[probably not for upstream] CodeGen, libcxx: Introduce __has_non_relocatable_fields.

In order to properly benchmark PFP we need to be able to do an A/B
comparison and make A and B as equal as possible. This includes not
disabling libc++'s non-standard trivially relocatable optimizations
wherever possible. In the upstream code we just made trivially_relocatable
equivalent to trivially_copyable but in the benchmarking version of
the code (also more aligned to what will be possible in C++26) restore
trivially_relocatable logic but also check whether any of the fields
are non-relocatable using a temporarily introduced builtin.

Author: pcc

clang/include/clang/Basic/TokenKinds.def

@@ -544,6 +544,7 @@ TYPE_TRAIT_2(__is_pointer_interconvertible_base_of, IsPointerInterconvertibleBas
 #include "clang/Basic/TransformTypeTraits.def"
 
 // Clang-only C++ Type Traits
+TYPE_TRAIT_1(__has_non_relocatable_fields, HasNonRelocatableFields, KEYCXX)
 TYPE_TRAIT_1(__is_trivially_equality_comparable, IsTriviallyEqualityComparable, KEYCXX)
 TYPE_TRAIT_1(__is_bounded_array, IsBoundedArray, KEYCXX)
 TYPE_TRAIT_1(__is_unbounded_array, IsUnboundedArray, KEYCXX)

clang/lib/Sema/SemaTypeTraits.cpp

@@ -547,6 +547,7 @@ static bool CheckUnaryTypeTraitTypeCompleteness(Sema &S, TypeTrait UTT,
   case UTT_IsTriviallyEqualityComparable:
   case UTT_IsCppTriviallyRelocatable:
   case UTT_IsReplaceable:
+  case UTT_HasNonRelocatableFields:
   case UTT_CanPassInRegs:
   // Per the GCC type traits documentation, T shall be a complete type, cv void,
   // or an array of unknown bound. But GCC actually imposes the same constraints
@@ -1149,6 +1150,10 @@ static bool EvaluateUnaryTypeTrait(Sema &Self, TypeTrait UTT,
     return C.hasUniqueObjectRepresentations(T);
   case UTT_IsTriviallyRelocatable:
     return IsTriviallyRelocatableType(Self, T);
+  case UTT_HasNonRelocatableFields:
+    return T->getAsCXXRecordDecl() &&
+           !C.arePFPFieldsTriviallyRelocatable(T->getAsCXXRecordDecl()) &&
+           C.hasPFPFields(T);
   case UTT_IsBitwiseCloneable:
     return T.isBitwiseCloneableType(C);
   case UTT_IsCppTriviallyRelocatable:

libcxx/include/__type_traits/is_trivially_relocatable.h

@@ -34,13 +34,14 @@ template <class _Tp, class = void>
 struct __libcpp_is_trivially_relocatable : is_trivially_copyable<_Tp> {};
 #endif
 
-// __trivially_relocatable on libc++'s builtin types does not currently return the right answer with PFP.
-#if !__has_feature(pointer_field_protection)
 template <class _Tp>
 struct __libcpp_is_trivially_relocatable<_Tp,
-                                         __enable_if_t<is_same<_Tp, typename _Tp::__trivially_relocatable>::value> >
-    : true_type {};
+                                         __enable_if_t<is_same<_Tp, typename _Tp::__trivially_relocatable>::value
+#if __has_builtin(__has_non_relocatable_fields)
+                                                       && !__has_non_relocatable_fields(_Tp)
 #endif
+                                                       > > : true_type {
+};
 
 _LIBCPP_END_NAMESPACE_STD
 

libcxx/test/libcxx/type_traits/is_trivially_relocatable.compile.pass.cpp

@@ -76,8 +76,8 @@ static_assert(!std::__libcpp_is_trivially_relocatable<NonTrivialDestructor>::val
 // ----------------------
 
 // __split_buffer
-static_assert(std::__libcpp_is_trivially_relocatable<std::__split_buffer<int> >::value == pfp_disabled, "");
-static_assert(std::__libcpp_is_trivially_relocatable<std::__split_buffer<NotTriviallyCopyable> >::value == pfp_disabled, "");
+static_assert(std::__libcpp_is_trivially_relocatable<std::__split_buffer<int> >::value, "");
+static_assert(std::__libcpp_is_trivially_relocatable<std::__split_buffer<NotTriviallyCopyable> >::value, "");
 static_assert(!std::__libcpp_is_trivially_relocatable<std::__split_buffer<int, test_allocator<int> > >::value, "");
 
