vect: CSE for bump and offset in strided load/store operations.

vect: CSE for bump and offset in strided load/store operations.

Every time "vect_get_strided_load_store_ops" is called, new bump and offset
variables and a series of stmts are created.  And IVOPTs is not able to
eliminate them.  The patch use "cse_and_gimplify_to_preheader" to CSE them.

2020-06-17  Bin Cheng  <bin.cheng@linux.alibaba.com>
	    Kaipeng Zhou  <zhoukaipeng3@huawei.com>

	PR tree-optimization/95199
	* tree-vect-stmts.c: Eliminate common stmts for bump and offset in
	strided load/store operations and remove redundant code.

2020-06-17  Bin Cheng  <bin.cheng@linux.alibaba.com>
	    Kaipeng Zhou  <zhoukaipeng3@huawei.com>

	PR tree-optimization/95199
	* gcc.target/aarch64/sve/pr95199.c: New test.