[clang] Implement __is_pointer_interconvertible_base_of()

[Endilll]

This patch implements intrinsic that supports std::is_pointer_interconvertible_base_of type trait from P0466R5 "Layout-compatibility and Pointer-interconvertibility Traits".

Normative wording:

Comment: If Base and Derived are non-union class types and are not (possibly cv-qualified) versions of the same type, Derived is a complete type.
Condition: Derived is unambiguously derived from Base without regard to cv-qualifiers, and each object of type Derived is pointer-interconvertible (6.7.2 [basic.compound]) with its Base subobject, or Base and Derived are not unions and name the same class type without regard to cv-qualifiers.

The paper also express the following intent:

Note that is_pointer_interconvertible_base_of_v<T,T> is always true under this wording, even though T is not derived from itself.

I find the treatment of unions in the wording contradictory to this intent, and I'm not able to find anything relevant in minutes or on the reflector. That said, this patch implements what the wording says, since it's very explicit about unions.

[llvmbot]

@llvm/pr-subscribers-clang

Author: Vlad Serebrennikov (Endilll)

Changes

This patch implements intrinsic that supports std::is_pointer_interconvertible_base_of type trait from P0466R5 "Layout-compatibility and Pointer-interconvertibility Traits".

Normative wording:
> Comment: If Base and Derived are non-union class types and are not (possibly cv-qualified) versions of the same type, Derived is a complete type.
> Condition: Derived is unambiguously derived from Base without regard to cv-qualifiers, and each object of type Derived is pointer-interconvertible (6.7.2 [basic.compound]) with its Base subobject, or Base and Derived are not unions and name the same class type without regard to cv-qualifiers.

The paper also express the following intent:
> Note that is pointer interconvertible base of v<T,T> is always true under this wording, even though T is not derived from itself.

I find the treatment of unions in the wording contradictory to this intent, and I'm not able to find anything relevant in minutes or on the reflector. That said, this patch implements what the wording says, since it's very explicit about unions.

---

Full diff: https://github.com/llvm/llvm-project/pull/88473.diff

5 Files Affected:

• (modified) clang/include/clang/Basic/TokenKinds.def (+1)
• (modified) clang/include/clang/Sema/Sema.h (+2)
• (modified) clang/lib/Sema/SemaChecking.cpp (+21)
• (modified) clang/lib/Sema/SemaExprCXX.cpp (+16)
• (modified) clang/test/SemaCXX/type-traits.cpp (+85-1)

diff --git a/clang/include/clang/Basic/TokenKinds.def b/clang/include/clang/Basic/TokenKinds.def
index 800af0e6d04480..a27fbed358a60c 100644
--- a/clang/include/clang/Basic/TokenKinds.def
+++ b/clang/include/clang/Basic/TokenKinds.def
@@ -521,6 +521,7 @@ TYPE_TRAIT_1(__is_union, IsUnion, KEYCXX)
 TYPE_TRAIT_1(__has_unique_object_representations,
              HasUniqueObjectRepresentations, KEYCXX)
 TYPE_TRAIT_2(__is_layout_compatible, IsLayoutCompatible, KEYCXX)
+TYPE_TRAIT_2(__is_pointer_interconvertible_base_of, IsPointerInterconvertibleBaseOf, KEYCXX)
 
 #define TRANSFORM_TYPE_TRAIT_DEF(_, Trait) KEYWORD(__##Trait, KEYCXX)
 #include "clang/Basic/TransformTypeTraits.def"
diff --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
index 0ee4f3c8e127f6..397c5ae8eee777 100644
--- a/clang/include/clang/Sema/Sema.h
+++ b/clang/include/clang/Sema/Sema.h
@@ -1975,6 +1975,8 @@ class Sema final : public SemaBase {
   };
 
   bool IsLayoutCompatible(QualType T1, QualType T2) const;
+  bool IsPointerInterconvertibleBaseOf(const TypeSourceInfo *Base,
+                                       const TypeSourceInfo *Derived);
 
   bool CheckFunctionCall(FunctionDecl *FDecl, CallExpr *TheCall,
                          const FunctionProtoType *Proto);
diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index abfd9a3031577b..bbe82672183508 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -19710,6 +19710,27 @@ bool Sema::IsLayoutCompatible(QualType T1, QualType T2) const {
   return isLayoutCompatible(getASTContext(), T1, T2);
 }
 
+//===-------------- Pointer interconvertibility ----------------------------//
+
+bool Sema::IsPointerInterconvertibleBaseOf(const TypeSourceInfo *Base,
+                                           const TypeSourceInfo *Derived) {
+  QualType BaseT = Base->getType().getCanonicalType().getUnqualifiedType();
+  QualType DerivedT =
+      Derived->getType().getCanonicalType().getUnqualifiedType();
+
+  if (!BaseT->isUnionType() && !DerivedT->isUnionType() &&
+      getASTContext().hasSameType(BaseT, DerivedT))
+    return true;
+
+  if (!IsDerivedFrom(Derived->getTypeLoc().getBeginLoc(), DerivedT, BaseT))
+    return false;
+
+  if (DerivedT->getAsCXXRecordDecl()->isStandardLayout())
+    return true;
+
+  return false;
+}
+
 //===--- CHECK: pointer_with_type_tag attribute: datatypes should match ----//
 
