Merge #10192: Cache full script execution results in addition to signatures

e3f9c05 Add CheckInputs() unit tests (Suhas Daftuar)
a3543af Better document CheckInputs parameter meanings (Matt Corallo)
309ee1a Update -maxsigcachesize doc clarify init logprints for it (Matt Corallo)
b014668 Add CheckInputs wrapper CCoinsViewMemPool -> non-consensus-critical (Matt Corallo)
eada04e Do not print soft-fork-script warning with -promiscuousmempool (Matt Corallo)
b5fea8d Cache full script execution results in addition to signatures (Matt Corallo)
6d22b2b Pull script verify flags calculation out of ConnectBlock (Matt Corallo)

Tree-SHA512: 0c6c3c79c64fcb21e17ab60290c5c96d4fac11624c49f841a4201eec21cb480314c52a07d1e3abd4f9c764785cc57bfd178511f495aa0469addb204e96214fe4

6 files changed, 449 insertions, 43 deletions

diff --git a/src/init.cpp b/src/init.cpp
index ec1f18faef..672ef77e80 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -447,7 +447,7 @@ std::string HelpMessage(HelpMessageMode mode)
     {
         strUsage += HelpMessageOpt("-logtimemicros", strprintf("Add microsecond precision to debug timestamps (default: %u)", DEFAULT_LOGTIMEMICROS));
         strUsage += HelpMessageOpt("-mocktime=<n>", "Replace actual time with <n> seconds since epoch (default: 0)");
-        strUsage += HelpMessageOpt("-maxsigcachesize=<n>", strprintf("Limit size of signature cache to <n> MiB (default: %u)", DEFAULT_MAX_SIG_CACHE_SIZE));
+        strUsage += HelpMessageOpt("-maxsigcachesize=<n>", strprintf("Limit sum of signature cache and script execution cache sizes to <n> MiB (default: %u)", DEFAULT_MAX_SIG_CACHE_SIZE));
         strUsage += HelpMessageOpt("-maxtipage=<n>", strprintf("Maximum tip age in seconds to consider node in initial block download (default: %u)", DEFAULT_MAX_TIP_AGE));
     }
     strUsage += HelpMessageOpt("-maxtxfee=<amt>", strprintf(_("Maximum total fees (in %s) to use in a single wallet transaction or raw transaction; setting this too low may abort large transactions (default: %s)"),
@@ -1191,6 +1191,7 @@ bool AppInitMain(boost::thread_group& threadGroup, CScheduler& scheduler)
     LogPrintf("Using at most %i automatic connections (%i file descriptors available)\n", nMaxConnections, nFD);
 
     InitSignatureCache();
+    InitScriptExecutionCache();
 
     LogPrintf("Using %u threads for script verification\n", nScriptCheckThreads);
     if (nScriptCheckThreads) {
diff --git a/src/script/sigcache.cpp b/src/script/sigcache.cpp
index befc5f5233..ceb573b2ec 100644
--- a/src/script/sigcache.cpp
+++ b/src/script/sigcache.cpp
@@ -74,10 +74,10 @@ void InitSignatureCache()
 {
     // nMaxCacheSize is unsigned. If -maxsigcachesize is set to zero,
     // setup_bytes creates the minimum possible cache (2 elements).
-    size_t nMaxCacheSize = std::min(std::max((int64_t)0, GetArg("-maxsigcachesize", DEFAULT_MAX_SIG_CACHE_SIZE)), MAX_MAX_SIG_CACHE_SIZE) * ((size_t) 1 << 20);
+    size_t nMaxCacheSize = std::min(std::max((int64_t)0, GetArg("-maxsigcachesize", DEFAULT_MAX_SIG_CACHE_SIZE) / 2), MAX_MAX_SIG_CACHE_SIZE) * ((size_t) 1 << 20);
     size_t nElems = signatureCache.setup_bytes(nMaxCacheSize);
-    LogPrintf("Using %zu MiB out of %zu requested for signature cache, able to store %zu elements\n",
-            (nElems*sizeof(uint256)) >>20, nMaxCacheSize>>20, nElems);
+    LogPrintf("Using %zu MiB out of %zu/2 requested for signature cache, able to store %zu elements\n",
+            (nElems*sizeof(uint256)) >>20, (nMaxCacheSize*2)>>20, nElems);
 }
 
 bool CachingTransactionSignatureChecker::VerifySignature(const std::vector<unsigned char>& vchSig, const CPubKey& pubkey, const uint256& sighash) const
diff --git a/src/test/test_bitcoin.cpp b/src/test/test_bitcoin.cpp
index c60379982e..579e96524c 100644
--- a/src/test/test_bitcoin.cpp
+++ b/src/test/test_bitcoin.cpp
@@ -38,6 +38,7 @@ BasicTestingSetup::BasicTestingSetup(const std::string& chainName)
         SetupEnvironment();
         SetupNetworking();
         InitSignatureCache();
+        InitScriptExecutionCache();
         fPrintToDebugLog = false; // don't want to write to debug.log file
         fCheckBlockIndex = true;
         SelectParams(chainName);
diff --git a/src/test/txvalidationcache_tests.cpp b/src/test/txvalidationcache_tests.cpp
index c5367208ba..a74f40251a 100644
--- a/src/test/txvalidationcache_tests.cpp
+++ b/src/test/txvalidationcache_tests.cpp
@@ -10,11 +10,17 @@
 #include "txmempool.h"
 #include "random.h"
 #include "script/standard.h"
+#include "script/sign.h"
 #include "test/test_bitcoin.h"
 #include "utiltime.h"
+#include "core_io.h"
+#include "keystore.h"
+#include "policy/policy.h"
 
