[Bug tree-optimization/56118] No constant propagation in vector field assignment

[glisse at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56118

--- Comment #1 from Marc Glisse <glisse at gcc dot gnu.org> 2013-01-26 17:57:13 UTC ---
Note that the case I am most interested in is actually when r is not
initialized:

  __m128d r;
  gimple_assign <real_cst, BIT_FIELD_REF <r, 64, 0>, 1.0e+0, NULL, NULL>
  gimple_assign <real_cst, BIT_FIELD_REF <r, 64, 64>, 2.0e+0, NULL, NULL>

because I've seen users fill in constant vectors this way. That could
complicate things a little as I'm not sure what r should be between the 2
assignments.

On the side, if SLP is extended to vectors, it might hide this issue (but for
now I've only managed to get an ICE because something takes the address of a
bit_field_ref).