[clang] [C++20] Deleting destructors can be noexcept (PR #118687)

Aaron Ballman via cfe-commits cfe-commits at lists.llvm.org
Wed Dec 4 12:08:27 PST 2024


https://github.com/AaronBallman updated https://github.com/llvm/llvm-project/pull/118687

>From 10985bcd5ae13f4533a9df4fa3035bd49e49af15 Mon Sep 17 00:00:00 2001
From: Aaron Ballman <aaron at aaronballman.com>
Date: Wed, 4 Dec 2024 14:31:48 -0500
Subject: [PATCH 1/3] [C++20] Deleting destructors can be noexcept

Given a `noexcept` operator with an operand that calls `delete`, Clang
was not considering whether the selected `operator delete` function was
a destroying delete or not when inspecting whether the deleted object
type has a throwing destructor. Thus, the operator would return `false`
for a type with a potentially throwing destructor even though that
destructor would not be called due to the destroying delete. Clang now
takes the kind of delete operator into consideration.

Fixes #118660
---
 clang/docs/ReleaseNotes.rst                   |  3 +++
 clang/lib/Sema/SemaExceptionSpec.cpp          |  5 +++--
 .../SemaCXX/noexcept-destroying-delete.cpp    | 21 +++++++++++++++++++
 3 files changed, 27 insertions(+), 2 deletions(-)
 create mode 100644 clang/test/SemaCXX/noexcept-destroying-delete.cpp

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 755418e9550cf4..ea5f8f921c4d31 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -654,6 +654,9 @@ Bug Fixes in This Version
 - Fixed a crash when GNU statement expression contains invalid statement (#GH113468).
 - Fixed a failed assertion when using ``__attribute__((noderef))`` on an
   ``_Atomic``-qualified type (#GH116124).
+- No longer return ``false`` for ``noexcept`` expressions involving a
+  ``delete`` which resolves to a destroying delete but the type of the object
+  being deleted as a potentially throwing destructor (#GH118660).
 
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Sema/SemaExceptionSpec.cpp b/clang/lib/Sema/SemaExceptionSpec.cpp
index ecfd79a50542c4..3e55e8b3d4d2ee 100644
--- a/clang/lib/Sema/SemaExceptionSpec.cpp
+++ b/clang/lib/Sema/SemaExceptionSpec.cpp
@@ -1205,11 +1205,12 @@ CanThrowResult Sema::canThrow(const Stmt *S) {
     if (DTy.isNull() || DTy->isDependentType()) {
       CT = CT_Dependent;
     } else {
-      CT = canCalleeThrow(*this, DE, DE->getOperatorDelete());
+      const FunctionDecl *OperatorDelete = DE->getOperatorDelete();
+      CT = canCalleeThrow(*this, DE, OperatorDelete);
       if (const RecordType *RT = DTy->getAs<RecordType>()) {
         const CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
         const CXXDestructorDecl *DD = RD->getDestructor();
-        if (DD)
+        if (DD && !OperatorDelete->isDestroyingOperatorDelete())
           CT = mergeCanThrow(CT, canCalleeThrow(*this, DE, DD));
       }
       if (CT == CT_Can)
diff --git a/clang/test/SemaCXX/noexcept-destroying-delete.cpp b/clang/test/SemaCXX/noexcept-destroying-delete.cpp
new file mode 100644
index 00000000000000..6a0902bfc01467
--- /dev/null
+++ b/clang/test/SemaCXX/noexcept-destroying-delete.cpp
@@ -0,0 +1,21 @@
+// RUN: %clang_cc1 -fsyntax-only -verify -fcxx-exceptions -Wno-unevaluated-expression -std=c++20 %s
+// expected-no-diagnostics
+
+namespace std {
+  struct destroying_delete_t {
+    explicit destroying_delete_t() = default;
+  };
+
+  inline constexpr destroying_delete_t destroying_delete{};
+}
+
+struct Explicit {
+    ~Explicit() noexcept(false) {}
+
+    void operator delete(Explicit*, std::destroying_delete_t) noexcept {
+    }
+};
+
+Explicit *qn = nullptr;
+// This assertion used to fail, see GH118660
+static_assert(noexcept(delete(qn)));

>From 1de3f1fa012bfeb6693d2bad7b762bee02e4e556 Mon Sep 17 00:00:00 2001
From: Aaron Ballman <aaron at aaronballman.com>
Date: Wed, 4 Dec 2024 14:56:21 -0500
Subject: [PATCH 2/3] Address review feedback

* Fixes a typo in the release notes
* Minor optimization
---
 clang/docs/ReleaseNotes.rst          |  2 +-
 clang/lib/Sema/SemaExceptionSpec.cpp | 15 ++++++++-------
 2 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index ea5f8f921c4d31..381f48e2cd206b 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -656,7 +656,7 @@ Bug Fixes in This Version
   ``_Atomic``-qualified type (#GH116124).
 - No longer return ``false`` for ``noexcept`` expressions involving a
   ``delete`` which resolves to a destroying delete but the type of the object
-  being deleted as a potentially throwing destructor (#GH118660).
+  being deleted has a potentially throwing destructor (#GH118660).
 
