i386: Add variable vec_set for 32bit vectors [PR97194]

i386: Add variable vec_set for 32bit vectors [PR97194]

To generate sane code a SSE4.1 variable PBLENDV instruction is needed.

Also enable variable vec_set through vec_setm_operand predicate
for TARGET_SSE4_1 instead of TARGET_AVX2.  ix86_expand_vector_init_duplicate
is able to emulate vpbroadcast{b,w} with pxor/pshufb.

2021-07-06  Uroš Bizjak  <ubizjak@gmail.com>

gcc/
	PR target/97194
	* config/i386/predicates.md (vec_setm_operand): Enable
	register_operand for TARGET_SSE4_1.
	* config/i386/mmx.md (vec_setv2hi): Use vec_setm_operand
	as operand 2 predicate.  Call ix86_expand_vector_set_var
	for non-constant index operand.
	(vec_setv4qi): Use vec_setm_mmx_operand as operand 2 predicate.
	Call ix86_expand_vector_set_var for non-constant index operand.

gcc/testsuite/

	PR target/97194
	* gcc.target/i386/sse4_1-vec-set-1a.c: New test.
	* gcc.target/i386/sse4_1-vec-set-2a.c: Ditto.