coinstats: avoid unnecessary Coin copy in ApplyHash #33410

1. 
   sashass1315 commented at 8:47 am on September 17, 2025: none

   Replace local Coin coin = it->second; with const Coin& coin = it->second; when iterating outputs in ApplyHash. The hash serialization path only reads from the Coin, and outputs remains valid for the loop’s duration, so copying is unnecessary. This reduces potential allocations (due to CTxOut/CScript) and improves performance without changing behavior.
2. coinstats: avoid unnecessary Coin copy in ApplyHash 5a56203f4e
3. 
   DrahtBot commented at 8:47 am on September 17, 2025: contributor

   The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.

   Code Coverage & Benchmarks

   For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/33410.

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4. in src/kernel/coinstats.cpp:96 in 5a56203f4e

   92@@ -93,7 +93,7 @@ static void ApplyHash(T& hash_obj, const Txid& hash, const std::map<uint32_t, Co
   93 {
   94     for (auto it = outputs.begin(); it != outputs.end(); ++it) {
   95         COutPoint outpoint = COutPoint(hash, it->first);
   96-        Coin coin = it->second;
   

   ---

   ---

   

   l0rinc commented at 4:18 pm on September 17, 2025:

   given the above warning, can you create a godbolt reproducer to check if the compiler can already deduce this or not?
5. 
   Raimo33 commented at 5:33 pm on September 17, 2025: none

   Concept ACK, I want to expand on l0rinc suggestion by saying that, given the above warning, I think this should only be merged if it results in a significant performance improvement. @sashass1315 are you able to run some before/after benchmarks?

Contributors
sashass1315 DrahtBot l0rinc Raimo33