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Use vector-of-structs of preds/semi for Lengauer-Tarjan #408

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Use vector-of-structs of preds/semi for Lengauer-Tarjan #408

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b66a6cc
Use vector-of-structs of preds/semi for Lengauer-Tarjan
samolisov Dec 21, 2024
7c27b39
Remove the 'set_' members from 'preds' struct
samolisov Dec 29, 2024
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67 changes: 46 additions & 21 deletions include/boost/graph/dominator_tree.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -62,6 +62,25 @@ namespace detail
Tag >(timeMap, v, t);
}

// Auxiliary structure of different kinds of predecessors are used to
// calculate the semidominators: ancestor, semidominator, and the ancestor
// with the lowest semidominator (`best`). Placing these predecessors in a
// structure let us organize a "vector of structs" what improves cache
// efficiency.
template < class Graph > struct preds
{
preds()
: semi(graph_traits< Graph >::null_vertex())
, ancestor(graph_traits< Graph >::null_vertex())
, best(graph_traits< Graph >::null_vertex())
{
}

typedef typename graph_traits< Graph >::vertex_descriptor Vertex;

Vertex semi, ancestor, best;
};

template < class Graph, class IndexMap, class TimeMap, class PredMap,
class DomTreePredMap >
class dominator_visitor
Expand All @@ -80,13 +99,9 @@ namespace detail
*/
dominator_visitor(const Graph& g, const Vertex& entry,
const IndexMap& indexMap, DomTreePredMap domTreePredMap)
: semi_(num_vertices(g))
, ancestor_(num_vertices(g), graph_traits< Graph >::null_vertex())
, samedom_(ancestor_)
, best_(semi_)
, semiMap_(make_iterator_property_map(semi_.begin(), indexMap))
, ancestorMap_(make_iterator_property_map(ancestor_.begin(), indexMap))
, bestMap_(make_iterator_property_map(best_.begin(), indexMap))
: preds_(num_vertices(g))
, predsMap_(make_iterator_property_map(preds_.begin(), indexMap))
, samedom_(num_vertices(g), graph_traits< Graph >::null_vertex())
, buckets_(num_vertices(g))
, bucketMap_(make_iterator_property_map(buckets_.begin(), indexMap))
, entry_(entry)
Expand Down Expand Up @@ -132,18 +147,20 @@ namespace detail
if (get(dfnumMap, v) <= get(dfnumMap, n))
s2 = v;
else
s2 = get(semiMap_, ancestor_with_lowest_semi_(v, dfnumMap));
s2 = get(predsMap_, ancestor_with_lowest_semi_(v, dfnumMap))
.semi;

if (get(dfnumMap, s2) < get(dfnumMap, s))
s = s2;
}
put(semiMap_, n, s);
preds< Graph >& preds_of_n = get(predsMap_, n);
preds_of_n.semi = s;

// 2. Calculation of n's dominator is deferred until
// the path from s to n has been linked into the forest
get(bucketMap_, s).push_back(n);
get(ancestorMap_, n) = p;
get(bestMap_, n) = n;
preds_of_n.ancestor = p;
preds_of_n.best = n;

// 3. Now that the path from p to v has been linked into
// the spanning forest, these lines calculate the dominator of v,
Expand All @@ -161,7 +178,7 @@ namespace detail
{
const Vertex v(*buckItr);
const Vertex y(ancestor_with_lowest_semi_(v, dfnumMap));
if (get(semiMap_, y) == get(semiMap_, v))
if (get(predsMap_, y).semi == get(predsMap_, v).semi)
put(domTreePredMap_, v, p);
else
put(samedomMap, v, y);
Expand All @@ -177,24 +194,32 @@ namespace detail
const Vertex ancestor_with_lowest_semi_(
const Vertex& v, const TimeMap& dfnumMap)
{
const Vertex a(get(ancestorMap_, v));
const Vertex a(get(predsMap_, v).ancestor);
const preds< Graph >& preds_of_a = get(predsMap_, a);

if (get(ancestorMap_, a) != graph_traits< Graph >::null_vertex())
preds< Graph >& preds_of_v = get(predsMap_, v);

if (preds_of_a.ancestor != graph_traits< Graph >::null_vertex())
{
const Vertex b(ancestor_with_lowest_semi_(a, dfnumMap));
const preds< Graph >& preds_of_b = get(predsMap_, b);

put(ancestorMap_, v, get(ancestorMap_, a));
preds_of_v.ancestor = preds_of_a.ancestor;

if (get(dfnumMap, get(semiMap_, b))
< get(dfnumMap, get(semiMap_, get(bestMap_, v))))
put(bestMap_, v, b);
if (get(dfnumMap, preds_of_b.semi)
< get(dfnumMap, get(predsMap_, preds_of_v.best).semi))
preds_of_v.best = b;
}

return get(bestMap_, v);
return preds_of_v.best;
}

std::vector< Vertex > semi_, ancestor_, samedom_, best_;
PredMap semiMap_, ancestorMap_, bestMap_;
std::vector< preds< Graph > > preds_;
iterator_property_map< typename std::vector< preds< Graph > >::iterator,
IndexMap >
predsMap_;

std::vector< Vertex > samedom_;
std::vector< std::vector< Vertex > > buckets_;

iterator_property_map<
Expand Down
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