 #include <boost/test/unit_test.hpp>
 
+bool CheckInputs(const CTransaction& tx, CValidationState &state, const CCoinsViewCache &inputs, bool fScriptChecks, unsigned int flags, bool cacheSigStore, bool cacheFullScriptStore, PrecomputedTransactionData& txdata, std::vector<CScriptCheck> *pvChecks);
+
 BOOST_AUTO_TEST_SUITE(tx_validationcache_tests)
 
 static bool
@@ -84,4 +90,282 @@ BOOST_FIXTURE_TEST_CASE(tx_mempool_block_doublespend, TestChain100Setup)
     BOOST_CHECK_EQUAL(mempool.size(), 0);
 }
 
+// Run CheckInputs (using pcoinsTip) on the given transaction, for all script
+// flags.  Test that CheckInputs passes for all flags that don't overlap with
+// the failing_flags argument, but otherwise fails.
+// CHECKLOCKTIMEVERIFY and CHECKSEQUENCEVERIFY (and future NOP codes that may
+// get reassigned) have an interaction with DISCOURAGE_UPGRADABLE_NOPS: if
+// the script flags used contain DISCOURAGE_UPGRADABLE_NOPS but don't contain
+// CHECKLOCKTIMEVERIFY (or CHECKSEQUENCEVERIFY), but the script does contain
+// OP_CHECKLOCKTIMEVERIFY (or OP_CHECKSEQUENCEVERIFY), then script execution
+// should fail.
+// Capture this interaction with the upgraded_nop argument: set it when evaluating
+// any script flag that is implemented as an upgraded NOP code.
+void ValidateCheckInputsForAllFlags(CMutableTransaction &tx, uint32_t failing_flags, bool add_to_cache, bool upgraded_nop)
+{
+    PrecomputedTransactionData txdata(tx);
+    // If we add many more flags, this loop can get too expensive, but we can
+    // rewrite in the future to randomly pick a set of flags to evaluate.
+    for (uint32_t test_flags=0; test_flags < (1U << 16); test_flags += 1) {
+        CValidationState state;
+        // Filter out incompatible flag choices
+        if ((test_flags & SCRIPT_VERIFY_CLEANSTACK)) {
+            // CLEANSTACK requires P2SH and WITNESS, see VerifyScript() in
+            // script/interpreter.cpp
+            test_flags |= SCRIPT_VERIFY_P2SH | SCRIPT_VERIFY_WITNESS;
+        }
+        if ((test_flags & SCRIPT_VERIFY_WITNESS)) {
+            // WITNESS requires P2SH
+            test_flags |= SCRIPT_VERIFY_P2SH;
+        }
+        bool ret = CheckInputs(tx, state, pcoinsTip, true, test_flags, true, add_to_cache, txdata, nullptr);
+        // CheckInputs should succeed iff test_flags doesn't intersect with
+        // failing_flags
+        bool expected_return_value = !(test_flags & failing_flags);
+        if (expected_return_value && upgraded_nop) {
+            // If the script flag being tested corresponds to an upgraded NOP,
+            // then script execution should fail if DISCOURAGE_UPGRADABLE_NOPS
+            // is set.
+            expected_return_value = !(test_flags & SCRIPT_VERIFY_DISCOURAGE_UPGRADABLE_NOPS);
+        }
+        BOOST_CHECK_EQUAL(ret, expected_return_value);
+
+        // Test the caching
+        if (ret && add_to_cache) {
+            // Check that we get a cache hit if the tx was valid
+            std::vector<CScriptCheck> scriptchecks;
+            BOOST_CHECK(CheckInputs(tx, state, pcoinsTip, true, test_flags, true, add_to_cache, txdata, &scriptchecks));
+            BOOST_CHECK(scriptchecks.empty());
+        } else {
+            // Check that we get script executions to check, if the transaction
+            // was invalid, or we didn't add to cache.
+            std::vector<CScriptCheck> scriptchecks;
+            BOOST_CHECK(CheckInputs(tx, state, pcoinsTip, true, test_flags, true, add_to_cache, txdata, &scriptchecks));
+            BOOST_CHECK_EQUAL(scriptchecks.size(), tx.vin.size());
+        }
+    }
+}
+
+BOOST_FIXTURE_TEST_CASE(checkinputs_test, TestChain100Setup)
+{
+    // Test that passing CheckInputs with one set of script flags doesn't imply
+    // that we would pass again with a different set of flags.
+    InitScriptExecutionCache();
+
