This patch introduces several changes to the new elaboration order
mechanism:

   * The concept of "strong" and "weak" edges is introduced. Strong
     edges are the byproduct of language-defined relations between
     units, such as with clauses. Weak edges are the byproduct of
     specilative invocations at elaboration time, which may or may not
     take place depending on control flow.

   * The elaboration order algorithm has been heavily modified to make
     use of the strong and weak edges, and operate on units compiled
     with different elaboration models.

   * The elaboration order algorithm employs the following logic:

        - Maintain two sets of vertices, one for all elaborable
          vertices, and one for all waiting vertices.

        - Pick the best elaborable vertex, and elaborate its component.

        - If no such elaborable vertex is available, pick the best
          weakly elaborable vertex whose unit has been compiled with the
          dynamic model, and elaborate its component.

        - If no such weakly elaborable vertex is available, then either
          all vertices were already elaborated, or the graph contains a
          cycle.

     The elaboration of a component employs the same logic, with an
     added step where all successors of some predecessor currently being
     elaborated are notified that they have one fewer predecessor to
     wait on. This may cause certain successors to become elaborable, in
     which case they are moved from the set of waiting vertices to the
     set of elaborable vertices.

   * Three new GNATbind debug switches are introduced, -d_a, -d_b, and
     -d_e, to eliminate the effects of pragmas Elaborate_All,
     Elaborate_Body, and Elaborate respectively.

   * The section on terminology is updated to include new entries.

