Detect when a record, tuple, or call can write in-place

[marijnh]

If you do x = rec(a=10 with x) or y = f(y) or similar, the result has to be constructed in a scratch space, rather than directly into the local variable's memory, because the local is needed to build the result. The alias analysis could mark expressions where this is not needed, so that we can avoid this scratch alloc + move as much as possible. (This is already done when the expression initializes the memory, rather than replacing an existing value.)

[marijnh]

I'm going to close this. Doing it correctly turned out to be harder than expected, and the win wouldn't be that big.