[sdcc-devel] SDCC Z80 code generation bug

[Oleg N. C. <al...@bk...>]

Dear SDCC developers,

I found a SDCC Z80 code generation bug.

 > 1.Attach the code you are compiling with SDCC

int main (void) {
   unsigned char i,mr2,sp;
   mr2 = 1; sp = 0; // (mr2-1)*sp = 0, i.e. for(i=1;i<=0;i++) ...
   /* and because i=1, and (1<=0) is FALSE, this loop must NOT BE RUNNED */
   for(i=1;i<=((mr2-1)*sp);i++) { // ... but this code IS RUNNED!!! :(
   }
   // Here is unreachable code, because loop is eternal.
}

 > 2.Specify the exact command you use to run SDCC, or attach your Makefile.

sdcc\sdcc -mz80 --code-loc 26000 --data-loc 0xF000 --no-std-crt0 
--opt-code-size --funsigned-char --disable-warning 59 -L z80 testbug.c

 > 3.Specify the SDCC version, your platform and operating system

C:\Soft\Dev-Zx\SDCC\bug\sdcc>sdcc -v
SDCC : mcs51/gbz80/z80/ds390/pic16/pic14/TININative/ds400/hc08 3.0.1 
#6183 (Jan 26 2011) (MINGW32)

 > 4.Provide an exact copy of any error message or incorrect output

The problem is eternal loop with incorrect code generation. More earlier
versions of SDCC generate the correct code. I tried old version:

C:\Soft\Dev-Zx\SDCC\bug\sdcc>sdcc -v
SDCC : mcs51/gbz80/z80/ds390/pic16/pic14/TININative/ds400/hc08 2.9.7 
#5839 (May 30 2010) (MINGW32)

and code was absolutely correct. Difference is:

SDCC VERSION 2.9.7 (CORRECT)      SDCC VERSION 3.0.1 (INCORRECT)
;---------------------------------------------------------------
;testbug.c:5: for(i=1;i<=((mr2-1)*sp);i++) { // ... but this code IS 
RUNNED!!! :(
       ld      c,#0x01                   ld      c,#0x01
00101$:                           00101$:
       ld      l,c                       ld      l,c
       ld      a,#0x00                   ld      a,#0x00
       ld      h,a                       ld      h,a
       sub     a,l                       sub     a, l
       ld      a,#0x00                   ld      a,#0x00
       sbc     a,h                       sbc     a, h
                                         jp      PO, 00110$
                                         xor     a, #0x80
                                   00110$:
       ret      M                        ret     M
       inc      c                        inc     c
       jr      00101$                    jr      00101$
;---------------------------------------------------------------


Thank you.

--
Oleg N. Cher, Vedanta Software