+    CScript p2pk_scriptPubKey = CScript() << ToByteVector(coinbaseKey.GetPubKey()) << OP_CHECKSIG;
+    CScript p2sh_scriptPubKey = GetScriptForDestination(CScriptID(p2pk_scriptPubKey));
+    CScript p2pkh_scriptPubKey = GetScriptForDestination(coinbaseKey.GetPubKey().GetID());
+    CScript p2wpkh_scriptPubKey = GetScriptForWitness(p2pkh_scriptPubKey);
+
+    CBasicKeyStore keystore;
+    keystore.AddKey(coinbaseKey);
+    keystore.AddCScript(p2pk_scriptPubKey);
+
+    // flags to test: SCRIPT_VERIFY_CHECKLOCKTIMEVERIFY, SCRIPT_VERIFY_CHECKSEQUENCE_VERIFY, SCRIPT_VERIFY_NULLDUMMY, uncompressed pubkey thing
+
+    // Create 2 outputs that match the three scripts above, spending the first
+    // coinbase tx.
+    CMutableTransaction spend_tx;
+
+    spend_tx.nVersion = 1;
+    spend_tx.vin.resize(1);
+    spend_tx.vin[0].prevout.hash = coinbaseTxns[0].GetHash();
+    spend_tx.vin[0].prevout.n = 0;
+    spend_tx.vout.resize(4);
+    spend_tx.vout[0].nValue = 11*CENT;
+    spend_tx.vout[0].scriptPubKey = p2sh_scriptPubKey;
+    spend_tx.vout[1].nValue = 11*CENT;
+    spend_tx.vout[1].scriptPubKey = p2wpkh_scriptPubKey;
+    spend_tx.vout[2].nValue = 11*CENT;
+    spend_tx.vout[2].scriptPubKey = CScript() << OP_CHECKLOCKTIMEVERIFY << OP_DROP << ToByteVector(coinbaseKey.GetPubKey()) << OP_CHECKSIG;
+    spend_tx.vout[3].nValue = 11*CENT;
+    spend_tx.vout[3].scriptPubKey = CScript() << OP_CHECKSEQUENCEVERIFY << OP_DROP << ToByteVector(coinbaseKey.GetPubKey()) << OP_CHECKSIG;
+
+    // Sign, with a non-DER signature
+    {
+        std::vector<unsigned char> vchSig;
+        uint256 hash = SignatureHash(p2pk_scriptPubKey, spend_tx, 0, SIGHASH_ALL, 0, SIGVERSION_BASE);
+        BOOST_CHECK(coinbaseKey.Sign(hash, vchSig));
+        vchSig.push_back((unsigned char) 0); // padding byte makes this non-DER
+        vchSig.push_back((unsigned char)SIGHASH_ALL);
+        spend_tx.vin[0].scriptSig << vchSig;
+    }
+
+    LOCK(cs_main);
+
+    // Test that invalidity under a set of flags doesn't preclude validity
+    // under other (eg consensus) flags.
+    // spend_tx is invalid according to DERSIG
+    CValidationState state;
+    {
+        PrecomputedTransactionData ptd_spend_tx(spend_tx);
+
+        BOOST_CHECK(!CheckInputs(spend_tx, state, pcoinsTip, true, SCRIPT_VERIFY_P2SH | SCRIPT_VERIFY_DERSIG, true, true, ptd_spend_tx, nullptr));
+
+        // If we call again asking for scriptchecks (as happens in
+        // ConnectBlock), we should add a script check object for this -- we're
+        // not caching invalidity (if that changes, delete this test case).
+        std::vector<CScriptCheck> scriptchecks;
+        BOOST_CHECK(CheckInputs(spend_tx, state, pcoinsTip, true, SCRIPT_VERIFY_P2SH | SCRIPT_VERIFY_DERSIG, true, true, ptd_spend_tx, &scriptchecks));
+        BOOST_CHECK_EQUAL(scriptchecks.size(), 1);
+
+        // Test that CheckInputs returns true iff DERSIG-enforcing flags are
+        // not present.  Don't add these checks to the cache, so that we can
+        // test later that block validation works fine in the absence of cached
+        // successes.
+        ValidateCheckInputsForAllFlags(spend_tx, SCRIPT_VERIFY_DERSIG | SCRIPT_VERIFY_LOW_S | SCRIPT_VERIFY_STRICTENC, false, false);
+
+        // And if we produce a block with this tx, it should be valid (DERSIG not
+        // enabled yet), even though there's no cache entry.
+        CBlock block;
+
+        block = CreateAndProcessBlock({spend_tx}, p2pk_scriptPubKey);
+        BOOST_CHECK(chainActive.Tip()->GetBlockHash() == block.GetHash());
+        BOOST_CHECK(pcoinsTip->GetBestBlock() == block.GetHash());
+    }
+
+    // Test P2SH: construct a transaction that is valid without P2SH, and
+    // then test validity with P2SH.
+    {
+        CMutableTransaction invalid_under_p2sh_tx;
+        invalid_under_p2sh_tx.nVersion = 1;
+        invalid_under_p2sh_tx.vin.resize(1);
