Avoid calling GetSerializeSize on each tx in a block if !fTxIndex

src/validation.cpp

@@ -1647,6 +1647,8 @@ static bool WriteUndoDataForBlock(const CBlockUndo& blockundo, CValidationState&
 
 static bool WriteTxIndexDataForBlock(const CBlock& block, CValidationState& state, CBlockIndex* pindex)
 {
+    if (!fTxIndex) return true;
+
     CDiskTxPos pos(pindex->GetBlockPos(), GetSizeOfCompactSize(block.vtx.size()));
     std::vector<std::pair<uint256, CDiskTxPos> > vPos;
     vPos.reserve(block.vtx.size());
@@ -1656,9 +1658,9 @@ static bool WriteTxIndexDataForBlock(const CBlock& block, CValidationState& stat
         pos.nTxOffset += ::GetSerializeSize(*tx, SER_DISK, CLIENT_VERSION);
     }
 
-    if (fTxIndex)
-        if (!pblocktree->WriteTxIndex(vPos))
-            return AbortNode(state, "Failed to write transaction index");
+    if (!pblocktree->WriteTxIndex(vPos)) {
+        return AbortNode(state, "Failed to write transaction index");
+    }
 
     return true;
 }