From bcbf3374fd75505395d33a09dd98962b054dd486 Mon Sep 17 00:00:00 2001
From: Brooks Prumo <brooks@solana.com>
Date: Tue, 13 Dec 2022 10:20:14 -0500
Subject: [PATCH] Avoids copying hashes when computing merkle root (#29225)

---
 runtime/src/accounts_db.rs   | 2 +-
 runtime/src/accounts_hash.rs | 8 ++++----
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/runtime/src/accounts_db.rs b/runtime/src/accounts_db.rs
index 89c8c33bbe..ac393efe3b 100644
--- a/runtime/src/accounts_db.rs
+++ b/runtime/src/accounts_db.rs
@@ -10496,7 +10496,7 @@ pub mod tests {
         let (storages, raw_expected) = sample_storages_and_accounts(&db);
         let expected_hash =
             AccountsHasher::compute_merkle_root_loop(raw_expected.clone(), MERKLE_FANOUT, |item| {
-                item.hash
+                &item.hash
             });
         let sum = raw_expected.iter().map(|item| item.lamports).sum();
         let result = db
diff --git a/runtime/src/accounts_hash.rs b/runtime/src/accounts_hash.rs
index 7d000ed1ab..77af53ed42 100644
--- a/runtime/src/accounts_hash.rs
+++ b/runtime/src/accounts_hash.rs
@@ -538,12 +538,12 @@ impl AccountsHasher {
     }
 
     pub fn compute_merkle_root(hashes: Vec<(Pubkey, Hash)>, fanout: usize) -> Hash {
-        Self::compute_merkle_root_loop(hashes, fanout, |t| t.1)
+        Self::compute_merkle_root_loop(hashes, fanout, |t| &t.1)
     }
 
     // this function avoids an infinite recursion compiler error
     pub fn compute_merkle_root_recurse(hashes: Vec<Hash>, fanout: usize) -> Hash {
-        Self::compute_merkle_root_loop(hashes, fanout, |t: &Hash| *t)
+        Self::compute_merkle_root_loop(hashes, fanout, |t| t)
     }
 
     pub fn div_ceil(x: usize, y: usize) -> usize {
@@ -558,7 +558,7 @@ impl AccountsHasher {
     // Using extractor allows us to avoid an unnecessary array copy on the first iteration.
     pub fn compute_merkle_root_loop<T, F>(hashes: Vec<T>, fanout: usize, extractor: F) -> Hash
     where
-        F: Fn(&T) -> Hash + std::marker::Sync,
+        F: Fn(&T) -> &Hash + std::marker::Sync,
         T: std::marker::Sync,
     {
         if hashes.is_empty() {
@@ -806,7 +806,7 @@ impl AccountsHasher {
     pub fn accumulate_account_hashes(mut hashes: Vec<(Pubkey, Hash)>) -> Hash {
         Self::sort_hashes_by_pubkey(&mut hashes);
 
-        Self::compute_merkle_root_loop(hashes, MERKLE_FANOUT, |i| i.1)
+        Self::compute_merkle_root_loop(hashes, MERKLE_FANOUT, |i| &i.1)
     }
 
     pub fn sort_hashes_by_pubkey(hashes: &mut Vec<(Pubkey, Hash)>) {