LRA: identify biggest access mode for hard_regs and use it in split_reg

LRA: identify biggest access mode for hard_regs and use it in split_reg

	PR target/70083
	* lra-lives.c (process_bb_lives): Also update biggest mode for hard
	regs.
	(lra_create_live_ranges_1): initialize hard register biggest_mode to
	VOIDmode.
	* lra-constraints.c (split_reg): For hard regs, try to find the
	biggest single-register mode used in the function.

testsuite/
	PR target/70083
	* gcc.dg/torture/pr70083.c: New test.
	* gcc.target/i386/pr70083.c: New test.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@234184 138bc75d-0d04-0410-961f-82ee72b054a4