bench: benchmark transaction creation process

Goal 1:
Benchmark the transaction creation process for pre-selected-inputs only.
Setting `m_allow_other_inputs=false` to disallow the wallet to include coins automatically.

Goal 2:
Benchmark the transaction creation process for pre-selected-inputs and coin selection.

-----------------------

Benchmark Setup:
1) Generates a 5k blockchain, loading the wallet with 5k transactions with two outputs each.
2) Fetch 4 random UTXO from the wallet's available coins and pre-select them as inputs inside CoinControl.

Benchmark (Goal 1):
Call `CreateTransaction` providing the coin control, who has set `m_allow_other_inputs=false` and
the manually selected coins.

Benchmark (Goal 2):
Call `CreateTransaction` providing the coin control, who has set `m_allow_other_inputs=true` and
the manually selected coins.

4 files changed, 153 insertions, 2 deletions

diff --git a/src/Makefile.bench.include b/src/Makefile.bench.include
index e1e2066877..0a3f9df463 100644
--- a/src/Makefile.bench.include
+++ b/src/Makefile.bench.include
@@ -79,6 +79,7 @@ if ENABLE_WALLET
 bench_bench_bitcoin_SOURCES += bench/coin_selection.cpp
 bench_bench_bitcoin_SOURCES += bench/wallet_balance.cpp
 bench_bench_bitcoin_SOURCES += bench/wallet_loading.cpp
+bench_bench_bitcoin_SOURCES += bench/wallet_create_tx.cpp
 bench_bench_bitcoin_LDADD += $(BDB_LIBS) $(SQLITE_LIBS)
 endif
 
