[validation] Cache merkle root and witness commitment checks

Slight performance improvement by avoiding duplicate work.

Author: dergoegge

src/primitives/block.h

@@ -71,8 +71,10 @@ class CBlock : public CBlockHeader
     // 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()
     {
@@ -95,6 +97,8 @@ class CBlock : public CBlockHeader
         CBlockHeader::SetNull();
         vtx.clear();
         fChecked = false;
+        m_checked_witness_commitment = false;
+        m_checked_merkle_root = false;
     }
 
     CBlockHeader GetBlockHeader() const

src/validation.cpp

@@ -3641,6 +3641,8 @@ 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 merkle_root = BlockMerkleRoot(block, &mutated);
     if (block.hashMerkleRoot != merkle_root) {
@@ -3660,6 +3662,7 @@ static bool CheckMerkleRoot(const CBlock& block, BlockValidationState& state)
             /*debug_message=*/"duplicate transaction");
     }
 
+    block.m_checked_merkle_root = true;
     return true;
 }
 
@@ -3672,6 +3675,8 @@ static bool CheckMerkleRoot(const CBlock& block, BlockValidationState& state)
 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) {
             assert(!block.vtx.empty() && !block.vtx[0]->vin.empty());
@@ -3697,6 +3702,7 @@ static bool CheckWitnessMalleation(const CBlock& block, bool expect_witness_comm
                     /*debug_message=*/strprintf("%s : witness merkle commitment mismatch", __func__));
             }
 
+            block.m_checked_witness_commitment = true;
             return true;
         }
     }