i386.c (ix86_expand_vec_perm): Add handle one-operand permutation for TARGET_AVX512F.

i386.c (ix86_expand_vec_perm): Add handle one-operand permutation for TARGET_AVX512F.

gcc/
	* config/i386/i386.c (ix86_expand_vec_perm): Add handle one-operand
	permutation for TARGET_AVX512F.
	(ix86_expand_vec_one_operand_perm_avx512): New function.
	(expand_vec_perm_1): Invoke introduced function.
	* tree-vect-loop.c (vect_transform_loop): Clear-up safelen value since
	it may be not valid after vectorization.

gcc/testsuite/
	* gcc/testsuite/gcc.target/i386/avx512f-vect-perm-1.c: New test.
	* gcc/testsuite/gcc.target/i386/avx512f-vect-perm-2.c: New test.

From-SVN: r237982