In any case, Java's stack-based bytecode is really a register machine in disguise. It isn't a general stack machine -- for instance, at a given "PC" the shape of the expression stack (i.e. the number and "basic" types of elements in it) needs to be constant.
The right way to look at Java's bytecode stream is opcodes for a register machine with _implicit_ input and output registers. Mapping it to a compiler IR would not be easy in the general case if that weren't true.
The right way to look at Java's bytecode stream is opcodes for a register machine with _implicit_ input and output registers. Mapping it to a compiler IR would not be easy in the general case if that weren't true.