+        invalid_under_p2sh_tx.vin[0].prevout.hash = spend_tx.GetHash();
+        invalid_under_p2sh_tx.vin[0].prevout.n = 0;
+        invalid_under_p2sh_tx.vout.resize(1);
+        invalid_under_p2sh_tx.vout[0].nValue = 11*CENT;
+        invalid_under_p2sh_tx.vout[0].scriptPubKey = p2pk_scriptPubKey;
+        std::vector<unsigned char> vchSig2(p2pk_scriptPubKey.begin(), p2pk_scriptPubKey.end());
+        invalid_under_p2sh_tx.vin[0].scriptSig << vchSig2;
+
+        ValidateCheckInputsForAllFlags(invalid_under_p2sh_tx, SCRIPT_VERIFY_P2SH, true, false);
+    }
+
+    // Test CHECKLOCKTIMEVERIFY
+    {
+        CMutableTransaction invalid_with_cltv_tx;
+        invalid_with_cltv_tx.nVersion = 1;
+        invalid_with_cltv_tx.nLockTime = 100;
+        invalid_with_cltv_tx.vin.resize(1);
+        invalid_with_cltv_tx.vin[0].prevout.hash = spend_tx.GetHash();
+        invalid_with_cltv_tx.vin[0].prevout.n = 2;
+        invalid_with_cltv_tx.vin[0].nSequence = 0;
+        invalid_with_cltv_tx.vout.resize(1);
+        invalid_with_cltv_tx.vout[0].nValue = 11*CENT;
+        invalid_with_cltv_tx.vout[0].scriptPubKey = p2pk_scriptPubKey;
+
+        // Sign
+        std::vector<unsigned char> vchSig;
+        uint256 hash = SignatureHash(spend_tx.vout[2].scriptPubKey, invalid_with_cltv_tx, 0, SIGHASH_ALL, 0, SIGVERSION_BASE);
+        BOOST_CHECK(coinbaseKey.Sign(hash, vchSig));
+        vchSig.push_back((unsigned char)SIGHASH_ALL);
+        invalid_with_cltv_tx.vin[0].scriptSig = CScript() << vchSig << 101;
+
+        ValidateCheckInputsForAllFlags(invalid_with_cltv_tx, SCRIPT_VERIFY_CHECKLOCKTIMEVERIFY, true, true);
+
+        // Make it valid, and check again
+        invalid_with_cltv_tx.vin[0].scriptSig = CScript() << vchSig << 100;
+        CValidationState state;
+        PrecomputedTransactionData txdata(invalid_with_cltv_tx);
+        BOOST_CHECK(CheckInputs(invalid_with_cltv_tx, state, pcoinsTip, true, SCRIPT_VERIFY_CHECKLOCKTIMEVERIFY, true, true, txdata, nullptr));
+    }
+
+    // TEST CHECKSEQUENCEVERIFY
+    {
+        CMutableTransaction invalid_with_csv_tx;
+        invalid_with_csv_tx.nVersion = 2;
+        invalid_with_csv_tx.vin.resize(1);
+        invalid_with_csv_tx.vin[0].prevout.hash = spend_tx.GetHash();
+        invalid_with_csv_tx.vin[0].prevout.n = 3;
+        invalid_with_csv_tx.vin[0].nSequence = 100;
+        invalid_with_csv_tx.vout.resize(1);
+        invalid_with_csv_tx.vout[0].nValue = 11*CENT;
+        invalid_with_csv_tx.vout[0].scriptPubKey = p2pk_scriptPubKey;
+
+        // Sign
+        std::vector<unsigned char> vchSig;
+        uint256 hash = SignatureHash(spend_tx.vout[3].scriptPubKey, invalid_with_csv_tx, 0, SIGHASH_ALL, 0, SIGVERSION_BASE);
+        BOOST_CHECK(coinbaseKey.Sign(hash, vchSig));
+        vchSig.push_back((unsigned char)SIGHASH_ALL);
+        invalid_with_csv_tx.vin[0].scriptSig = CScript() << vchSig << 101;
+
+        ValidateCheckInputsForAllFlags(invalid_with_csv_tx, SCRIPT_VERIFY_CHECKSEQUENCEVERIFY, true, true);
+
+        // Make it valid, and check again
+        invalid_with_csv_tx.vin[0].scriptSig = CScript() << vchSig << 100;
+        CValidationState state;
+        PrecomputedTransactionData txdata(invalid_with_csv_tx);
+        BOOST_CHECK(CheckInputs(invalid_with_csv_tx, state, pcoinsTip, true, SCRIPT_VERIFY_CHECKSEQUENCEVERIFY, true, true, txdata, nullptr));
+    }
+
+    // TODO: add tests for remaining script flags
+
+    // Test that passing CheckInputs with a valid witness doesn't imply success
+    // for the same tx with a different witness.
+    {
+        CMutableTransaction valid_with_witness_tx;
+        valid_with_witness_tx.nVersion = 1;
+        valid_with_witness_tx.vin.resize(1);
+        valid_with_witness_tx.vin[0].prevout.hash = spend_tx.GetHash();
+        valid_with_witness_tx.vin[0].prevout.n = 1;
+        valid_with_witness_tx.vout.resize(1);
