#3387 SDCC generates invalid opcode "jp NZ, (hl)" for calling a function pointer

[bbbbbr]

SDCC : z80/sm83/mos6502 4.2.2 #13350 (Linux)

For the gbz80/sm83: when conditionally calling a function pointer retrieved from an array, SDCC will generate an invalid opcode: jp NZ,(hl).

This causes the linker to fail with:
?ASlink-Warning-Undefined Global 'hl' referenced by module 'main'

• The error does not happen if the function pointer is directly retrieved with:
  void (*p_func)(void) = &some_func;

• The error also does not happen if the variable used to store the function pointer is a global or static local.

Minimal example:

void some_func(void) {
}

void (*func_list[])(void) = {
    &some_func
};

void main(void)
{

    void (*p_func)(void) = func_list[0];
    if (p_func)
        (*p_func)();
}

Relevant ASM output

;main.c:13: void (*p_func)(void) = func_list[0];
    ld  hl, #_func_list
    ld  a, (hl+)
    ld  c, a
    ld  a, (hl)
    ld  l, c
;   spillPairReg hl
;   spillPairReg hl
    ld  h, a
;   spillPairReg hl
;   spillPairReg hl
;main.c:14: if (p_func)
    or  a, c
;main.c:15: (*p_func)();
    jp  NZ,(hl)
;main.c:17: }

[Philipp Klaus Krause]

Looks like z80 is affected, too.
Workaround until the bug is fixed: --no-peep.

[Sebastian Riedel]

Peephole rules 79 - 82 are bugged. They don’t check if the second jump goes to a label.
It only gets triggered now because jp (hl) gets generated more.

    or  a, c
    jp  Z, 00103$
    call    ___sdcc_call_hl
00103$:
    ret

became

    or  a, c
    jp  Z, 00103$
    jp  (hl)
00103$:
    ret

[bbbbbr]

Good to know that --no-peep is a usable workaround, though being able to have the peephole rules enabled would be nice

[Maarten Brock]

Would it not be enough to change the condition of those rules to
} if operandsNotRelated(%2 'hl' 'ix' 'iy'), labelRefCountChange(%1 -1)

[Sebastian Riedel]

Turning

replace restart {
    jp  NC,%1
    jp  %2
%1:
} by {
    jp  C,%2
    ; common peephole 79 removed jp by using inverse jump logic
%1:
} if labelRefCountChange(%1 -1)

into

} by {
    jp  C,%2
    ; common peephole 79 removed jp by using inverse jump logic
%1:
} if operandsNotRelated(%2 '(hl)' '(ix)' '(iy)'), labelRefCountChange(%1 -1)

might suffice, yes.

[Maarten Brock]

Fixed in SDCC [r13503].

[Maarten Brock]

On a related note: what is the difference between common z80 peephole rule 85a and 88?

[Sebastian Riedel]

Looks like a duplicate.