How does HLVM's GC work?
HLVM injects code into managed user-code functions that keep two data structures up to date: The shadow stack lists all references held on the stack or in registers and acts as the set of global roots into the heap. If a function accepts an argument of a reference type or allocates then the value is pushed onto the shadow stack. On function exit, the shadow stack is reset back to the way it was when the function was entered. The allocated list gives all of the references that have been allocated by the program. When a function allocates, the value is appended onto the allocated list. When the allocation quota is exceeeded a garbage collection occurs. This is composed of two phases: Mark. Starting from the global roots on the shadow stack, all reachable data in the heap are marked as reachable (and the rest left marked as unreachable). Sweep. The allocated list is traversed, unreachable values are freed and all values have their mark state set back to unreachable. This functionality ...