[rebalancer] initialize gain cache in initialize method instead of re…

…fine

Lazy gain cache initializiation can be invalid in deep multilevel since
it is possible that the wrong k is used (if initialization happens after
changeNumberOfBlocks).

Note: An alternative fix could work by saving both the original and the
current k in the gain cache.

mt-kahypar/partition/refinement/rebalancing/advanced_rebalancer.cpp

@@ -424,10 +424,6 @@ namespace impl {
  Metrics& best_metric) {
  auto& phg = utils::cast<PartitionedHypergraph>(hypergraph);
 
- if (!_gain_cache.isInitialized()) {
- _gain_cache.initializeGainCache(phg);
- }
-
  _overloaded_blocks.clear();
  _is_overloaded.assign(_context.partition.k, false);
  for (PartitionID k = 0; k < _context.partition.k; ++k) {
@@ -505,7 +501,10 @@ bool AdvancedRebalancer<GraphAndGainTypes>::refineImpl(mt_kahypar_partitioned_hy
 template <typename GraphAndGainTypes>
 void AdvancedRebalancer<GraphAndGainTypes>::initializeImpl(mt_kahypar_partitioned_hypergraph_t& hypergraph) {
  auto& phg = utils::cast<PartitionedHypergraph>(hypergraph);
- unused(phg);
+
+ if (!_gain_cache.isInitialized()) {
+ _gain_cache.initializeGainCache(phg);
+ }
 }
 
 template <typename GraphAndGainTypes>