[sdcc-devel] [ sdcc-Bugs-3299577 ] Z80 multiplication code bug

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Bugs item #3299577, was opened at 2011-05-09 20:38
Message generated for change (Comment added) made by spth
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Category: z80 port
Group: None
Status: Closed
Resolution: Fixed
Priority: 5
Private: No
Submitted By: Oleg N. Cher (oleg-n-cher)
Assigned to: Philipp Klaus Krause (spth)
Summary: Z80 multiplication code bug

Initial Comment:
1.

// This SDCC test program demonstrates a serious Z80 multiplication bug
// This bug present with internal loop if called a procedure with statement

// if we define THE_BUG, the bug is present. DoProc() not returns.
#define THE_BUG
// if we define CORRECT, the bug is hidden (masked). DoProc() returns.
//#define CORRECT

void TheBug (void);
void DoProc (signed char col, signed char row, unsigned char spr);

unsigned char y;

int main (void) {
  y=1; TheBug();
  return 0;
}

void TheBug (void)
{
  unsigned char i,j,n,spr;
  for (j=0; j<=1; j++) {
    for (n=1; n<=7; n++) {
      for (i=2; i<=7; i++) {
        #ifdef THE_BUG
          DoProc(30, i*y, spr); // Here i*y == 1 every time
        #endif
        #ifdef CORRECT
          DoProc(30, y*i, spr); // Here is correct
        #endif
      }
    }
  }
}

void DoProc (signed char col, signed char row, unsigned char spr) {
  if(row!=1) return;
  for(;;);
}

2.
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.
SDCC : mcs51/gbz80/z80/ds390/pic16/pic14/TININative/ds400/hc08 3.0.2 #6489 (May 9 2011) (MINGW32)

4. if change 'y*i' to 'i*y', we will have the serious problem. Possible reasons are deep internal loop + statement calculated in calling a fn + optimizations in SDCC code generation. I've no ideas, sorry. Thanks

5. My e-mail is allot )at( ukr.net

----------------------------------------------------------------------

>Comment By: Philipp Klaus Krause (spth)
Date: 2011-06-10 22:28

Message:
I don't remember, but suppose that initializing it e.g. to 0 wouldn't
change the behaviour, since the initialization would be outside all control
structures.

Philipp


----------------------------------------------------------------------

Comment By: Maarten Brock (maartenbrock)
Date: 2011-06-10 15:47

Message:
Is the fact that spr is uninitialized part of this bug or can we initialize
it in the regression test to remove the warning?

----------------------------------------------------------------------

Comment By: Philipp Klaus Krause (spth)
Date: 2011-05-26 11:23

Message:
Fixed in revision #6555.

Philipp


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