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

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whitequark 2019-01-06 19:51:37 +00:00
parent 2fcc1ee72e
commit 8b44198e23
1 changed files with 10 additions and 7 deletions
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17
passes/techmap/flowmap.cc
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@ -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, // 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. // 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 // 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/yosys.h"
#include "kernel/sigtools.h" #include "kernel/sigtools.h"
@ -356,10 +357,12 @@ struct FlowGraph
NodePrime source_prime = {source, true}; NodePrime source_prime = {source, true};
NodePrime sink_prime = {sink, false}; NodePrime sink_prime = {sink, false};
pool<NodePrime> worklist = {source_prime}, visited; pool<NodePrime> visited;
vector<NodePrime> worklist = {source_prime};
while (!worklist.empty()) while (!worklist.empty())
{ {
auto node_prime = worklist.pop(); auto node_prime = worklist.back();
worklist.pop_back();
if (visited[node_prime]) if (visited[node_prime])
continue; continue;
visited.insert(node_prime); visited.insert(node_prime);
@ -372,18 +375,18 @@ struct FlowGraph
if (!node_prime.is_bottom) // top if (!node_prime.is_bottom) // top
{ {
if (node_flow[node_prime.node] < MAX_NODE_FLOW) 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]) for (auto node_pred : edges_bw[node_prime.node])
if (edge_flow[{node_pred, node_prime.node}] > 0) if (edge_flow[{node_pred, node_prime.node}] > 0)
worklist.insert(NodePrime::bottom(node_pred)); worklist.push_back(NodePrime::bottom(node_pred));
} }
else // bottom else // bottom
{ {
if (node_flow[node_prime.node] > 0) 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]) for (auto node_succ : edges_fw[node_prime.node])
if (true /* edge_flow[...] < ∞ */) if (true /* edge_flow[...] < ∞ */)
worklist.insert(NodePrime::top(node_succ)); worklist.push_back(NodePrime::top(node_succ));
} }
} }