[clang] [clang] Disable type-aware allocator lookup for older C++ versions (PR #213430)

[via cfe-commits]

https://github.com/nots1dd created https://github.com/llvm/llvm-project/pull/213430

References to issue #212675

Type-aware delete should only be considered in cpp23 and later.

In older language modes (< cpp23), deleting an incomplete type is only a warning, so Clang can still reach CodeGen. If a type-aware operator delete is selected there, CodeGen may assert because the deleted type is incomplete.

So, this commit disables type-aware allocator selection before cpp23 and adds a cpp17 regression test for the crash.

I have run all the clang tests along with the newly added one and it seems to be passing them, can confirm with gh ci as well if there are any problems with this logic

>From aee1f87dd31f93d7ec5ef055e83ab7ec1982ba5c Mon Sep 17 00:00:00 2001
From: nots1dd <sid9.karanam at gmail.com>
Date: Sat, 1 Aug 2026 16:25:34 +0530
Subject: [PATCH] [clang] Disable type-aware allocator lookup for older C++
 versions

References to issue #212675

Type-aware delete should only be considered in C++23 and later.

In older language modes (< cpp23), deleting an incomplete type is only a
warning, so Clang can still reach CodeGen. If a type-aware operator
delete is selected there, CodeGen may assert because the deleted type is
incomplete.

So, this commit disables type-aware allocator selection before cpp23 and
adds a cpp17 regression test for the crash.
---
 clang/lib/Sema/SemaDeclCXX.cpp                |  3 +++
 .../type-aware-delete-pre-cxx23.cpp           | 21 +++++++++++++++++++
 2 files changed, 24 insertions(+)
 create mode 100644 clang/test/CodeGenCXX/type-aware-delete-pre-cxx23.cpp

diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 47b01b913b428..49704ba8c2e0f 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -16656,6 +16656,9 @@ bool Sema::CompleteConstructorCall(CXXConstructorDecl *Constructor,
 }
 
 TypeAwareAllocationMode Sema::ShouldUseTypeAwareOperatorNewOrDelete() const {
+  if (!LangOpts.CPlusPlus23)
+    return TypeAwareAllocationMode::No;
+
   bool SeenTypedOperators = Context.hasSeenTypeAwareOperatorNewOrDelete();
   return typeAwareAllocationModeFromBool(SeenTypedOperators);
 }
diff --git a/clang/test/CodeGenCXX/type-aware-delete-pre-cxx23.cpp b/clang/test/CodeGenCXX/type-aware-delete-pre-cxx23.cpp
new file mode 100644
index 0000000000000..d744a5fe0c5ea
--- /dev/null
+++ b/clang/test/CodeGenCXX/type-aware-delete-pre-cxx23.cpp
@@ -0,0 +1,21 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -std=c++17 -emit-llvm -o - %s | FileCheck %s
+
+class Foo;
+typedef __SIZE_TYPE__ size_t;
+
+namespace std {
+enum class align_val_t : size_t {};
+template <class T> struct type_identity {
+  typedef T type;
+};
+} // namespace std
+
+template <class T>
+void operator delete(std::type_identity<T>, void *, size_t, std::align_val_t);
+
+// CHECK-LABEL: define{{.*}} void @_Z1fP3Foo(
+// CHECK: call void @_ZdlPv(
+// CHECK-NOT: call void @_ZdlI3FooEvSt13type_identityIT_EPvmSt11align_val_t(
+void f(Foo *o) {
+  delete o;
+}