
+                     std::vector<T> &active_stack)
+    {
+        if (active_cells.count(n)) {
+            found_loops = true;
+            if (analyze_loops) {
+                std::set<T, C> loop;
+                for (int i = int(active_stack.size()) - 1; i >= 0; i--) {
+                    loop.insert(active_stack[i]);
+                    if (active_stack[i] == n)
+                        break;
+                }
+                loops.insert(loop);
+            }
+            return;
+        }
+
+        if (marked_cells.count(n))
+            return;
+
+        if (!database.at(n).empty()) {
+            if (analyze_loops)
+                active_stack.push_back(n);
+            active_cells.insert(n);
+
+            for (auto &left_n : database.at(n))
+                sort_worker(left_n, marked_cells, active_cells, active_stack);
+
+            if (analyze_loops)
+                active_stack.pop_back();
+            active_cells.erase(n);
+        }
+
+        marked_cells.insert(n);
+        sorted.push_back(n);
+    }
+
+    bool sort()
+    {
+        loops.clear();
+        sorted.clear();
+        found_loops = false;
+
+        std::set<T, C> marked_cells;
+        std::set<T, C> active_cells;
+        std::vector<T> active_stack;
+
+        for (auto &it : database)
+            sort_worker(it.first, marked_cells, active_cells, active_stack);
+
+        NPNR_ASSERT(sorted.size() == database.size());
+        return !found_loops;
+    }
+};
+
 NEXTPNR_NAMESPACE_END
 
 #endif