Run pass_sink_code once more before store_merging

Run pass_sink_code once more before store_merging

Gimple sink code pass runs quite early, there may be some new
oppertunities exposed by later gimple optmization passes, this patch
runs the sink code pass once more before store_merging.  For detailed
discussion, please refer to:
https://gcc.gnu.org/pipermail/gcc-patches/2020-December/562352.html

Tested the SPEC2017 performance on P8LE, 544.nab_r is improved
by 2.43%, but no big changes to other cases, GEOMEAN is improved quite
small with 0.25%.

gcc/ChangeLog:

2021-05-18  Xionghu Luo  <luoxhu@linux.ibm.com>

	* passes.def: Add sink_code pass before store_merging.
	* tree-ssa-sink.c (pass_sink_code:clone): New.

gcc/testsuite/ChangeLog:

2021-05-18  Xionghu Luo  <luoxhu@linux.ibm.com>

	* gcc.dg/tree-ssa/ssa-sink-1.c: Adjust.
	* gcc.dg/tree-ssa/ssa-sink-2.c: Ditto.
	* gcc.dg/tree-ssa/ssa-sink-3.c: Ditto.
	* gcc.dg/tree-ssa/ssa-sink-4.c: Ditto.
	* gcc.dg/tree-ssa/ssa-sink-5.c: Ditto.
	* gcc.dg/tree-ssa/ssa-sink-6.c: Ditto.
	* gcc.dg/tree-ssa/ssa-sink-7.c: Ditto.
	* gcc.dg/tree-ssa/ssa-sink-8.c: Ditto.
	* gcc.dg/tree-ssa/ssa-sink-9.c: Ditto.
	* gcc.dg/tree-ssa/ssa-sink-10.c: Ditto.
	* gcc.dg/tree-ssa/ssa-sink-13.c: Ditto.
	* gcc.dg/tree-ssa/ssa-sink-14.c: Ditto.
	* gcc.dg/tree-ssa/ssa-sink-16.c: Ditto.
	* gcc.dg/tree-ssa/ssa-sink-17.c: Ditto.
	* gcc.dg/tree-ssa/ssa-sink-18.c: New.