#4163 struct initialised from ternary of dereferences loads the pointer's contents as an address (double dereference)

[Under4Mhz]

The following code reproduces the problem:

/// GPL 2.0 or later
/// SDCC z80 miscompiles a local struct initialised from a ternary of dereferences:
///     room2 = room ? *room : *RoomGet();
/// The generated code loads 2 bytes from the struct and uses them as an address (double dereference).
#include <stdio.h>
#include <stdint.h>

typedef struct {

    uint8_t x;
    uint8_t y;

} point;

point room1 = { 11, 12 };

const point *RoomGet(void) { return &room1; }

// Expect room2 = 5,6 (copied from room). Broken on sdcc z80
static void Initialiser( const point *room ) {

    point room2 = room ? *room : *RoomGet();

    printf( "Initialiser   %d,%d (expect 5,6)\n", room2.x, room2.y );
}

// Workaround, select pointer first
static void Workaround( const point *room ) {

    if ( room == 0 ) room = RoomGet();
    point room2 = *room;

    printf( "Workaround    %d,%d (expect 5,6)\n", room2.x, room2.y );
}

void main( void ) {

    point room = { 5, 6 };

    Initialiser( &room );
    Workaround( &room );
}

#ifdef __SDCC
__sfr __at 0xff sif;
int putchar( int c ) {

    sif = 'p';
    sif = c;

    return c;
}
#endif

// sdcc -mz80 --fverbose-asm ./ternary_deref_init.c -o ternary_deref_init.ihx && ucsim_z80 -I if=outputs[0xff] ternary_deref_init.ihx
// gcc ./ternary_deref_init.c && ./a.out

$ gcc ./ternary_deref_init.c && ./a.out
Initialiser   5,6 (expect 5,6)
Workaround    5,6 (expect 5,6)

$ sdcc -mz80 --fverbose-asm ./ternary_deref_init.c -o ternary_deref_init.ihx && ucsim_z80 -I if=outputs[0xff] ternary_deref_init.ihx
r
Initialiser   84,202 (expect 5,6)
Workaround    5,6 (expect 5,6)

SDCC : z80/sm83/ez80/z80n/mos6502/mos65c02/huc6280 4.6.4 #17016 (Linux)

[Christopher Bazley]

I believe that the existing candidate fix for [bugs:#4131] (awaiting approval) also fixes this bug.