PR rtl-optimization/20756:
	* basic-block.h (PROP_DEAD_INSN): Define.
	* flow.c (propagate_one_insn): Set during mark_set_regs call
	for a dead insn.
	(mark_set_1): Emit a clobber when we are about to delete a dead insn
	that kills a live register.

From-SVN: r99655