+        valid_with_witness_tx.vout[0].nValue = 11*CENT;
+        valid_with_witness_tx.vout[0].scriptPubKey = p2pk_scriptPubKey;
+
+        // Sign
+        SignatureData sigdata;
+        ProduceSignature(MutableTransactionSignatureCreator(&keystore, &valid_with_witness_tx, 0, 11*CENT, SIGHASH_ALL), spend_tx.vout[1].scriptPubKey, sigdata);
+        UpdateTransaction(valid_with_witness_tx, 0, sigdata);
+
+        // This should be valid under all script flags.
+        ValidateCheckInputsForAllFlags(valid_with_witness_tx, 0, true, false);
+
+        // Remove the witness, and check that it is now invalid.
+        valid_with_witness_tx.vin[0].scriptWitness.SetNull();
+        ValidateCheckInputsForAllFlags(valid_with_witness_tx, SCRIPT_VERIFY_WITNESS, true, false);
+    }
+
+    {
+        // Test a transaction with multiple inputs.
+        CMutableTransaction tx;
+
+        tx.nVersion = 1;
+        tx.vin.resize(2);
+        tx.vin[0].prevout.hash = spend_tx.GetHash();
+        tx.vin[0].prevout.n = 0;
+        tx.vin[1].prevout.hash = spend_tx.GetHash();
+        tx.vin[1].prevout.n = 1;
+        tx.vout.resize(1);
+        tx.vout[0].nValue = 22*CENT;
+        tx.vout[0].scriptPubKey = p2pk_scriptPubKey;
+
+        // Sign
+        for (int i=0; i<2; ++i) {
+            SignatureData sigdata;
+            ProduceSignature(MutableTransactionSignatureCreator(&keystore, &tx, i, 11*CENT, SIGHASH_ALL), spend_tx.vout[i].scriptPubKey, sigdata);
+            UpdateTransaction(tx, i, sigdata);
+        }
+
+        // This should be valid under all script flags
+        ValidateCheckInputsForAllFlags(tx, 0, true, false);
+
+        // Check that if the second input is invalid, but the first input is
+        // valid, the transaction is not cached.
+        // Invalidate vin[1]
+        tx.vin[1].scriptWitness.SetNull();
+
+        CValidationState state;
+        PrecomputedTransactionData txdata(tx);
+        // This transaction is now invalid under segwit, because of the second input.
+        BOOST_CHECK(!CheckInputs(tx, state, pcoinsTip, true, SCRIPT_VERIFY_P2SH | SCRIPT_VERIFY_WITNESS, true, true, txdata, nullptr));
+
+        std::vector<CScriptCheck> scriptchecks;
+        // Make sure this transaction was not cached (ie because the first
+        // input was valid)
+        BOOST_CHECK(CheckInputs(tx, state, pcoinsTip, true, SCRIPT_VERIFY_P2SH | SCRIPT_VERIFY_WITNESS, true, true, txdata, &scriptchecks));
+        // Should get 2 script checks back -- caching is on a whole-transaction basis.
+        BOOST_CHECK_EQUAL(scriptchecks.size(), 2);
+    }
+}
+
 BOOST_AUTO_TEST_SUITE_END()
diff --git a/src/validation.cpp b/src/validation.cpp
index 0fe7f775af..975cbcc79f 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -14,6 +14,7 @@
 #include "consensus/merkle.h"
 #include "consensus/tx_verify.h"
 #include "consensus/validation.h"
+#include "cuckoocache.h"
 #include "fs.h"
 #include "hash.h"
 #include "init.h"
@@ -189,7 +190,7 @@ enum FlushStateMode {
 static bool FlushStateToDisk(const CChainParams& chainParams, CValidationState &state, FlushStateMode mode, int nManualPruneHeight=0);
 static void FindFilesToPruneManual(std::set<int>& setFilesToPrune, int nManualPruneHeight);
 static void FindFilesToPrune(std::set<int>& setFilesToPrune, uint64_t nPruneAfterHeight);
-static bool CheckInputs(const CTransaction& tx, CValidationState &state, const CCoinsViewCache &inputs, bool fScriptChecks, unsigned int flags, bool cacheStore, PrecomputedTransactionData& txdata, std::vector<CScriptCheck> *pvChecks = NULL);
+bool CheckInputs(const CTransaction& tx, CValidationState &state, const CCoinsViewCache &inputs, bool fScriptChecks, unsigned int flags, bool cacheSigStore, bool cacheFullScriptStore, PrecomputedTransactionData& txdata, std::vector<CScriptCheck> *pvChecks = nullptr);
 static FILE* OpenUndoFile(const CDiskBlockPos &pos, bool fReadOnly = false);
 
