[Bug middle-end/81502] In some cases the data is moved to memory unnecessarily [partial regression]

["rguenth at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81502

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |rguenth at gcc dot gnu.org

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
So the rewrite into SSA should work now.  I'm not sure the pattern combining
BIT_INSERT_EXPR and VECTOR_CST into a CONSTRUCTOR is desirable, a single insert
into a loaded constant vector is likely cheaper so some cost modeling would be
in order.

So from

int bar(void*) (void * ptr)
{
  int res;
  __m128i word;
  long long int _2;
  unsigned int _4;

  <bb 2> [100.00%] [count: INV]:
  _2 = (long long int) ptr_6(D);
  word_3 = BIT_INSERT_EXPR <{ 0, 0 }, _2, 0 (64 bits)>;
  _4 = BIT_FIELD_REF <word_3, 32, 0>;
  res_5 = (int) _4;
  return res_5;

the desired pattern is combining BIT_FIELD_REF and BIT_INSERT_EXPR.  We'd
combine
that into

  _4 = BIT_FIELD_REF <_2, 32, 0>;

will try to come up with a match.pd rule once time permits.