#1030 Pointers to struct

[Ragozini Arturo]

The code generated for loops that access to an array of structs trough pointers could improve enormously by using IY and IX.

Look at this example, where SwSprite[] is an array of struct

            SwSpPntr = &SwSprite[0];
            for (u8 i=0; i<TotSprt;i++)     {
                SwSpPntr->x1 = SwSpPntr->lx;
                SwSpPntr->y1 = SwSpPntr->ly;
                SwSpPntr++;             
            }

Using SDCC you get this UGE and SLOW piece of code:

;./Lift.c:707: SwSpPntr = &SwSprite[0];
    ld  hl, #_SwSprite
    ld  (_SwSpPntr), hl
;./Lift.c:708: for (u8 i=0; i<TotSprt;i++)  {
    ld  -1 (ix), #0x00
00143$:
    ld  a, -1 (ix)
    sub a, #0x26
    jr  NC, 00112$
;./Lift.c:603: SwSpPntr->lx = (i*16 + MyX ); 
    ld  hl, (_SwSpPntr)
;./Lift.c:709: SwSpPntr->x1 = SwSpPntr->lx;
    ld  c, l
    ld  b, h
    inc bc
    inc bc
    ld  a, (hl)
    ld  (bc), a
;./Lift.c:603: SwSpPntr->lx = (i*16 + MyX ); 
    ld  bc, (_SwSpPntr)
;./Lift.c:710: SwSpPntr->y1 = SwSpPntr->ly;
    ld  hl, #0x0008
    add hl, bc
    ex  de, hl
    ld  hl, #4
    add hl, bc
    ld  c, (hl)
    inc hl
    ld  b, (hl)
    ld  a, c
    ld  (de), a
    inc de
    ld  a, b
    ld  (de), a
;./Lift.c:711: SwSpPntr++;              
    ld  hl, #_SwSpPntr
    ld  a, (hl)
    add a, #0x10
    ld  (hl), a
    jr  NC, 00239$
    inc hl
    inc (hl)
00239$:
;./Lift.c:708: for (u8 i=0; i<TotSprt;i++)  {
    inc -1 (ix)
    jp  00143$
00112$:

Note that te burden is related to the use of HL as pointer to the struct
Instead, using IY, you get:

    ld  iy, #_SwSprite
    ld  de, #0x0010
    ld  b, #0x26
03999$:
    ld  a,  0 (iy)
    ld  2 (iy) ,a       ; SwSpPntr->x1 = SwSpPntr->lx;

    ld  l, 4 (iy)
    ld  h, 5 (iy)
    ld   8 (iy),l
    ld   9 (iy),h       ; SwSpPntr->y1 = SwSpPntr->ly;

    add iy, de          ; SwSpPntr++;
    djnz    03999$

Would it be possible to suggest to SDCCto allocate pointers to structs in IY (and IX if available) ?

[Philipp Klaus Krause]

Which version of SDCC, used with which command-line options? Do you have a small compileable code sample to reproduce this?

[Ragozini Arturo]

This is with current version 4.6, as you can see the issue is unchanged

;./AdrianLift.c:707: SwSpPntr = &SwSprite[0];
    ld  hl, #_SwSprite
    ld  (_SwSpPntr), hl
;./AdrianLift.c:708: for (u8 i=0; i<TotSprt;i++)    {
    ld  c, #0x00
00143$:
    ld  a, c
    sub a, #0x26
    jr  nc, 00112$
;./AdrianLift.c:709: SwSpPntr->x1 = SwSpPntr->lx;
    ld  de, (_SwSpPntr)
    inc de
    inc de
    ld  hl, (_SwSpPntr)
    ld  a, (hl)
    ld  (de), a
;./AdrianLift.c:604: SwSpPntr->ly = (Field.ly + MyY ); 
    ld  hl, (_SwSpPntr)
;./AdrianLift.c:710: SwSpPntr->y1 = SwSpPntr->ly;
    ld  a, l
    add a, #0x08
    ld  e, a
    ld  a, h
    inc hl
    inc hl
    inc hl
    inc hl
    adc a, #0x00
    ld  d, a
    ld  b, (hl)
    inc hl
    ld  l, (hl)
    ld  a, b
    ld  (de), a
    inc de
    ld  a, l
    ld  (de), a
;./AdrianLift.c:711: SwSpPntr++;                
    ld  hl, #_SwSpPntr
    ld  a, (hl)
    add a, #0x10
    ld  (hl), a
    jr  nc, 00274$
    inc hl
    inc (hl)
00274$:
;./AdrianLift.c:708: for (u8 i=0; i<TotSprt;i++)    {
    inc c
    jp  00143$
00112$:

[Ragozini Arturo]

To compile the above C this could work

struct MyObj {
    u8 lx;          // Logical x
    u8 x0,x1,x2;    // Physical x's in the 3 pages
    i16 ly;         // Logical Y
    u16 y0,y1,y2;   // Physical y's in the 3 pages
    u16 frame;
    i8 dx;          // x direction
    i8 dy;          // y direction
};

#define TotDem  (32)
#define TotSprt (32+6)

struct MyObj SwSprite[TotSprt];

void main() {
            SwSpPntr = &SwSprite[0];
            for (u8 i=0; i<TotSprt;i++)     {
                SwSpPntr->x1 = SwSpPntr->lx;
                SwSpPntr->y1 = SwSpPntr->ly;
                SwSpPntr++;             
            }
}