#3674 Explicit cast ignored when va args argument is a function return value

[bbbbbr]

sdcc -v SDCC : z80/sm83/mos6502/mos65c02 TD- 4.3.2 #14228 (Linux)

(Issue found by Toxa, who reports it may also happen for z80 in addition to sm83)

When using va args, explicit casts to uint8_t work for passed variables (stack local, global,
etc). However if the passed parameter is a function return value then the explicit cast is ignored
and instead is passed as a 16 bit value.

It seems possible to overcome it ignoring explicit cast in this scenario by doing a
double explicit cast (uint8_t)(uint16_t).

Using --std-c2x for example forces all parameters to be passed as 16 bit, but that is the opposite of what is desired here. Explicitly using the --std-sdcc** arguments does not seem to change the behavior.

Command line used
sdcc -msm83 --no-std-crt0 --fsigned-char --use-stdout -D__PORT_sm83 -Wa-pogn -I"../../../../"lib/gb -I"../../../../"include -c vaargs_test.c -o vaargs_test.o

Simplified example:

#include <stdio.h>
#include <stdint.h>
#include <stdarg.h>

volatile uint8_t ga, gb;

void vafunc(int count, ...)
{
    volatile uint8_t temp;
    int c;
    va_list ap;
    va_start(ap, count);
    for(c=0; c < count; c++)
        temp = va_arg(ap, unsigned char);
    va_end(ap);
}

uint8_t u8func(void) {
    return (uint8_t)8u;
}

void main(void)
{
        ga = u8func();
        gb = u8func();

        vafunc(2, (uint8_t)ga, (uint8_t)gb);
        vafunc(2, (uint8_t)u8func(), (uint8_t)u8func());
        vafunc(2, (uint8_t)(uint16_t)u8func(), (uint8_t)(uint16_t)u8func());
}

_main::
;vaargs_test.c:24: ga = u8func();
    call    _u8func
    ld  (#_ga),a
;vaargs_test.c:25: gb = u8func();
    call    _u8func
    ld  hl, #_gb
    ld  (hl), a

;vaargs_test.c:27: vafunc(2, (uint8_t)ga, (uint8_t)gb);
    ld  a, (hl)
    push    af
    inc sp
    ld  a, (#_ga)
    push    af
    inc sp
    ld  de, #0x0002
    push    de
    call    _vafunc
    add sp, #4

;vaargs_test.c:28: vafunc(2, (uint8_t)u8func(), (uint8_t)u8func());
    call    _u8func
    ld  e, a
    ld  d, #0x00
    push    de
    call    _u8func
    pop de
    ld  b, #0x00
    push    de
    ld  c, a
    push    bc
    ld  de, #0x0002
    push    de
    call    _vafunc
    add sp, #6

;vaargs_test.c:29: vafunc(2, (uint8_t)(uint16_t)u8func(), (uint8_t)(uint16_t)u8func());
    call    _u8func
    ld  b, a
    push    bc
    call    _u8func
    inc sp
    push    af
    inc sp
    ld  de, #0x0002
    push    de
    call    _vafunc
    add sp, #4
;vaargs_test.c:30: }
    ret

[Tony Pavlov]

other targets affected as well, say z80 and mos6502