treat argp-based mem as frame related in dse

treat argp-based mem as frame related in dse

The issue mentioned in PR112525 would be able to be handled by
updating dse.cc to treat arg_pointer_rtx similarly with frame_pointer_rtx.
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=30271#c10 also mentioned
this idea.

And arpg area may be used to pass argument to callee. So, it would
be needed to check if call insns are using that mem.

	PR rtl-optimization/112525
	PR target/30271

gcc/ChangeLog:

	* dse.cc (get_group_info): Add arg_pointer_rtx as frame_related.
	(check_mem_read_rtx): Add parameter to indicate if it is checking mem
	for call insn.
	(scan_insn): Add mem checking on call usage.

gcc/testsuite/ChangeLog:

	* gcc.target/powerpc/pr112525.c: New test.
	* gcc.target/powerpc/pr30271.c: New test.