`CCoinsViewCache::GetValueIn(…)` performs money summation like this:

```c++
CAmount CCoinsViewCache::GetValueIn(const CTransaction& tx) const
{
    if (tx.IsCoinBase())
        return 0;

    CAmount nResult = 0;
    for (unsigned int i = 0; i < tx.vin.size(); i++)
        nResult += AccessCoin(tx.vin[i].prevout).out.nValue;

    return nResult;
}
```

Note that no check is done to make sure that the resulting `nResult` is such that it stays within the money bounds (`MoneyRange(nResult)`), or that the summation does not trigger a signed integer overflow.

Proof of concept output:

```
coins.cpp:243:17: runtime error: signed integer overflow: 9223200000000000000 + 2100000000000000 cannot be represented in type 'long'
GetValueIn = -9221444073709551616
```

Proof of concept code:

```c++
CMutableTransaction mutable_transaction;
mutable_transaction.vin.resize(4393);

Coin coin;
coin.out.nValue = MAX_MONEY;
assert(MoneyRange(coin.out.nValue));

CCoinsCacheEntry coins_cache_entry;
coins_cache_entry.coin = coin;
coins_cache_entry.flags = CCoinsCacheEntry::DIRTY;

CCoinsView backend_coins_view;
CCoinsViewCache coins_view_cache{&backend_coins_view};
CCoinsMap coins_map;
coins_map.emplace(COutPoint{}, std::move(coins_cache_entry));
coins_view_cache.BatchWrite(coins_map, {});

const CAmount total_value_in = coins_view_cache.GetValueIn(CTransaction{mutable_transaction});
std::cout << "GetValueIn = " << total_value_in << std::endl;
```

As far as I can tell `CCoinsViewCache::GetValueIn` is unused outside of tests:

```sh
$ git grep GetValueIn ":(exclude)src/test/" ":(exclude)src/bench/"
src/coins.cpp:CAmount CCoinsViewCache::GetValueIn(const CTransaction& tx) const
src/coins.h:    CAmount GetValueIn(const CTransaction& tx) const;
src/primitives/transaction.h:    // GetValueIn() is a method on CCoinsViewCache, because
```

I suggest we drop the unused `CCoinsViewCache::GetValueIn(…)`.

Any objections? :)
throw std::logic_error("CCoinsViewCache cursor iteration not supported.");
    }
    /**
     * Check if we have the given utxo already loaded in this cache.
     * The semantics are the same as HaveCoin(), but no calls to
     * the backing CCoinsView are made.
     */
    bool HaveCoinInCache(const COutPoint &outpoint) const;
    /**
     * Return a reference to Coin in the cache, or coinEmpty if not found. This is
     * more efficient than GetCoin.
     *
     * Generally, do not hold the reference returned for more than a short scope.
     * While the current implementation allows for modifications to the contents
     * of the cache while holding the reference, this behavior should not be relied
     * on! To be safe, best to not hold the returned reference through any other
     * calls to this cache.
     */
    const Coin& AccessCoin(const COutPoint &output) const;
    /**
     * Add a coin. Set possible_overwrite to true if an unspent version may
     * already exist in the cache.
     */
    void AddCoin(const COutPoint& outpoint, Coin&& coin, bool possible_overwrite);
    /**
     * Spend a coin. Pass moveto in order to get the deleted data.