[gcc r13-3667] ada: Skip dynamic interface conversion under configurable runtime

[gcc r13-3667] ada: Skip dynamic interface conversion under configurable runtime

[Marc Poulhi?s]

https://gcc.gnu.org/g:5150978dfe1b049f16bed80aad2163c43be039cf

commit r13-3667-g5150978dfe1b049f16bed80aad2163c43be039cf
Author: Javier Miranda <miranda@adacore.com>
Date:   Thu Oct 6 21:44:43 2022 +0000

    ada: Skip dynamic interface conversion under configurable runtime
    
    gcc/ada/
    
            * exp_disp.adb
            (Expand_Interface_Conversion): Under configurable runtime, when
            the target type is an interface that is an ancestor of the operand
            type, skip generating code to displace the pointer to reference
            the target dispatch table.
            * sem_disp.adb
            (Propagate_Tag): Handle class-wide types when checking for the
            addition of an implicit interface conversion.

Diff:
---
 gcc/ada/exp_disp.adb | 32 +++++++++++++++++++++-----------
 gcc/ada/sem_disp.adb | 15 ++++++++++++---
 2 files changed, 33 insertions(+), 14 deletions(-)

diff --git a/gcc/ada/exp_disp.adb b/gcc/ada/exp_disp.adb
index 43ae2e0f34d..d8a45ffb7c9 100644
--- a/gcc/ada/exp_disp.adb
+++ b/gcc/ada/exp_disp.adb
@@ -1304,17 +1304,24 @@ package body Exp_Disp is
            and then Is_Ancestor (Iface_Typ, Opnd, Use_Full_View => True)
          then
             return;
-         end if;
 
-         --  When the type of the operand and the target interface type match,
-         --  it is generally safe to skip generating code to displace the
-         --  pointer to the object to reference the secondary dispatch table
-         --  associated with the target interface type. The exception to this
-         --  general rule is when the underlying object of the type conversion
-         --  is an object built by means of a dispatching constructor (since in
-         --  such case the expansion of the constructor call is a direct call
-         --  to an object primitive, i.e. without thunks, and the expansion of
-         --  the constructor call adds an explicit conversion to the target
+         --  When the target type is an interface type that is an ancestor of
+         --  the operand type, it is generally safe to skip generating code to
+         --  displace the pointer to the object to reference the secondary
+         --  dispatch table of the target interface type. Two scenaries are
+         --  possible here:
+         --    1) The operand type is a regular tagged type
+         --    2) The operand type is an interface type
+         --  In the former case the target interface and the regular tagged
+         --  type share the primary dispatch table of the object; in the latter
+         --  case the operand interface has all the primitives of the ancestor
+         --  interface type (and exactly in the same dispatch table slots).
+         --
+         --  The exception to this general rule is when the underlying object
+         --  is built by means of a dispatching constructor (since in such case
+         --  the expansion of the constructor call is a direct call to an
+         --  object primitive, i.e. without thunks, and the expansion of
+         --  the constructor call adds this explicit conversion to the target
          --  interface type to force the displacement of the pointer to the
          --  object to reference the corresponding secondary dispatch table
          --  (cf. Make_DT and Expand_Dispatching_Constructor_Call)).
@@ -1326,7 +1333,10 @@ package body Exp_Disp is
          --  to the object, because generic dispatching constructors are not
          --  supported.
 
-         if Opnd = Iface_Typ and then not RTE_Available (RE_Displace) then
+         elsif Is_Interface (Iface_Typ)
+           and then Is_Ancestor (Iface_Typ, Opnd, Use_Full_View => True)
+           and then not RTE_Available (RE_Displace)
+         then
             return;
          end if;
       end;
diff --git a/gcc/ada/sem_disp.adb b/gcc/ada/sem_disp.adb
index ee1d96ec389..af260136bc0 100644
--- a/gcc/ada/sem_disp.adb
+++ b/gcc/ada/sem_disp.adb
@@ -3072,18 +3072,27 @@ package body Sem_Disp is
 
       if Tagged_Type_Expansion then
          declare
-            Call_Typ : constant Entity_Id := Etype (Call_Node);
+            Call_Typ : Entity_Id := Etype (Call_Node);
+            Ctrl_Typ : Entity_Id := Etype (Control);
 
          begin
             Expand_Dispatching_Call (Call_Node);
 
+            if Is_Class_Wide_Type (Call_Typ) then
+               Call_Typ := Root_Type (Call_Typ);
+            end if;
+
+            if Is_Class_Wide_Type (Ctrl_Typ) then
+               Ctrl_Typ := Root_Type (Ctrl_Typ);
+            end if;
+
             --  If the controlling argument is an interface type and the type
             --  of Call_Node differs then we must add an implicit conversion to
             --  force displacement of the pointer to the object to reference
             --  the secondary dispatch table of the interface.
 
-            if Is_Interface (Etype (Control))
-              and then Etype (Control) /= Call_Typ
+            if Is_Interface (Ctrl_Typ)
+              and then Ctrl_Typ /= Call_Typ
             then
                --  Cannot use Convert_To because the previous call to
                --  Expand_Dispatching_Call leaves decorated the Call_Node