Implement structure inlining

[pschachte]

Where a member of one structure type is an instance of another, consider embedding the inner structure directly in the outer one. This will save an allocation, an indirection every time the inner structure is accessed, and a word of memory. This is the difference between (in C)

struct foo {
    struct bar *ptr;
    ...
}

and

struct foo {
    struct bar actual_struct;
    ...
}

The cost of doing this is that duplicating the outer structure entails copying the inner one, too, so more memory must be allocated and copied (ie, the data structure is not persistent). Also, destructively modifying the outer structure to replace the inner one would require copying the whole inner structure, rather than just storing one pointer, so we wouldn't want to always do this. Obviously, we can't do it for a recursive structure.

Finding a heuristic for determining when this is desirable is an interesting research project.