[Ada] Expand NRV optimization in gigi

[Eric Botcazou]

This expands the recently implemented NRV optimization to the unconstrained 
case, both for array types and discriminated record types with variant part.

Tested on i586-suse-linux, applied on the mainline.


2011-11-20  Eric Botcazou  <ebotcazou@adacore.com>

	* gcc-interface/trans.c (struct language_function): Add GNAT_RET.
	(f_gnat_ret): New macro.
	(struct nrv_data): Add GNAT_RET.
	(finalize_nrv_unc_r): New helper function.
	(finalize_nrv): Add GNAT_RET parameter.  Copy it into DATA.  If the
	function returns unconstrained, use finalize_nrv_unc_r as callback.
	(return_value_ok_for_nrv_p): Test the alignment of RET_OBJ only if
	RET_OBJ is non-null.
	(Subprogram_Body_to_gnu): Pass GNAT_RET to finalize_nrv.
	(gnat_to_gnu) <N_Return_Statement>: In the return-unconstrained case,
	if optimization is enabled, record candidates for the Named Return
	Value optimization.


-- 
Eric Botcazou
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