re PR tree-optimization/91940 (__builtin_bswap16 loop optimization)

re PR tree-optimization/91940 (__builtin_bswap16 loop optimization)

	PR tree-optimization/91940
	* tree-vect-patterns.c: Include tree-vector-builder.h and
	vec-perm-indices.h.
	(vect_recog_rotate_pattern): Also handle __builtin_bswap16, either by
	unpromoting the argument back to uint16_t, or by converting into a
	rotate, or into shifts plus ior.

	* gcc.dg/vect/vect-bswap16.c: Add -msse4 on x86, run on all targets,
	expect vectorized 1 loops message on both vect_bswap and sse4_runtime
	targets.
	* gcc.dg/vect/vect-bswap16a.c: New test.

From-SVN: r276442