Support vec_set/vec_extract/vec_init for V4HF/V2HF.

gcc/ChangeLog:

	* config/i386/i386-expand.cc
	(ix86_expand_vector_init_duplicate): Handle V4HF/V4BF and
	V2HF/V2BF.
	(ix86_expand_vector_init_one_nonzero): Ditto.
	(ix86_expand_vector_init_one_var): Ditto.
	(ix86_expand_vector_init_general): Ditto.
	(ix86_expand_vector_set_var): Ditto.
	(ix86_expand_vector_set): Ditto.
	(ix86_expand_vector_extract): Ditto.
	* config/i386/mmx.md
	(mmxdoublevecmode): Extend to V4HF/V4BF/V2HF/V2BF.
	(*mmx_pinsrw): Extend to V4FI_64, add a new alternative (&x,
	x, x), add a new define_split after the pattern.
	(*mmx_pextrw<mode>): New define_insn.
	(mmx_pshufw_1): Rename to ..
	(mmx_pshufw<mode>_1): .. this, extend to V4FI_64.
	(*mmx_pblendw64): Extend to V4FI_64.
	(*vec_dup<mode>): New define_insn.
	(vec_setv4hi): Rename to ..
	(vec_set<mode>): .. this, and extend to V4FI_64
	(vec_extractv4hihi): Rename to ..
	(vec_extract<mode><mmxscalarmodelower>): .. this, and extend
	to V4FI_64.
	(vec_init<mode><mmxscalarmodelower>): New define_insn.
	(*pinsrw): Extend to V2FI_32, add a new alternative (&x,
	x, x), and add a new define_split after it.
	(*pextrw<mode>): New define_insn.
	(vec_setv2hi): Rename to ..
	(vec_set<mode>): .. this, extend to V2FI_32.
	(vec_extractv2hihi): Rename to ..
	(vec_extract<mode><mmxscalarmodelower>): .. this, extend to
	V2FI_32.
	(*punpckwd): Extend to V2FI_32.
	(*pshufw_1): Rename to ..
	(*pshufw<mode>_1): .. this, extend to V2FI_32.
	(vec_initv2hihi): Rename to ..
	(vec_init<mode><mmxscalarmodelower>): .. this, and extend to
	V2FI_32.
	(*vec_dup<mode>): New define_insn.
	* config/i386/sse.md (*vec_extract<mode>): Refine constraint
	from v to Yw.

gcc/testsuite/ChangeLog:

	* gcc.target/i386/part-vect-vec_elem-1.c: New test.
	* gcc.target/i386/part-vect-vec_elem-2.c: New test.