Clever VM

Instructions

Clever VM works using TAC (thread-address code [1]) to describe its intermediate code. Currently it’s represented as:

struct IR {
        Opcode opcode;
        Operand op1, op2, result;
        location loc;
};

See core/ir.h for futher details.

Where the operand is represented as:

struct Operand {
        OperandType op_type;
        ValueOffset voffset;
        size_t jmp_addr;
};

The operand can work with four diferent informations, see below:

Operand type	Description
FETCH_VAR	For fetching a variable from the environment
FETCH_CONST	For fetching a constant from the environment
FETCH_TMP	For fetching a temporary storage from the environment
JMP_ADDR	For jumping over the code

For futher details on Environment, see our wiki [2].

Basically, each function and class has its environment. Global scope and its local scope uses the same environment. In compiler-time we assign an identifier for each variable name to its respective index relative to the environment which it is found. For threating the relative location of the variable, we assign a identifier to the relative environment, beyond the index for the variable.

Hence ‘FETCH_VAR` means that a variable must be fetched according to its relative environment location.

For constant values (literal ones like true, 1, etc), we do use a constant environment which is global for the execution, thus using FETCH_CONST to fetch the literal value based on the index associated to it on compile-time.

The FETCH_TMP works under the temporary environment which is located in the current environment. This is, each environment can have its temporary environment to store computed result to future access. (e.g. 1 + 1 / 2)

And about JMP_ADDR we can describe it as an address to the instrunction pointer to be jumped over, like a goto operation.

Opcodes

A list of our available opcodes can be seen in the file core/opcode.h.

When building Clever in debug mode, the option -d is available to provide us a way to see the generated code. See below:

$ ./clever -d -qr 'println(1);'
[000] OP_SEND_VAL  |  0:  3  (FETCH_CONST) |          (UNUSED     ) |          (UNUSED     ) |
[001] OP_FCALL     |  0: 41  (FETCH_VAR  ) |          (UNUSED     ) |   0:  0  (FETCH_TMP  ) |
[002] OP_HALT      |         (UNUSED     ) |          (UNUSED     ) |          (UNUSED     ) |

[1]	http://en.wikipedia.org/wiki/Three_address_code

[2]	https://github.com/clever-lang/clever/wiki/RFC-%230002—-Lexical-scopes,-environments,-stack-frames-and-the-call-stack