$ gcc -v 
Reading specs from /pdv/.tools/pkg/gcc/3.4.3/bin/../lib/gcc/powerpc-ibm-
aix5.2.0.0/3.4.3/specs
Configured with: ../gcc-3.4.3/configure --prefix=/tools/pkg/gcc/3.4.3 --with-
ld=/bin/ld --with-as=/bin/as --disable-threads --enable-languages=c,c++
Thread model: aix
gcc version 3.4.3

// foo.c //

#include <stdio.h>

inline void
reverse( char* beg, char* end )
{
  while( beg < --end )
  {
    char t = *end;
    *end = *beg;
    *beg++ = t;
  }
}

void doIt( int* val )
{
  reverse( (char*)val, (char*)val + sizeof( *val ) );
}

int main()
{
  int d = 0x12345678;
  printf( "%x\n", d );
  doIt( &d );
  printf( "%x\n", d );
  return 0;
}

////

$ gcc -o foo foo.c -O2
$ foo
12345678
78345612

$ gcc -o foo foo.c
$ foo
12345678
78563412

Works with GCC 3.3.3