From 0627f978bc7792adb1152dce6df75386bb9e5ecc Mon Sep 17 00:00:00 2001
From: Rose Hudson <rose.hudson@sony.com>
Date: Thu, 13 Nov 2025 10:51:30 +0000
Subject: [PATCH] [Clang][Sema] properly remove qualifiers in
 __is_pointer_interconvertible_base_of

getCanonicalTypeUnqualified() doesn't actually remove cv qualifiers if
the type is a SubstTemplateTypeParmType. Use getUnqualifiedType()
instead, which does.

Fixes: #135273
---
 clang/lib/Sema/SemaChecking.cpp               |  4 ++--
 ...ointer-interconvertible-template-param.cpp | 22 +++++++++++++++++++
 2 files changed, 24 insertions(+), 2 deletions(-)
 create mode 100644 clang/test/Sema/pointer-interconvertible-template-param.cpp

diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index a8e3fe6c07b12..73473f1878ed1 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -15607,8 +15607,8 @@ bool Sema::IsLayoutCompatible(QualType T1, QualType T2) const {
 
 bool Sema::IsPointerInterconvertibleBaseOf(const TypeSourceInfo *Base,
                                            const TypeSourceInfo *Derived) {
-  QualType BaseT = Base->getType()->getCanonicalTypeUnqualified();
-  QualType DerivedT = Derived->getType()->getCanonicalTypeUnqualified();
+  QualType BaseT = Base->getType().getUnqualifiedType();
+  QualType DerivedT = Derived->getType().getUnqualifiedType();
 
   if (BaseT->isStructureOrClassType() && DerivedT->isStructureOrClassType() &&
       getASTContext().hasSameType(BaseT, DerivedT))
diff --git a/clang/test/Sema/pointer-interconvertible-template-param.cpp b/clang/test/Sema/pointer-interconvertible-template-param.cpp
new file mode 100644
index 0000000000000..174ac9a44a639
--- /dev/null
+++ b/clang/test/Sema/pointer-interconvertible-template-param.cpp
@@ -0,0 +1,22 @@
+// RUN: %clangxx %s -o %t
+// RUN: %t | FileCheck %s
+
+#include <iostream>
+
+class A {};
+class B : public A {};
+
+template <class _Base, class _Derived>
+inline constexpr bool is_pointer_interconvertible_base_of_v = __is_pointer_interconvertible_base_of(_Base, _Derived);
+
+int main() {
+    // CHECK: 1
+    std::cout << __is_pointer_interconvertible_base_of(const A, A) << std::endl;
+    // CHECK-NEXT: 1
+    std::cout << is_pointer_interconvertible_base_of_v<const A, A> << std::endl;
+
+    // CHECK-NEXT: 1
+    std::cout << __is_pointer_interconvertible_base_of(const A, B) << std::endl;
+    // CHECK-NEXT: 1
+    std::cout << is_pointer_interconvertible_base_of_v<const A, B> << std::endl;
+}