Hello.

One another updated version of the patch.
Changes from the previous version:
- I fixed:
  gimple *stmt1 = (gimple *) XALLOCAVEC (char, gimple_size (GIMPLE_ASSIGN, 2));
  into gimple_size (GIMPLE_ASSIGN, 3)
- I simplified condition in gimple_simplified_result_is_gimple_val
- optimize_vec_cond_expr is using build_same_sized_truth_vector_type

Patch can bootstrap on x86_64-linux-gnu and survives regression tests.

Ready to be installed?
Thanks,
Martin