ada: Implementation of support for storage models in gigi

ada: Implementation of support for storage models in gigi

It is based on a new LOAD_EXPR node in GENERIC that is later turned into
a bona-fide temporary during gimplification.

gcc/ada/

	* gcc-interface/ada-tree.def (LOAD_EXPR): New expression code.
	* gcc-interface/gigi.h (build_storage_model_load): Declare.
	(build_storage_model_store): Likewise.
	(instantiate_load_in_expr): Likewise.
	(INSTANTIATE_LOAD_IN_EXPR): New macro.
	(instantiate_load_in_array_ref): Declare.
	* gcc-interface/decl.cc (gnat_to_gnu_entity) <E_Record_Type>: Set a
	fake discriminant number on the fields of the template type.
	(gnat_to_gnu_field): Use integer for DECL_DISCRIMINANT_NUMBER.
	* gcc-interface/misc.cc (gnat_init_ts): Mark LOAD_EXPR as typed.
	* gcc-interface/trans.cc (fold_constant_decl_in_expr) <ARRAY_REF>:
	Also preserve the 4th operand.
	(Attribute_to_gnu): Deal with LOAD_EXPR of unconstrained array type.
	<Attr_Size>: Call INSTANTIATE_LOAD_IN_EXPR for a storage model.
	<Attr_Length>: Likewise.
	<Attr_Bit_Position>: Likewise.
	(get_storage_model): New function.
	(get_storage_model_access): Likewise.
	(storage_model_access_required_p): Likewise.
	(Call_to_gnu): Add GNAT_STORAGE_MODEL parameter and deal with it.
	Also deal with actual parameters that have a storage model.
	(gnat_to_gnu) <N_Object_Declaratio>: Adjust call to Call_to_gnu.
	<N_Explicit_Dereference>: Deal with a storage model access.
	<N_Indexed_Component>: Likewise.
	<N_Slice>: Likewise.
	<N_Selected_Component>: Likewise.
	<N_Assignment_Statement>: Adjust call to Call_to_gnu.  Deal with a
	storage model access either on the LHS, on the RHS or on both.
	<N_Function_Cal>: Adjust call to Call_to_gnu.
	<N_Free_Statement>: Deal with a pool that is a storage model.
	Replace test for UNCONSTRAINED_ARRAY_REF with test on the type.
	(gnat_gimplify_expr) <CALL_EXPR>: Tidy up.
	<LOAD_EXPR>: New case.
	<UNCONSTRAINED_ARRAY_REF>: Move down.
	* gcc-interface/utils.cc (maybe_unconstrained_array): Deal with a
	LOAD_EXPR by recursing on its first operand.
	* gcc-interface/utils2.cc (build_allocator): Deal with a pool that
	is a storage model.
	(build_storage_model_copy): New function.
	(build_storage_model_load): Likewise.
	(build_storage_model_store): Likewise.
	(instantiate_load_in_expr): Likewise.
	(instantiate_load_in_array_ref): Likewise.
	(gnat_rewrite_reference) <ARRAY_REF>: Also preserve the 4th operand.
	(get_inner_constant_reference) <ARRAY_REF>: Remove useless test.
	(gnat_invariant_expr) <ARRAY_REF>: Rewrite test.