JIT code has much higher cost for helper function calls

Native:
```
Hash-table Map Read,72,72
```

JIT:
```
Hash-table Map Read,158,158
```

Start by reproducing the Native and JIT Hash-table Map Read measurements shown in the issue and compare the helper-function call paths. Trace where the JIT adds the extra cost; done means the JIT measurement is investigated and the performance gap is reduced or explained with supporting benchmark results.

Written by the indexing model from the issue text.