2019-07-08  Hristian Kirtchev  <kirtchev@adacore.com>

gcc/ada/

	* bindo.adb: Update the section on terminology to include new
	concepts.  Update the section on switches to include new
	entries.
	* bindo.ads: Add type Precedence_Kind.
	* bindo-builders.adb: Add with and use clauses for Debug and
	Bindo.Validators.  Add use clauses for
	Bindo.Validators.Invocation_Graph_Validators and
	Bindo.Validators.Library_Graph_Validators.
	(Build_Invocation_Graph): Validate the graph immediately after
	it was built.
	(Build_Library_Graph): Update the parameter profile. The
	creation of the graph is now elaboration model-agnostic.
	Validate the graph immediately after it was built.
	(Create_With_Edge): Create regular with edges for Elaborate and
	Elaborate_All edges when the appropriate debug switches are in
	effect.
	* bindo-builders.ads (Build_Library_Graph): Update the parameter
	profile.
	* bindo-diagnostics.adb (Diagnose_Cycle): Track the presence of
	an Elaborate_All edge throughout the inspection of the cycle's
	edges.
	(Output_Dynamic_Model_Suggestions): Output the suggestion only
	when the cycle contains at least one weak edge where the
	successor was statically elaborated.
	(Output_Elaborate_Body_Transition, Output_Forced_Transition,
	Output_With_Transition): Update the assertions.
	* bindo-elaborators.adb: Remove use clauses for
	Bindo.Validators.Invocation_Graph_Validators and
	Bindo.Validators.Library_Graph_Validators.  Remove strings
	Add_To_All_Candidates_Msg and Add_To_Comp_Candidates_Msg.
	Remove type String_Ptr.
	(Add_Vertex, Add_Vertex_If_Elaborable, Create_All_Candidates_Set
	Create_Component_Candidates_Set): Remove.
	(Create_Component_Vertex_Sets, Create_Vertex_Sets): New routine.
	(Elaborate_Component): Update the parameter profile and the
	comment on usage.  Reimplement the elaboration of a component.
	The algorithm will now attempt to elaborate as many vertices
	possible. If this is not possible, and a weakly elaborable
	vertex is available use unit was compiled using the dynamic
	model, the algorithm will elaborate it.
	(Elaborate_Library_Graph): Reimplement the elaboration of the
	graph. The algorithm will now attempt to elaborate as many
	vertices along with their components as possible. If this is not
	possible, and a weakly elaborable vertex is available use unit
	was compiled using the dynamic model, the algorithm will
	elaborate it along with its component.
	(Elaborate_Units): Merge with the functionality of
	Elaborate_Units_Common.
	(Elaborate_Units_Common, Elaborate_Units_Dynamic,
	Elaborate_Units_Static): Remove.
	(Elaborate_Vertex): Update the parameter profile and the comment
	on usage.  Reimplemented.
	(Find_Best_Candidate): Remove.
	(Find_Best_Elaborable_Vertex, Find_Best_Vertex,
	Find_Best_Weakly_Elaborable_Vertex, Has_Elaborable_Body,
	Insert_Elaborable_Successor, Insert_Vertex): New routines.
	(Is_Better_Candidate): Remove.
	(Is_Better_Elaborable_Vertex,
	Is_Better_Weakly_Elaborable_Vertex,
	Is_Suitable_Elaborable_Vertex,
	Is_Suitable_Weakly_Elaborable_Vertex): New routines.
	(Trace_Candidate_Vertices): Remove.
	(Trace_Component): Output the number of strong and weak
	predecessors.
	(Trace_Unelaborated_Vertices): Remove.
	(Trace_Vertex): Output the number of strong and weak
	predecessors.
	(Trace_Vertices): New routine.
	(Update_Successor, Update_Successors): Update the parameter
	profile and the comment on usage.
	* bindo-graphs.adb: Remove type Precedence_Kind.
	(Add_Edge_With_Return): Update the increment of pending
	predecessors.
	(Add_Vertex): Provide default values for strong and weak
	predecessors.
	(Complementary_Vertex): Move the initial declaration to the
	spec. Update the parameter profile and the comment on usage.
	(Contains_Weak_Static_Successor): New routine.
	(Create): Update the parameter profile. The creation of the
	graph is now elaboration model-agnostic.
	(Decrement_Pending_Predecessors): Update the parameter profile
	and the comment on usage. Reimplemented.
	(Delete_Edge): Update the decrement of pending predecesors.
	(Has_Elaborate_Body): Do not treat a vertex as being subject to
	Elaborate_Body when a debug switch is in effect.
	(Increment_Pending_Predecessors): Update the parameter profile
	and the comment on usage. Reimplemented.
	(Is_Elaborable_Component): Reimplemented.
	(Is_Elaborable_Vertex): Move the initial declaration to the
	spec.  Reimplemented.
	(Is_Elaborate_Body_Pair): New routine.
	(Is_Dynamically_Elaborated): Update the parameter profile.
	Reimplemented.
	(Is_Weakly_Elaborable_Vertex): New routine.
	(Pending_Predecessors): Removed.
	(Pending_Predecessors_For_Elaboration,
	Pending_Strong_Predecessors, Pending_Weak_Predecessors,
	Update_Pending_Predecessors): New routines.
	(Update_Pending_Predecessors_Of_Components): Update the
	increment of pending predecessors.
	* bindo-graphs.ads: Update the components of type
	Component_Attributes.  Update the components of type
	Library_Graph_Attributes.  Update the components of type
	Library_Graph_Vertex_Attributes.  Update the initialization of
	No_Component_Attributes.  Update the initialization of
	No_Library_Graph_Vertex_Attributes.
	(Complementary_Vertex, Contains_Weak_Static_Successor): New
	routines.
	(Create): Update the parameter profile and the comment on usage.
	(Decrement_Pending_Predecessors, Is_Dynamically_Elaborated):
	Update the parameter profile and the comment on usage.
	(Is_Elaborate_Body_Pair, Is_Weakly_Elaborable_Vertex): New
	routines.
	(Pending_Predecessors): Removed.
	(Pending_Predecessors_For_Elaboration,
	Pending_Strong_Predecessors, Pending_Weak_Predecessors): New
	routines.
	* bindo-writers.adb (Write_Components): Moved from the spec.
	(Write_Component): Output the strong and weak predecessors.
	(Write_Library_Graph): Output the components as part of the
	graph.
	(Write_Library_Graph_Vertex): Output the strong and weak
	predecessors.
	* bindo-writers.ads (Write_Components): Moved to the body.
	* debug.adb: Add and document new GNATbind switches -d_a, -d_b,
	-d_e.
	* bindo-validators.adb: Minor reformattings.

From-SVN: r273209