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.

From-SVN: r234184