Abstract machine

The semantics of Hylo IR is defined in terms of an abstract machine. A language implementation shall interpret or compile native programs that follow the same behavior.

The Val abstract machine consists of a collection of threads and a global memory space. A thread consists of a register map that associates local register names to objects or locations in the machine's global memory, a control stack that contains instructions, and a call stack that contains register maps.

A thread is similar to a SECD machine without a register stack. Just like in ANF, instruction operands are either constants or names denoting the value of a local register.

When a basic block is loaded into a thread, its instructions are pushed onto the stack in reverse order (i.e., the last instruction is pushed first).

Program execution

Program execution starts by adding a thread to the abstract machine, which gets designated as the main thread. The register map and call stack of the main thread are initialized empty. The control stack is initialized by loading the entry block of the main function of the program's entry module.