Deduplicate missing parents of orphan transactions

Summary:
In the logic for requesting missing parents of orphan transactions, parent
transactions with multiple outputs being spent by the given orphan were being
processed multiple times. Fix this by deduplicating the set of missing parent
txids first.

Co-authored-by: Anthony Towns <aj@erisian.com.au>

This is a backport of [[bitcoin/bitcoin#19596 | core#19596]] [2/2]
bitcoin/bitcoin@4c0731f

Depends on D10066

Test Plan: `ninja all check-all`

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D10067

src/net_processing.cpp

@@ -3643,21 +3643,33 @@ void PeerManager::ProcessMessage(const Config &config, CNode &pfrom,
             // It may be the case that the orphans parents have all been
             // rejected.
             bool fRejectedParents = false;
+
+            // Deduplicate parent txids, so that we don't have to loop over
+            // the same parent txid more than once down below.
+            std::vector<TxId> unique_parents;
+            unique_parents.reserve(tx.vin.size());
             for (const CTxIn &txin : tx.vin) {
-                if (recentRejects->contains(txin.prevout.GetTxId())) {
+                // We start with all parents, and then remove duplicates below.
+                unique_parents.push_back(txin.prevout.GetTxId());
+            }
+            std::sort(unique_parents.begin(), unique_parents.end());
+            unique_parents.erase(
+                std::unique(unique_parents.begin(), unique_parents.end()),
+                unique_parents.end());
+            for (const TxId &parent_txid : unique_parents) {
+                if (recentRejects->contains(parent_txid)) {
                     fRejectedParents = true;
                     break;
                 }
             }
             if (!fRejectedParents) {
                 const auto current_time = GetTime<std::chrono::microseconds>();
 
-                for (const CTxIn &txin : tx.vin) {
+                for (const TxId &parent_txid : unique_parents) {
                     // FIXME: MSG_TX should use a TxHash, not a TxId.
-                    const TxId _txid = txin.prevout.GetTxId();
-                    pfrom.AddKnownTx(_txid);
-                    if (!AlreadyHaveTx(_txid, m_mempool)) {
-                        AddTxAnnouncement(pfrom, _txid, current_time);
+                    pfrom.AddKnownTx(parent_txid);
+                    if (!AlreadyHaveTx(parent_txid, m_mempool)) {
+                        AddTxAnnouncement(pfrom, parent_txid, current_time);
                     }
                 }
                 AddOrphanTx(ptx, pfrom.GetId());