[Ada] Suppression of elaboration-related warnings

[Ada] Suppression of elaboration-related warnings

This patch changes the behavior of elaboration-related warnings as follows:

   * If a scenario or a target has [elaboration] warnings suppressed, then
     any further elaboration-related warnings along the paths rooted at the
     scenario are also suppressed.

   * Elaboration-related warnings related to task activation can now be
     suppressed when either the task object, task type, or the activation
     call have [elaboration] warnings suppressed.

   * Elaboration-related warnings related to calls can now be suppressed when
     either the target or the call have [elaboration] warnings suppressed.

   * Elaboration-related warnings related to instantiations can now be
     suppressed when the instantiation has [elaboration] warnings suppressed.

The patch also cleans up the way the state of the Processing phase is updated
with each new node along a path. It is now preferable to update the state in
routines

   Process_Conditional_ABE_Activation_Impl
   Process_Conditional_ABE_Call
   Process_Conditional_ABE_Instantiation

rather than within their language-specific versions.

2018-05-23  Hristian Kirtchev  <kirtchev@adacore.com>

gcc/ada/

	* einfo.adb: Flag304 is now Is_Elaboration_Warnings_OK_Id.
	(Is_Elaboration_Warnings_OK_Id): New routine.
	(Set_Is_Elaboration_Warnings_OK_Id): New routine.
	(Write_Entity_Flags): Output Flag304.
	* einfo.ads: Add new attribute Is_Elaboration_Warnings_OK_Id along with
	occurrences in entities.
	(Is_Elaboration_Warnings_OK_Id): New routine along with pragma Inline.
	(Set_Is_Elaboration_Warnings_OK_Id): New routine along with pragma
	Inline.
	* sem_attr.adb (Analyze_Access_Attribute): Capture the state of
	elaboration warnings.
	* sem_ch3.adb (Analyze_Object_Declaration): Capture the state of
	elaboration warnings.
	* sem_ch6.adb (Analyze_Abstract_Subprogram_Declaration): Capture the
	state of elaboration warnings.
	(Analyze_Subprogram_Body_Helper): Capture the state of elaboration
	warnings.
	(Analyze_Subprogram_Declaration): Capture the state of elaboration
	warnings.
	* sem_ch9.adb (Analyze_Entry_Declaration): Capture the state of
	elaboration warnings.
	(Analyze_Single_Task_Declaration): Capture the state of elaboration
	warnings.
	(Analyze_Task_Type_Declaration): Capture the state of elaboration
	warnings.
	* sem_ch12.adb (Analyze_Generic_Package_Declaration): Capture the state
	of elaboration warnings.
	(Analyze_Generic_Subprogram_Declaration): Capture the state of
	elaboration warnings.
	* sem_elab.adb: Add a section on suppressing elaboration warnings.
	Type Processing_Attributes includes component Suppress_Warnings
	intended to suppress any elaboration warnings along a path in the
	graph.  Update Initial_State to include a value for this component.
	Types Target_Attributes and Task_Attriutes include component
	Elab_Warnings_OK to indicate whether the target or task has elaboration
	warnings enabled.  component Elab_Warnings_OK.
	(Build_Access_Marker): Propagate attribute
	Is_Elaboration_Warnings_OK_Node from the attribute to the generated
	call marker.
	(Extract_Instantiation_Attributes): Set the value for Elab_Warnings_OK.
	(Extract_Target_Attributes): Set the value for Elab_Warnings_OK.
	(Extract_Task_Attributes): Set the value for Elab_Warnings_OK.
	(Process_Conditional_ABE_Access): Suppress futher elaboration warnings
	when already in this mode or when the attribute or target have warnings
	suppressed.
	(Process_Conditional_ABE_Activation_Impl): Do not emit any diagnostics
	if warnings are suppressed.
	(Process_Conditional_ABE_Call): Suppress further elaboration warnings
	when already in this mode, or the target or call have warnings
	suppressed.
	(Process_Conditional_ABE_Call_Ada): Do not emit any diagnostics if
	warnings are suppressed.
	(Process_Conditional_ABE_Call_SPARK): Do not emit any diagnostics if
	warnings are suppressed.
	(Process_Conditional_ABE_Instantiation): Suppress further elaboration
	warnings when already in this mode or when the instantiation has
	warnings suppressed.
	(Process_Conditional_ABE_Instantiation_Ada): Do not emit any
	diagnostics if warnings are suppressed.
	(Process_Conditional_ABE_Variable_Assignment_Ada): Use the more
	specific Is_Elaboration_Warnings_OK_Id rather than Warnings_Off.
	(Process_Conditional_ABE_Variable_Assignment_SPARK): Use the more
	specific Is_Elaboration_Warnings_OK_Id rather than Warnings_Off.
	(Process_Task_Object): Suppress further elaboration warnings when
	already in this mode, or when the object, activation call, or task type
	have warnings suppressed. Update the processing state to indicate that
	the path goes through a task body.
	* sinfo.adb (Is_Elaboration_Warnings_OK_Node): Accept attribute
	references.
	(Set_Is_Elaboration_Warnings_OK_Node): Accept attribute references.
	* sinfo.ads: Attribute Is_Elaboration_Warnings_OK_Node now applies to
	attribute references.

gcc/testsuite/

	* gnat.dg/elab4.adb, gnat.dg/elab4_pkg.adb, gnat.dg/elab4_pkg.ads: New
	testcase.

From-SVN: r260578