From fd79bb753080ca98b368a9c0437c477b1f7477b3 Mon Sep 17 00:00:00 2001
From: Pieter Wuille <sipa@ulyssis.org>
Date: Thu, 1 Apr 2021 17:46:22 -0300
Subject: [PATCH] Optimize ActivateBestChain for long chains

Github-Pull: #2290
Rebased-From: 8d15cf58ca0fd3f97fd6bcaf671b2b7e9f62caa9
---
 src/validation.cpp | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/src/validation.cpp b/src/validation.cpp
index ef9a3e728d69c..3ec2b5773ccc2 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -2138,12 +2138,11 @@ static void PruneBlockIndexCandidates()
  * Try to make some progress towards making pindexMostWork the active block.
  * pblock is either NULL or a pointer to a CBlock corresponding to pindexMostWork.
  */
-static bool ActivateBestChainStep(CValidationState& state, CBlockIndex* pindexMostWork, const std::shared_ptr<const CBlock>& pblock, bool fAlreadyChecked, ConnectTrace& connectTrace)
+static bool ActivateBestChainStep(CValidationState& state, CBlockIndex* pindexMostWork, const std::shared_ptr<const CBlock>& pblock, bool fAlreadyChecked, bool& fInvalidFound, ConnectTrace& connectTrace)
 {
     AssertLockHeld(cs_main);
     if (pblock == NULL)
         fAlreadyChecked = false;
-    bool fInvalidFound = false;
     const CBlockIndex* pindexOldTip = chainActive.Tip();
     const CBlockIndex* pindexFork = chainActive.FindFork(pindexMostWork);
 
@@ -2246,16 +2245,23 @@ bool ActivateBestChain(CValidationState& state, std::shared_ptr<const CBlock> pb
             ConnectTrace connectTrace(mempool); // Destructed before cs_main is unlocked
 
             CBlockIndex *pindexOldTip = chainActive.Tip();
-            pindexMostWork = FindMostWorkChain();
+            if (pindexMostWork == nullptr) {
+                pindexMostWork = FindMostWorkChain();
+            }
 
             // Whether we have anything to do at all.
-            if (pindexMostWork == NULL || pindexMostWork == chainActive.Tip())
+            if (pindexMostWork == nullptr || pindexMostWork == chainActive.Tip())
                 return true;
 
+            bool fInvalidFound = false;
             std::shared_ptr<const CBlock> nullBlockPtr;
-            if (!ActivateBestChainStep(state, pindexMostWork, pblock && pblock->GetHash() == pindexMostWork->GetBlockHash() ? pblock : nullBlockPtr, fAlreadyChecked, connectTrace))
+            if (!ActivateBestChainStep(state, pindexMostWork, pblock && pblock->GetHash() == pindexMostWork->GetBlockHash() ? pblock : nullBlockPtr, fAlreadyChecked, fInvalidFound, connectTrace))
                 return false;
 
+            if (fInvalidFound) {
+                // Wipe cache, we may need another branch now.
+                pindexMostWork = nullptr;
+            }
             pindexNewTip = chainActive.Tip();
             pindexFork = chainActive.FindFork(pindexOldTip);
             fInitialDownload = IsInitialBlockDownload();