GCN's 64-lane vectors tend to make RTL dumps very long.  This patch makes them
far more bearable by eliding long sequences of the same element into "repeated"
messages.

This also takes care of reading repeated sequences in the RTL front-end.

There are self tests for both reading and writing.

2018-10-11  Andrew Stubbs  <ams@codesourcery.com>
	    Jan Hubicka  <jh@suse.cz>
	    Martin Jambor  <mjambor@suse.cz>

	gcc/
	* print-rtl.c (print_rtx_operand_codes_E_and_V): Print how many times
	the same elements are repeated rather than printing all of them.
	* read-rtl.c (rtx_reader::read_rtx_operand): Recognize and expand
	"repeated" elements.
	* read-rtl-function.c (test_loading_repeat): New function.
	(read_rtl_function_c_tests): Call test_loading_repeat.
	* rtl-tests.c (test_dumping_repeat): New function.
	(rtl_tests_c_tests): Call test_dumping_repeat.

	gcc/testsuite/
	* selftests/repeat.rtl: New file.

Co-Authored-By: Jan Hubicka <jh@suse.cz>
Co-Authored-By: Martin Jambor <mjambor@suse.cz>

From-SVN: r265042