[Ada] Tech debt: Expansion of contracts

[Ada] Tech debt: Expansion of contracts

This patch modifies the expansion of contracts such that the statements
and declarations of a subprogram with post-execution checks get moved to
a local internally generated subprogram which the original subprogram
calls directly followed by the required post-execution checks.

This differs from the current implementation which requires delicate
machinary which coordinates with the finalization process to emulate the
desired behavior within the "at end" procedure.

gcc/ada/

	* contracts.adb, contracts.ads
	(Analyze_Pragmas_In_Declarations): Added to aid in the new
	expansion model so that pragmas relating to contracts can get
	processed early before the rest of the subprogram containing them.
	(Build_Subprogram_Contract_Wrapper): Created to do the majority of
	expansion for postconditions. It builds a local wrapper with the
	statements and declarations within a given subprogram.
	(Is_Prologue_Renaming): Moved out from Process_Preconditions to be
	used generally within the contracts package.
	(Build_Entry_Contract_Wrapper): Moved from exp_ch7.
	(Expand_Subprogram_Contract): Add new local variable Decls to
	store expanded declarations needed for evaluation of contracts.
	Call new wrapper building procedure and modify comments to match
	new expansion model.
	(Get_Postcond_Enabled): Deleted.
	(Get_Result_Object_For_Postcond): Deleted.
	(Get_Return_Success_For_Postcond): Deleted.
	(Process_Contract_Cases): Add new parameter to store declarations.
	(Process_Postconditions): Add new parameter to store declarations.
	(Process_Preconditions): Add new parameter to store declarations.
	Add code to move entry-call prologue renamings
	* einfo.ads: Document new field Wrapped_Statements and modify
	comment for Postconditions_Proc.
	* exp_attr.adb
	(Analyze_Attribute): Modify expansion of the 'Old attribute to
	recognize new expansion model and use Wrapped_Statements instead
	of Postconditions_Proc.
	* exp_ch6.adb
	(Add_Return): Remove special expansion for postconditions.
	(Expand_Call): Modify condition checking for calls to access
	subprogram wrappers to handle new expansion models.
	(Expand_Call_Helper): Remove special expansion for postconditions.
	(Expand_Non_Function_Return): Remove special expansion for
	postconditions.
	(Expand_Simple_Function_Return): Remove special expansion for
	postconditions.
	* exp_ch7.adb
	(Build_Finalizer): Deleted, but replaced by code in
	Build_Finalizer_Helper
	(Build_Finalizer_Helper): Renamed to Build_Finalizer, and special
	handling of 'Old objects removed.
	* exp_ch9.adb
	(Build_Contract_Wrapper): Renamed and moved to contracts package.
	* exp_prag.adb
	(Expand_Pragma_Contract_Cases): Delay analysis of contracts since
	they now instead get analyzed as part of the wrapper generation
	instead of after analysis of their corresponding subprogram's
	body.
	(Expand_Pragma_Check): Label expanded if-statements which come
	from the expansion of assertion statements as
	Comes_From_Check_Or_Contract.
	* freeze.adb
	(Freeze_Entity): Add special case to avoid freezing when a freeze
	node gets generated as part of the expansion of a postcondition
	check.
	* gen_il-gen-gen_nodes.adb: Add new flag
	Comes_From_Check_Or_Contract.
	* gen_il-fields.ads: Add new field Wrapped_Statements. Add new
	flag Comes_From_Check_Or_Contract.
	* gen_il-gen-gen_entities.adb: Add new field Wrapped_Statements.
	* ghost.adb
	(Is_OK_Declaration): Replace Name_uPostconditions with
	Name_uWrapped_Statements.
	(Is_OK_Statement): Simplify condition due to the loss of
	Original_Node as a result of the new expansion model of contracts
	and use new flag Comes_From_Check_Or_Contract in its place.
	* inline.adb
	(Declare_Postconditions_Result): Replace Name_uPostconditions with
	Name_uWrapped_Statements.
	(Expand_Inlined_Call): Replace Name_uPostconditions with
	Name_uWrapped_Statements.
	* lib.adb, lib.ads
	(ipu): Created to aid in debugging.
	* lib-xref.adb
	(Generate_References): Remove special handling for postcondition
	procedures.
	* sem_attr.adb
	(Analyze_Attribute_Old_Result): Add new context in which 'Old can
	appear due to the changes in expansion. Replace
	Name_uPostconditions with Name_uWrapped_Statements.
	(Result): Replace Name_uPostconditions with
	Name_uWrapped_Statements.
	* sem_ch11.adb
	(Analyze_Handled_Statements): Remove check to exclude warnings on
	useless assignments within postcondition procedures since
	postconditions no longer get isolated into separate subprograms.
	* sem_ch6.adb
	(Analyze_Generic_Subprogram_Body): Modify expansion of generic
	subprogram bodies so that contracts (and their associated pragmas)
	get analyzed first.
	(Analyze_Subprogram_Body_Helper): Remove global HSS variable due
	to the HSS of the body potentially changing during the expansion
	of contracts. In cases where it was used instead directly call
	Handled_Statement_Sequence. Modify expansion of subprogram bodies
	so that contracts (and their associated pragmas) get analyzed
	first.
	(Check_Missing_Return): Create local HSS variable instead of using
	a global one.
	(Move_Pragmas): Use new pragma table instead of an explicit list.
	* sem_elab.adb
	(Is_Postconditions_Proc): Deleted since the new scheme of
	expansion no longer divides postcondition checks to a separate
	subprogram and so cannot be easily identified (similar to
	pre-condition checks).
	(Info_Call): Remove info printing for _Postconditions subprograms.
	(Is_Assertion_Pragma_Target): Remove check for postconditions
	procedure
	(Is_Bridge_Target): Remove check for postconditions procedure.
	(Get_Invocation_Attributes): Remove unneeded local variables and
	check for postconditions procedure.
	(Output_Call): Remove info printing for _Postconditions
	subprograms.
	* sem_prag.adb, sem_prag.ads: Add new Pragma table for pragmas
	significant to subprograms, along with tech-debt comment.
	(Check_Arg_Is_Local_Name): Modified to recognize the new
	_Wrapped_Statements internal subprogram and the new expansion
	model.
	(Relocate_Pragmas_To_Body): Replace Name_uPostconditions with
	Name_uWrapped_Statements.
	* sem_res.adb
	(Resolve_Entry_Call): Add conditional to detect both contract
	based wrappers of entries, but also wrappers generated as part of
	general contract expansion (e.g. local postconditions
	subprograms).
	* sem_util.adb
	(Accessibility_Level): Verify 'Access is not taken based on a
	component of a function result.
	(Has_Significant_Contracts): Replace Name_uPostconditions with
	Name_uWrapped_Statements.
	(Same_Or_Aliased_Subprogram): Add conditional to detect and obtain
	the original subprogram based on the new concept of
	"postcondition" wrappers.
	* sinfo.ads: Add documentation for new flag
	Comes_From_Check_Or_Contract.
	* snames.ads-tmpl: Remove Name_uPostconditions and add
	Name_uWrapped_Statements