[Bug tree-optimization/17949] New: Tree loop optimization generates unaligned access (STRICT_ALIGNMENT is set)

[sje at cup dot hp dot com]

IA64 sets STRICT_ALIGNMENT to 1 but the tree loop optimizer is converting byte
loads into a unaligned word load (and thus creating an unaligned access).

The attached program compiles and runs with no optimization, fails with -O1 and
works with -O1 -fno-tree-loop-optimize.  With -O1 running the executable core
dumps on IA64 HP-UX and gives an "Unaligned Access" error message on IA64 Linux.

Test case:

    typedef struct
    {
        short i __attribute__ ((packed));
        int f[2] __attribute__ ((packed));
    } A;

    A a;
    int i;

    main ()
    {
        int j;
        for (j = 0; j < 2; j++)
                i += a.f[j];
    }

-- 
           Summary: Tree loop optimization generates unaligned access
                    (STRICT_ALIGNMENT is set)
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: sje at cup dot hp dot com
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: ia64-hp-hpux11.23
  GCC host triplet: ia64-hp-hpux11.23
GCC target triplet: ia64-hp-hpux11.23


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17949