Function luaK_posfix

depends/lua/src/lcode.c:1124–1171

** Finalize code for binary operation, after reading 2nd operand. ** For '(a .. b .. c)' (which is '(a .. (b .. c))', because ** concatenation is right associative), merge second CONCAT into first ** one. */

** one.
*/
void luaK_posfix (FuncState *fs, BinOpr op,
                  expdesc *e1, expdesc *e2, int line) {
  switch (op) {
    case OPR_AND: {
      lua_assert(e1->t == NO_JUMP);  /* list closed by 'luK_infix' */
      luaK_dischargevars(fs, e2);
      luaK_concat(fs, &e2->f, e1->f);
      *e1 = *e2;
      break;
    }
    case OPR_OR: {
      lua_assert(e1->f == NO_JUMP);  /* list closed by 'luK_infix' */
      luaK_dischargevars(fs, e2);
      luaK_concat(fs, &e2->t, e1->t);
      *e1 = *e2;
      break;
    }
    case OPR_CONCAT: {
      luaK_exp2val(fs, e2);
      if (e2->k == VRELOCABLE &&
          GET_OPCODE(getinstruction(fs, e2)) == OP_CONCAT) {
        lua_assert(e1->u.info == GETARG_B(getinstruction(fs, e2))-1);
        freeexp(fs, e1);
        SETARG_B(getinstruction(fs, e2), e1->u.info);
        e1->k = VRELOCABLE; e1->u.info = e2->u.info;
      }
      else {
        luaK_exp2nextreg(fs, e2);  /* operand must be on the 'stack' */
        codebinexpval(fs, OP_CONCAT, e1, e2, line);
      }
      break;
    }
    case OPR_ADD: case OPR_SUB: case OPR_MUL: case OPR_DIV:
    case OPR_IDIV: case OPR_MOD: case OPR_POW:
    case OPR_BAND: case OPR_BOR: case OPR_BXOR:
    case OPR_SHL: case OPR_SHR: {
      if (!constfolding(fs, op + LUA_OPADD, e1, e2))
        codebinexpval(fs, cast(OpCode, op + OP_ADD), e1, e2, line);
      break;
    }
    case OPR_EQ: case OPR_LT: case OPR_LE:
    case OPR_NE: case OPR_GT: case OPR_GE: {
      codecomp(fs, op, e1, e2);
      break;
    }
    default: lua_assert(0);
  }
}


/*