Re: optimization/6475: zlib miscompilation with gcc-3.1

Re: optimization/6475: zlib miscompilation with gcc-3.1

[Jakub Jelinek]

The following reply was made to PR optimization/6475; it has been noted by GNATS.

From: Jakub Jelinek <jakub@redhat.com>
To: gbeauchesne@mandrakesoft.com, gcc-bugs@gcc.gnu.org, gcc-prs@gcc.gnu.org,
   gcc-gnats@gcc.gnu.org
Cc:  
Subject: Re: optimization/6475: zlib miscompilation with gcc-3.1
Date: Fri, 26 Apr 2002 12:37:51 -0400

 Reduced testcase below, it segfaults when run.
 The problem seems to be stack slot reusal and new memattr code:
 
 Reload decides to spill off (reg/f:SI 219) into:
 ($ebp - 272 [27 p S4 A8]), (reg/v/f: SI 78) into
 ($ebp - 224 [17 p S4 A8]) and (reg/v/f:SI 82) into
 ($ebp - 272 [27 xx S4 A8]) (ie. reusing slot for pseudo 219).
 All uses of pseudo 219 are before all uses of pseudo 82, so this
 doesn't look like something reload cannot do (I'll leave now the
 question why pseudo 219 was ever created, it is some GCSE silliness
 which apparently does consider ((frame + const_int) + const_int)
 as good candidate for elimination and increases register preasure
 when it is always cheaper to recompute it when needed).
 When scheduler is run, it compares ($ebp - 272 [27 p S4 A8])
 with ($ebp - 272 [27 xx S4 A8]) and since they are for different
 variables, thinks they are independent and swaps them.
 Any ideas what to do here?
 
 lreg:
 (insn 358 356 363 (set (mem/s:SI (plus:SI (reg/f:SI 20 frame)
                 (const_int -188 [0xffffff44])) [3 x+4 S4 A32])
         (const_int 0 [0x0])) 45 {*movsi_1} (nil)
     (nil))
 
 (insn 363 358 368 (set (reg/v/f:SI 78)
         (reg/f:SI 219)) 45 {*movsi_1} (nil)
     (expr_list:REG_DEAD (reg/f:SI 219)
         (nil)))
 
 (insn 368 363 1098 (parallel[
             (set (reg/v/f:SI 82)
                 (plus:SI (reg/f:SI 20 frame)
                     (const_int -184 [0xffffff48])))
             (clobber (reg:CC 17 flags))
         ] ) 207 {*addsi_1} (nil)
     (expr_list:REG_UNUSED (reg:CC 17 flags)
         (expr_list:REG_UNUSED (reg:CC 17 flags)
             (nil))))
 
 greg:
 (insn 358 356 1411 (set (mem/s:SI (plus:SI (reg/f:SI 6 ebp)
                 (const_int -196 [0xffffff3c])) [3 x+4 S4 A32])
         (const_int 0 [0x0])) 45 {*movsi_1} (nil)
     (nil))
 
 (insn 1411 358 363 (set (reg:SI 1 edx)
         (mem:SI (plus:SI (reg/f:SI 6 ebp)
                 (const_int -272 [0xfffffef0])) [27 p S4 A8])) 45 {*movsi_1} (nil)
     (nil))
 
 (insn 363 1411 368 (set (mem:SI (plus:SI (reg/f:SI 6 ebp)
                 (const_int -224 [0xffffff20])) [17 p S4 A8])
         (reg:SI 1 edx)) 45 {*movsi_1} (nil)
     (nil))
 
 (insn 368 363 1414 (parallel[
             (set (reg:SI 2 ecx)
                 (plus:SI (reg/f:SI 6 ebp)
                     (const_int -192 [0xffffff40])))
             (clobber (reg:CC 17 flags))
         ] ) 207 {*addsi_1} (nil)
     (nil))
 
