ada: Further fixes to handling of private views in instances

This removes more bypasses for private views in instances that are present
in type predicates (Conforming_Types, Covers, Specific_Type and Wrong_Type),
which in exchange requires additional work in Sem_Ch12 to restore the proper
view of types during the instantiation of generic bodies.

The main mechanism for this is the Has_Private_View flag, but it comes with
the limitations that 1) there must be a direct reference to the global type
in the generic construct (either a reference to a global object of this type
or the explicit declaration of a local object of this type), which is not
always the case e.g. for loop parameters and 2) it can deal with a single
type at a time, e.g. it cannot deal with an array type and its component
type if their respective views are not the same in the instance.

To overcome the second limitation, a new Has_Secondary_Private_View flag
is introduced to deal with a secondary type, which as of this writing is
either the component type of an array type or the designated type of an
access type (together they make up the vast majority of the problematic
cases for the Has_Private_View flag alone). This new mechanism subsumes
a specific treatment for them that was added in Copy_Generic_Node a few
years ago, although a specific treatment still needs to be preserved for
comparison and equality operators in a narrower case.

Additional handling is also introduced to overcome the first limitation
for loop parameters in Copy_Generic_Node, and a relaxed condition is used
in Exp_Ch7.Convert_View to generate an unchecked conversion between views.

gcc/ada/

	* exp_ch7.adb (Convert_View): Detect more cases of mismatches for
	private types and use Implementation_Base_Type as main criterion.
	* gen_il-fields.ads (Opt_Field_Enum): Add
	Has_Secondary_Private_View
	* gen_il-gen-gen_nodes.adb (N_Expanded_Name): Likewise.
	(N_Direct_Name): Likewise.
	(N_Op): Likewise.
	* sem_ch12.ads (Check_Private_View): Document the usage of second
	flag Has_Secondary_Private_View.
	* sem_ch12.adb (Get_Associated_Entity): New function to retrieve
	the ultimate associated entity, if any.
	(Check_Private_View): Implement Has_Secondary_Private_View
	support.
	(Copy_Generic_Node): Remove specific treatment for Component_Type
	of an array type and Designated_Type of an access type. Add
	specific treatment for comparison and equality operators, as well
	as iterator and loop parameter specifications.
	(Instantiate_Type): Implement Has_Secondary_Private_View support.
	(Requires_Delayed_Save): Call Get_Associated_Entity.
	(Set_Global_Type): Implement Has_Secondary_Private_View support.
	* sem_ch6.adb (Conforming_Types): Remove bypass for private views
	in instances.
	* sem_type.adb (Covers): Return true if Is_Subtype_Of does so.
	Remove bypass for private views in instances.
	(Specific_Type): Likewise.
	* sem_util.adb (Wrong_Type): Likewise.
	* sinfo.ads (Has_Secondary_Private_View): Document new flag.

1 files changed, 26 insertions, 13 deletions

diff --git a/gcc/ada/sinfo.ads b/gcc/ada/sinfo.ads
index 8040a59..57fd704 100644
--- a/gcc/ada/sinfo.ads
+++ b/gcc/ada/sinfo.ads
@@ -389,21 +389,23 @@ package Sinfo is
    --  abbreviations are used:
 
    --    "plus fields for binary operator"
-   --       Chars                     Name_Id for the operator
-   --       Left_Opnd                 left operand expression
-   --       Right_Opnd                right operand expression
-   --       Entity                    defining entity for operator
-   --       Associated_Node           for generic processing
-   --       Do_Overflow_Check         set if overflow check needed
-   --       Has_Private_View          set in generic units.
+   --       Chars                       Name_Id for the operator
+   --       Left_Opnd                   left operand expression
+   --       Right_Opnd                  right operand expression
+   --       Entity                      defining entity for operator
+   --       Associated_Node             for generic processing
+   --       Do_Overflow_Check           set if overflow check needed
+   --       Has_Private_View            set in generic units
+   --       Has_Secondary_Private_View  set in generic units
 
    --    "plus fields for unary operator"
-   --       Chars                     Name_Id for the operator
-   --       Right_Opnd                right operand expression
-   --       Entity                    defining entity for operator
-   --       Associated_Node           for generic processing
-   --       Do_Overflow_Check         set if overflow check needed
-   --       Has_Private_View          set in generic units.
+   --       Chars                       Name_Id for the operator
+   --       Right_Opnd                  right operand expression
+   --       Entity                      defining entity for operator
+   --       Associated_Node             for generic processing
+   --       Do_Overflow_Check           set if overflow check needed
+   --       Has_Private_View            set in generic units
+   --       Has_Secondary_Private_View  set in generic units
 
    --    "plus fields for expression"
    --       Paren_Count               number of parentheses levels
@@ -1457,6 +1459,13 @@ package Sinfo is
    --    A flag present in N_Subprogram_Body and N_Task_Definition nodes to
    --    flag the presence of a pragma Relative_Deadline.
 
+   --  Has_Secondary_Private_View
+   --    A flag present in generic nodes that have an entity, to indicate that
+   --    the node is either of an access type whose Designated_Type is private
+   --    or of an array type whose Component_Type is private. Used to exchange
+   --    private and full declarations if the visibility at instantiation is
+   --    different from the visibility at generic definition.
+
    --  Has_Self_Reference
    --    Present in N_Aggregate and N_Extension_Aggregate. Indicates that one
    --    of the expressions contains an access attribute reference to the
@@ -2522,6 +2531,7 @@ package Sinfo is
       --  Is_SPARK_Mode_On_Node
       --  Is_Elaboration_Warnings_OK_Node
       --  Has_Private_View (set in generic units)
+      --  Has_Secondary_Private_View (set in generic units)
       --  Redundant_Use
       --  Atomic_Sync_Required
       --  plus fields for expression
@@ -2605,6 +2615,7 @@ package Sinfo is
       --  Entity
       --  Associated_Node
       --  Has_Private_View (set in generic units)
+      --  Has_Secondary_Private_View (set in generic units)
       --  plus fields for expression
 
       --  Note: the Entity field will be missing (set to Empty) for character
@@ -5388,6 +5399,7 @@ package Sinfo is
       --  Associated_Node Note this is shared with Entity
       --  Etype
       --  Has_Private_View (set in generic units)
+      --  Has_Secondary_Private_View (set in generic units)
 
       --  Note: the Strval field may be set to No_String for generated
       --  operator symbols that are known not to be string literals
@@ -8030,6 +8042,7 @@ package Sinfo is
       --  Is_SPARK_Mode_On_Node
       --  Is_Elaboration_Warnings_OK_Node
       --  Has_Private_View (set in generic units)
+      --  Has_Secondary_Private_View (set in generic units)
       --  Redundant_Use
       --  Atomic_Sync_Required
       --  plus fields for expression