tree-vect-loop.c (vect_transform_loop): Fix nb_iterations_upper_bound computation for vectorized loop.

gcc/

	* tree-vect-loop.c (vect_transform_loop): Fix
	nb_iterations_upper_bound computation for vectorized loop.

gcc/testsuite/

	* gcc.target/i386/vect-unpack-2.c (avx512bw_test): Avoid
	optimization of vector loop.
	* gcc.target/i386/vect-unpack-3.c: New test.
	* gcc.dg/vect/vect-nb-iter-ub-1.c: New test.
	* gcc.dg/vect/vect-nb-iter-ub-2.c: New test.
	* gcc.dg/vect/vect-nb-iter-ub-3.c: New test.

From-SVN: r235639