[llvm-branch-commits] [clang] release/19.x: [clang] Avoid triggering vtable instantiation for C++23 constexpr dtor (#102605) (PR #102924)

[via llvm-branch-commits]

https://github.com/llvmbot created https://github.com/llvm/llvm-project/pull/102924

Backport d469794d0cdfd2fea50a6ce0c0e33abb242d744c

Requested by: @llvmbot

>From d6beb484536981c00754e94c99d666f895b56fcd Mon Sep 17 00:00:00 2001
From: Mariya Podchishchaeva <mariya.podchishchaeva at intel.com>
Date: Mon, 12 Aug 2024 09:08:46 +0200
Subject: [PATCH] [clang] Avoid triggering vtable instantiation for C++23
 constexpr dtor (#102605)

In C++23 anything can be constexpr, including a dtor of a class whose
members and bases don't have constexpr dtors. Avoid early triggering of
vtable instantiation int this case.

Fixes https://github.com/llvm/llvm-project/issues/102293

(cherry picked from commit d469794d0cdfd2fea50a6ce0c0e33abb242d744c)
---
 clang/lib/Sema/SemaDeclCXX.cpp  | 29 ++++++++++++++++++++++++++++-
 clang/test/SemaCXX/gh102293.cpp | 22 ++++++++++++++++++++++
 2 files changed, 50 insertions(+), 1 deletion(-)
 create mode 100644 clang/test/SemaCXX/gh102293.cpp

diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 04b8d88cae217b..38e1842040fb38 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -7042,11 +7042,38 @@ void Sema::CheckCompletedCXXClass(Scope *S, CXXRecordDecl *Record) {
       }
     }
 
+    bool EffectivelyConstexprDestructor = true;
+    // Avoid triggering vtable instantiation due to a dtor that is not
+    // "effectively constexpr" for better compatibility.
+    // See https://github.com/llvm/llvm-project/issues/102293 for more info.
+    if (isa<CXXDestructorDecl>(M)) {
+      auto Check = [](QualType T, auto &&Check) -> bool {
+        const CXXRecordDecl *RD =
+            T->getBaseElementTypeUnsafe()->getAsCXXRecordDecl();
+        if (!RD || !RD->isCompleteDefinition())
+          return true;
+
+        if (!RD->hasConstexprDestructor())
+          return false;
+
+        for (const CXXBaseSpecifier &B : RD->bases())
+          if (!Check(B.getType(), Check))
+            return false;
+        for (const FieldDecl *FD : RD->fields())
+          if (!Check(FD->getType(), Check))
+            return false;
+        return true;
+      };
+      EffectivelyConstexprDestructor =
+          Check(QualType(Record->getTypeForDecl(), 0), Check);
+    }
+
     // Define defaulted constexpr virtual functions that override a base class
     // function right away.
     // FIXME: We can defer doing this until the vtable is marked as used.
     if (CSM != CXXSpecialMemberKind::Invalid && !M->isDeleted() &&
-        M->isDefaulted() && M->isConstexpr() && M->size_overridden_methods())
+        M->isDefaulted() && M->isConstexpr() && M->size_overridden_methods() &&
+        EffectivelyConstexprDestructor)
       DefineDefaultedFunction(*this, M, M->getLocation());
 
     if (!Incomplete)
diff --git a/clang/test/SemaCXX/gh102293.cpp b/clang/test/SemaCXX/gh102293.cpp
new file mode 100644
index 00000000000000..30629fc03bf6a9
--- /dev/null
+++ b/clang/test/SemaCXX/gh102293.cpp
@@ -0,0 +1,22 @@
+// RUN: %clang_cc1 -std=c++23 -fsyntax-only -verify %s
+// expected-no-diagnostics
+
+template <typename T> static void destroy() {
+    T t;
+    ++t;
+}
+
+struct Incomplete;
+
+template <typename = int> struct HasD {
+  ~HasD() { destroy<Incomplete*>(); }
+};
+
+struct HasVT {
+  virtual ~HasVT();
+};
+
+struct S : HasVT {
+  HasD<> v;
+};
+