 bool CheckFinalTx(const CTransaction &tx, int flags)
@@ -312,6 +313,9 @@ bool CheckSequenceLocks(const CTransaction &tx, int flags, LockPoints* lp, bool
     return EvaluateSequenceLocks(index, lockPair);
 }
 
+// Returns the script flags which should be checked for a given block
+static unsigned int GetBlockScriptFlags(const CBlockIndex* pindex, const Consensus::Params& chainparams);
+
 static void LimitMempoolSize(CTxMemPool& pool, size_t limit, unsigned long age) {
     int expired = pool.Expire(GetTime() - age);
     if (expired != 0) {
@@ -395,6 +399,42 @@ void UpdateMempoolForReorg(DisconnectedBlockTransactions &disconnectpool, bool f
     LimitMempoolSize(mempool, GetArg("-maxmempool", DEFAULT_MAX_MEMPOOL_SIZE) * 1000000, GetArg("-mempoolexpiry", DEFAULT_MEMPOOL_EXPIRY) * 60 * 60);
 }
 
+// Used to avoid mempool polluting consensus critical paths if CCoinsViewMempool
+// were somehow broken and returning the wrong scriptPubKeys
+static bool CheckInputsFromMempoolAndCache(const CTransaction& tx, CValidationState &state, const CCoinsViewCache &view, CTxMemPool& pool,
+                 unsigned int flags, bool cacheSigStore, PrecomputedTransactionData& txdata) {
+    AssertLockHeld(cs_main);
+
+    // pool.cs should be locked already, but go ahead and re-take the lock here
+    // to enforce that mempool doesn't change between when we check the view
+    // and when we actually call through to CheckInputs
+    LOCK(pool.cs);
+
+    assert(!tx.IsCoinBase());
+    for (const CTxIn& txin : tx.vin) {
+        const Coin& coin = view.AccessCoin(txin.prevout);
+
+        // At this point we haven't actually checked if the coins are all
+        // available (or shouldn't assume we have, since CheckInputs does).
+        // So we just return failure if the inputs are not available here,
+        // and then only have to check equivalence for available inputs.
+        if (coin.IsSpent()) return false;
+
+        const CTransactionRef& txFrom = pool.get(txin.prevout.hash);
+        if (txFrom) {
+            assert(txFrom->GetHash() == txin.prevout.hash);
+            assert(txFrom->vout.size() > txin.prevout.n);
+            assert(txFrom->vout[txin.prevout.n] == coin.out);
+        } else {
+            const Coin& coinFromDisk = pcoinsTip->AccessCoin(txin.prevout);
+            assert(!coinFromDisk.IsSpent());
+            assert(coinFromDisk.out == coin.out);
+        }
+    }
+
+    return CheckInputs(tx, state, view, true, flags, cacheSigStore, true, txdata);
+}
+
 static bool AcceptToMemoryPoolWorker(const CChainParams& chainparams, CTxMemPool& pool, CValidationState& state, const CTransactionRef& ptx, bool fLimitFree,
                               bool* pfMissingInputs, int64_t nAcceptTime, std::list<CTransactionRef>* plTxnReplaced,
                               bool fOverrideMempoolLimit, const CAmount& nAbsurdFee, std::vector<COutPoint>& coins_to_uncache)
@@ -751,32 +791,51 @@ static bool AcceptToMemoryPoolWorker(const CChainParams& chainparams, CTxMemPool
         // Check against previous transactions
         // This is done last to help prevent CPU exhaustion denial-of-service attacks.
         PrecomputedTransactionData txdata(tx);
-        if (!CheckInputs(tx, state, view, true, scriptVerifyFlags, true, txdata)) {
+        if (!CheckInputs(tx, state, view, true, scriptVerifyFlags, true, false, txdata)) {
             // SCRIPT_VERIFY_CLEANSTACK requires SCRIPT_VERIFY_WITNESS, so we
             // need to turn both off, and compare against just turning off CLEANSTACK
             // to see if the failure is specifically due to witness validation.
             CValidationState stateDummy; // Want reported failures to be from first CheckInputs
-            if (!tx.HasWitness() && CheckInputs(tx, stateDummy, view, true, scriptVerifyFlags & ~(SCRIPT_VERIFY_WITNESS | SCRIPT_VERIFY_CLEANSTACK), true, txdata) &&
-                !CheckInputs(tx, stateDummy, view, true, scriptVerifyFlags & ~SCRIPT_VERIFY_CLEANSTACK, true, txdata)) {
+            if (!tx.HasWitness() && CheckInputs(tx, stateDummy, view, true, scriptVerifyFlags & ~(SCRIPT_VERIFY_WITNESS | SCRIPT_VERIFY_CLEANSTACK), true, false, txdata) &&
+                !CheckInputs(tx, stateDummy, view, true, scriptVerifyFlags & ~SCRIPT_VERIFY_CLEANSTACK, true, false, txdata)) {
                 // Only the witness is missing, so the transaction itself may be fine.
                 state.SetCorruptionPossible();
             }
             return false; // state filled in by CheckInputs
         }
 
-        // Check again against just the consensus-critical mandatory script
-        // verification flags, in case of bugs in the standard flags that cause
+        // Check again against the current block tip's script verification
+        // flags to cache our script execution flags. This is, of course,
+        // useless if the next block has different script flags from the
+        // previous one, but because the cache tracks script flags for us it
+        // will auto-invalidate and we'll just have a few blocks of extra
+        // misses on soft-fork activation.
+        //
+        // This is also useful in case of bugs in the standard flags that cause
         // transactions to pass as valid when they're actually invalid. For
         // instance the STRICTENC flag was incorrectly allowing certain
         // CHECKSIG NOT scripts to pass, even though they were invalid.
         //
         // There is a similar check in CreateNewBlock() to prevent creating
-        // invalid blocks, however allowing such transactions into the mempool
-        // can be exploited as a DoS attack.
-        if (!CheckInputs(tx, state, view, true, MANDATORY_SCRIPT_VERIFY_FLAGS, true, txdata))
+        // invalid blocks (using TestBlockValidity), however allowing such
+        // transactions into the mempool can be exploited as a DoS attack.
+        unsigned int currentBlockScriptVerifyFlags = GetBlockScriptFlags(chainActive.Tip(), Params().GetConsensus());
+        if (!CheckInputsFromMempoolAndCache(tx, state, view, pool, currentBlockScriptVerifyFlags, true, txdata))
         {
-            return error("%s: BUG! PLEASE REPORT THIS! ConnectInputs failed against MANDATORY but not STANDARD flags %s, %s",
-                __func__, hash.ToString(), FormatStateMessage(state));
+            // If we're using promiscuousmempoolflags, we may hit this normally
+            // Check if current block has some flags that scriptVerifyFlags
+            // does not before printing an ominous warning
+            if (!(~scriptVerifyFlags & currentBlockScriptVerifyFlags)) {
+                return error("%s: BUG! PLEASE REPORT THIS! ConnectInputs failed against latest-block but not STANDARD flags %s, %s",
+                    __func__, hash.ToString(), FormatStateMessage(state));
+            } else {
+                if (!CheckInputs(tx, state, view, true, MANDATORY_SCRIPT_VERIFY_FLAGS, true, false, txdata)) {
+                    return error("%s: ConnectInputs failed against MANDATORY but not STANDARD flags due to promiscuous mempool %s, %s",
+                        __func__, hash.ToString(), FormatStateMessage(state));
+                } else {
+                    LogPrintf("Warning: -promiscuousmempool flags set to not include currently enforced soft forks, this may break mining or otherwise cause instability!\n");
+                }
+            }
         }
 
         // Remove conflicting transactions from the mempool
@@ -1152,12 +1211,34 @@ int GetSpendHeight(const CCoinsViewCache& inputs)
     return pindexPrev->nHeight + 1;
 }
 
