Is this actually feasible to detect for vectors? I can easily imagine heap-to-stack optimizations for mutable structs because the size is fixed, and while I’m not as certain, I think >=2-dimensional arrays also can’t change their size. But vectors definitely have dynamic sizes, and while it’s simple enough to check for push!, popat!, etc. in the method, these calls could also happen in very nested method calls. Is the compiler capable of ruling out resizing in all nested non-inlined calls, or would it just give up even when the programmer knows none of those methods resize the array?
That said, mutable StaticArrays could end up on the stack more readily than they already do.