This patch modifies several mechanisms in the compiler:

1) The handling of Ghost regions now records the start of the outermost ignored
   Ghost region which is currently in effect.

2) Generation of freeze actions for an arbitrary entity now inserts the actions
   prior to the start of the outermost ignored Ghost region when the freezing
   takes effect within an ignored Ghost region, but the entity being frozen is
   "living". This ensures that any freeze actions associated with the living
   entity will not be eliminated from the tree once ignored Ghost code is
   stripped away.

3) The Default_Initial_Condition and Invariant procedures are not treated as
   primitives even when they apply to tagged types. These procedures already
   employ class-wide precondition-like semantics to handle inheritance and
   overriding. In addition, the procedures cannot be invoked from source and
   should not be targets of dispatching calls.

2018-05-24  Hristian Kirtchev  <kirtchev@adacore.com>

gcc/ada/

	* expander.adb (Expand): Update the save and restore of the Ghost
	region.
	* exp_ch3.adb (Freeze_Type): Likewise.
	* exp_disp.adb (Make_DT): Likewise.
	* exp_util.adb (Build_DIC_Procedure_Body): Likewise.
	(Build_DIC_Procedure_Declaration): Likewise.
	(Build_Invariant_Procedure_Body): Likewise.
	(Build_Invariant_Procedure_Declaration): Likewise.
	(Make_Predicate_Call): Likewise.
	* freeze.adb (Add_To_Result): Insert the freeze action of a living
	entity prior to the start of the enclosing ignored Ghost region.
	(Freeze_Entity): Update the save and restore of the Ghost region.
	* ghost.adb (Install_Ghost_Mode): Reimplemented.
	(Install_Ghost_Region): New routine.
	(Mark_And_Set_Ghost_Assignment): Install a region rather than a mode.
	(Mark_And_Set_Ghost_Body): Likewise.
	(Mark_And_Set_Ghost_Completion): Likewise.
	(Mark_And_Set_Ghost_Declaration): Likewise.
	(Mark_And_Set_Ghost_Instantiation): Likewise.
	(Mark_And_Set_Ghost_Procedure_Call): Likewise.
	(Name_To_Ghost_Mode): New routine.
	(Restore_Ghost_Region): New routine.
	* ghost.ads (Install_Ghost_Region): New routine.
	(Restore_Ghost_Region): New routine.
	* opt.ads: Add new global variable Ignored_Ghost_Region.
	* rtsfind.adb (Load_RTU): Update the save and restore of the Ghost
	region. Install a clean region.
	* sem.adb (Analyze): Likewise.
	(Do_Analyze): Likewise.
	* sem_ch3.adb (Analyze_Object_Declaration): Likewise
	(Derive_Progenitor_Subprograms): Use local variable Iface_Alias to
	capture the ultimate alias of the current primitive.
	(Process_Full_View): Update the save and restore of the Ghost region.
	Do not inherit DIC and invariant procedures.
	* sem_ch5.adb (Analyze_Assignment): Update the save and restore of the
	Ghost region.
	* sem_ch6.adb (Analyze_Procedure_Call): Likewise.
	(Analyze_Subprogram_Body_Helper): Likewise.
	* sem_ch7.adb (Analyze_Package_Body_Helper): Likewise.
	* sem_ch12.adb (Analyze_Package_Instantiation): Likewise.
	(Analyze_Subprogram_Instantiation): Likewise.
	(Instantiate_Package_Body): Likewise.
	(Instantiate_Subprogram_Body): Likewise.
	* sem_ch13.adb (Build_Predicate_Functions): Likewise.
	(Build_Predicate_Function_Declaration): Likewise.
	* sem_disp.adb
	(Add_Dispatching_Operation): Do not consider DIC and invariant
	procedures.
	(Check_Dispatching_Operation): Use Add_Dispatching_Operation to collect
	a dispatching subprogram.
	(Check_Operation_From_Private_View): Likewise.
	(Override_Dispatching_Operation): Likewise.
	* sem_prag.adb (Analyze_Contract_Cases_In_Decl_Part): Update the save
	and restore of the Ghost region.
	(Analyze_Initial_Condition_In_Decl_Part): Likewise.
	(Analyze_Pragma): Update the save and restore of the Ghost region.
	(Analyze_Pre_Post_Condition_In_Decl_Part): Likewise.
	* sem_util.adb (Is_Suitable_Primitive): New routine.
	* sem_util.ads (Is_Suitable_Primitive): New routine.
	* sinfo.ads: Update the section of Ghost regions.

gcc/testsuite/

	* gnat.dg/formal_containers.adb: New testcase.

From-SVN: r260648