Optimize __builtin_shuffle_vector.

Optimize __builtin_shuffle_vector.

1. Support vpermw/vpermb in ix86_expand_vec_one_operand_perm_avx512.
2. Support 256/128-bits vpermi2b ix86_expand_vec_perm_vpermt2.
3. Add define_insn_and_split to optimize specific vector permutation to opmov{dw,wb,qd}.

gcc/ChangeLog:

	PR target/101846
	* config/i386/i386-expand.c (ix86_expand_vec_perm_vpermt2):
	Support vpermi2b for V32QI/V16QImode.
	(ix86_extract_perm_from_pool_constant): New function.
	(ix86_expand_vec_one_operand_perm_avx512): Support
	vpermw/vpermb under TARGET_AVX512BW/TARGET_AVX512VBMI.
	(expand_vec_perm_1): Adjust comments for upper.
	* config/i386/i386-protos.h (ix86_extract_perm_from_pool_constant):
	New declare.
	* config/i386/predicates.md (permvar_truncate_operand): New predicate.
	(pshufb_truncv4siv4hi_operand): Ditto.
	(pshufb_truncv8hiv8qi_operand): Ditto.
	* config/i386/sse.md (*avx512bw_permvar_truncv16siv16hi_1):
	New pre_reload define_insn_and_split.
	(*avx512f_permvar_truncv8siv8hi_1): Ditto.
	(*avx512f_vpermvar_truncv8div8si_1): Ditto.
	(*avx512f_permvar_truncv32hiv32qi_1): Ditto.
	(*avx512f_permvar_truncv16hiv16qi_1): Ditto.
	(*avx512f_permvar_truncv4div4si_1): Ditto.
	(*avx512f_pshufb_truncv8hiv8qi_1): Ditto.
	(*avx512f_pshufb_truncv4siv4hi_1): Ditto.
	(*avx512f_pshufd_truncv2div2si_1): Ditto.

gcc/testsuite/ChangeLog:

	PR target/101846
	* gcc.target/i386/pr101846-2.c: New test.
	* gcc.target/i386/pr101846-3.c: New test.
	* gcc.target/i386/pr101846-4.c: New test.