Avoid duplicate CheckBlock checks

(cherry picked from commit bitcoin/bitcoin@3b33ec85ed)

src/main.cpp

@@ -4730,6 +4730,9 @@ bool CheckBlock(const CBlock& block,
 {
     // These are checks that are independent of context.
 
+    if (block.fChecked)
+        return true;
+
     // Check that the header is valid (particularly PoW).  This is mostly
     // redundant with the call in AcceptBlockHeader.
     if (!CheckBlockHeader(block, state, chainparams, fCheckPOW))
@@ -4788,6 +4791,9 @@ bool CheckBlock(const CBlock& block,
         return state.DoS(100, error("CheckBlock(): out-of-bounds SigOpCount"),
                          REJECT_INVALID, "bad-blk-sigops", true);
 
+    if (fCheckPOW && fCheckMerkleRoot)
+        block.fChecked = true;
+
     return true;
 }
 

src/primitives/block.h

@@ -89,6 +89,9 @@ public:
     // network and disk
     std::vector<CTransaction> vtx;
 
+    // memory only
+    mutable bool fChecked;
+
     CBlock()
     {
         SetNull();
@@ -112,6 +115,7 @@ public:
     {
         CBlockHeader::SetNull();
         vtx.clear();
+        fChecked = false;
     }
 
     CBlockHeader GetBlockHeader() const