IBD: do not check PoW (Yespower) during Downloading headers

This means PoW check during IBD is not actually skipped, but still its checking in another places. What we skipped is only when Downloading headers, but not else. This makes IBD much faster.

src/validation.cpp

@@ -3047,6 +3047,13 @@ static bool CheckBlockHeader(const CBlockHeader& block, CValidationState& state,
     if (fCheckPOW && !CheckProofOfWork(block.GetPoWHash_cached(), block.nBits, consensusParams))
         return state.DoS(50, false, REJECT_INVALID, "high-hash", false, "proof of work failed");
 
+    // FIXME.SUGAR // PoW check: SKIPPED during IBD
+    // You can see this log when IBD.
+    // This means PoW check during IBD is not actually skipped, but still its checking in another places.
+    // What we skipped is only when Downloading headers, but not else. This makes IBD much faster.
+    if (IsInitialBlockDownload())
+        printf("%s IBD=%d CBH=%s\n", DateTimeStrFormat("%Y-%m-%d %H:%M:%S", GetTime()).c_str(), IsInitialBlockDownload(), block.GetHash().ToString().c_str());
+
     return true;
 }
 
@@ -3334,7 +3341,9 @@ bool CChainState::AcceptBlockHeader(const CBlockHeader& block, CValidationState&
             return true;
         }
 
-        if (!CheckBlockHeader(block, state, chainparams.GetConsensus()))
+        // FIXME.SUGAR // PoW check: SKIPPED during IBD
+        // IBD: Do not PoW check during "Downloading Headers" for performance reason
+        if (!IsInitialBlockDownload() && !CheckBlockHeader(block, state, chainparams.GetConsensus()))
             return error("%s: Consensus::CheckBlockHeader: %s, %s", __func__, hash.ToString(), FormatStateMessage(state));
 
         // Get prev block index