PR target/12900
	* reg-stack (move_for_stack_reg): New prototype.  Return
	whether a control flow insn was deleted.
	(subst_stack_regs_pat): Likewise, using the information provided
	by move_for_stack_reg.
	(subst_stack_regs): Likewise, using the information provided
	by subst_stack_regs_pat.
	(convert_regs_1): Record whether a control flow insn was deleted,
	using the information provided by subst_stack_regs.  Purge dead
	edges only if a control flow insn was deleted.

From-SVN: r73977