[clang] [clang] Add another test case for CWG78 (PR #93708)

Wed May 29 10:37:28 PDT 2024

https://github.com/Endilll created https://github.com/llvm/llvm-project/pull/93708

This issue is concerned with initialization of static objects that are not of non-POD class types. It affirms that default initialization of such objects that typically leaves them with an indeterminate value does not apply to static objects. Instead, such objects undergo zero initialization.

Quoting the period correct wording from N1316 (8.5 Initializers):
> §6
> [core 178: The memory occupied by any → Every ] object of static storage duration shall be zero-initialized at program startup before any other initialization takes place. [_Note:_ in some cases, additional initialization is done later. ]

> §9
> If no initializer is specified for an object, and the object is of (possibly cv-qualified) non-POD class type (or array thereof), the object shall be default-initialized; if the object is of const-qualified type, the underlying class type shall have a user-declared default constructor. Otherwise, if no initializer is specified for [core 78: an object, → a non-static object, ] the object and its subobjects, if any, have an indeterminate initial value (90); if the object or any of its subobjects are of const-qualified type, the program is ill-formed.
> (90) This does not apply to aggregate objects with automatic storage duration initialized with an incomplete brace-enclosed _initializer-list_; see 8.5.1.

The current wording still supports this Core issue (http://eel.is/c++draft/basic.start#static-2.sentence-2):
> If constant initialization is not performed, a variable with static storage duration ([[basic.stc.static]](http://eel.is/c++draft/basic.stc.static)) or thread storage duration ([[basic.stc.thread]](http://eel.is/c++draft/basic.stc.thread)) is zero-initialized ([[dcl.init]](http://eel.is/c++draft/dcl.init))[.](http://eel.is/c++draft/basic.start#static-2.sentence-2)

It's unfortunate that we have to test this twice: once in `-verify` mode, once using `FileCheck`, but they are not compatible. This will be rectified once we implement CWG78.

>From 210d58b7133aeb007d423464bcd40d016fc25863 Mon Sep 17 00:00:00 2001
From: Vlad Serebrennikov <serebrennikov.vladislav at gmail.com>
Date: Wed, 29 May 2024 15:57:30 +0300
Subject: [PATCH] [clang] Add another test case for CWG78

---
 clang/test/CXX/drs/cwg0xx.cpp |  8 +-------
 clang/test/CXX/drs/cwg78.cpp  | 34 ++++++++++++++++++++++++++++++++++
 clang/www/cxx_dr_status.html  |  2 +-
 3 files changed, 36 insertions(+), 8 deletions(-)
 create mode 100644 clang/test/CXX/drs/cwg78.cpp

diff --git a/clang/test/CXX/drs/cwg0xx.cpp b/clang/test/CXX/drs/cwg0xx.cpp
index 6c600bbc7c3f6..abfaca7fe06e7 100644
--- a/clang/test/CXX/drs/cwg0xx.cpp
+++ b/clang/test/CXX/drs/cwg0xx.cpp
@@ -1180,13 +1180,7 @@ namespace cwg77 { // cwg77: yes
   };
 }
 
-namespace cwg78 { // cwg78: sup ????
-  // Under CWG78, this is valid, because 'k' has static storage duration, so is
-  // zero-initialized.
-  const int k;
-  // expected-error at -1 {{default initialization of an object of const type 'const int'}}
-}
-
+// cwg78 is in cwg78.cpp
 // cwg79: na
 