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Sema/SemaExceptionSpec.cpp b/clang/lib/Sema/SemaExceptionSpec.cpp
index 3e55e8b3d4d2ee..e0797209c2c9ee 100644
--- a/clang/lib/Sema/SemaExceptionSpec.cpp
+++ b/clang/lib/Sema/SemaExceptionSpec.cpp
@@ -1206,15 +1206,16 @@ CanThrowResult Sema::canThrow(const Stmt *S) {
       CT = CT_Dependent;
     } else {
       const FunctionDecl *OperatorDelete = DE->getOperatorDelete();
-      CT = canCalleeThrow(*this, DE, OperatorDelete);
-      if (const RecordType *RT = DTy->getAs<RecordType>()) {
-        const CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
-        const CXXDestructorDecl *DD = RD->getDestructor();
-        if (DD && !OperatorDelete->isDestroyingOperatorDelete())
+      if (!OperatorDelete->isDestroyingOperatorDelete()) {
+        CT = canCalleeThrow(*this, DE, OperatorDelete);
+        if (const RecordType *RT = DTy->getAs<RecordType>()) {
+          const CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
+          const CXXDestructorDecl *DD = RD->getDestructor();
           CT = mergeCanThrow(CT, canCalleeThrow(*this, DE, DD));
+        }
+        if (CT == CT_Can)
+          return CT;
       }
-      if (CT == CT_Can)
-        return CT;
     }
     return mergeCanThrow(CT, canSubStmtsThrow(*this, DE));
   }

>From f463154f228d1db4422c806213e5e94b46875113 Mon Sep 17 00:00:00 2001
From: Aaron Ballman <aaron at aaronballman.com>
Date: Wed, 4 Dec 2024 15:07:52 -0500
Subject: [PATCH 3/3] Fix think-o and add test coverage to ensure it doesn't
 happen again

---
 clang/lib/Sema/SemaExceptionSpec.cpp              |  2 +-
 clang/test/SemaCXX/noexcept-destroying-delete.cpp | 12 ++++++++++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/clang/lib/Sema/SemaExceptionSpec.cpp b/clang/lib/Sema/SemaExceptionSpec.cpp
index e0797209c2c9ee..5d658c0383bab8 100644
--- a/clang/lib/Sema/SemaExceptionSpec.cpp
+++ b/clang/lib/Sema/SemaExceptionSpec.cpp
@@ -1206,8 +1206,8 @@ CanThrowResult Sema::canThrow(const Stmt *S) {
       CT = CT_Dependent;
     } else {
       const FunctionDecl *OperatorDelete = DE->getOperatorDelete();
+      CT = canCalleeThrow(*this, DE, OperatorDelete);
       if (!OperatorDelete->isDestroyingOperatorDelete()) {
-        CT = canCalleeThrow(*this, DE, OperatorDelete);
         if (const RecordType *RT = DTy->getAs<RecordType>()) {
           const CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
           const CXXDestructorDecl *DD = RD->getDestructor();
diff --git a/clang/test/SemaCXX/noexcept-destroying-delete.cpp b/clang/test/SemaCXX/noexcept-destroying-delete.cpp
index 6a0902bfc01467..92ccbc1fb3f96b 100644
--- a/clang/test/SemaCXX/noexcept-destroying-delete.cpp
+++ b/clang/test/SemaCXX/noexcept-destroying-delete.cpp
@@ -19,3 +19,15 @@ struct Explicit {
 Explicit *qn = nullptr;
 // This assertion used to fail, see GH118660
 static_assert(noexcept(delete(qn)));
+
+struct ThrowingDestroyingDelete {
+    ~ThrowingDestroyingDelete() noexcept(false) {}
+
+    void operator delete(ThrowingDestroyingDelete*, std::destroying_delete_t) noexcept(false) {
+    }
+};
+
+ThrowingDestroyingDelete *pn = nullptr;
+// noexcept should return false here because the destroying delete itself is a
+// potentially throwing function.
+static_assert(!noexcept(delete(pn)));



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