This patch actually improves generated code, because REG_DEAD notes
used by the old insn scan are not always present.  On x86_64, see
gcc/wide-int-print.o:print_hex for an example of a function that is
smaller and uses one less callee saved reg.

	* ira.c (combine_and_move_insns): Rather than scanning insns,
	use DF infrastucture to find use and def insns.

From-SVN: r235660