c/4258: gcc-2.95.2 produces wrong code

[rohloff at in dot tum dot de]

>Number:         4258
>Category:       c
>Synopsis:       gcc-2.95.2 produces wrong code
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          wrong-code
>Submitter-Id:   net
>Arrival-Date:   Fri Sep 07 08:46:00 PDT 2001
>Closed-Date:
>Last-Modified:
>Originator:     Ingo Rohloff
>Release:        gcc-2.95.2
>Organization:
>Environment:
Linux 2.4.9 i686
>Description:
Compiling the attached code with -O2 produces a 
binary which skips a loop iteration.
>How-To-Repeat:
Compile the following code with -O2 and execute
the resulting binary.
------------------------------------------------
struct epic_rx_desc {
  unsigned int next;
};

struct epic_private {
  struct epic_rx_desc *rx_ring;
  unsigned int rx_ring_dma;
  unsigned char* rx_skbuff[32];
};

static void epic_init_ring(struct epic_private *ep)
{
  int i;

  for (i = 0; i < 32; i++) {
    ep->rx_ring[i].next = ep->rx_ring_dma +
              (i+1)*sizeof(struct epic_rx_desc);
    ep->rx_skbuff[i] = 0;
  }
  ep->rx_ring[i-1].next = ep->rx_ring_dma;
}

int main()
{
  struct epic_private ep;
  struct epic_rx_desc rx_ring[32];
  int i;

  for (i=0;i<32;i++)
    rx_ring[i].next=0;

  ep.rx_ring=rx_ring;
  ep.rx_ring_dma=(unsigned int)rx_ring;
  epic_init_ring(&ep);

  for (i=0;i<5;i++)
  {
    printf("%8X\n",ep.rx_ring[i].next);
  }
}  
>Fix:
Compile with -O1.
>Release-Note:
>Audit-Trail:
>Unformatted: