[Issue 7157] Optimiser is O(n^2) w.r.t. function length

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=7157

--- Comment #9 from Martin Nowak <code at dawg.eu> ---
Could we fix this for now by letting dmd backoff from very big functions?
Or if someone understands accumaecpx well enough, maybe the optimization can be
windowed to 1000 expressions/statements or so.

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