optimization/10185: Wrong code with 3-int-structs & optimization

optimization/10185: Wrong code with 3-int-structs & optimization

[rassahah]

>Number:         10185
>Category:       optimization
>Synopsis:       Wrong code with 3-int-structs & optimization
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          wrong-code
>Submitter-Id:   net
>Arrival-Date:   Fri Mar 21 15:16:01 UTC 2003
>Closed-Date:
>Last-Modified:
>Originator:     Rasmus Hahn
>Release:        gcc-3.3, gcc-3.4 cvs
>Organization:
>Environment:
i686-pc-linux-gnu
>Description:
the how to repeat program should scan a list of some 3-int-structs for members with a specific depth and maximal bits_per_pixel field, and fails.
Insertion of a dummy function-call (printf in how-to-repeat) or changing the size of the struct makes the program work (as does compiling without optimization).
Suspect this has to to with i386-specific optimization for multiplying by 3, 5 or more with lea-instruction when indexing the array.
this bug is in my Versions of gcc:
  gcc version 3.4 20030321 (experimental)
  gcc version 3.3 20021104 (experimental)
when compiling with -O2.
>How-To-Repeat:
typedef struct {
  int depth, bits_per_pixel, scanline_pad;
  /* change size by adding another int, removing one & it works, add 2 or more and it wont */
} XPixmapFormatValues;

XPixmapFormatValues *XListPixmapFormats (int *i);

main () /* compile with -O2 */
{
  XPixmapFormatValues *pfm;
  int i, bpp = 0;
  pfm = XListPixmapFormats (&i); /* returns 3 in i */
  while (i--) {
    //printf ("a"); /* comment this in & it works */
    if ((pfm[i].depth == 24) && (pfm[i].bits_per_pixel > bpp)) {
      bpp = pfm[i].bits_per_pixel;
    }
  }
  if (bpp < 8) { abort (); /* should not abort */ }
}

/* dummy version of X-Function for testing */
XPixmapFormatValues * XListPixmapFormats (int *i)
{
  static XPixmapFormatValues rv[3] = {
    {16, 16, 32}, {24, 32, 32}, {32, 32, 32},
  };
  *i = 3;
  return rv;
}
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted: