[PATCH 2/2 v2] Ada: Finalization of constrained subtypes of unconstrained synchronized private extensions

[Richard Wai <richard@annexi-strayline.com>]

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Somehow an error worked its way into the original diff (the diff itself),
making the previous patch fail to apply.

 

Fixed version attached.

 

Richard Wai

ANNEXI-STRAYLINE

 

From: Richard Wai <richard@annexi-strayline.com> 
Sent: Thursday, August 10, 2023 1:27 AM
To: 'gcc-patches@gcc.gnu.org' <gcc-patches@gcc.gnu.org>
Cc: 'Eric Botcazou' <ebotcazou@adacore.com>; 'Arnaud Charlet'
<charlet@adacore.com>; 'Stephen Baird' <baird@adacore.com>
Subject: [PATCH 2/2] Ada: Finalization of constrained subtypes of
unconstrained synchronized private extensions

 

When generating TSS address finalization bodies for a tagged class-wide
subtype, GNAT climbs the parent chain looking for the first
"non-constrained" type. That type's underlying type's class-wide type is
used as a "designated" type for a dispatching TSS deep finalize call to the
designated class-wide type. In the case of a constrained subtype of an
unconstrained synchronized private extension, this ends up designating the
underlying type of that private extension. This means it targets the
class-wide type of the actual underlying concurrent type rather than the
corresponding record. Ultimately it ends up generating a call to the
corresponding record's deep finalizer, but with incompatible types
(concurrent_type'Class -> concurrent_typeV'Class). This causes compilation
to fail.

 

This patch adds extra logic to exp_ch7(Make_Finalize_Address_Stmts) to
identify such cases and ensure that the designated type is the corresponding
record type's class-wide type in that situation.

 

Patch file is attached.

 

--  Begin change log entry -

 

ada: TSS finalize address subprogram generation for constrained subtypes of
unconstrained synchronized private extensions should take care to designate
the corresponding record of the underlying concurrent type.

 

When generating TSS finalize address subprograms for class-wide types of
constrained root types, it follows the parent chain looking for the first
"non-constrained" type. It is possible that such a type is a private
extension with the "synchronized" keyword, in which case the underlying type
is a concurrent type. When that happens, the designated type of the finalize
address subprogram should be the corresponding record's class-wide-type.

 

Gcc/ada/

                * exp_ch3(Expand_Freeze_Class_Wide_Type): Expanded comments
explaining why TSS Finalize_Address is not generated for concurrent
class-wide types.

                * exp_ch7(Make_Finalize_Address_Stmts): Handle cases where
the underlying non-constrained parent type is a concurrent type, and adjust
the designated type to be the corresponding record's class-wide type.

 

--  End change log entry -

 

This patch was bootstrapped on x86_64-*-freebsd13.2. One new test cases was
added. Note that 4 gnat test cases fail currently on master and are
unrelated to this patch.

 

Check-ada output of this patch:

 

                                === acats tests ===

Running chapter a ...

Running chapter c2 ...

Running chapter c3 ...

Running chapter c4 ...

Running chapter c5 ...

Running chapter c6 ...

Running chapter c7 ...

Running chapter c8 ...

Running chapter c9 ...

Running chapter ca ...

Running chapter cb ...

Running chapter cc ...

Running chapter cd ...

Running chapter ce ...

Running chapter cxa ...

Running chapter cxb ...

Running chapter cxf ...

Running chapter cxg ...

Running chapter cxh ...

Running chapter cz ...

Running chapter d ...

Running chapter e ...

Running chapter l ...

                                === acats Summary ===

# of expected passes                       2328

# of unexpected failures                 0

 

Native configuration is x86_64-unknown-freebsd13.2

 

                                === gnat tests ===

 

Schedule of variations:

    unix

 

Running target unix

FAIL: gnat.dg/specs/alignment2.ads  (test for warnings, line 14)

FAIL: gnat.dg/specs/alignment2.ads  (test for warnings, line 20)

FAIL: gnat.dg/specs/alignment2.ads  (test for warnings, line 38)

FAIL: gnat.dg/specs/alignment2.ads  (test for warnings, line 42)

 

                                === gnat Summary ===

 

# of expected passes                       3401

# of unexpected failures                 4

# of expected failures                      23

# of unsupported tests                   10

gnatmake version 14.0.0 20230809 (experimental)

 

 

Richard Wai

ANNEXI-STRAYLINE


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From 73582f931e77e506b64b311486b8804a03b8a87f Mon Sep 17 00:00:00 2001
From: Richard Wai <richard@annexi-strayline.com>
Date: Wed, 9 Aug 2023 01:45:54 -0400
Subject: [PATCH 2/2] ada: fix designated type selection for the creation of
 finalize address bodies in the case of a constrained subtype of a unconstrained synchronized private extension.

