[clang] [Clang] remove qualifiers in getCanonicalTypeUnqualified (PR #170271)

[Rose Hudson via cfe-commits]

https://github.com/rosefromthedead updated https://github.com/llvm/llvm-project/pull/170271

>From 387cb54f97c889338bc3227303979a96d1878fdd Mon Sep 17 00:00:00 2001
From: Rose Hudson <rose.hudson at sony.com>
Date: Fri, 28 Nov 2025 09:38:26 +0000
Subject: [PATCH 1/2] [Clang] remove qualifiers in getCanonicalTypeUnqualified

It was assumed that since this is a method on Type, there are no quals
present because usually you get a Type by using operator-> on a QualType.
However, quals aren't always stored in the outermost QualType. For
example, if const A is used as a template parameter, the outer QualType
does not have the const flag set. The const actually lives in the
canonical type inside a SubstTemplateTypeParmType. We therefore need to
explicitly remove quals before returning.

Fixes #135273
---
 clang/include/clang/AST/CanonicalType.h |  3 ++-
 clang/test/SemaCXX/type-traits.cpp      | 10 ++++++++++
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/clang/include/clang/AST/CanonicalType.h b/clang/include/clang/AST/CanonicalType.h
index 87bbd7b5d885d..b46fc8f50fa23 100644
--- a/clang/include/clang/AST/CanonicalType.h
+++ b/clang/include/clang/AST/CanonicalType.h
@@ -213,7 +213,8 @@ inline bool operator!=(CanQual<T> x, CanQual<U> y) {
 using CanQualType = CanQual<Type>;
 
 inline CanQualType Type::getCanonicalTypeUnqualified() const {
-  return CanQualType::CreateUnsafe(getCanonicalTypeInternal());
+  return CanQualType::CreateUnsafe(
+      getCanonicalTypeInternal().getUnqualifiedType());
 }
 
 inline const StreamingDiagnostic &operator<<(const StreamingDiagnostic &DB,
diff --git a/clang/test/SemaCXX/type-traits.cpp b/clang/test/SemaCXX/type-traits.cpp
index 9ef44d0346b48..561c9ca8286b9 100644
--- a/clang/test/SemaCXX/type-traits.cpp
+++ b/clang/test/SemaCXX/type-traits.cpp
@@ -1812,6 +1812,11 @@ union Union {};
 union UnionIncomplete;
 struct StructIncomplete; // #StructIncomplete
 
+#if __cplusplus >= 201402L
+template<class _Base, class _Derived>
+inline constexpr bool IsPointerInterconvertibleBaseOfV = __is_pointer_interconvertible_base_of(_Base, _Derived);
+#endif
+
 void is_pointer_interconvertible_base_of(int n)
 {
   static_assert(__is_pointer_interconvertible_base_of(Base, Derived));
@@ -1880,6 +1885,11 @@ void is_pointer_interconvertible_base_of(int n)
   static_assert(!__is_pointer_interconvertible_base_of(void(&)(int), void(&)(char)));
   static_assert(!__is_pointer_interconvertible_base_of(void(*)(int), void(*)(int)));
   static_assert(!__is_pointer_interconvertible_base_of(void(*)(int), void(*)(char)));
+
+#if __cplusplus >= 201402L
+  static_assert(IsPointerInterconvertibleBaseOfV<const Base, Base>);
+  static_assert(IsPointerInterconvertibleBaseOfV<const Base, Derived>);
+#endif
 }
 }
 

>From 24b993c66b3d56c1b4a6f21378404ad097a3a5bc Mon Sep 17 00:00:00 2001
From: Rose Hudson <rose.hudson at sony.com>
Date: Tue, 2 Dec 2025 16:12:01 +0000
Subject: [PATCH 2/2] add release note

---
 clang/docs/ReleaseNotes.rst | 1 +
 1 file changed, 1 insertion(+)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index da064534c25d9..0aa899817f3ea 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -567,6 +567,7 @@ Bug Fixes to C++ Support
 - Fix a crash when extracting unavailable member type from alias in template deduction. (#GH165560)
 - Fix incorrect diagnostics for lambdas with init-captures inside braced initializers. (#GH163498)
 - Fixed spurious diagnoses of certain nested lambda expressions. (#GH149121) (#GH156579)
+- Fix the result of ``__is_pointer_interconvertible_base_of`` when arguments are qualified and passed via template parameters. (#GH135273)
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^