[Bug c/41946] New: tree-vrp eliminates needed conditioanl

[Bug c/41946] New: tree-vrp eliminates needed conditioanl

[kevfox at cisco dot com]

# 1 "strcmp.c"
# 1 "<built-in>"
# 1 "<command-line>"
# 1 "strcmp.c"
int strcmp (const char *, const char *);

int
strcmp (const char *s1, const char *s2)
{

    if ((!s1 && s2) || (s1 && !s2))
        return (int) (s1 - s2);

    if (s1 == s2)
        return 0;

    while (*s1 == *s2++)
        if (*s1++ == '\0')
             return 0;

    return (*(unsigned char *)s1 - *(unsigned char *)--s2);
}

The first conditional is eliminated causing a crash when a pointer is null.
Code is correct when -fno-tree-vrp is specified.

Using built-in specs.
Target: i486-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 4.4.1-4ubuntu8'
--with-bugurl=file:///usr/share/doc/gcc-4.4/README.Bugs
--enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --enable-shared
--enable-multiarch --enable-linker-build-id --with-system-zlib
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--with-gxx-include-dir=/usr/include/c++/4.4 --program-suffix=-4.4 --enable-nls
--enable-clocale=gnu --enable-libstdcxx-debug --enable-objc-gc
--enable-targets=all --disable-werror --with-arch-32=i486 --with-tune=generic
--enable-checking=release --build=i486-linux-gnu --host=i486-linux-gnu
--target=i486-linux-gnu
Thread model: posix
gcc version 4.4.1 (Ubuntu 4.4.1-4ubuntu8)
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-O3' '-c' '-mtune=generic'
'-march=i486'
 /usr/lib/gcc/i486-linux-gnu/4.4.1/cc1 -E -quiet -v strcmp.c
-D_FORTIFY_SOURCE=2 -mtune=generic -march=i486 -O3 -fpch-preprocess
-fstack-protector -o strcmp.i
ignoring nonexistent directory "/usr/local/include/i486-linux-gnu"
ignoring nonexistent directory
"/usr/lib/gcc/i486-linux-gnu/4.4.1/../../../../i486-linux-gnu/include"
ignoring nonexistent directory "/usr/include/i486-linux-gnu"
#include "..." search starts here:
#include <...> search starts here:
 /usr/local/include
 /usr/lib/gcc/i486-linux-gnu/4.4.1/include
 /usr/lib/gcc/i486-linux-gnu/4.4.1/include-fixed
 /usr/include
End of search list.
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-O3' '-c' '-mtune=generic'
'-march=i486'
 /usr/lib/gcc/i486-linux-gnu/4.4.1/cc1 -fpreprocessed strcmp.i -quiet -dumpbase
strcmp.c -mtune=generic -march=i486 -auxbase strcmp -O3 -version
-fstack-protector -o strcmp.s
GNU C (Ubuntu 4.4.1-4ubuntu8) version 4.4.1 (i486-linux-gnu)
        compiled by GNU C version 4.4.1, GMP version 4.3.1, MPFR version
2.4.1-p2.
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 293503c4ddf766b61fc5ff6a5ff38cdc
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-O3' '-c' '-mtune=generic'
'-march=i486'
 as -V -Qy -o strcmp.o strcmp.s
GNU assembler version 2.20 (i486-linux-gnu) using BFD version (GNU Binutils for
Ubuntu) 2.20
COMPILER_PATH=/usr/lib/gcc/i486-linux-gnu/4.4.1/:/usr/lib/gcc/i486-linux-gnu/4.4.1/:/usr/lib/gcc/i486-linux-gnu/:/usr/lib/gcc/i486-linux-gnu/4.4.1/:/usr/lib/gcc/i486-linux-gnu/:/usr/lib/gcc/i486-linux-gnu/4.4.1/:/usr/lib/gcc/i486-linux-gnu/
LIBRARY_PATH=/usr/lib/gcc/i486-linux-gnu/4.4.1/:/usr/lib/gcc/i486-linux-gnu/4.4.1/:/usr/lib/gcc/i486-linux-gnu/4.4.1/../../../../lib/:/lib/../lib/:/usr/lib/../lib/:/usr/lib/gcc/i486-linux-gnu/4.4.1/../../../:/lib/:/usr/lib/:/usr/lib/i486-linux-gnu/
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-O3' '-c' '-mtune=generic'
'-march=i486'


-- 
           Summary: tree-vrp eliminates needed conditioanl
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: kevfox at cisco dot com
  GCC host triplet: i486-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41946

[Bug c/41946] tree-vrp eliminates needed conditioanl

[rguenth at gcc dot gnu dot org]

------- Comment #1 from rguenth at gcc dot gnu dot org  2009-11-05 10:07 -------
Use -fno-builtin-strcmp or name your function differently.  The standard
does not allow NULL arguments to strcmp.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41946