[Bug c/53024] Power of 2 requirement on vector_size not documented

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53024

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |documentation
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2012-04-18
     Ever Confirmed|0                           |1

--- Comment #1 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-04-18 10:15:29 UTC ---
Confirmed as documentation issue.  We can't easily lift this restriction
because we have

/* For a VECTOR_TYPE, this is the number of sub-parts of the vector.  */
#define TYPE_VECTOR_SUBPARTS(VECTOR_TYPE) \
  (((unsigned HOST_WIDE_INT) 1) \
   << VECTOR_TYPE_CHECK (VECTOR_TYPE)->type_common.precision)

and

struct GTY(()) tree_type_common {
...
  unsigned int precision : 10;

10 bits of precision would limit us to vectors with 1024 elements if we'd
not have the power-of-two restriction.  (not sure what a sane limit would be,
but 1024 byte vectors do not look too far off).