#3135 GBZ80 accessing variable on stack spoils result in HL

[Tony Pavlov]

offset of (Actor)[hit].hit_1_ptr is calculated into HL. then SDCC fetches value of stack-allocated variable to make conditional jump, that spoils HL. then it adds address of actors array to HL, assuming it still contains offset:

;test9.c:45: TestFn2(&actors[hit].hit_1_ptr);
    ld  e, l
    ld  d, #0x00
    ld  l, e
    ld  h, d
    add hl, hl
    add hl, de
    add hl, hl
;test9.c:44: if (projectiles[i].col_group == 2) {
    ldhl    sp, #0
    ld  a, (hl)
    sub a, #0x02
    jr  NZ, 00104$
;test9.c:45: TestFn2(&actors[hit].hit_1_ptr);
    ld  de, #_actors
    add hl, de

that behaviour is very fragile. for example --max-allocs-per-node 50000 fixes that by eliminating stack-allocated projectiles[i].col_group.

version:

SDCC : mcs51/z80/z180/r2k/r2ka/r3ka/gbz80/tlcs90/ez80_z80/z80n/ds390/pic16/pic14/TININative/ds400/hc08/s08/stm8/pdk13/pdk14/pdk15 4.0.3 #11916 (MINGW64)

commandline:

sdcc -mgbz80 --fsigned-char --no-std-crt0 -I ..\..\gbdk\include -I ..\..\gbdk\include\asm -I src\include -c test9.c -o build\test9.rel

[Philipp Klaus Krause]

I haven't been able to reproduce this on my Debian GNU/Linux testing system so far, but will keep looking into it further.

P.S.: In [r11923], I added a test, which I hope will trigger this bug on some of the systems in the compile farm.

P.P.S.: Could you add the test.asm when compiling with --fverbose-asm --no-peep --i-code-in-asm?

[Tony Pavlov]

how can i help you here? maybe provide some additional info?

SDCC 4.0.4 #11922 (MINGW64)

generates:

;   genMove_o
;test9.c:45: TestFn2(&actors[hit].hit_1_ptr);
;   genMult
;fetchPairLong
; common peephole 1 removed dead load from l into e.
; common peephole 1 removed dead load from #0x00 into d.
; common peephole 1 removed dead load from e into l.
; common peephole 1 removed dead load from d into h.
; common peephole 2a removed add hl,hl due to unused result.
; common peephole 2a removed add hl,de due to unused result.
; common peephole 2a removed add hl,hl due to unused result.
;   genMove_o
;   genMove_o
;test9.c:44: if (projectiles[i].col_group == 2) {
;   genCmpEq
;   AOP_STK for _TestFn_sloc0_1_0
    ldhl    sp, #0
    ld  a, (hl)
    sub a, #0x02
; common peephole 81 removed jp by using inverse jump logic
; common peephole 158 removed unused label 00135$.
; common peephole 163 changed absolute to relative conditional jump.
    jr  NZ, 00104$
; common peephole 82 removed jp by using inverse jump logic
; common peephole 158 removed unused label 00136$.
;test9.c:45: TestFn2(&actors[hit].hit_1_ptr);
;   genPlus
;fetchPairLong
;fetchLitPair
    ld  de, #_actors
    add hl, de

with disabled PH rules:

;   genMove_o
;test9.c:45: TestFn2(&actors[hit].hit_1_ptr);
;   genMult
;fetchPairLong
    ld  e, l
    ld  d, #0x00
    ld  l, e
    ld  h, d
    add hl, hl
    add hl, de
    add hl, hl
;   genMove_o
;   genMove_o
;test9.c:44: if (projectiles[i].col_group == 2) {
;   genCmpEq
;   AOP_STK for _TestFn_sloc0_1_0
    ldhl    sp, #0
    ld  a, (hl)
    sub a, #0x02
    jp  NZ,00135$
    jp  00136$
00135$:
    jp  00104$
00136$:
;test9.c:45: TestFn2(&actors[hit].hit_1_ptr);
;   genPlus
;fetchPairLong
;fetchLitPair
    ld  de, #_actors
    add hl, de

[Tony Pavlov]

sdcc -mgbz80 --fsigned-char --no-std-crt0 -I ..\..\gbdk\include -I ..\..\gbdk\include\asm -I src\include -c --fverbose-asm --no-peep --i-code-in-asm test9.c -o build\test9.rel

what is the code here, generated by linux port, i wonder?

full asm in attach below:

[Philipp Klaus Krause]

This should be fixed in [r11924]. Please test.
On my Debian GNU/Linux testing system, projectiles[i].col_group got allocated to register b.

[Tony Pavlov]

just released r11925 works perfect! thank you, Philipp!