[Ada] AI-318

[Arnaud Charlet <charlet at adacore dot com>]

Tested on i686-linux, committed on trunk

Implement AI-318: extended return statements.
This is a quite delicate and significant language extension, which required
lots of changes in various areas of the front-end and run-time.

In particular, in the case of function result types with task parts.  This
involves passing two extra parameters to such functions: (1) The master of the
object. This depends on the destination of the call. For "new T'(F(...))" we
use the master of the access type. For "return R : T := F (...)", we pass
along the master passed in to THIS function. In all other cases, we use the
current master. (2) The activation chain. We always use the current activation
chain at the call site. On successful completion of a return statement, the
return statement's activation chain is moved to the caller's chain, so that
the caller will take care of activating the tasks in the return object. In
addition, the master of these tasks is set to the one passed in by the
caller. In case of UNsuccessful completion of a return statement, completion
of the return statement master will terminate all the never-to-be-activated
tasks.

Another delicate area is the case of function result types with controlled
parts.
This involves passing an extra parameter to such functions, which is a pointer
to the caller's finalization list. On successful completion of a return
statement, the return statement's finalization list is moved to the caller's
finalization list, so that the caller will take care of finalizing the return
object. In case of Unsuccessful completion of a return statement, the return
statement's finalization list is finalized.

Various other code clean ups (e.g. removal of no longer used entities).

2007-04-06  Robert Dewar  <dewar@adacore.com>
	    Thomas Quinot  <quinot@adacore.com>
	    Ed Schonberg  <schonberg@adacore.com>
	    Bob Duff  <duff@adacore.com>

	* einfo.ads, einfo.adb: (First_Component_Or_Discriminant): New function
	(Next_Component_Or_Discriminant): New function and procedure
	(First_Index, First_Literal, Master_Id,
	Set_First_Index, Set_First_Literal, Set_Master_Id):
	Add missing Ekind assertions.
	(Is_Access_Protected_Subprogram_Type): New predicate.
	(Has_RACW): New entity flag, set on package entities to indicate that
	the package contains the declaration of a remote accecss-to-classwide
	type.
	(E_Return_Statement): This node type has the Finalization_Chain_Entity
	attribute, in case the result type has controlled parts.
	(Requires_Overriding): Add this new flag, because "requires
	overriding" is subtly different from "is abstract" (see AI-228).
	(Is_Abstract): Split Is_Abstract flag into Is_Abstract_Subprogram and
	Is_Abstract_Type. Make sure these are called only when appropriate.
	(Has_Pragma_Unreferenced_Objects): New flag

	* exp_ch5.adb (Expand_N_Assignment_Statement): If the left-hand side is
	class-wide, the tag of the right-hand side must be an exact match, not
	an ancestor of that of the object on left-hand side.
	(Move_Activation_Chain): New procedure to create the call to
	System.Tasking.Stages.Move_Activation_Chain.
	(Expand_N_Extended_Return_Statement): Generate code to call
	System.Finalization_Implementation.Move_Final_List at the end of a
	return statement if the function's result type has controlled parts.
	Move asserts to Build_In_Place_Formal.
	(Move_Final_List): New function to create the call statement.
	(Expand_N_Assignment_Statement): In case of assignment to a class-wide
	tagged type, replace generation of call to the run-time subprogram
	CW_Membership by call to Build_CW_Membership.
	(Expand_N_Return_Statement): Replace generation of call to the run-time
	subprogram Get_Access_Level by call to Build_Get_Access_Level.
	(Expand_N_Simple_Function_Return): Replace generation of call to the
	run-time subprogram Get_Access_Level by call to Build_Get_Access_Level.

	* exp_ch6.ads, exp_ch6.adb (Expand_Call): Use new predicate
	Is_Access_Protected_Subprogram_Type, to handle both named and anonymous
	access to protected operations.
	(Add_Task_Actuals_To_Build_In_Place_Call): New procedure to add the
	master and chain actual parameters to a build-in-place function call
	involving tasks.
	(BIP_Formal_Suffix): Add new enumeration literals to complete the case
	statement.
	(Make_Build_In_Place_Call_In_Allocator,
	Make_Build_In_Place_Call_In_Anonymous_Context,
	Make_Build_In_Place_Call_In_Assignment,
	Make_Build_In_Place_Call_In_Object_Declaration): Call
	Add_Task_Actuals_To_Build_In_Place_Call with the appropriate master.
	(Expand_Inlined_Call): If the subprogram is a null procedure, or a
	stubbed procedure with a null body, replace the call with a null
	statement without using the full inlining machinery, for efficiency
	and to avoid invalid values in source file table entries.

