Merge #18401: Refactor: Initialize PrecomputedTransactionData in CheckInputScripts

f63dec189c3c8eee1ab2187681d5d0b2513b1b2e [REFACTOR] Initialize PrecomputedTransactionData in CheckInputScripts (Pieter Wuille)

Pull request description:

  This is a single commit taken from the Schnorr/Taproot PR #17977.

  Add a default constructor to `PrecomputedTransactionData`, which doesn't initialize the struct's members. Instead they're initialized inside the `CheckInputScripts()` function. This allows a later commit to add the spent UTXOs to that structure. The spent UTXOs are required for the schnorr signature hash, since it commits to the scriptPubKeys. See https://github.com/bitcoin/bips/blob/master/bip-0341.mediawiki#common-signature-message for details.

  By itself, this isn't really an improvement to the code, but I think it makes sense to separate out the refactor/moveonly commits from PR #17977 so that PR is only the logical changes needed for Schnorr/Taproot.

ACKs for top commit:
  jonatack:
    Re-ACK f63dec1  `git diff 851908d f63dec1` shows no change since last ACK.
  sipa:
    utACK f63dec189c3c8eee1ab2187681d5d0b2513b1b2e
  theStack:
    re-ACK f63dec189c3c8eee1ab2187681d5d0b2513b1b2e
  fjahr:
    Re-ACK f63dec189c3c8eee1ab2187681d5d0b2513b1b2e
  ariard:
    Code Review ACK f63dec1

Tree-SHA512: ecf9154077824ae4c274b4341e985797f3648c0cb0c31cb25ce382163b923a3acbc7048683720be4ae3663501801129cd0f48c441a36f049cc304ebe9f30994e

2 files changed, 20 insertions, 4 deletions

diff --git a/src/script/interpreter.cpp b/src/script/interpreter.cpp
index 50f7806ba5..d70960a8bd 100644
--- a/src/script/interpreter.cpp
+++ b/src/script/interpreter.cpp
@@ -1291,18 +1291,29 @@ uint256 GetOutputsHash(const T& txTo)
 } // namespace
 
 template <class T>
-PrecomputedTransactionData::PrecomputedTransactionData(const T& txTo)
+void PrecomputedTransactionData::Init(const T& txTo)
 {
+    assert(!m_ready);
+
     // Cache is calculated only for transactions with witness
     if (txTo.HasWitness()) {
         hashPrevouts = GetPrevoutHash(txTo);
         hashSequence = GetSequenceHash(txTo);
         hashOutputs = GetOutputsHash(txTo);
-        ready = true;
     }
+
+    m_ready = true;
+}
+
+template <class T>
+PrecomputedTransactionData::PrecomputedTransactionData(const T& txTo)
+{
+    Init(txTo);
 }
 
 // explicit instantiation
+template void PrecomputedTransactionData::Init(const CTransaction& txTo);
+template void PrecomputedTransactionData::Init(const CMutableTransaction& txTo);
 template PrecomputedTransactionData::PrecomputedTransactionData(const CTransaction& txTo);
 template PrecomputedTransactionData::PrecomputedTransactionData(const CMutableTransaction& txTo);
 
@@ -1315,7 +1326,7 @@ uint256 SignatureHash(const CScript& scriptCode, const T& txTo, unsigned int nIn
         uint256 hashPrevouts;
         uint256 hashSequence;
         uint256 hashOutputs;
-        const bool cacheready = cache && cache->ready;
+        const bool cacheready = cache && cache->m_ready;
 
         if (!(nHashType & SIGHASH_ANYONECANPAY)) {
             hashPrevouts = cacheready ? cache->hashPrevouts : GetPrevoutHash(txTo);
diff --git a/src/script/interpreter.h b/src/script/interpreter.h
index 2b104a608c..71f2436369 100644
--- a/src/script/interpreter.h
+++ b/src/script/interpreter.h
@@ -121,7 +121,12 @@ bool CheckSignatureEncoding(const std::vector<unsigned char> &vchSig, unsigned i
 struct PrecomputedTransactionData
 {
     uint256 hashPrevouts, hashSequence, hashOutputs;
-    bool ready = false;
+    bool m_ready = false;
+
+    PrecomputedTransactionData() = default;
+
+    template <class T>
+    void Init(const T& tx);
 
     template <class T>
     explicit PrecomputedTransactionData(const T& tx);