Set insn_last_address in final_1

final_1 already sets insn_current_address for each instruction, making
it possible to use some of the address functions in final.c during
assembly generation.  This patch also sets insn_last_address, since
as the comment says, we can treat final as a shorten_branches pass that
does nothing.  It's then possible to use insn_current_reference_address
during final as well.

This is needed for the aarch64.md definitions of far_branch to work:

   (set (attr "far_branch")
	(if_then_else (and (ge (minus (match_dup 2) (pc)) (const_int -1048576))
			   (lt (minus (match_dup 2) (pc)) (const_int 1048572)))
		      (const_int 0)
		      (const_int 1)))]

This value (tested only during final) uses the difference between
the INSN_ADDRESSES of operand 2 and insn_current_reference_address
to calculate a conservatively-correct estimate of the branch distance.
It takes into account the worst-case gap due to alignment, whereas
a direct comparison of INSN_ADDRESSES would give an unreliable,
optimistic result.

2018-04-10  Richard Sandiford  <richard.sandiford@linaro.org>

gcc/
	* final.c (final_1): Set insn_last_address as well as
	insn_current_address.

From-SVN: r259267

gcc/ChangeLog

+2018-04-10  Richard Sandiford  <richard.sandiford@linaro.org>
+
+	* final.c (final_1): Set insn_last_address as well as
+	insn_current_address.
+
 2018-04-10  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
 
 	PR target/85173

gcc/final.c

@@ -2081,6 +2081,9 @@ final_1 (rtx_insn *first, FILE *file, int seen, int optimize_p)
 	    }
 	  else
 	    insn_current_address = INSN_ADDRESSES (INSN_UID (insn));
+	  /* final can be seen as an iteration of shorten_branches that
+	     does nothing (since a fixed point has already been reached).  */
+	  insn_last_address = insn_current_address;
 	}
 
       dump_basic_block_info (file, insn, start_to_bb, end_to_bb,