+
+static CuckooCache::cache<uint256, SignatureCacheHasher> scriptExecutionCache;
+static uint256 scriptExecutionCacheNonce(GetRandHash());
+
+void InitScriptExecutionCache() {
+    // nMaxCacheSize is unsigned. If -maxsigcachesize is set to zero,
+    // setup_bytes creates the minimum possible cache (2 elements).
+    size_t nMaxCacheSize = std::min(std::max((int64_t)0, GetArg("-maxsigcachesize", DEFAULT_MAX_SIG_CACHE_SIZE) / 2), MAX_MAX_SIG_CACHE_SIZE) * ((size_t) 1 << 20);
+    size_t nElems = scriptExecutionCache.setup_bytes(nMaxCacheSize);
+    LogPrintf("Using %zu MiB out of %zu/2 requested for script execution cache, able to store %zu elements\n",
+            (nElems*sizeof(uint256)) >>20, (nMaxCacheSize*2)>>20, nElems);
+}
+
 /**
  * Check whether all inputs of this transaction are valid (no double spends, scripts & sigs, amounts)
- * This does not modify the UTXO set. If pvChecks is not NULL, script checks are pushed onto it
- * instead of being performed inline.
+ * This does not modify the UTXO set.
+ *
+ * If pvChecks is not NULL, script checks are pushed onto it instead of being performed inline. Any
+ * script checks which are not necessary (eg due to script execution cache hits) are, obviously,
+ * not pushed onto pvChecks/run.
+ *
+ * Setting cacheSigStore/cacheFullScriptStore to false will remove elements from the corresponding cache
+ * which are matched. This is useful for checking blocks where we will likely never need the cache
+ * entry again.
+ *
+ * Non-static (and re-declared) in src/test/txvalidationcache_tests.cpp
  */
-static bool CheckInputs(const CTransaction& tx, CValidationState &state, const CCoinsViewCache &inputs, bool fScriptChecks, unsigned int flags, bool cacheStore, PrecomputedTransactionData& txdata, std::vector<CScriptCheck> *pvChecks)
+bool CheckInputs(const CTransaction& tx, CValidationState &state, const CCoinsViewCache &inputs, bool fScriptChecks, unsigned int flags, bool cacheSigStore, bool cacheFullScriptStore, PrecomputedTransactionData& txdata, std::vector<CScriptCheck> *pvChecks)
 {
     if (!tx.IsCoinBase())
     {
@@ -1177,6 +1258,21 @@ static bool CheckInputs(const CTransaction& tx, CValidationState &state, const C
         // Of course, if an assumed valid block is invalid due to false scriptSigs
         // this optimization would allow an invalid chain to be accepted.
         if (fScriptChecks) {
+            // First check if script executions have been cached with the same
+            // flags. Note that this assumes that the inputs provided are
+            // correct (ie that the transaction hash which is in tx's prevouts
+            // properly commits to the scriptPubKey in the inputs view of that
+            // transaction).
+            uint256 hashCacheEntry;
+            // We only use the first 19 bytes of nonce to avoid a second SHA
+            // round - giving us 19 + 32 + 4 = 55 bytes (+ 8 + 1 = 64)
+            static_assert(55 - sizeof(flags) - 32 >= 128/8, "Want at least 128 bits of nonce for script execution cache");
+            CSHA256().Write(scriptExecutionCacheNonce.begin(), 55 - sizeof(flags) - 32).Write(tx.GetWitnessHash().begin(), 32).Write((unsigned char*)&flags, sizeof(flags)).Finalize(hashCacheEntry.begin());
+            AssertLockHeld(cs_main); //TODO: Remove this requirement by making CuckooCache not require external locks
+            if (scriptExecutionCache.contains(hashCacheEntry, !cacheFullScriptStore)) {
+                return true;
+            }
+
             for (unsigned int i = 0; i < tx.vin.size(); i++) {
                 const COutPoint &prevout = tx.vin[i].prevout;
                 const Coin& coin = inputs.AccessCoin(prevout);
@@ -1191,7 +1287,7 @@ static bool CheckInputs(const CTransaction& tx, CValidationState &state, const C
                 const CAmount amount = coin.out.nValue;
 
                 // Verify signature
-                CScriptCheck check(scriptPubKey, amount, tx, i, flags, cacheStore, &txdata);
+                CScriptCheck check(scriptPubKey, amount, tx, i, flags, cacheSigStore, &txdata);
                 if (pvChecks) {
                     pvChecks->push_back(CScriptCheck());
                     check.swap(pvChecks->back());
@@ -1204,7 +1300,7 @@ static bool CheckInputs(const CTransaction& tx, CValidationState &state, const C
                         // avoid splitting the network between upgraded and
                         // non-upgraded nodes.
                         CScriptCheck check2(scriptPubKey, amount, tx, i,
-                                flags & ~STANDARD_NOT_MANDATORY_VERIFY_FLAGS, cacheStore, &txdata);
+                                flags & ~STANDARD_NOT_MANDATORY_VERIFY_FLAGS, cacheSigStore, &txdata);
                         if (check2())
                             return state.Invalid(false, REJECT_NONSTANDARD, strprintf("non-mandatory-script-verify-flag (%s)", ScriptErrorString(check.GetScriptError())));
                     }
@@ -1218,6 +1314,12 @@ static bool CheckInputs(const CTransaction& tx, CValidationState &state, const C
                     return state.DoS(100,false, REJECT_INVALID, strprintf("mandatory-script-verify-flag-failed (%s)", ScriptErrorString(check.GetScriptError())));
                 }
             }
+
+            if (cacheFullScriptStore && !pvChecks) {
+                // We executed all of the provided scripts, and were told to
+                // cache the result. Do so now.
+                scriptExecutionCache.insert(hashCacheEntry);
+            }
         }
     }
 
@@ -1481,6 +1583,41 @@ public:
 // Protected by cs_main
 static ThresholdConditionCache warningcache[VERSIONBITS_NUM_BITS];
 
