use const refs in for loops for non tiny types

src/blockchain_utilities/blockchain_import.cpp

@@ -459,7 +459,7 @@ int import_from_file(cryptonote::core& core, const std::string& import_file_path
 
           // tx number 1: coinbase tx
           // tx number 2 onwards: archived_txs
-          for (transaction tx : archived_txs)
+          for (const transaction &tx : archived_txs)
           {
             // add blocks with verification.
             // for Blockchain and blockchain_storage add_new_block().

src/cryptonote_protocol/block_queue.cpp

@@ -385,7 +385,7 @@ float block_queue::get_speed(const boost::uuids::uuid &connection_id) const
       i->second = (i->second + span.rate) / 2;
   }
   float conn_rate = -1, best_rate = 0;
-  for (auto i: speeds)
+  for (const auto &i: speeds)
   {
     if (i.first == connection_id)
       conn_rate = i.second;

src/daemon/rpc_command_executor.cpp

@@ -1611,7 +1611,7 @@ bool t_rpc_command_executor::alt_chain_info()
   }
 
   tools::msg_writer() << boost::lexical_cast<std::string>(res.chains.size()) << " alternate chains found:";
-  for (const auto chain: res.chains)
+  for (const auto &chain: res.chains)
   {
     uint64_t start_height = (chain.height - chain.length + 1);
     tools::msg_writer() << chain.length << " blocks long, from height " << start_height << " (" << (ires.height - start_height - 1)

src/debug_utilities/object_sizes.cpp

@@ -51,7 +51,7 @@ class size_logger
 public:
   ~size_logger()
   {
-    for (const auto i: types)
+    for (const auto &i: types)
       std::cout << std::to_string(i.first) << "\t" << i.second << std::endl;
   }
   void add(const char *type, size_t size) { types.insert(std::make_pair(size, type)); }

src/wallet/wallet2.cpp

@@ -5126,7 +5126,7 @@ void wallet2::get_outs(std::vector<std::vector<tools::wallet2::get_outs_entry>>
       // if there are just enough outputs to mix with, use all of them.
       // Eventually this should become impossible.
       uint64_t num_outs = 0, num_recent_outs = 0;
-      for (auto he: resp_t.result.histogram)
+      for (const auto &he: resp_t.result.histogram)
       {
         if (he.amount == amount)
         {