Dont create pcoinsTip until after ReplayBlocks.

This requires that we not access pcoinsTip in InitBlockIndex's
FlushStateToDisk (so we just skip it until later in AppInitMain)
and the LoadChainTip in LoadBlockIndex (which there is already one
later in AppinitMain, after ReplayBlocks, so skipping it there is
fine).

Includes some simplifications by Suhas Daftuar and Pieter Wuille.

src/init.cpp

@@ -1567,7 +1567,6 @@ bool AppInitMain()
                 pblocktree = new CBlockTreeDB(nBlockTreeDBCache, false, fReindex);
                 pcoinsdbview = new CCoinsViewDB(nCoinDBCache, false, fReindex);
                 pcoinscatcher = new CCoinsViewErrorCatcher(pcoinsdbview);
-                pcoinsTip = new CCoinsViewCache(pcoinscatcher);
 
                 if (fReindex) {
                     pblocktree->WriteReindexing(true);
@@ -1620,7 +1619,7 @@ bool AppInitMain()
                     strLoadError = _("Unable to replay blocks. You will need to rebuild the database using -reindex-chainstate.");
                     break;
                 }
-                pcoinsTip->SetBestBlock(pcoinsdbview->GetBestBlock()); // TODO: only initialize pcoinsTip after ReplayBlocks
+                pcoinsTip = new CCoinsViewCache(pcoinscatcher);
                 LoadChainTip(chainparams);
 
                 // Populate list of invalid/fraudulent outpoints that are banned from the chain

src/txdb.cpp

@@ -96,6 +96,7 @@ bool CCoinsViewDB::BatchWrite(CCoinsMap& mapCoins,
     size_t changed = 0;
     size_t batch_size = (size_t) gArgs.GetArg("-dbbatchsize", nDefaultDbBatchSize);
     int crash_simulate = gArgs.GetArg("-dbcrashratio", 0);
+    assert(!hashBlock.IsNull());
 
     uint256 old_tip = GetBestBlock();
     if (old_tip.IsNull()) {
@@ -107,13 +108,6 @@ bool CCoinsViewDB::BatchWrite(CCoinsMap& mapCoins,
         }
     }
 
-    if (hashBlock.IsNull()) {
-        // Initial flush, nothing to write.
-        assert(mapCoins.empty());
-        assert(old_tip.IsNull());
-        return true;
-    }
-
     // In the first batch, mark the database as being in the middle of a
     // transition from old_tip to hashBlock.
     // A vector is used for future extensibility, as we may want to support

src/validation.cpp

@@ -3554,7 +3554,6 @@ bool static LoadBlockIndexDB(std::string& strError)
     // If this is written true before the next client init, then we know the shutdown process failed
     pblocktree->WriteFlag("shutdown", false);
 
-    LoadChainTip(chainparams);
     return true;
 }
 
@@ -3817,8 +3816,6 @@ bool InitBlockIndex()
             CBlockIndex* pindex = AddToBlockIndex(block);
             if (!ReceivedBlockTransactions(block, state, pindex, blockPos))
                 return error("LoadBlockIndex() : genesis block not accepted");
-            // Force a chainstate write so that when we VerifyDB in a moment, it doesnt check stale data
-            return FlushStateToDisk(state, FLUSH_STATE_ALWAYS);
         } catch (const std::runtime_error& e) {
             return error("LoadBlockIndex() : failed to initialize block database: %s", e.what());
         }