i386: Add init pattern for V2HI vectors [PR100637]

i386: Add init pattern for V2HI vectors [PR100637]

2021-06-03  Uroš Bizjak  <ubizjak@gmail.com>

gcc/
	PR target/100637
	* config/i386/i386-expand.c (ix86_expand_vector_init_duplicate):
	Handle V2HI mode.
	(ix86_expand_vector_init_general): Ditto.
	Use SImode instead of word_mode for logic operations
	when GET_MODE_SIZE (mode) < UNITS_PER_WORD.
	(expand_vec_perm_even_odd_1): Assert that V2HI mode should be
	implemented by expand_vec_perm_1.
	(expand_vec_perm_broadcast_1): Assert that V2HI and V4HI modes
	should be implemented using standard shuffle patterns.
	(ix86_vectorize_vec_perm_const): Handle V2HImode.  Add V4HI and
	V2HI modes to modes, implementable with shuffle for one operand.
	* config/i386/mmx.md (*punpckwd): New insn_and_split pattern.
	(*pshufw_1): New insn pattern.
	(*vec_dupv2hi): Ditto.
	(vec_initv2hihi): New expander.

gcc/testsuite/

	PR target/100637
	* gcc.dg/vect/slp-perm-9.c (dg-final): Adjust dumps for vect32 targets.