	* exp_ch8.adb (Expand_N_Object_Renaming_Declaration): Add support for
	renamings of calls to build-in-place functions.

	* rtsfind.adb (RTE_Record_Component_Available): New subprogram that
	provides the functionality of RTE_Available to record components.
	(RTU_Entity): The function Entity has been renamed to RTU_Entity
	to avoid undesired overloading.
	(Entity): New subprogram that returns the entity for the referened
	unit. If this unit has not been loaded, it returns Empty.
	(RE_Activation_Chain_Access, RE_Move_Activation_Chain): New entities.
	Remove no longer used entities.
	(RE_Finalizable_Ptr_Ptr, RE_Move_Final_List): New entities.
	(RE_Type_Specific_Data): New entity.
	(RE_Move_Any_Value): New entity.
	(RE_TA_A, RE_Get_Any_Type): New entities.
	(RE_Access_Level, RE_Dispatch_Table, E_Default_Prim_Op_Count,
	 RE_Prims_Ptr, RE_RC_Offset, RE_Remotely_Callable,
	 RE_DT_Typeinfo_Ptr_Size, RE_Cstring_Ptr, RE_DT_Expanded_Name): Added.
	(Entity): New subprogram that returns the entity for the referened
	unit. If this unit has not been loaded, it returns Empty.
	(RTE): Addition of a new formal that extends the search to the scopes
	of the record types found in the chain of the package.

	* sem_ch6.ads, sem_ch6.adb (Check_Overriding_Indicator): Print
	"abstract subprograms must be visible" message, whether or not the type
	is an interface; that is, remove the special case for interface types.
	(Analyze_Function_Return): Remove error message "return of task objects
	is not yet implemented" because this is now implemented.
	(Create_Extra_Formals): Add the extra master and activation chain
	formals in case the result type has tasks.
	Remove error message "return of limited controlled objects is not yet
	implemented".
	(Create_Extra_Formals): Add the extra caller's finalization list formal
	in case the result type has controlled parts.
	(Process_Formals): In case of access formal types there is no need
	to continue with the analysis of the formals if we already notified
	errors.
	(Check_Overriding_Indicator): Add code to check overriding of predefined
	operators.
	(Create_Extra_Formals): Prevent creation of useless Extra_Constrained
	flags for formals that do not require them,.
	(Enter_Overloaded_Entity): Do not give -gnatwh warning message unless
	hidden entity is use visible or directly visible.
	(Analyze_Abstract_Subprogram_Declaration,Analyze_Subprogram_Body,
	Analyze_Subprogram_Declaration,Analyze_Subprogram_Specification,
	Check_Conventions,Check_Delayed_Subprogram,Make_Inequality_Operator,
	New_Overloaded_Entity): Split Is_Abstract flag into
	Is_Abstract_Subprogram and Is_Abstract_Type.

	* s-finimp.ads, s-finimp.adb (Move_Final_List): New procedure to move
	a return statement's finalization list to the caller's list, used for
	build-in-place functions with result type with controlled parts.
	Remove no longer used entities.

	* s-taskin.ads (Activation_Chain): Remove pragma Volatile. It is no
	longer needed, because the full type is now limited, and therefore a
	pass-by-reference type.
	(Foreign_Task_Level): New constant.

	* s-tassta.ads, s-tassta.adb (Move_Activation_Chain): New procedure to
	move tasks from the activation chain belonging to a return statement to
	the one passed in by the caller, and update the master to the one
	passed in by the caller.
	(Vulnerable_Complete_Master, Check_Unactivated_Tasks): Check the master
	of unactivated tasks, so we don't kill the ones that are being returned
	by a build-in-place function.
	(Create_Task): Ignore AI-280 for foreign threads.

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