Fix initialization of setBlockIndexCandidates when working with multi…

…ple chainstates

When using assumeutxo and multiple chainstates are active, the background
chainstate should consider all HAVE_DATA blocks on the snapshotted chain that
have more work than the tip as potential candidates.

src/validation.cpp

@@ -4462,9 +4462,6 @@ bool ChainstateManager::LoadBlockIndex()
         std::sort(vSortedByHeight.begin(), vSortedByHeight.end(),
                   CBlockIndexHeightOnlyComparator());
 
-        // Find start of assumed-valid region.
-        int first_assumed_valid_height = std::numeric_limits<int>::max();
-
         for (const CBlockIndex* block : vSortedByHeight) {
             if (block->IsAssumedValid()) {
                 auto chainstates = GetAll();
@@ -4477,9 +4474,6 @@ bool ChainstateManager::LoadBlockIndex()
                 assert(any_chain([](auto chainstate) { return chainstate->reliesOnAssumedValid(); }));
                 assert(any_chain([](auto chainstate) { return !chainstate->reliesOnAssumedValid(); }));
 
-                first_assumed_valid_height = block->nHeight;
-                LogPrintf("Saw first assumedvalid block at height %d (%s)\n",
-                        first_assumed_valid_height, block->ToString());
                 break;
             }
         }
@@ -4490,34 +4484,8 @@ bool ChainstateManager::LoadBlockIndex()
                     (pindex->IsValid(BLOCK_VALID_TRANSACTIONS) &&
                      (pindex->HaveTxsDownloaded() || pindex->pprev == nullptr))) {
 
-                // Fill each chainstate's block candidate set. Only add assumed-valid
-                // blocks to the tip candidate set if the chainstate is allowed to rely on
-                // assumed-valid blocks.
-                //
-                // If all setBlockIndexCandidates contained the assumed-valid blocks, the
-                // background chainstate's ActivateBestChain() call would add assumed-valid
-                // blocks to the chain (based on how FindMostWorkChain() works). Obviously
-                // we don't want this since the purpose of the background validation chain
-                // is to validate assued-valid blocks.
-                //
-                // Note: This is considering all blocks whose height is greater or equal to
-                // the first assumed-valid block to be assumed-valid blocks, and excluding
-                // them from the background chainstate's setBlockIndexCandidates set. This
-                // does mean that some blocks which are not technically assumed-valid
-                // (later blocks on a fork beginning before the first assumed-valid block)
-                // might not get added to the background chainstate, but this is ok,
-                // because they will still be attached to the active chainstate if they
-                // actually contain more work.
-                //
-                // Instead of this height-based approach, an earlier attempt was made at
-                // detecting "holistically" whether the block index under consideration
-                // relied on an assumed-valid ancestor, but this proved to be too slow to
-                // be practical.
                 for (Chainstate* chainstate : GetAll()) {
-                    if (chainstate->reliesOnAssumedValid() ||
-                            pindex->nHeight < first_assumed_valid_height) {
-                        chainstate->setBlockIndexCandidates.insert(pindex);
-                    }
+                    chainstate->TryAddBlockIndexCandidate(pindex);
                 }
             }
             if (pindex->nStatus & BLOCK_FAILED_MASK && (!m_best_invalid || pindex->nChainWork > m_best_invalid->nChainWork)) {