re PR tree-optimization/59591 (ICE in vect_get_vec_def_for_stmt_copy, at tree-vect-stmts.c:156 for -march=core-avx2)

	PR tree-optimization/59591
	* tree-vect-stmts.c (vectorizable_mask_load_store): Fix up handling
	of modifier = NARROW masked gathers.
	(permute_vec_elements): Use gimple_get_lhs instead of
	gimple_assign_lhs.

	* gcc.dg/vect/pr59591-1.c: New test.
	* gcc.dg/vect/pr59591-2.c: New test.
	* gcc.target/i386/pr59591-1.c: New test.
	* gcc.target/i386/pr59591-2.c: New test.

From-SVN: r206248