---
 gcc/ada/exp_ch3.adb                         |  4 ++
 gcc/ada/exp_ch7.adb                         | 26 ++++++++-
 gcc/testsuite/gnat.dg/sync_tag_finalize.adb | 60 +++++++++++++++++++++
 3 files changed, 88 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/gnat.dg/sync_tag_finalize.adb

diff --git a/gcc/ada/exp_ch3.adb b/gcc/ada/exp_ch3.adb
index 04c3ad8c631..bb015986200 100644
--- a/gcc/ada/exp_ch3.adb
+++ b/gcc/ada/exp_ch3.adb
@@ -5000,6 +5000,10 @@ package body Exp_Ch3 is
       --  Do not create TSS routine Finalize_Address for concurrent class-wide
       --  types. Ignore C, C++, CIL and Java types since it is assumed that the
       --  non-Ada side will handle their destruction.
+      --
+      --  Concurrent Ada types are functionally represented by an associated
+      --  "corresponding record type" (typenameV), which owns the actual TSS
+      --  finalize bodies for the type (and technically class-wide type).
 
       elsif Is_Concurrent_Type (Root)
         or else Is_C_Derivation (Root)
diff --git a/gcc/ada/exp_ch7.adb b/gcc/ada/exp_ch7.adb
index aa16c707887..5b4381697c5 100644
--- a/gcc/ada/exp_ch7.adb
+++ b/gcc/ada/exp_ch7.adb
@@ -8512,7 +8512,8 @@ package body Exp_Ch7 is
           Is_Empty_Elmt_List (Discriminant_Constraint (Root_Type (Typ)))
       then
          declare
-            Parent_Typ : Entity_Id;
+            Parent_Typ  : Entity_Id;
+            Parent_Utyp : Entity_Id;
 
          begin
             --  Climb the parent type chain looking for a non-constrained type
@@ -8533,7 +8534,28 @@ package body Exp_Ch7 is
                Parent_Typ := Underlying_Record_View (Parent_Typ);
             end if;
 
-            Desig_Typ := Class_Wide_Type (Underlying_Type (Parent_Typ));
+            Parent_Utyp := Underlying_Type (Parent_Typ);
+
+            --  Handle views created for a synchronized private extension with
+            --  known, non-defaulted discriminants. In that case, parent_typ
+            --  will be the private extension, as it is the first "non
+            --  -constrained" type in the parent chain. Unfortunately, the
+            --  underlying type, being a protected or task type, is not the
+            --  "real" type needing finalization. Rather, the "corresponding
+            --  record type" should be the designated type here. In fact, TSS
+            --  finalizer generation is specifically skipped for the nominal
+            --  class-wide type of (the full view of) a concurrent type (see
+            --  exp_ch7.Expand_Freeze_Class_Wide_Type). If we don't designate
+            --  the underlying record (Tprot_typeVC), we will end up trying to
+            --  dispatch to prot_typeVDF from an incorrectly designated
+            --  Tprot_typeC, which is, of course, not actually a member of
+            --  prot_typeV'Class, and thus incompatible.
+
+            if Present (Corresponding_Record_Type (Parent_Utyp)) then
+               Parent_Utyp := Corresponding_Record_Type (Parent_Utyp);
+            end if;
+
+            Desig_Typ := Class_Wide_Type (Parent_Utyp);
          end;
 
       --  General case
diff --git a/gcc/testsuite/gnat.dg/sync_tag_finalize.adb b/gcc/testsuite/gnat.dg/sync_tag_finalize.adb
new file mode 100644
index 00000000000..1e9df0edbaa
--- /dev/null
+++ b/gcc/testsuite/gnat.dg/sync_tag_finalize.adb
@@ -0,0 +1,60 @@
+--  In previous versions of GNAT there was a curious bug that caused
+--  compilation to fail in the case of a synchronized private extension
+--  with non-default discriminants, where the creation of a constrained object
+--  (and thus subtype) caused the TSS deep finalize machinery of the internal
+--  class-wide constratined subtype (TConstrainedC) to construct a malformed
+--  TSS finalize address body. The issue was that the machinery climbs
+--  the type parent chain looking for a "non-constrained" type to use as a
+--  designated (class-wide) type for a dispatching call to a higher TSS DF
+--  subprogram. When there is a discriminated synchronized private extension
+--  with known, non-default discriminants (thus unconstrained/indefinite), 
+--  that search ends up at that private extension declaration. Since the
+--  underlying type is actually a concurrent type, class-wide TSS finalizers
+--  are not built for the type, but rather the corresponding record type. The
+--  TSS machinery that selects the designated type was prevsiously unaware of
+--  this caveat, and thus selected an incompatible designated type, leading to
+--  failed compilation.
+--
+--  TL;DR: When creating a constrained subtype of a synchronized private
+--  extension with known non-defaulted disciminants, the class-wide TSS
+--  address finalization body for the constrained subtype should dispatch to
+--  the corresponding record (class-wide) type deep finalize subprogram.
+
+--  { dg-do compile }
+
+procedure Sync_Tag_Finalize is
+   
+   package Ifaces is
+      
+      type Test_Interface is synchronized interface;
+      
+      procedure Interface_Action (Test: in out Test_Interface) is abstract;
+      
+   end Ifaces;
+   
+   
+   package Implementation is
+      type Test_Implementation
+        (Constraint: Positive) is
+        synchronized new Ifaces.Test_Interface with private;
+      
+   private
+      protected type Test_Implementation
+        (Constraint: Positive)
+      is new Ifaces.Test_Interface with
+      
+         overriding procedure Interface_Action;
+         
+      end Test_Implementation;
+   end Implementation;
+   
+   package body Implementation is
+      protected body Test_Implementation is
+         procedure Interface_Action is null;
+      end;
+   end Implementation;
+   
+   Constrained: Implementation.Test_Implementation(2);
+begin
+   null;
+end;
-- 
2.40.1