On May 23, 2020 9:32:32 AM EDT, Andreas Klebinger
Surely, the RTS must be able to count the number of times a constructor is used. It can't. For one there are different kinds of "uses" for constructors.
This is a fair point. I had assumed that Richard was debugging a residency issue but i suppose that was an ungrounded assumption on my part.
* Allocations - They might be dead by the time we gc the nursery, so the RTS never get's to see them.
Indeed I thought that the ticky-ticky profiler could do precisely this but it seems I was mistaken; it can only report thunks. Indeed it doesn't seem like it would be hard to introduce this.
* Accessing the Constructor? That's even harder to track.
Indeed, this is not possible as written. However, the LDV profiler allows a slightly weaker version on this (reporting whether the closure as been read at all). Allowing full tracking of closure reads this would incur a significant overhead.