bench/blockencodings: add compact block reconstruction benchmark

diff --git a/src/bench/CMakeLists.txt b/src/bench/CMakeLists.txt
index c976f134..0bf469c7 100644
--- a/src/bench/CMakeLists.txt
+++ b/src/bench/CMakeLists.txt
@@ -12,6 +12,7 @@ add_executable(bench_bitcoin
   bech32.cpp
   bip324_ecdh.cpp
   block_assemble.cpp
+  blockencodings.cpp
   ccoins_caching.cpp
   chacha20.cpp
   checkblock.cpp
diff --git a/src/bench/blockencodings.cpp b/src/bench/blockencodings.cpp
new file mode 100644
index 00000000..7e942395
--- /dev/null
+++ b/src/bench/blockencodings.cpp
@@ -0,0 +1,131 @@
+// Copyright (c) 2025-present 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/bench.h>
+#include <blockencodings.h>
+#include <consensus/amount.h>
+#include <kernel/cs_main.h>
+#include <net_processing.h>
+#include <primitives/transaction.h>
+#include <script/script.h>
+#include <sync.h>
+#include <test/util/setup_common.h>
+#include <test/util/txmempool.h>
+#include <txmempool.h>
+#include <util/check.h>
+
+#include <memory>
+#include <vector>
+
+
+static void AddTx(const CTransactionRef& tx, const CAmount& fee, CTxMemPool& pool) EXCLUSIVE_LOCKS_REQUIRED(cs_main, pool.cs)
+{
+    LockPoints lp;
+    AddToMempool(pool, CTxMemPoolEntry(tx, fee, /*time=*/0, /*entry_height=*/1, /*entry_sequence=*/0, /*spends_coinbase=*/false, /*sigops_cost=*/4, lp));
+}
+
+namespace {
+class BenchCBHAST : public CBlockHeaderAndShortTxIDs
+{
+private:
+    static CBlock DummyBlock()
+    {
+        CBlock block;
+        block.nVersion = 5;
+        block.hashPrevBlock.SetNull();
+        block.hashMerkleRoot.SetNull();
+        block.nTime = 1231006505;
+        block.nBits = 0x1d00ffff;
+        block.nNonce = 2083236893;
+        block.fChecked = false;
+        CMutableTransaction tx;
+        tx.vin.resize(1);
+        tx.vout.resize(1);
+        block.vtx.emplace_back(MakeTransactionRef(tx)); // dummy coinbase
+        return block;
+    }
+
+public:
+    BenchCBHAST(InsecureRandomContext& rng, int txs) : CBlockHeaderAndShortTxIDs(DummyBlock(), rng.rand64())
+    {
+        shorttxids.reserve(txs);
+        while (txs-- > 0) {
+            shorttxids.push_back(rng.randbits<SHORTTXIDS_LENGTH*8>());
+        }
+    }
+};
+} // anon namespace
+
+static void BlockEncodingBench(benchmark::Bench& bench, size_t n_pool, size_t n_extra)
+{
+    const auto testing_setup = MakeNoLogFileContext<const ChainTestingSetup>(ChainType::MAIN);
+    CTxMemPool& pool = *Assert(testing_setup->m_node.mempool);
+    InsecureRandomContext rng(11);
+
+    LOCK2(cs_main, pool.cs);
+
+    std::vector<CTransactionRef> extratxn;
+    extratxn.reserve(n_extra);
+
+    // bump up the size of txs
+    std::array<std::byte,200> sigspam;
+    sigspam.fill(std::byte(42));
+
+    // a reasonably large mempool of 50k txs, ~10MB total
+    std::vector<CTransactionRef> refs;
+    refs.reserve(n_pool + n_extra);
+    for (size_t i = 0; i < n_pool + n_extra; ++i) {
+        CMutableTransaction tx = CMutableTransaction();
+        tx.vin.resize(1);
+        tx.vin[0].scriptSig = CScript() << sigspam;
+        tx.vin[0].scriptWitness.stack.push_back({1});
+        tx.vout.resize(1);
+        tx.vout[0].scriptPubKey = CScript() << OP_1 << OP_EQUAL;
+        tx.vout[0].nValue = i;
+        refs.push_back(MakeTransactionRef(tx));
+    }
+
+    // ensure mempool ordering is different to memory ordering of transactions,
+    // to simulate a mempool that has changed over time
+    std::shuffle(refs.begin(), refs.end(), rng);
+
+    for (size_t i = 0; i < n_pool; ++i) {
+        AddTx(refs[i], /*fee=*/refs[i]->vout[0].nValue, pool);
+    }
+    for (size_t i = n_pool; i < n_pool + n_extra; ++i) {
+        extratxn.push_back(refs[i]);
+    }
+
+    BenchCBHAST cmpctblock{rng, 3000};
+
+    bench.run([&] {
+        PartiallyDownloadedBlock pdb{&pool};
+        auto res = pdb.InitData(cmpctblock, extratxn);
+
+        // if there were duplicates the benchmark will be invalid
+        // (eg, extra txns will be skipped) and we will receive
+        // READ_STATUS_FAILED
+        assert(res == READ_STATUS_OK);
+    });
+}
+
+static void BlockEncodingNoExtra(benchmark::Bench& bench)
+{
+    BlockEncodingBench(bench, 50000, 0);
+}
+
+static void BlockEncodingStdExtra(benchmark::Bench& bench)
+{
+    static_assert(DEFAULT_BLOCK_RECONSTRUCTION_EXTRA_TXN == 100);
+    BlockEncodingBench(bench, 50000, 100);
+}
+
+static void BlockEncodingLargeExtra(benchmark::Bench& bench)
+{
+    BlockEncodingBench(bench, 50000, 5000);
+}
+
+BENCHMARK(BlockEncodingNoExtra, benchmark::PriorityLevel::HIGH);
+BENCHMARK(BlockEncodingStdExtra, benchmark::PriorityLevel::HIGH);
+BENCHMARK(BlockEncodingLargeExtra, benchmark::PriorityLevel::HIGH);