[validation] Cache merkle root and witness commitment checks

Slight performance improvement by avoiding duplicate work.

Github-Pull: #29412
Rebased-From: 1ec6bbeb8d

src/primitives/block.h

@@ -71,8 +71,10 @@ public:
     // network and disk
     std::vector<CTransactionRef> vtx;
 
-    // memory only
-    mutable bool fChecked;
+    // Memory-only flags for caching expensive checks
+    mutable bool fChecked;                            // CheckBlock()
+    mutable bool m_checked_witness_commitment{false}; // CheckWitnessCommitment()
+    mutable bool m_checked_merkle_root{false};        // CheckMerkleRoot()
 
     CBlock()
     {
@@ -96,6 +98,8 @@ public:
         CBlockHeader::SetNull();
         vtx.clear();
         fChecked = false;
+        m_checked_witness_commitment = false;
+        m_checked_merkle_root = false;
     }
 
     CBlockHeader GetBlockHeader() const

src/validation.cpp

@@ -3488,6 +3488,8 @@ static bool CheckBlockHeader(const CBlockHeader& block, BlockValidationState& st
 
 static bool CheckMerkleRoot(const CBlock& block, BlockValidationState& state)
 {
+    if (block.m_checked_merkle_root) return true;
+
     bool mutated;
     uint256 hashMerkleRoot2 = BlockMerkleRoot(block, &mutated);
     if (block.hashMerkleRoot != hashMerkleRoot2)
@@ -3499,12 +3501,15 @@ static bool CheckMerkleRoot(const CBlock& block, BlockValidationState& state)
     if (mutated)
         return state.Invalid(BlockValidationResult::BLOCK_MUTATED, "bad-txns-duplicate", "duplicate transaction");
 
+    block.m_checked_merkle_root = true;
     return true;
 }
 
 static bool CheckWitnessMalleation(const CBlock& block, bool expect_witness_commitment, BlockValidationState& state)
 {
     if (expect_witness_commitment) {
+        if (block.m_checked_witness_commitment) return true;
+
         int commitpos = GetWitnessCommitmentIndex(block);
         if (commitpos != NO_WITNESS_COMMITMENT) {
             bool malleated = false;
@@ -3520,6 +3525,7 @@ static bool CheckWitnessMalleation(const CBlock& block, bool expect_witness_comm
                 return state.Invalid(BlockValidationResult::BLOCK_MUTATED, "bad-witness-merkle-match", strprintf("%s : witness merkle commitment mismatch", __func__));
             }
 
+            block.m_checked_witness_commitment = true;
             return true;
         }
     }