Bug#263854: gcc-3.3: Generates bad code

[Sylvain COUTANT]

Package: gcc-3.3
Version: 1:3.3.4-3
Severity: normal



-- System Information:
Debian Release: 3.1
  APT prefers testing
  APT policy: (500, 'testing')
Architecture: i386 (i686)
Kernel: Linux 2.4.24-bf2.4
Locale: LANG=C, LC_CTYPE=C

Versions of packages gcc-3.3 depends on:
ii  binutils                   2.14.90.0.7-8 The GNU assembler, linker and bina
ii  cpp-3.3                    1:3.3.4-3     The GNU C preprocessor
ii  gcc-3.3-base               1:3.3.4-3     The GNU Compiler Collection (base 
ii  libc6                      2.3.2.ds1-13  GNU C Library: Shared libraries an
ii  libgcc1                    1:3.3.4-3     GCC support library

-- no debconf information

The following code compiles badly for the my_strncpy_bug function : the
if( *tmp ) ++ tmp; is never generated.

The difference between both loops is the use of an inside loop temp
variable.

Execution :

[EMAIL PROTECTED]:/tmp$ gcc -O2 -o y y.c
[EMAIL PROTECTED]:/tmp$ ./y
t1:My First string for this test ... t2:
t1:My First string for this test ... t2:My First string for this test
....
t1:My First string for this test ... t2:
t1:My First string for this test ...
t2:MMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMBefore
 buggy
[EMAIL PROTECTED]:/tmp$


--begining of source code for y.c


#include <stdio.h>

char *my_strncpy_bug( char *dst, const char *src, unsigned int n ) {
        char *work = dst;
        
        while( n ) {
                const char *tmp = src;

                *work = *tmp;
                ++ work;
                if( *tmp )
                        ++ tmp;
                -- n;
        }
        return dst;
}

char *my_strncpy( char *dst, const char *src, unsigned int n ) {
        char *work = dst;
        
        while( n ) {
                *work = *src;
                ++ work;
                if( *src )
                        ++ src;
                -- n;
        }
        return dst;
}


int main( int argc, char **argv ) {
        char tmp1[] = "My First string for this test ...";
        char tmp_bug3[] = "Before buggy";
        char tmp_bug2[256] = { 0 };
        char tmp_nobug3[] = "Before no bug";
        char tmp_nobug2[256] = { 0 };

        printf( "t1:%s t2:%s\n", tmp1, tmp_nobug2 );
        my_strncpy( tmp_nobug2, tmp1, 256 );
        printf( "t1:%s t2:%s\n", tmp1, tmp_nobug2 );

        printf( "t1:%s t2:%s\n", tmp1, tmp_bug2 );
        my_strncpy_bug( tmp_bug2, tmp1, 256 );
        printf( "t1:%s t2:%s\n", tmp1, tmp_bug2 );

        return 0;
}

--end of source code for y.c