**Describe the situation**
multiIf works 10 times slower than If with single condition.

**How to reproduce**
ClickHouse version 21.10

```

SELECT count()
FROM numbers_mt(1000000000)
WHERE NOT ignore(multiIf(number = 0, NULL, toNullable(number)))

┌────count()─┐
│ 1000000000 │
└────────────┘

1 rows in set. Elapsed: 10.267 sec. Processed 1.00 billion rows, 8.00 GB (97.41 million rows/s., 779.25 MB/s.)

SELECT count()
FROM numbers_mt(1000000000)
WHERE NOT ignore(If(number = 0, NULL, toNullable(number)))

┌────count()─┐
│ 1000000000 │
└────────────┘

1 rows in set. Elapsed: 1.010 sec. Processed 1.00 billion rows, 8.00 GB (990.63 million rows/s., 7.93 GB/s.)
```

**Expected performance**
The same performance for multiIf and if.

if (implicit_distinct.empty())
            return {};
    }
    
    for (const auto & id : select.select()->children)
    {
        String alias = id->tryGetAlias();
        if (const auto * identifier = id->as<ASTIdentifier>())
        {
            const String & name = identifier->shortName();
            if (select.distinct || implicit_distinct.contains(name))
            {
                if (alias.empty())
                    names.insert(name);
                else
                    names.insert(alias);
            }
        }
        else if (select.distinct && !alias.empty())
        {
            
            names.insert(alias);
        }
    }
    
    if (!select.distinct && names.size() != implicit_distinct.size())
        return {};
    return names;
}
void optimizeDuplicateDistinct(ASTSelectQuery & select)