flowmap: construct a max-volume max-flow min-cut, not just any one.

diff --git a/passes/techmap/flowmap.cc b/passes/techmap/flowmap.cc
index 8c127cb65be0dedd0adc6274985f8639c2624ef2..be70b579ba1eef32a292a9a0480f2fd21db48295 100644 (file)
--- a/passes/techmap/flowmap.cc
+++ b/passes/techmap/flowmap.cc
@@ -51,7 +51,8 @@
 // 3. The paper ambiguously states: "Moreover, we can find such a cut (X′′, X̅′′) by performing a depth first search starting at the source s,
 // and including in X′′ all the nodes which are reachable from s." This actually refers to a specific kind of search, mincut computation.
 // Mincut computation involves computing the set of nodes reachable from s by an undirected path with no full (i.e. zero capacity) forward
-// edges or empty (i.e. no flow) backward edges.
+// edges or empty (i.e. no flow) backward edges. In addition, the depth first search is required to compute a max-volume max-flow min-cut
+// specifically, because a max-flow min-cut is not, in general, unique.
 
 #include "kernel/yosys.h"
 #include "kernel/sigtools.h"
@@ -356,10 +357,12 @@ struct FlowGraph
 
                NodePrime source_prime = {source, true};
                NodePrime sink_prime = {sink, false};
-               pool<NodePrime> worklist = {source_prime}, visited;
+               pool<NodePrime> visited;
+               vector<NodePrime> worklist = {source_prime};
                while (!worklist.empty())
                {
-                       auto node_prime = worklist.pop();
+                       auto node_prime = worklist.back();
+                       worklist.pop_back();
                        if (visited[node_prime])
                                continue;
                        visited.insert(node_prime);
@@ -372,18 +375,18 @@ struct FlowGraph
                        if (!node_prime.is_bottom) // top
                        {
                                if (node_flow[node_prime.node] < MAX_NODE_FLOW)
-                                       worklist.insert(node_prime.as_bottom());
+                                       worklist.push_back(node_prime.as_bottom());
                                for (auto node_pred : edges_bw[node_prime.node])
                                        if (edge_flow[{node_pred, node_prime.node}] > 0)
-                                               worklist.insert(NodePrime::bottom(node_pred));
+                                               worklist.push_back(NodePrime::bottom(node_pred));
                        }
                        else // bottom
                        {
                                if (node_flow[node_prime.node] > 0)
-                                       worklist.insert(node_prime.as_top());
+                                       worklist.push_back(node_prime.as_top());
                                for (auto node_succ : edges_fw[node_prime.node])
                                        if (true /* edge_flow[...] < ∞ */)
-                                               worklist.insert(NodePrime::top(node_succ));
+                                               worklist.push_back(NodePrime::top(node_succ));
                        }
                }