corelang/bytecode_interpreter.cpp

//
// Instructions
//
enum{
  INS_PUSH_S64,
  INS_PUSH_S32,
  INS_PUSH_S16,
  INS_PUSH_S8 ,
  INS_PUSH_U64,
  INS_PUSH_U32,
  INS_PUSH_U16,
  INS_PUSH_U8 ,
  INS_PUSH_F64 ,
  INS_PUSH_F32 ,
  INS_POP,

  INS_ADD,
  INS_SUB,
  INS_MUL,
  INS_DIV,
};

//
// Bytecode interpreter context
//
struct Bc{
  U8 *ins_pointer;
  U8 *stack_pointer;
  U8 *stack_bottom;
  Arena instructions;
  Arena stack;
};
#define C(type, data) ((type *)data)[0] // Cast value to type and unpack the pointer so you can write to it
#include "bytecode_interpreter_generated.cpp"

function Bc
create_bytecode_interp(){
  Bc b = {};
  {
    arena_init(&b.instructions, "Bytecode instructions"_s);
    b.instructions.alignment = 1;

    // Commit
    arena_push_size(&b.instructions, 16);
    arena_clear(&b.instructions);
    b.ins_pointer = b.instructions.memory.data;
  }

  {
    arena_init(&b.stack, "Bytecode stack"_s);
    b.stack.alignment = 8;

    // Commit
    arena_push_size(&b.stack, 16);
    arena_clear(&b.stack);
    b.stack_pointer = b.stack_bottom = b.stack.memory.data;
  }

  return b;
}

force_inline void
emit_pop(Bc *bc){
  U8 *instruction = (U8 *)arena_push_size(&bc->instructions, sizeof(U8));
  *instruction = INS_POP;
}

force_inline void *
stack_pop(Bc *b){
  assert_msg(b->stack_pointer != b->stack_bottom, "Reached bottom of bytecode interpreter stack");
  b->stack_pointer -= sizeof(U64);
  // @warning we don't do anything with type for now
  Ast_Type_Kind *type = (Ast_Type_Kind *)b->stack_pointer;
  b->stack_pointer -= sizeof(U64);
  return b->stack_pointer;
}

function void
run_bytecode_interp(Bc *b){
  for(;;){
    U8 instruction = *b->ins_pointer++;
    switch(instruction){

      case INS_POP:{
        void *value = stack_pop(b);
        S64 *s64 = (S64 *)value;
        F64 *f64 = (F64 *)value;
        U64 *u64 = (U64 *)value;
      } break;

      //
      // Generated using code_generating_script.py
      //

      case INS_PUSH_S64:{
        // Fetch value from instruction
        // instructions are tightly packed so we
        // move pointer by the type size
        auto value = (S64 *)b->ins_pointer;
        b->ins_pointer += sizeof(S64);
        stack_push_s64(b, *value);
      } break;

      case INS_PUSH_S32:{
        // Fetch value from instruction
        // instructions are tightly packed so we
        // move pointer by the type size
        auto value = (S32 *)b->ins_pointer;
        b->ins_pointer += sizeof(S32);
        stack_push_s32(b, *value);
      } break;

      case INS_PUSH_S16:{
        // Fetch value from instruction
        // instructions are tightly packed so we
        // move pointer by the type size
        auto value = (S16 *)b->ins_pointer;
        b->ins_pointer += sizeof(S16);
        stack_push_s16(b, *value);
      } break;

      case INS_PUSH_S8:{
        // Fetch value from instruction
        // instructions are tightly packed so we
        // move pointer by the type size
        auto value = (S8 *)b->ins_pointer;
        b->ins_pointer += sizeof(S8);
        stack_push_s8(b, *value);
      } break;

      case INS_PUSH_U64:{
        // Fetch value from instruction
        // instructions are tightly packed so we
        // move pointer by the type size
        auto value = (U64 *)b->ins_pointer;
        b->ins_pointer += sizeof(U64);
        stack_push_u64(b, *value);
      } break;

      case INS_PUSH_U32:{
        // Fetch value from instruction
        // instructions are tightly packed so we
        // move pointer by the type size
        auto value = (U32 *)b->ins_pointer;
        b->ins_pointer += sizeof(U32);
        stack_push_u32(b, *value);
      } break;

      case INS_PUSH_U16:{
        // Fetch value from instruction
        // instructions are tightly packed so we
        // move pointer by the type size
        auto value = (U16 *)b->ins_pointer;
        b->ins_pointer += sizeof(U16);
        stack_push_u16(b, *value);
      } break;

      case INS_PUSH_U8:{
        // Fetch value from instruction
        // instructions are tightly packed so we
        // move pointer by the type size
        auto value = (U8 *)b->ins_pointer;
        b->ins_pointer += sizeof(U8);
        stack_push_u8(b, *value);
      } break;

      case INS_PUSH_F32:{
        // Fetch value from instruction
        // instructions are tightly packed so we
        // move pointer by the type size
        auto value = (F32 *)b->ins_pointer;
        b->ins_pointer += sizeof(F32);
        stack_push_f32(b, *value);
      } break;

      case INS_PUSH_F64:{
        // Fetch value from instruction
        // instructions are tightly packed so we
        // move pointer by the type size
        auto value = (F64 *)b->ins_pointer;
        b->ins_pointer += sizeof(F64);
        stack_push_f64(b, *value);
      } break;

      //
      // **End** of generated using code_generating_script.py
      //

      default: invalid_codepath;
    }


  }
}

function void
test_interpreter(){
  Bc b = create_bytecode_interp();
  emit_push_s64(&b, 1);
  emit_push_f64(&b, 2.42f);
  emit_push_s8(&b, 3);
  emit_push_u16(&b, 4);
  emit_pop(&b);
  emit_pop(&b);
  emit_pop(&b);
  emit_pop(&b);
  run_bytecode_interp(&b);
}