diff --git a/src/bench/wallet_create_tx.cpp b/src/bench/wallet_create_tx.cpp
new file mode 100644
index 0000000000..207b22c584
--- /dev/null
+++ b/src/bench/wallet_create_tx.cpp
@@ -0,0 +1,142 @@
+// Copyright (c) 2022 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or https://www.opensource.org/licenses/mit-license.php.
+
+#include <bench/bench.h>
+#include <chainparams.h>
+#include <wallet/coincontrol.h>
+#include <consensus/merkle.h>
+#include <kernel/chain.h>
+#include <node/context.h>
+#include <test/util/setup_common.h>
+#include <test/util/wallet.h>
+#include <validation.h>
+#include <wallet/spend.h>
+#include <wallet/wallet.h>
+
+using wallet::CWallet;
+using wallet::CreateMockWalletDatabase;
+using wallet::DBErrors;
+using wallet::WALLET_FLAG_DESCRIPTORS;
+
+struct TipBlock
+{
+    uint256 prev_block_hash;
+    int64_t prev_block_time;
+    int tip_height;
+};
+
+TipBlock getTip(const CChainParams& params, const node::NodeContext& context)
+{
+    auto tip = WITH_LOCK(::cs_main, return context.chainman->ActiveTip());
+    return (tip) ? TipBlock{tip->GetBlockHash(), tip->GetBlockTime(), tip->nHeight} :
+           TipBlock{params.GenesisBlock().GetHash(), params.GenesisBlock().GetBlockTime(), 0};
+}
+
+void generateFakeBlock(const CChainParams& params,
+                       const node::NodeContext& context,
+                       CWallet& wallet,
+                       const CScript& coinbase_out_script)
+{
+    TipBlock tip{getTip(params, context)};
+
+    // Create block
+    CBlock block;
+    CMutableTransaction coinbase_tx;
+    coinbase_tx.vin.resize(1);
+    coinbase_tx.vin[0].prevout.SetNull();
+    coinbase_tx.vout.resize(2);
+    coinbase_tx.vout[0].scriptPubKey = coinbase_out_script;
+    coinbase_tx.vout[0].nValue = 49 * COIN;
+    coinbase_tx.vin[0].scriptSig = CScript() << ++tip.tip_height << OP_0;
+    coinbase_tx.vout[1].scriptPubKey = coinbase_out_script; // extra output
+    coinbase_tx.vout[1].nValue = 1 * COIN;
+    block.vtx = {MakeTransactionRef(std::move(coinbase_tx))};
+
+    block.nVersion = VERSIONBITS_LAST_OLD_BLOCK_VERSION;
+    block.hashPrevBlock = tip.prev_block_hash;
+    block.hashMerkleRoot = BlockMerkleRoot(block);
+    block.nTime = ++tip.prev_block_time;
+    block.nBits = params.GenesisBlock().nBits;
+    block.nNonce = 0;
+
+    {
+        LOCK(::cs_main);
+        // Add it to the index
+        CBlockIndex* pindex{context.chainman->m_blockman.AddToBlockIndex(block, context.chainman->m_best_header)};
+        // add it to the chain
+        context.chainman->ActiveChain().SetTip(*pindex);
+    }
+
+    // notify wallet
+    const auto& pindex = WITH_LOCK(::cs_main, return context.chainman->ActiveChain().Tip());
+    wallet.blockConnected(kernel::MakeBlockInfo(pindex, &block));
+}
+
+struct PreSelectInputs {
+    // How many coins from the wallet the process should select
+    int num_of_internal_inputs;
+    // future: this could have external inputs as well.
+};
+
+static void WalletCreateTx(benchmark::Bench& bench, const OutputType output_type, bool allow_other_inputs, std::optional<PreSelectInputs> preset_inputs)
+{
+    const auto test_setup = MakeNoLogFileContext<const TestingSetup>();
+
+    CWallet wallet{test_setup->m_node.chain.get(), "", gArgs, CreateMockWalletDatabase()};
+    {
+        LOCK(wallet.cs_wallet);
+        wallet.SetWalletFlag(WALLET_FLAG_DESCRIPTORS);
+        wallet.SetupDescriptorScriptPubKeyMans();
+        if (wallet.LoadWallet() != DBErrors::LOAD_OK) assert(false);
+    }
+
+    // Generate destinations
+    CScript dest = GetScriptForDestination(getNewDestination(wallet, output_type));
+
+    // Generate chain; each coinbase will have two outputs to fill-up the wallet
+    const auto& params = Params();
+    unsigned int chain_size = 5000; // 5k blocks means 10k UTXO for the wallet (minus 200 due COINBASE_MATURITY)
+    for (unsigned int i = 0; i < chain_size; ++i) {
+        generateFakeBlock(params, test_setup->m_node, wallet, dest);
+    }
+
+    // Check available balance
+    auto bal = wallet::GetAvailableBalance(wallet); // Cache
+    assert(bal == 50 * COIN * (chain_size - COINBASE_MATURITY));
+
+    wallet::CCoinControl coin_control;
+    coin_control.m_allow_other_inputs = allow_other_inputs;
+
+    CAmount target = 0;
+    if (preset_inputs) {
+        // Select inputs, each has 49 BTC
+        const auto& res = WITH_LOCK(wallet.cs_wallet,
+                                    return wallet::AvailableCoins(wallet, nullptr, std::nullopt, 1, MAX_MONEY,
+                                                                  MAX_MONEY, preset_inputs->num_of_internal_inputs));
+        for (int i=0; i < preset_inputs->num_of_internal_inputs; i++) {
+            const auto& coin{res.coins.at(output_type)[i]};
+            target += coin.txout.nValue;
+            coin_control.Select(coin.outpoint);
+        }
+    }
+
+    // If automatic coin selection is enabled, add the value of another UTXO to the target
+    if (coin_control.m_allow_other_inputs) target += 50 * COIN;
+    std::vector<wallet::CRecipient> recipients = {{dest, target, true}};
+
+    bench.epochIterations(5).run([&] {
+        LOCK(wallet.cs_wallet);
+        const auto& tx_res = CreateTransaction(wallet, recipients, -1, coin_control);
+        assert(tx_res);
+    });
+}
+
+static void WalletCreateTxUseOnlyPresetInputs(benchmark::Bench& bench) { WalletCreateTx(bench, OutputType::BECH32, /*allow_other_inputs=*/false,
+                                                                                        {{/*num_of_internal_inputs=*/4}}); }
+
+static void WalletCreateTxUsePresetInputsAndCoinSelection(benchmark::Bench& bench) { WalletCreateTx(bench, OutputType::BECH32, /*allow_other_inputs=*/true,
+                                                                                                    {{/*num_of_internal_inputs=*/4}}); }
+
+BENCHMARK(WalletCreateTxUseOnlyPresetInputs, benchmark::PriorityLevel::LOW)
+BENCHMARK(WalletCreateTxUsePresetInputsAndCoinSelection, benchmark::PriorityLevel::LOW)
diff --git a/src/test/util/wallet.cpp b/src/test/util/wallet.cpp
index b54774cbb9..2dadffafb4 100644
--- a/src/test/util/wallet.cpp
+++ b/src/test/util/wallet.cpp
@@ -21,7 +21,12 @@ const std::string ADDRESS_BCRT1_UNSPENDABLE = "bcrt1qqqqqqqqqqqqqqqqqqqqqqqqqqqq
 std::string getnewaddress(CWallet& w)
 {
     constexpr auto output_type = OutputType::BECH32;
-    return EncodeDestination(*Assert(w.GetNewDestination(output_type, "")));
+    return EncodeDestination(getNewDestination(w, output_type));
+}
+
+CTxDestination getNewDestination(CWallet& w, OutputType output_type)
+{
+    return *Assert(w.GetNewDestination(output_type, ""));
 }
 
 #endif // ENABLE_WALLET
diff --git a/src/test/util/wallet.h b/src/test/util/wallet.h
index 31281bf70e..d8f1db3fd7 100644
--- a/src/test/util/wallet.h
+++ b/src/test/util/wallet.h
@@ -5,6 +5,7 @@
 #ifndef BITCOIN_TEST_UTIL_WALLET_H
 #define BITCOIN_TEST_UTIL_WALLET_H
 
+#include <outputtype.h>
 #include <string>
 
 namespace wallet {
@@ -19,8 +20,10 @@ extern const std::string ADDRESS_BCRT1_UNSPENDABLE;
 
 /** Import the address to the wallet */
 void importaddress(wallet::CWallet& wallet, const std::string& address);
-/** Returns a new address from the wallet */
+/** Returns a new encoded destination from the wallet (hardcoded to BECH32) */
 std::string getnewaddress(wallet::CWallet& w);
+/** Returns a new destination, of an specific type, from the wallet */
+CTxDestination getNewDestination(wallet::CWallet& w, OutputType output_type);
 
 
 #endif // BITCOIN_TEST_UTIL_WALLET_H