 /// Given a type tag expression find the type tag itself.
diff --git a/clang/lib/Sema/SemaExprCXX.cpp b/clang/lib/Sema/SemaExprCXX.cpp
index 12f42f66e5e21b..1416dab9eb3a0e 100644
--- a/clang/lib/Sema/SemaExprCXX.cpp
+++ b/clang/lib/Sema/SemaExprCXX.cpp
@@ -6082,6 +6082,22 @@ static bool EvaluateBinaryTypeTrait(Sema &Self, TypeTrait BTT, const TypeSourceI
       Self.Diag(Rhs->getTypeLoc().getBeginLoc(), diag::err_vla_unsupported)
           << 1 << tok::kw___is_layout_compatible;
     return Self.IsLayoutCompatible(LhsT, RhsT);
+  }
+  case BTT_IsPointerInterconvertibleBaseOf: {
+    if (!LhsT->isUnionType() && !RhsT->isUnionType() &&
+        !Self.getASTContext().hasSameUnqualifiedType(LhsT, RhsT)) {
+      Self.RequireCompleteType(Rhs->getTypeLoc().getBeginLoc(), RhsT,
+                               diag::err_incomplete_type);
+    }
+
+    if (LhsT->isVariableArrayType())
+      Self.Diag(Lhs->getTypeLoc().getBeginLoc(), diag::err_vla_unsupported)
+          << 1 << tok::kw___is_pointer_interconvertible_base_of;
+    if (RhsT->isVariableArrayType())
+      Self.Diag(Rhs->getTypeLoc().getBeginLoc(), diag::err_vla_unsupported)
+          << 1 << tok::kw___is_pointer_interconvertible_base_of;
+
+    return Self.IsPointerInterconvertibleBaseOf(Lhs, Rhs);
   }
     default: llvm_unreachable("not a BTT");
   }
diff --git a/clang/test/SemaCXX/type-traits.cpp b/clang/test/SemaCXX/type-traits.cpp
index 421d3007d27ffe..7c22a7659de9e8 100644
--- a/clang/test/SemaCXX/type-traits.cpp
+++ b/clang/test/SemaCXX/type-traits.cpp
@@ -1740,7 +1740,7 @@ void is_layout_compatible(int n)
   static_assert(!__is_layout_compatible(void, int));
   static_assert(__is_layout_compatible(void, const void));
   static_assert(__is_layout_compatible(void, volatile void));
-  static_assert(__is_layout_compatible(const int, volatile int));
+  static_assert(__is_layout_compatible(const void, volatile void));
   static_assert(__is_layout_compatible(int, int));
   static_assert(__is_layout_compatible(int, const int));
   static_assert(__is_layout_compatible(int, volatile int));
@@ -1839,6 +1839,90 @@ void is_layout_compatible(int n)
   static_assert(!__is_layout_compatible(EnumClassForward, int));
 }
 
+namespace IPIBO {
+struct Base {};
+struct Base2 {};
+struct Base3 : Base {};
+struct Base3Virtual : virtual Base {};
+struct Derived : Base {};
+struct DerivedIndirect : Base3 {};
+struct DerivedMultiple : Base, Base2 {};
+struct DerivedAmbiguous : Base, Base3 {};
+/* expected-warning@-1 {{direct base 'Base' is inaccessible due to ambiguity:
+    struct IPIBO::DerivedAmbiguous -> Base
+    struct IPIBO::DerivedAmbiguous -> Base3 -> Base}} */
+struct DerivedPrivate : private Base {};
+struct DerivedVirtual : virtual Base {};
+
+union Union {};
+union UnionIncomplete;
+struct StructIncomplete;
+
+void is_pointer_interconvertible_base_of(int n)
+{
+  static_assert(__is_pointer_interconvertible_base_of(Base, Derived));
+  static_assert(!__is_pointer_interconvertible_base_of(Base2, Derived));
+  static_assert(__is_pointer_interconvertible_base_of(Base, DerivedIndirect));
+  static_assert(__is_pointer_interconvertible_base_of(Base, DerivedMultiple));
+  static_assert(!__is_pointer_interconvertible_base_of(Base3, DerivedMultiple));
+  static_assert(!__is_pointer_interconvertible_base_of(Base, DerivedAmbiguous));
+  static_assert(__is_pointer_interconvertible_base_of(Base, DerivedPrivate));
+  static_assert(!__is_pointer_interconvertible_base_of(Base, DerivedVirtual));
+  static_assert(!__is_pointer_interconvertible_base_of(Union, Union));
+  static_assert(!__is_pointer_interconvertible_base_of(UnionIncomplete, UnionIncomplete));
+  static_assert(__is_pointer_interconvertible_base_of(StructIncomplete, StructIncomplete));
+  static_assert(__is_pointer_interconvertible_base_of(StructIncomplete, const StructIncomplete));
+  static_assert(__is_pointer_interconvertible_base_of(StructIncomplete, volatile StructIncomplete));
+  static_assert(__is_pointer_interconvertible_base_of(const StructIncomplete, volatile StructIncomplete));
+  static_assert(!__is_pointer_interconvertible_base_of(CStruct2, CppStructNonStandardByBase2));
+  static_assert(__is_pointer_interconvertible_base_of(void, void));
+  static_assert(!__is_pointer_interconvertible_base_of(void, int));
+  static_assert(__is_pointer_interconvertible_base_of(void, const void));
+  static_assert(__is_pointer_interconvertible_base_of(void, volatile void));
+  static_assert(__is_pointer_interconvertible_base_of(const void, volatile void));
+  static_assert(__is_pointer_interconvertible_base_of(int, int));
+  static_assert(__is_pointer_interconvertible_base_of(int, const int));
+  static_assert(__is_pointer_interconvertible_base_of(int, volatile int));
+  static_assert(__is_pointer_interconvertible_base_of(const int, volatile int));
+  static_assert(__is_pointer_interconvertible_base_of(int *, int * __restrict));
+  static_assert(!__is_pointer_interconvertible_base_of(int, _Atomic int));
+  static_assert(__is_pointer_interconvertible_base_of(_Atomic(int), _Atomic int));
+  static_assert(!__is_pointer_interconvertible_base_of(int, unsigned int));
+  static_assert(!__is_pointer_interconvertible_base_of(char, unsigned char));
+  static_assert(!__is_pointer_interconvertible_base_of(char, signed char));
+  static_assert(!__is_pointer_interconvertible_base_of(unsigned char, signed char));
+  using function_type = void();
+  using function_type2 = void(char);
+  static_assert(__is_pointer_interconvertible_base_of(const function_type, const function_type));
+  // expected-warning@-1 {{'const' qualifier on function type 'function_type' (aka 'void ()') has no effect}}
+  // expected-warning@-2 {{'const' qualifier on function type 'function_type' (aka 'void ()') has no effect}}
+  static_assert(__is_pointer_interconvertible_base_of(function_type, const function_type));
+  // expected-warning@-1 {{'const' qualifier on function type 'function_type' (aka 'void ()') has no effect}}
+  static_assert(!__is_pointer_interconvertible_base_of(const function_type, const function_type2));
+  // expected-warning@-1 {{'const' qualifier on function type 'function_type' (aka 'void ()') has no effect}}
+  // expected-warning@-2 {{'const' qualifier on function type 'function_type2' (aka 'void (char)') has no effect}}
+  static_assert(__is_pointer_interconvertible_base_of(int CStruct2::*, int CStruct2::*));
+  static_assert(!__is_pointer_interconvertible_base_of(int CStruct2::*, char CStruct2::*));
+  static_assert(__is_pointer_interconvertible_base_of(void(CStruct2::*)(int), void(CStruct2::*)(int)));
+  static_assert(!__is_pointer_interconvertible_base_of(void(CStruct2::*)(int), void(CStruct2::*)(char)));
+  static_assert(__is_pointer_interconvertible_base_of(int[], int[]));
+  static_assert(__is_pointer_interconvertible_base_of(int[2], int[2]));
+  static_assert(!__is_pointer_interconvertible_base_of(int[n], int[2]));
+  // expected-error@-1 {{variable length arrays are not supported in '__is_pointer_interconvertible_base_of'}}
+  static_assert(!__is_pointer_interconvertible_base_of(int[n], int[n]));
+  // expected-error@-1 {{variable length arrays are not supported in '__is_pointer_interconvertible_base_of'}}
+  // expected-error@-2 {{variable length arrays are not supported in '__is_pointer_interconvertible_base_of'}}
+  static_assert(__is_pointer_interconvertible_base_of(int&, int&));
+  static_assert(!__is_pointer_interconvertible_base_of(int&, char&));
+  static_assert(__is_pointer_interconvertible_base_of(void(int), void(int)));
+  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)));
+  static_assert(__is_pointer_interconvertible_base_of(void(*)(int), void(*)(int)));
+  static_assert(!__is_pointer_interconvertible_base_of(void(*)(int), void(*)(char)));
+}
+}
+
 void is_signed()
 {
   //static_assert(__is_signed(char));

[Endilll]

Relevant issue: #48204

[Sirraide]

Just pointed out some minor things I noticed, otherwise this looks right to me.

I at least can’t think of any more test cases that wouldn’t just end up being tests for IsDerivedFrom() or isStandardLayout(), so I think this is enough.

[cor3ntin]

Thanks for working on this!