[Bug tree-optimization/20188] [4.0 Regression] glibc-2.3.4 misscompilation.

[pluto at pld-linux dot org]

------- Additional Comments From pluto at pld-linux dot org  2005-02-24 23:44 -------
(In reply to comment #6) 
> I have no idea what is going on here but I will note that "-O3 
-fno-tree-dominator-opts" works. 
> "-O3 -fno-ivopts" does not work 
> "-O3 -fno-strict-aliasing" does not work. 
 
I've looked into final tree-dump and found something interesting. 
In the source we can find a [2] strcpy(startbuf, ...) 
which can change the state of startbuf between [1] and [3]. 
 
if (usestart) { 
[1]    if (*startbuf == '\0' && 
           zp->z_format != NULL && 
           strchr(zp->z_format, '%') == NULL && 
           strchr(zp->z_format, '/') == NULL) 
[2]             (void) strcpy(startbuf, zp->z_format); 
           eat(zp->z_filename, zp->z_linenum); 
[3]        if (*startbuf == '\0') 
                 error(_("can't determine time zone abbreviation to use 
                          just after until time")); 
           else 
               addtt(starttime, 
                     addtype(startoff, startbuf, 
                             startoff != zp->z_gmtoff, 
                             startttisstd, 
                             startttisgmt)); 
} 
 
Diff shows that the optimizer assumed D.10077=startbuf[0] incorrectly 
as const because <L219> can change state of startbuf. 
 
--- 03-zic.i.t70.final_cleanup-no-tree-dominator-opts   2005-02-25 
00:26:09.340849848 +0100 
+++ 03-zic.i.t70.final_cleanup  2005-02-25 00:26:03.792693296 +0100 
@@ -2,48 +2,44 @@ 
   if (usestart != 0) goto <L213>; else goto <L237>; 
 
 <L213>:; 
-  if (startbuf[0] == 0) goto <L214>; else goto <L220>; 
+  D.10077 = startbuf[0]; 
+  if (D.10077 == 0) goto <L214>; else goto <L220>; 
 
 <L214>:; 
-  if (*((const char * *) ivtmp.1013 + 128B) != 0B) goto <L215>; else goto 
<L220>; 
+  D.10028 = *(D.16876 + 128B); 
+  if (D.10028 != 0B) goto <L215>; else goto <L220>; 
 
 <L215>:; 
-  __s = *((const char * *) ivtmp.1013 + 128B); 
-  __asm__ __volatile__("1:\n\tmovb\t(%0),%%al\n\tcmpb\t%%ah,
%%al\n\tje\t2f\n\tleal\t1(%0),%0\n\ttestb\t%%al,%%al\n\tjne\t1b\n\txorl\t%0,
%0\n2:":"=r" __res, "=&a" __d0:"0" __s, "1" 9472, "m" *(struct 
+  __s.107 = (struct 
   { 
     char __x[268435455]; 
-  } *) __s:"cc"); 
+  } *) D.10028; 
+  __asm__ __volatile__("1:\n\tmovb\t(%0),%%al\n\tcmpb\t%%ah,
%%al\n\tje\t2f\n\tleal\t1(%0),%0\n\ttestb\t%%al,%%al\n\tjne\t1b\n\txorl\t%0,
%0\n2:":"=r" __res, "=&a" __d0:"0" D.10028, "1" 9472, "m" *__s.107:"cc"); 
   if (__res == 0B) goto <L217>; else goto <L220>; 
 
 <L217>:; 
-  __s = *((const char * *) ivtmp.1013 + 128B); 
-  __asm__ __volatile__("1:\n\tmovb\t(%0),%%al\n\tcmpb\t%%ah,
%%al\n\tje\t2f\n\tleal\t1(%0),%0\n\ttestb\t%%al,%%al\n\tjne\t1b\n\txorl\t%0,
%0\n2:":"=r" __res, "=&a" __d0:"0" __s, "1" 12032, "m" *(struct 
-  { 
-    char __x[268435455]; 
-  } *) __s:"cc"); 
+  __asm__ __volatile__("1:\n\tmovb\t(%0),%%al\n\tcmpb\t%%ah,
%%al\n\tje\t2f\n\tleal\t1(%0),%0\n\ttestb\t%%al,%%al\n\tjne\t1b\n\txorl\t%0,
%0\n2:":"=r" __res, "=&a" __d0:"0" D.10028, "1" 12032, "m" *__s.107:"cc"); 
   if (__res == 0B) goto <L219>; else goto <L220>; 
 
 <L219>:; 
-  __src = *((const char * *) ivtmp.1013 + 128B); 
   __dest.50 = (struct 
   { 
     char __x[268435455]; 
   } *) &startbuf; 
-  __asm__ __volatile__("1:\n\tmovb\t(%0),%b2\n\tleal\t1(%0),%0\n\tmovb\t%b2,
(%1)\n\tleal\t1(%1),%1\n\ttestb\t%b2,%b2\n\tjne\t1b":"=&r" __src.1132, "=&r" 
__tmp, "=&q" __dummy, "=m" *__dest.50:"0" __src, "1" &startbuf, "m" *(struct 
+  __asm__ __volatile__("1:\n\tmovb\t(%0),%b2\n\tleal\t1(%0),%0\n\tmovb\t%b2,
(%1)\n\tleal\t1(%1),%1\n\ttestb\t%b2,%b2\n\tjne\t1b":"=&r" __src, "=&r" __tmp, 
"=&q" __dummy, "=m" *__dest.50:"0" D.10028, "1" &startbuf, "m" *(struct 
   { 
     char __x[268435455]; 
-  } *) __src:"cc"); 
+  } *) D.10028:"cc"); 
 
 <L220>:; 
-  num = *((int *) ivtmp.1013 + 112B); 
-  name = *((const char * *) ivtmp.1013 + 108B); 
-  filename = name; 
+  num = *D.16875; 
+  filename = *D.16877; 
   linenum = num; 
   rfilename = 0B; 
   rlinenum = -1; 
-  if (startbuf[0] == 0) goto <L225>; else goto <L226>; 
+  if (D.10077 == 0) goto <L225>; else goto <L226>; 
 
 <L225>:; 
   D.10084 = __dcgettext (&_libc_intl_domainname, &"can\'t determine time zone 
abbreviation to use just after until time"[0], 5); 
   error (D.10084); 
-  goto <bb 173> (<L237>); 
+  goto <bb 155> (<L237>); 
 

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20188