[gcc r13-523] [Ada] Implement calls to abstract subprograms in class-wide pre/post-conditions

[gcc r13-523] [Ada] Implement calls to abstract subprograms in class-wide pre/post-conditions

[Pierre-Marie de Rodat]

https://gcc.gnu.org/g:a08f366ae875ae70fba5014c94956cdbf7bf91db

commit r13-523-ga08f366ae875ae70fba5014c94956cdbf7bf91db
Author: Javier Miranda <miranda@adacore.com>
Date:   Tue Mar 15 13:20:24 2022 -0700

    [Ada] Implement calls to abstract subprograms in class-wide pre/post-conditions
    
    In some special cases involving class-wide pre/post conditions, Ada
    allows a non-dispatching call to an abstract function (which is usually
    illegal).  Fix a bug in the implementation of Ada's rules about the
    run-time behavior of such a call. Thanks to Javier Miranda for producing
    this patch.
    
    gcc/ada/
    
            * contracts.adb (Build_Call_Helper_Body): Improve handling of
            the case of a (legal) non-dispatching call to an abstract
            subprogram.

Diff:
---
 gcc/ada/contracts.adb | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/gcc/ada/contracts.adb b/gcc/ada/contracts.adb
index 7ce3cfac91d..9463642556f 100644
--- a/gcc/ada/contracts.adb
+++ b/gcc/ada/contracts.adb
@@ -3899,7 +3899,16 @@ package body Contracts is
             Set_Corresponding_Body (Helper_Decl, Body_Id);
             Set_Must_Override (Body_Spec, False);
 
-            if Present (Class_Preconditions (Subp_Id)) then
+            if Present (Class_Preconditions (Subp_Id))
+            --  Evaluate the expression if we are building a dynamic helper
+            --  or we are building a static helper for a non-abstract tagged
+            --  type; for abstract tagged types the helper just returns True
+            --  since it is called by the indirect call wrapper (ICW).
+              and then
+                (Is_Dynamic
+                   or else
+                      not Is_Abstract_Type (Find_Dispatching_Type (Subp_Id)))
+            then
                Return_Expr :=
                  Copy_And_Update_References (Class_Preconditions (Subp_Id));
 
@@ -3910,7 +3919,8 @@ package body Contracts is
             --  enabled.
 
             else
-               pragma Assert (Present (Ignored_Class_Preconditions (Subp_Id)));
+               pragma Assert (Present (Ignored_Class_Preconditions (Subp_Id))
+                 or else Is_Abstract_Type (Find_Dispatching_Type (Subp_Id)));
                Return_Expr := New_Occurrence_Of (Standard_True, Loc);
             end if;