Benchmark Merkle root computation

src/Makefile.bench.include

@@ -21,6 +21,7 @@ bench_bench_bitcoin_SOURCES = \
   bench/rollingbloom.cpp \
   bench/crypto_hash.cpp \
   bench/ccoins_caching.cpp \
+  bench/merkle_root.cpp \
   bench/mempool_eviction.cpp \
   bench/verify_script.cpp \
   bench/base58.cpp \

src/bench/merkle_root.cpp

@@ -0,0 +1,26 @@
+// Copyright (c) 2016 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include "bench.h"
+
+#include "uint256.h"
+#include "random.h"
+#include "consensus/merkle.h"
+
+static void MerkleRoot(benchmark::State& state)
+{
+    FastRandomContext rng(true);
+    std::vector<uint256> leaves;
+    leaves.resize(9001);
+    for (auto& item : leaves) {
+        item = rng.rand256();
+    }
+    while (state.KeepRunning()) {
+        bool mutation = false;
+        uint256 hash = ComputeMerkleRoot(leaves, &mutation);
+        leaves[mutation] = hash;
+    }
+}
+
+BENCHMARK(MerkleRoot, 800);