From bd83111a0fcfdb97204a0180bcf861d3b53bb6c2 Mon Sep 17 00:00:00 2001
From: Pieter Wuille <pieter.wuille@gmail.com>
Date: Tue, 25 Apr 2017 11:29:27 -0700
Subject: [PATCH] Optimization: Coin&& to ApplyTxInUndo

This avoids a prevector copy in ApplyTxInUndo.
---
 src/test/coins_tests.cpp |  6 +++---
 src/validation.cpp       | 10 +++++-----
 2 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/src/test/coins_tests.cpp b/src/test/coins_tests.cpp
index e86c71994..9c758ee9a 100644
--- a/src/test/coins_tests.cpp
+++ b/src/test/coins_tests.cpp
@@ -17,7 +17,7 @@
 
 #include <boost/test/unit_test.hpp>
 
-int ApplyTxInUndo(const Coin& undo, CCoinsViewCache& view, const COutPoint& out);
+int ApplyTxInUndo(Coin&& undo, CCoinsViewCache& view, const COutPoint& out);
 void UpdateCoins(const CTransaction& tx, CCoinsViewCache& inputs, CTxUndo &txundo, int nHeight);
 
 namespace
@@ -371,8 +371,8 @@ BOOST_AUTO_TEST_CASE(updatecoins_simulation_test)
             // restore inputs
             if (!tx.IsCoinBase()) {
                 const COutPoint &out = tx.vin[0].prevout;
-                const Coin &undoin = undo.vprevout[0];
-                ApplyTxInUndo(undoin, *(stack.back()), out);
+                Coin coin = undo.vprevout[0];
+                ApplyTxInUndo(std::move(coin), *(stack.back()), out);
             }
             // Store as a candidate for reconnection
             disconnectedids.insert(undohash);
diff --git a/src/validation.cpp b/src/validation.cpp
index dad0e1a3e..d6cc59b48 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -1256,7 +1256,7 @@ enum DisconnectResult
  * @param out The out point that corresponds to the tx input.
  * @return A DisconnectResult as an int
  */
-int ApplyTxInUndo(const Coin& undo, CCoinsViewCache& view, const COutPoint& out)
+int ApplyTxInUndo(Coin&& undo, CCoinsViewCache& view, const COutPoint& out)
 {
     bool fClean = true;
 
@@ -1277,7 +1277,7 @@ int ApplyTxInUndo(const Coin& undo, CCoinsViewCache& view, const COutPoint& out)
     if (coins->IsAvailable(out.n)) fClean = false; // overwriting existing output
     if (coins->vout.size() < out.n+1)
         coins->vout.resize(out.n+1);
-    coins->vout[out.n] = undo.out;
+    coins->vout[out.n] = std::move(undo.out);
 
     return fClean ? DISCONNECT_OK : DISCONNECT_UNCLEAN;
 }
@@ -1326,18 +1326,18 @@ static DisconnectResult DisconnectBlock(const CBlock& block, const CBlockIndex*
 
         // restore inputs
         if (i > 0) { // not coinbases
-            const CTxUndo &txundo = blockUndo.vtxundo[i-1];
+            CTxUndo &txundo = blockUndo.vtxundo[i-1];
             if (txundo.vprevout.size() != tx.vin.size()) {
                 error("DisconnectBlock(): transaction and undo data inconsistent");
                 return DISCONNECT_FAILED;
             }
             for (unsigned int j = tx.vin.size(); j-- > 0;) {
                 const COutPoint &out = tx.vin[j].prevout;
-                const Coin &undo = txundo.vprevout[j];
-                int res = ApplyTxInUndo(undo, view, out);
+                int res = ApplyTxInUndo(std::move(txundo.vprevout[j]), view, out);
                 if (res == DISCONNECT_FAILED) return DISCONNECT_FAILED;
                 fClean = fClean && res != DISCONNECT_UNCLEAN;
             }
+            // At this point, all of txundo.vprevout should have been moved out.
         }
     }