Merge #8330: Structure Packing Optimizations in C{,Mutable}Transaction

37495e0d8 Reorder C{,Mutable}Transaction for better packing (Jeremy Rubin)

Pull request description:

  These commits revise the layout of a few key classes to eliminate padding, eliminating useless memory overhead.

  -This reduces CTransaction from 96 bytes to 88 bytes

Tree-SHA512: 91d1fec363edebbb1f1a5b98142c767511e99d3be857148a76e31cc512c9ab3d153083fa6b46b6407974d3b88de984b436c33e8606fbb2b273d74c825195aa17

src/primitives/transaction.cpp

@@ -55,7 +55,7 @@ std::string CTxOut::ToString() const
 }
 
 CMutableTransaction::CMutableTransaction() : nVersion(CTransaction::CURRENT_VERSION), nLockTime(0) {}
-CMutableTransaction::CMutableTransaction(const CTransaction& tx) : nVersion(tx.nVersion), vin(tx.vin), vout(tx.vout), nLockTime(tx.nLockTime) {}
+CMutableTransaction::CMutableTransaction(const CTransaction& tx) : vin(tx.vin), vout(tx.vout), nVersion(tx.nVersion), nLockTime(tx.nLockTime) {}
 
 uint256 CMutableTransaction::GetHash() const
 {
@@ -76,9 +76,9 @@ uint256 CTransaction::GetWitnessHash() const
 }
 
 /* For backward compatibility, the hash is initialized to 0. TODO: remove the need for this default constructor entirely. */
-CTransaction::CTransaction() : nVersion(CTransaction::CURRENT_VERSION), vin(), vout(), nLockTime(0), hash() {}
-CTransaction::CTransaction(const CMutableTransaction &tx) : nVersion(tx.nVersion), vin(tx.vin), vout(tx.vout), nLockTime(tx.nLockTime), hash(ComputeHash()) {}
-CTransaction::CTransaction(CMutableTransaction &&tx) : nVersion(tx.nVersion), vin(std::move(tx.vin)), vout(std::move(tx.vout)), nLockTime(tx.nLockTime), hash(ComputeHash()) {}
+CTransaction::CTransaction() : vin(), vout(), nVersion(CTransaction::CURRENT_VERSION), nLockTime(0), hash() {}
+CTransaction::CTransaction(const CMutableTransaction &tx) : vin(tx.vin), vout(tx.vout), nVersion(tx.nVersion), nLockTime(tx.nLockTime), hash(ComputeHash()) {}
+CTransaction::CTransaction(CMutableTransaction &&tx) : vin(std::move(tx.vin)), vout(std::move(tx.vout)), nVersion(tx.nVersion), nLockTime(tx.nLockTime), hash(ComputeHash()) {}
 
 CAmount CTransaction::GetValueOut() const
 {

src/primitives/transaction.h

@@ -278,9 +278,9 @@ public:
     // actually immutable; deserialization and assignment are implemented,
     // and bypass the constness. This is safe, as they update the entire
     // structure, including the hash.
-    const int32_t nVersion;
     const std::vector<CTxIn> vin;
     const std::vector<CTxOut> vout;
+    const int32_t nVersion;
     const uint32_t nLockTime;
 
 private:
@@ -361,9 +361,9 @@ public:
 /** A mutable version of CTransaction. */
 struct CMutableTransaction
 {
-    int32_t nVersion;
     std::vector<CTxIn> vin;
     std::vector<CTxOut> vout;
+    int32_t nVersion;
     uint32_t nLockTime;
 
     CMutableTransaction();