 // standard library types
@@ -105,17 +105,17 @@ struct NotTriviallyRelocatableCharTraits : constexpr_char_traits<T> {
 };
 
 static_assert(std::__libcpp_is_trivially_relocatable<
-                  std::basic_string<char, std::char_traits<char>, std::allocator<char> > >::value == pfp_disabled,
+                  std::basic_string<char, std::char_traits<char>, std::allocator<char> > >::value,
               "");
 static_assert(std::__libcpp_is_trivially_relocatable<
-                  std::basic_string<char, NotTriviallyRelocatableCharTraits<char>, std::allocator<char> > >::value == pfp_disabled,
+                  std::basic_string<char, NotTriviallyRelocatableCharTraits<char>, std::allocator<char> > >::value,
               "");
 static_assert(std::__libcpp_is_trivially_relocatable<
-                  std::basic_string<MyChar, constexpr_char_traits<MyChar>, std::allocator<MyChar> > >::value == pfp_disabled,
+                  std::basic_string<MyChar, constexpr_char_traits<MyChar>, std::allocator<MyChar> > >::value,
               "");
 static_assert(
     std::__libcpp_is_trivially_relocatable<
-        std::basic_string<MyChar, NotTriviallyRelocatableCharTraits<MyChar>, std::allocator<MyChar> > >::value == pfp_disabled,
+        std::basic_string<MyChar, NotTriviallyRelocatableCharTraits<MyChar>, std::allocator<MyChar> > >::value,
     "");
 static_assert(!std::__libcpp_is_trivially_relocatable<
                   std::basic_string<char, std::char_traits<char>, test_allocator<char> > >::value,
@@ -127,18 +127,18 @@ static_assert(
 #endif
 
 // deque
-static_assert(std::__libcpp_is_trivially_relocatable<std::deque<int> >::value == pfp_disabled, "");
-static_assert(std::__libcpp_is_trivially_relocatable<std::deque<NotTriviallyCopyable> >::value == pfp_disabled, "");
+static_assert(std::__libcpp_is_trivially_relocatable<std::deque<int> >::value, "");
+static_assert(std::__libcpp_is_trivially_relocatable<std::deque<NotTriviallyCopyable> >::value, "");
 static_assert(!std::__libcpp_is_trivially_relocatable<std::deque<int, test_allocator<int> > >::value, "");
 
 // exception_ptr
 #ifndef _LIBCPP_ABI_MICROSOFT // FIXME: Is this also the case on windows?
-static_assert(std::__libcpp_is_trivially_relocatable<std::exception_ptr>::value == pfp_disabled, "");
+static_assert(std::__libcpp_is_trivially_relocatable<std::exception_ptr>::value, "");
 #endif
 
 // expected
 #if TEST_STD_VER >= 23
-static_assert(std::__libcpp_is_trivially_relocatable<std::expected<int, int> >::value == pfp_disabled);
+static_assert(std::__libcpp_is_trivially_relocatable<std::expected<int, int> >::value);
 static_assert(std::__libcpp_is_trivially_relocatable<std::expected<std::unique_ptr<int>, int>>::value == pfp_disabled);
 static_assert(std::__libcpp_is_trivially_relocatable<std::expected<int, std::unique_ptr<int>>>::value == pfp_disabled);
 static_assert(std::__libcpp_is_trivially_relocatable<std::expected<std::unique_ptr<int>, std::unique_ptr<int>>>::value == pfp_disabled);
@@ -151,7 +151,7 @@ static_assert(
 
 // locale
 #ifndef TEST_HAS_NO_LOCALIZATION
-static_assert(std::__libcpp_is_trivially_relocatable<std::locale>::value == pfp_disabled, "");
+static_assert(std::__libcpp_is_trivially_relocatable<std::locale>::value, "");
 #endif
 
 // optional
@@ -162,7 +162,7 @@ static_assert(std::__libcpp_is_trivially_relocatable<std::optional<std::unique_p
 #endif // TEST_STD_VER >= 17
 
 // pair
-static_assert(std::__libcpp_is_trivially_relocatable<std::pair<int, int> >::value == pfp_disabled, "");
+static_assert(std::__libcpp_is_trivially_relocatable<std::pair<int, int> >::value, "");
 static_assert(!std::__libcpp_is_trivially_relocatable<std::pair<NotTriviallyCopyable, int> >::value, "");
 static_assert(!std::__libcpp_is_trivially_relocatable<std::pair<int, NotTriviallyCopyable> >::value, "");
 static_assert(!std::__libcpp_is_trivially_relocatable<std::pair<NotTriviallyCopyable, NotTriviallyCopyable> >::value,
@@ -177,11 +177,11 @@ static_assert(std::__libcpp_is_trivially_relocatable<std::shared_ptr<NotTriviall
 #if TEST_STD_VER >= 11
 static_assert(std::__libcpp_is_trivially_relocatable<std::tuple<> >::value, "");
 
-static_assert(std::__libcpp_is_trivially_relocatable<std::tuple<int> >::value == pfp_disabled, "");
+static_assert(std::__libcpp_is_trivially_relocatable<std::tuple<int> >::value, "");
 static_assert(!std::__libcpp_is_trivially_relocatable<std::tuple<NotTriviallyCopyable> >::value, "");
 static_assert(std::__libcpp_is_trivially_relocatable<std::tuple<std::unique_ptr<int> > >::value == pfp_disabled, "");
 
-static_assert(std::__libcpp_is_trivially_relocatable<std::tuple<int, int> >::value == pfp_disabled, "");
+static_assert(std::__libcpp_is_trivially_relocatable<std::tuple<int, int> >::value, "");
 static_assert(!std::__libcpp_is_trivially_relocatable<std::tuple<NotTriviallyCopyable, int> >::value, "");
 static_assert(!std::__libcpp_is_trivially_relocatable<std::tuple<int, NotTriviallyCopyable> >::value, "");
 static_assert(!std::__libcpp_is_trivially_relocatable<std::tuple<NotTriviallyCopyable, NotTriviallyCopyable> >::value,