 (insn 1414 368 1098 (set (mem:SI (plus:SI (reg/f:SI 6 ebp)
                 (const_int -272 [0xfffffef0])) [27 xx S4 A8])
         (reg:SI 2 ecx)) 45 {*movsi_1} (nil)
     (nil))
 
 sched2:
 (insn:TI 1414 368 1768 (set (mem:SI (plus:SI (reg/f:SI 6 ebp)
                 (const_int -272 [0xfffffef0])) [27 xx S4 A8])
         (reg:SI 2 ecx)) 45 {*movsi_1} (insn_list 368 (nil))
     (expr_list:REG_DEAD (reg:SI 2 ecx)
         (nil)))
 
 (insn:TI 1768 1414 1411 (parallel[
             (set (reg:SI 0 eax [133])
                 (plus:SI (reg:SI 0 eax [133])
                     (reg:SI 1 edx)))
             (clobber (reg:CC 17 flags))
         ] ) 207 {*addsi_1} (insn_list 1767 (nil))
     (expr_list:REG_DEAD (reg:SI 1 edx)
         (expr_list:REG_UNUSED (reg:CC 17 flags)
             (nil))))
 
 (insn 1411 1768 353 (set (reg:SI 1 edx)
         (mem:SI (plus:SI (reg/f:SI 6 ebp)
                 (const_int -272 [0xfffffef0])) [27 p S4 A8])) 45 {*movsi_1} (insn_list...))
 
 typedef struct
 {
   union
   {
     struct
     {
       unsigned char a3;
       unsigned char a4;
     } a2;
     unsigned int a5;
   } a0;
   unsigned int a1;
 } A;
 
 static int
 foo (unsigned int *b, unsigned int n, unsigned int s, const unsigned int *d,
      const unsigned int *e, A **t, unsigned int *m, A *hp, unsigned int *hn,
      unsigned int *v)
 {
   unsigned int a, c[15 + 1], f;
   int g, h;
   unsigned int i, j, k;
   int l;
   unsigned int ee;
   unsigned int *p;
   A *q, r, *u[15];
   int w;
   unsigned int x[15 + 1], *xx;
   int y;
   unsigned int z;
   p = c;
   *p++ = 0; *p++ = 0; *p++ = 0; *p++ = 0;
   *p++ = 0; *p++ = 0; *p++ = 0; *p++ = 0;
   *p++ = 0; *p++ = 0; *p++ = 0; *p++ = 0;
   *p++ = 0; *p++ = 0; *p++ = 0; *p++ = 0;
   p = b;
   i = n;
   do
     c[*p++]++;
   while (--i);
   if (c[0] == n)
     {
       *t = (A *) 0;
       *m = 0;
       return 0;
     }
   l = *m;
   for (j = 1; j <= 15; j++)
     if (c[j])
       break;
   k = j;
   if ((unsigned int) l < j)
     l = j;
   for (i = 15; i; i--)
     if (c[i])
       break;
   g = i;
   if ((unsigned int) l > i)
     l = i;
   *m = l;
   for (y = 1 << j; j < i; j++, y <<= 1)
     if ((y -= c[j]) < 0)
       return -3;
   if ((y -= c[i]) < 0)
     return -3;
   c[i] += y;
   x[1] = j = 0;
   p = c + 1;
   xx = x + 2;
   while (--i)
     *xx++ = (j += *p++);
   p = b;
   i = 0;
   do
     if ((j = *p++) != 0)
       v[x[j]++] = i;
   while (++i < n);
   n = x[g];
   x[0] = i = 0;
   p = v;
   h = -1;
   w = -l;
   u[0] = (A *) 0;
   q = (A *) 0;
   z = 0;
   for (; k <= g; k++)
     {
       a = c[k];
       while (a--)
         {
           while (k > w + l)
             {
               h++;
               w += l;
               z = g - w;
               z = z > (unsigned int) l ? l : z;
               if ((f = 1 << (j = k - w)) > a + 1)
                 {
                   f -= a + 1;
                   xx = c + k;
                   if (j < z)
                     while (++j < z)
                       {
                         if ((f <<= 1) <= *++xx)
                           break;
                         f -= *xx;
                       }
                 }
               z = 1 << j;
               if (*hn + z > 1440)
                 return -3;
               u[h] = q = hp + *hn;
               *hn += z;
               if (h)
                 {
                   x[h] = i;
                   r.a0.a2.a4 = (unsigned char) l;
                   r.a0.a2.a3 = (unsigned char) j;
                   j = i >> (w - l);
                   r.a1 = (unsigned int) (q - u[h - 1] - j);
                   u[h - 1][j] = r;
                 }
               else
                 *t = q;
             }
           r.a0.a2.a4 = (unsigned char) (k - w);
           if (p >= v + n)
             r.a0.a2.a3 = 128 + 64;
           else if (*p < s)
             {
               r.a0.a2.a3 = (unsigned char) (*p < 256 ? 0 : 32 + 64);
               r.a1 = *p++;
             }
           else
             {
               r.a0.a2.a3 = (unsigned char) (e[*p - s] + 16 + 64);
               r.a1 = d[*p++ - s];
             }
           f = 1 << (k - w);
           for (j = i >> w; j < z; j += f)
             q[j] = r;
           for (j = 1 << (k - 1); i & j; j >>= 1)
             i ^= j;
           i ^= j;
           ee = (1 << w) - 1;
           while ((i & ee) != x[h])
             {
               h--;
               w -= l;
               ee = (1 << w) - 1;
             }
         }
     }
   return y != 0 && g != 1 ? (-5) : 0;
 }
 
