If we support multiple ABIs in the same translation unit, it can
sometimes be the case that a callee clobbers more registers than
its caller is allowed to.  We need to call df_set_regs_ever_live
on these extra registers so that the prologue and epilogue code
can handle them appropriately.

This patch does that in IRA.  I wanted to avoid another full
instruction walk just for this, so I combined it with the existing
set_paradoxical_subreg walk.  This happens before the first
calculation of elimination offsets.

2019-09-30  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* function-abi.h (function_abi_aggregator): New class.
	* function-abi.cc (function_abi_aggregator::caller_save_regs): New
	function.
	* ira.c (update_equiv_regs_prescan): New function.  Call
	set_paradoxical_subreg here rather than...
	(update_equiv_regs): ...here.
	(ira): Call update_equiv_regs_prescan.

From-SVN: r276339