[Bug regression/24956] New: Optimizer and uninitialised variables.

[s_a_white at email dot com]

#include <stdint.h>
#include <stdio.h>

void test (int c)
{
    uint8_t a[4] = {0, 1, 2, 3};
    uint_least32_t b;
    b &= (uint_least32_t) 0xffffff00;
    b |= (uint_least32_t) a[3];
    b &= (uint_least32_t) 0xffff00ff;
    b |= (uint_least32_t) (a[2] << 8);
    b &= (uint_least32_t) 0xff00ffff;
    b |= (uint_least32_t) (a[1] << 16);
    b &= (uint_least32_t) 0x00ffffff;
    b |= (uint_least32_t) (a[0] << 24);

    printf ("b=%08x\n", b);
    if (c)
    {
        printf ("here\n");
        b = ~0;
        printf ("here2\n");
    }
    printf ("b=%08x\n", b);
}

int main ()
{
    test (0);
    return 0;
}


Output of gcc -O0 bug.cpp -o bug -lstdc++ is:

b=00010203
b=00010203

Output of gcc -O2 bug.cpp -o bug -lstdc++ is:

b=00010203
b=ffffffff

Doing either of these obtains the correct output:

-    uint_least32_t b;
+    uint_least32_t b = 0;

or

-        b = ~0;


System: Fresh install of Mandriva Linux Free 2006.0 with all
        patches applied as of 19/11/2005
gcc -v reports:

Using built-in specs.
Target: i586-mandriva-linux-gnu
Configured with: ../configure --prefix=/usr --libexecdir=/usr/lib
--with-slibdir=/lib --mandir=/usr/share/man --infodir=/usr/share/info
--enable-shared --enable-threads=posix --disable-checking
--enable-languages=c,c++,ada,f95,objc,java --host=i586-mandriva-linux-gnu
--with-system-zlib --enable-long-long --enable-__cxa_atexit
--enable-clocale=gnu --disable-libunwind-exceptions --enable-java-awt=gtk
--with-java-home=/usr/lib/jvm/java-1.4.2-gcj-1.4.2.0/jre --enable-gtk-cairo
--disable-libjava-multilib
Thread model: posix
gcc version 4.0.1 (4.0.1-5mdk for Mandriva Linux release 2006.0)


-- 
           Summary: Optimizer and uninitialised variables.
           Product: gcc
           Version: 4.0.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: regression
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: s_a_white at email dot com
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24956