-O2 bug in gcc 3.2, 3.3 and 3.4 with 64 bit integers on x86

[Anders Torger]

/*

  C program below. This mail can be extracted into test.c

  on x86, sizeof(long long) == 8, sizeof(long) == 4
  gcc -O2 -S test.c

  hash:
          pushl   %ebp
          movl    %esp, %ebp
          subl    $8, %esp
          movl    -4(%ebp), %eax
          xorl    -8(%ebp), %eax
          leave
          ret

  Where did the ull = *(unsigned long long *)key; assignment go?
  The compiler allocates stack space, and uses it, but without
  putting anything into it first. The asm generated without
  optimisation (without -O2) is correct.

  Debian Linux Pentium 4 system, gcc installed from package system
  from unstable as of 9 Nov 2004.

  gcc -O2 -S test.c

  no messages are generated at compilation.

  gcc 2.95 generates correct code.
  gcc 3.2.3 fails
  gcc 3.3.5 fails
  gcc 3.4.2 fails

  /Anders Torger

 */

#include <stdio.h>

unsigned long
hash(void *key)
{
    unsigned long long ull;
    ull = *(unsigned long long *)key;
    return ((unsigned long *)&ull)[0] ^ ((unsigned long *)&ull)[1];
}

int
main(void)
{
    unsigned long long ull;
    ull = ~0;
    fprintf(stderr, "%u\n", hash(&ull));
    return 0;
}