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Most VMs use one or more stacks for passing temporary data between VM instructions. Another option is to use a register machine architecture for the virtual machine; we believe that using a stack architecture is usually both simpler and faster.
however, this option is slower or significantly more complex to implement than a stack machine architecture.
Vmgen has special support and optimizations for stack VMs, making their implementation easy and efficient.
You can also implement a register VM with Vmgen (see Register Machines), and you will still profit from most Vmgen features.
Stack items all have the same size, so they typically will be as wide as an integer, pointer, or floating-point value. Vmgen supports treating two consecutive stack items as a single value, but anything larger is best kept in some other memory area (e.g., the heap), with pointers to the data on the stack.
Another source of data is immediate arguments VM instructions (in the VM instruction stream). The VM instruction stream is handled similar to a stack in Vmgen.
Vmgen has no built-in support for, nor restrictions against garbage collection. If you need garbage collection, you need to provide it in your run-time libraries. Using reference counting is probably harder, but might be possible (contact us if you are interested).