#1036 Local static variables are allocated in uninitialised instead of initialised external ram data

[Christopher Bazley]

The following program can be compiled by SDCC 4.6.0 with -mmos65c02 --stack-auto --std-c23 --max-allocs-per-node 1:

static int i = 99;

int main(void)
{
    static int j = 101;
    return 0;
}

https://godbolt.org/z/a7bsaGo9b

Surprisingly, although both i and j have static storage duration and therefore their initial values must be constant expressions, only the value of i is placed in .area XINIT and only storage for i is allocated in .area DATA:

        .module example

        .r65c02
        .optsdcc -mmos65c02

        .globl _main
        .area ZP      (PAG)
        .area BSS
_main_j_10000_2:
        .ds 2
        .area DABS    (ABS)
        .area DATA
_i:
        .ds 2
        .area _CODE
        .area GSINIT
        .area GSFINAL
        .area GSINIT
        ldx     #0x65
        stx     _main_j_10000_2
        stz     (_main_j_10000_2+1)
        .area _CODE
        .area _CODE
        .area CODE
_main:
        lda     #0x00
        tax
        rts
        .area CODE
        .area RODATA
        .area XINIT
__xinit__i:
        .dw #0x0063
        .area CABS    (ABS)

That seems like a misfeature because the initialisation code for j is less efficient than .dw:

        ldx     #0x65
        stx     _main_j_10000_2
        stz     (_main_j_10000_2+1)

Initialising j requires eight bytes of instructions, whereas its initial value occupies only two bytes. Since this program already needs startup copying of initialised data for i, placing j in the same initialisation image appears to reduce code size without requiring another initialisation mechanism. Could block-scope static objects use that mechanism too?

[Philipp Klaus Krause]

See also [feature-requests:#455].