+static unsigned int GetBlockScriptFlags(const CBlockIndex* pindex, const Consensus::Params& consensusparams) {
+    AssertLockHeld(cs_main);
+
+    // BIP16 didn't become active until Apr 1 2012
+    int64_t nBIP16SwitchTime = 1333238400;
+    bool fStrictPayToScriptHash = (pindex->GetBlockTime() >= nBIP16SwitchTime);
+
+    unsigned int flags = fStrictPayToScriptHash ? SCRIPT_VERIFY_P2SH : SCRIPT_VERIFY_NONE;
+
+    // Start enforcing the DERSIG (BIP66) rule
+    if (pindex->nHeight >= consensusparams.BIP66Height) {
+        flags |= SCRIPT_VERIFY_DERSIG;
+    }
+
+    // Start enforcing CHECKLOCKTIMEVERIFY (BIP65) rule
+    if (pindex->nHeight >= consensusparams.BIP65Height) {
+        flags |= SCRIPT_VERIFY_CHECKLOCKTIMEVERIFY;
+    }
+
+    // Start enforcing BIP68 (sequence locks) and BIP112 (CHECKSEQUENCEVERIFY) using versionbits logic.
+    if (VersionBitsState(pindex->pprev, consensusparams, Consensus::DEPLOYMENT_CSV, versionbitscache) == THRESHOLD_ACTIVE) {
+        flags |= SCRIPT_VERIFY_CHECKSEQUENCEVERIFY;
+    }
+
+    // Start enforcing WITNESS rules using versionbits logic.
+    if (IsWitnessEnabled(pindex->pprev, consensusparams)) {
+        flags |= SCRIPT_VERIFY_WITNESS;
+        flags |= SCRIPT_VERIFY_NULLDUMMY;
+    }
+
+    return flags;
+}
+
+
+
 static int64_t nTimeCheck = 0;
 static int64_t nTimeForks = 0;
 static int64_t nTimeVerify = 0;
@@ -1584,34 +1721,14 @@ static bool ConnectBlock(const CBlock& block, CValidationState& state, CBlockInd
         }
     }
 
-    // BIP16 didn't become active until Apr 1 2012
-    int64_t nBIP16SwitchTime = 1333238400;
-    bool fStrictPayToScriptHash = (pindex->GetBlockTime() >= nBIP16SwitchTime);
-
-    unsigned int flags = fStrictPayToScriptHash ? SCRIPT_VERIFY_P2SH : SCRIPT_VERIFY_NONE;
-
-    // Start enforcing the DERSIG (BIP66) rule
-    if (pindex->nHeight >= chainparams.GetConsensus().BIP66Height) {
-        flags |= SCRIPT_VERIFY_DERSIG;
-    }
-
-    // Start enforcing CHECKLOCKTIMEVERIFY (BIP65) rule
-    if (pindex->nHeight >= chainparams.GetConsensus().BIP65Height) {
-        flags |= SCRIPT_VERIFY_CHECKLOCKTIMEVERIFY;
-    }
-
     // Start enforcing BIP68 (sequence locks) and BIP112 (CHECKSEQUENCEVERIFY) using versionbits logic.
     int nLockTimeFlags = 0;
     if (VersionBitsState(pindex->pprev, chainparams.GetConsensus(), Consensus::DEPLOYMENT_CSV, versionbitscache) == THRESHOLD_ACTIVE) {
-        flags |= SCRIPT_VERIFY_CHECKSEQUENCEVERIFY;
         nLockTimeFlags |= LOCKTIME_VERIFY_SEQUENCE;
     }
 
-    // Start enforcing WITNESS rules using versionbits logic.
-    if (IsWitnessEnabled(pindex->pprev, chainparams.GetConsensus())) {
-        flags |= SCRIPT_VERIFY_WITNESS;
-        flags |= SCRIPT_VERIFY_NULLDUMMY;
-    }
+    // Get the script flags for this block
+    unsigned int flags = GetBlockScriptFlags(pindex, chainparams.GetConsensus());
 
     int64_t nTime2 = GetTimeMicros(); nTimeForks += nTime2 - nTime1;
     LogPrint(BCLog::BENCH, "    - Fork checks: %.2fms [%.2fs]\n", 0.001 * (nTime2 - nTime1), nTimeForks * 0.000001);
@@ -1672,7 +1789,7 @@ static bool ConnectBlock(const CBlock& block, CValidationState& state, CBlockInd
 
             std::vector<CScriptCheck> vChecks;
             bool fCacheResults = fJustCheck; /* Don't cache results if we're actually connecting blocks (still consult the cache, though) */
-            if (!CheckInputs(tx, state, view, fScriptChecks, flags, fCacheResults, txdata[i], nScriptCheckThreads ? &vChecks : NULL))
+            if (!CheckInputs(tx, state, view, fScriptChecks, flags, fCacheResults, fCacheResults, txdata[i], nScriptCheckThreads ? &vChecks : NULL))
                 return error("ConnectBlock(): CheckInputs on %s failed with %s",
                     tx.GetHash().ToString(), FormatStateMessage(state));
             control.Add(vChecks);
diff --git a/src/validation.h b/src/validation.h
index 8a721dd7a2..a9f995abb8 100644
--- a/src/validation.h
+++ b/src/validation.h
@@ -393,6 +393,9 @@ public:
     ScriptError GetScriptError() const { return error; }
 };
 
+/** Initializes the script-execution cache */
+void InitScriptExecutionCache();
+
 
 /** Functions for disk access for blocks */
 bool ReadBlockFromDisk(CBlock& block, const CDiskBlockPos& pos, const Consensus::Params& consensusParams);