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Ok ok this may not make a lot of sense but I am *extremely* happy to have gotten this code working!! So I feel compelled to share. (And yes, I wrote my own macro-assembler for #wasm in JavaScript. That's how much fun I'm having, and yes I mean that sincerely.) 1/x

For many nodes, we know how many children there will be, so we can allocate the correct amount of space directly in the parent node. This is conceptually simple, and cache-friendly too. 3/x

But an iteration node can have any # of children! So when the parent node is allocated, we don't know how big to make it. My solution: • Allocate space for a fixed (power of 2) # of children • If necessary, use the last child slot to point to an overflow node. 4/x

My favourite part is that by using a power of two size, I can: • Use `popcnt` to detect when it's time to grow (when only 1 bit is set) • Use `clz` (count leading zeros) to know how many overflow nodes there are. 5/x

Can you allocate the parent after the children ?