tree-vect-data-refs.c (vect_shift_permute_load_chain): Extend shift permutations on power of 2 cases.

gcc/

        * tree-vect-data-refs.c (vect_shift_permute_load_chain): Extend shift
	permutations on power of 2 cases.

gcc/testsuites/

	* gcc.target/i386/pr52252-atom-1.c: New.

From-SVN: r217359