 namespace cwg80 { // cwg80: 2.9
diff --git a/clang/test/CXX/drs/cwg78.cpp b/clang/test/CXX/drs/cwg78.cpp
new file mode 100644
index 0000000000000..e0c3b72c537cf
--- /dev/null
+++ b/clang/test/CXX/drs/cwg78.cpp
@@ -0,0 +1,34 @@
+// RUN: %clang_cc1 -std=c++98 %s -verify -DVERIFY -fexceptions -fcxx-exceptions -pedantic-errors -triple %itanium_abi_triple
+// RUN: %clang_cc1 -std=c++11 %s -verify -DVERIFY -fexceptions -fcxx-exceptions -pedantic-errors -triple %itanium_abi_triple
+// RUN: %clang_cc1 -std=c++14 %s -verify -DVERIFY -fexceptions -fcxx-exceptions -pedantic-errors -triple %itanium_abi_triple
+// RUN: %clang_cc1 -std=c++17 %s -verify -DVERIFY -fexceptions -fcxx-exceptions -pedantic-errors -triple %itanium_abi_triple
+// RUN: %clang_cc1 -std=c++20 %s -verify -DVERIFY -fexceptions -fcxx-exceptions -pedantic-errors -triple %itanium_abi_triple
+// RUN: %clang_cc1 -std=c++23 %s -verify -DVERIFY -fexceptions -fcxx-exceptions -pedantic-errors -triple %itanium_abi_triple
+// RUN: %clang_cc1 -std=c++23 %s -verify -DVERIFY -fexceptions -fcxx-exceptions -pedantic-errors -triple %itanium_abi_triple
+
+// RUN: %clang_cc1 -std=c++98 %s -triple %itanium_abi_triple -emit-llvm -disable-llvm-passes -o - -fexceptions -fcxx-exceptions -pedantic-errors | llvm-cxxfilt -n | FileCheck %s --check-prefixes CHECK
+// RUN: %clang_cc1 -std=c++11 %s -triple %itanium_abi_triple -emit-llvm -disable-llvm-passes -o - -fexceptions -fcxx-exceptions -pedantic-errors | llvm-cxxfilt -n | FileCheck %s --check-prefixes CHECK
+// RUN: %clang_cc1 -std=c++14 %s -triple %itanium_abi_triple -emit-llvm -disable-llvm-passes -o - -fexceptions -fcxx-exceptions -pedantic-errors | llvm-cxxfilt -n | FileCheck %s --check-prefixes CHECK
+// RUN: %clang_cc1 -std=c++17 %s -triple %itanium_abi_triple -emit-llvm -disable-llvm-passes -o - -fexceptions -fcxx-exceptions -pedantic-errors | llvm-cxxfilt -n | FileCheck %s --check-prefixes CHECK
+// RUN: %clang_cc1 -std=c++20 %s -triple %itanium_abi_triple -emit-llvm -disable-llvm-passes -o - -fexceptions -fcxx-exceptions -pedantic-errors | llvm-cxxfilt -n | FileCheck %s --check-prefixes CHECK
+// RUN: %clang_cc1 -std=c++23 %s -triple %itanium_abi_triple -emit-llvm -disable-llvm-passes -o - -fexceptions -fcxx-exceptions -pedantic-errors | llvm-cxxfilt -n | FileCheck %s --check-prefixes CHECK
+// RUN: %clang_cc1 -std=c++2c %s -triple %itanium_abi_triple -emit-llvm -disable-llvm-passes -o - -fexceptions -fcxx-exceptions -pedantic-errors | llvm-cxxfilt -n | FileCheck %s --check-prefixes CHECK
+
+namespace cwg78 { // cwg78: partial
+// Under CWG78, this is valid, because 'k' has static storage duration, so is
+// zero-initialized.
+#ifdef VERIFY
+const int k;
+// expected-error at -1 {{default initialization of an object of const type 'const int'}}
+#endif
+
+int f() {
+  static int i;
+  return i;
+}
+
+// Checking that static variable is zero-initialized,
+// and not default-initialized (which means no initialization in this case).
+
+// CHECK: @cwg78::f()::i = {{.*}} i32 0
+} // namespace cwg78
diff --git a/clang/www/cxx_dr_status.html b/clang/www/cxx_dr_status.html
index 4cce88fe0490f..ff50a11c3f525 100755
--- a/clang/www/cxx_dr_status.html
+++ b/clang/www/cxx_dr_status.html
@@ -506,7 +506,7 @@ <h2 id="cxxdr">C++ defect report implementation status</h2>
     <td><a href="https://cplusplus.github.io/CWG/issues/78.html">78</a></td>
     <td>CD1</td>
     <td>Section 8.5 paragraph 9 should state it only applies to non-static objects</td>
-    <td class="none" align="center">Superseded by <a href="#????">????</a></td>
+    <td class="partial" align="center">Partial</td>
   </tr>
   <tr id="79">
     <td><a href="https://cplusplus.github.io/CWG/issues/79.html">79</a></td>