 int a[19] = { 3, 4, 0, 2, 2,[17] = 3, 3 };
 int d[19];
 A h[1440];
 
 int
 main (void)
 {
   int b = 0, c = 0;
   A *e = 0;
   foo (a, 19, 19, 0, 0, &e, &b, h, &c, d);
 }
 
 	Jakub

Re: optimization/6475: zlib miscompilation with gcc-3.1

[jakub]

Synopsis: zlib miscompilation with gcc-3.1

State-Changed-From-To: analyzed->closed
State-Changed-By: jakub
State-Changed-When: Mon Apr 29 02:17:04 2002
State-Changed-Why:
    Fixed.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=6475

Re: optimization/6475: zlib miscompilation with gcc-3.1

[jakub]

Synopsis: zlib miscompilation with gcc-3.1

State-Changed-From-To: open->analyzed
State-Changed-By: jakub
State-Changed-When: Fri Apr 26 05:54:19 2002
State-Changed-Why:
    Fails with -O2 -mcpu=i686 -fPIC as well (though a different
    test) before 20020420 or if http://gcc.gnu.org/ml/gcc-patches/2002-04/msg01041.html
    is backed out from current source; that patch looks just
    if it is hiding the symptoms of a bug.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=6475

Re: optimization/6475: zlib miscompilation with gcc-3.1

[jakub]

Synopsis: zlib miscompilation with gcc-3.1

Responsible-Changed-From-To: unassigned->jakub
Responsible-Changed-By: jakub
Responsible-Changed-When: Fri Apr 26 03:29:57 2002
Responsible-Changed-Why:
    Reproduced, working on it.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=6475

optimization/6475: zlib miscompilation with gcc-3.1

[gbeauchesne]

>Number:         6475
>Category:       optimization
>Synopsis:       zlib miscompilation with gcc-3.1
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          wrong-code
>Submitter-Id:   net
>Arrival-Date:   Fri Apr 26 03:06:01 PDT 2002
>Closed-Date:
>Last-Modified:
>Originator:     Gwenole Beauchesne
>Release:        3.1 20020425 (prerelease)
>Organization:
>Environment:
i586-mandrake-linux-gnu
>Description:
make test fails with a particular combination, and only that combination so far, of optimization flags.

CFLAGS="-O2 -frename-registers -fomit-frame-pointer -mcpu=pentiumpro -fPIC"
>How-To-Repeat:
I am sorry but I don't have a testcase at this point.

1) Get zlib-1.1.4 sources
2) Configure as follows: CFLAGS="-O2 -frename-registers -fomit-frame-pointer -mcpu=pentiumpro -fPIC" ./configure --shared
3) make; make test
>Fix:
Remove one (any of) the CFLAGS.
>Release-Note:
>Audit-Trail:
>Unformatted: