[Bug tree-optimization/42652] vectorizer created unaligned vector insns

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42652

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Blocks|                            |53947
             Status|UNCONFIRMED                 |RESOLVED
      Known to work|                            |4.4.7, 4.5.4
         Resolution|                            |FIXED
   Target Milestone|---                         |4.5.4

--- Comment #19 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-07-13 
09:01:19 UTC ---
Link to vectorizer missed-optimization meta-bug.

--- Comment #20 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-07-19 
11:37:30 UTC ---
The testcase is invalid.  To quote:

typedef struct __attribute__ ((__packed__)) Palette
{
  unsigned short pad;
  unsigned int ents[0];
} Palette;

int
main ()
{
  unsigned char *buf = new unsigned char[sizeof (Palette) + 256 * sizeof
(unsigned int) + 16];
  Palette *palette = (Palette *) (buf);
  unsigned int *now = palette->ents;
  unsigned int *end = now + 256;
  for (; now < end; now++)
    *now = 69;
}

you are dereferencing a pointer of type unsigned int * which is not
properly aligned.

Fixed at least since 4.5.4 if you properly do

typedef struct __attribute__ ((__packed__)) Palette
{
  unsigned short pad;
  unsigned int ents[0];
} Palette;
typedef unsigned int uuint __attribute__((aligned(1)));
int
main ()
{
  unsigned char *buf = new unsigned char[sizeof (Palette) + 256 * sizeof
(unsigned int) + 16];
  Palette *palette = (Palette *) (buf);
  uuint *now = palette->ents;
  uuint *end = now + 256;
  for (; now < end; now++)
    *now = 69;
}

-Wcast-align does not warn about the original

  unsigned int *now = palette->ents;

stmt though.