Performs a function call, with register R(A) holding the reference to the function object to be called. Parameters to the function are placed in the registers following R(A). If B is 1, the function has no parameters. If B is 2 or more, there are (B-1) parameters. If B >= 2, then upon entry to the called function, R(A+B-1) will become the ``base``.
If B is 0, the function parameters range from R(A+1) to the top of the stack. This form is used when the
number of parameters to pass is set by the previous VM instrauction, which has to be one of '``OP_CALL``',
'``OP_VARARG``' or '``OP_SETLIST``'. In this case, upon entry to the called function, ``base`` is set to the register beyond the vararg section, which means that the varargs sit between the R(A) and ``base`` (`adjust_varargs() <http://www.lua.org/source/5.3/ldo.c.html#adjust_varargs>`_).
number of parameters to pass is set by the previous VM instruction, which has to be one of '``OP_CALL``' or
'``OP_VARARG``'. In this case, upon entry to the called function, ``base`` is set to the register beyond the vararg section, which means that the varargs sit between the R(A) and ``base`` (`adjust_varargs() <http://www.lua.org/source/5.3/ldo.c.html#adjust_varargs>`_).
Example of '``OP_VARARG``' followed by '``OP_CALL``'::
function y(...) print(...) end
1 [1] GETTABUP 0 0 -1 ; _ENV "print"
2 [1] VARARG 1 0 ; VARARG will set L->top
3 [1] CALL 0 0 1 ; B=0 so L->top set by previous instruction
4 [1] RETURN 0 1
Example of '``OP_CALL``' followed by '``OP_CALL``'::
function z1() y(x()) end
1 [1] GETTABUP 0 0 -1 ; _ENV "y"
2 [1] GETTABUP 1 0 -2 ; _ENV "x"
3 [1] CALL 1 1 0 ; C=0 so return values indicated by L->top
4 [1] CALL 0 0 1 ; B=0 so L->top set by previous instruction
5 [1] RETURN 0 1
Thus upon entry to a function ``base`` is always the location of the first fixed parameter if any or else ``local`` if any. The three possibilities are shown below.
Dibyendu Majumdar
9 years ago