[gcc r16-1135] ada: Fix compile-time failure due to duplicated attribute subprograms.

[Marc Poulhies]

https://gcc.gnu.org/g:755f3d9ba29953f2bee6e46644a5233b31ea2f4f

commit r16-1135-g755f3d9ba29953f2bee6e46644a5233b31ea2f4f
Author: Steve Baird <baird@adacore.com>
Date:   Mon Jan 13 14:18:26 2025 -0800

    ada: Fix compile-time failure due to duplicated attribute subprograms.
    
    For a given type, and for certain attributes (the 4 streaming attributes
    and, for Ada2022, the Put_Image attribute), the compiler needs to keep track
    of whether a subprogram has already been generated for the given
    type/attribute pair. In some cases this was being done incorrectly;
    the compiler ended up generating duplicate subprograms (with the same
    name), resulting in compilation failures. This could occur if the prefix
    of an attribute reference denoted a subtype (more precisely, a non-first
    subtype). This includes the case of a subtype declaration that is implicitly
    introduced by the compiler to capture the binding between a formal type
    in a generic and the corresponding actual type in an instantiation.
    
    gcc/ada/ChangeLog:
    
            * exp_attr.adb (Expand_N_Attribute_Reference): When accessing the
            maps declared in package Cached_Attribute_Ops, the key value
            passed to Get or to Set should never be the entity node for a
            subtype. Use the entity of the corresponding type declaration
            instead.

Diff:
---
 gcc/ada/exp_attr.adb | 39 ++++++++++++++++++++++++---------------
 1 file changed, 24 insertions(+), 15 deletions(-)

diff --git a/gcc/ada/exp_attr.adb b/gcc/ada/exp_attr.adb
index b896228a70e3..aea9e8ad3afd 100644
--- a/gcc/ada/exp_attr.adb
+++ b/gcc/ada/exp_attr.adb
@@ -88,8 +88,10 @@ package body Exp_Attr is
       function Attribute_Op_Hash (Id : Entity_Id) return Header_Num is
         (Header_Num (Id mod Map_Size));
 
-      --  Cache used to avoid building duplicate subprograms for a single
-      --  type/streaming-attribute pair.
+      --  Caches used to avoid building duplicate subprograms for a single
+      --  type/attribute pair (where the attribute is either Put_Image or
+      --  one of the four streaming attributes). The type used as a key in
+      --  in accessing these maps should not be the entity of a subtype.
 
       package Read_Map is new GNAT.HTable.Simple_HTable
         (Header_Num => Header_Num,
@@ -4669,7 +4671,7 @@ package body Exp_Attr is
          end if;
 
          if not Is_Tagged_Type (P_Type) then
-            Cached_Attribute_Ops.Input_Map.Set (P_Type, Fname);
+            Cached_Attribute_Ops.Input_Map.Set (U_Type, Fname);
          end if;
       end Input;
 
@@ -5750,7 +5752,7 @@ package body Exp_Attr is
          Rewrite_Attribute_Proc_Call (Pname);
 
          if not Is_Tagged_Type (P_Type) then
-            Cached_Attribute_Ops.Output_Map.Set (P_Type, Pname);
+            Cached_Attribute_Ops.Output_Map.Set (U_Type, Pname);
          end if;
       end Output;
 
@@ -6669,7 +6671,7 @@ package body Exp_Attr is
          Rewrite_Attribute_Proc_Call (Pname);
 
          if not Is_Tagged_Type (P_Type) then
-            Cached_Attribute_Ops.Read_Map.Set (P_Type, Pname);
+            Cached_Attribute_Ops.Read_Map.Set (U_Type, Pname);
          end if;
       end Read;
 
@@ -8349,7 +8351,7 @@ package body Exp_Attr is
          Rewrite_Attribute_Proc_Call (Pname);
 
          if not Is_Tagged_Type (P_Type) then
-            Cached_Attribute_Ops.Write_Map.Set (P_Type, Pname);
+            Cached_Attribute_Ops.Write_Map.Set (U_Type, Pname);
          end if;
       end Write;
 
@@ -8951,15 +8953,22 @@ package body Exp_Attr is
          return Empty;
       end if;
 
-      if Nam = TSS_Stream_Read then
-         Ent := Cached_Attribute_Ops.Read_Map.Get (Typ);
-      elsif Nam = TSS_Stream_Write then
-         Ent := Cached_Attribute_Ops.Write_Map.Get (Typ);
-      elsif Nam = TSS_Stream_Input then
-         Ent := Cached_Attribute_Ops.Input_Map.Get (Typ);
-      elsif Nam = TSS_Stream_Output then
-         Ent := Cached_Attribute_Ops.Output_Map.Get (Typ);
-      end if;
+      declare
+         function U_Base return Entity_Id is
+           (Underlying_Type (Base_Type (Typ)));
+         --  Return the right type node for use in a C_A_O map lookup.
+         --  In particular, we do not want the entity for a subtype.
+      begin
+         if Nam = TSS_Stream_Read then
+            Ent := Cached_Attribute_Ops.Read_Map.Get (U_Base);
+         elsif Nam = TSS_Stream_Write then
+            Ent := Cached_Attribute_Ops.Write_Map.Get (U_Base);
+         elsif Nam = TSS_Stream_Input then
+            Ent := Cached_Attribute_Ops.Input_Map.Get (U_Base);
+         elsif Nam = TSS_Stream_Output then
+            Ent := Cached_Attribute_Ops.Output_Map.Get (U_Base);
+         end if;
+      end;
 
       Cached_Attribute_Ops.Validate_Cached_Candidate
         (Subp => Ent, Attr_Ref => Attr_Ref);