[clang][Sema] Track trivial-relocatability as a type trait

To resolve #69394, this patch separates trivial-relocatability's logic from `canPassInRegisters` to decide if a type is trivial-relocatable. A type passed in registers doesn't necessarily mean trivial-relocatability of that type(e.g. on Windows) i.e. it gives us an unintended false positive. This change would be beneficial for Abseil since they rely upon these semantics.
By these changes now:
User-provided special members prevent natural trivial-relocatabilitiy.
    It's important because Abseil and maybe others assume the assignment operator doesn't have an impact on the trivial-relocatability of a type.
    In fact, it does have an effect, and with a user-provided assignment operator, the compiler should only accept it as trivial-relocatable if it's implied by the `[[clang::trivial_abi]]` attribute.
Just because a type can pass in registers doesn't necessarily mean it's trivial-relocatable.
The `[[clang::trivial_abi]]` attribute always implies trivial-relocatability, even if it can't pass in registers.
The trait has extensive tests for both old and new behaviors. Test aggregation of
both kinds of types as data members; inheritance; virtual member functions
and virtual bases; const and reference data members; and reference types.

Fixes #69394

Author: AMP999

clang/include/clang/AST/CXXRecordDeclDefinitionBits.def

@@ -189,6 +189,11 @@ FIELD(DeclaredNonTrivialSpecialMembers, 6, MERGE_OR)
 /// SMF_MoveConstructor, and SMF_Destructor are meaningful here.
 FIELD(DeclaredNonTrivialSpecialMembersForCall, 6, MERGE_OR)
 
+/// True when this class's bases and fields are all trivially relocatable
+/// or references, and the class itself has no user-provided special
+/// member functions.
+FIELD(IsNaturallyTriviallyRelocatable, 1, NO_MERGE)
+
 /// True when this class has a destructor with no semantic effect.
 FIELD(HasIrrelevantDestructor, 1, NO_MERGE)
 

clang/include/clang/AST/DeclCXX.h

@@ -1386,6 +1386,9 @@ class CXXRecordDecl : public RecordDecl {
         (SMF_CopyConstructor | SMF_MoveConstructor | SMF_Destructor);
   }
 
+  /// Determine whether this class is trivially relocatable
+  bool isTriviallyRelocatable() const;
+
   /// Determine whether declaring a const variable with this type is ok
   /// per core issue 253.
   bool allowConstDefaultInit() const {

clang/lib/AST/DeclCXX.cpp

@@ -95,7 +95,8 @@ CXXRecordDecl::DefinitionData::DefinitionData(CXXRecordDecl *D)
       DefaultedDestructorIsDeleted(false), HasTrivialSpecialMembers(SMF_All),
       HasTrivialSpecialMembersForCall(SMF_All),
       DeclaredNonTrivialSpecialMembers(0),
-      DeclaredNonTrivialSpecialMembersForCall(0), HasIrrelevantDestructor(true),
+      DeclaredNonTrivialSpecialMembersForCall(0),
+      IsNaturallyTriviallyRelocatable(true), HasIrrelevantDestructor(true),
       HasConstexprNonCopyMoveConstructor(false),
       HasDefaultedDefaultConstructor(false),
       DefaultedDefaultConstructorIsConstexpr(true),
@@ -279,6 +280,10 @@ CXXRecordDecl::setBases(CXXBaseSpecifier const * const *Bases,
 
       //   An aggregate is a class with [...] no virtual functions.
       data().Aggregate = false;
+
+      // A trivially relocatable class is a class:
+      // -- which has no virtual member functions or virtual base classes
+      data().IsNaturallyTriviallyRelocatable = false;
     }
 
     // C++0x [class]p7:
@@ -293,6 +298,9 @@ CXXRecordDecl::setBases(CXXBaseSpecifier const * const *Bases,
     if (!hasNonLiteralTypeFieldsOrBases() && !BaseType->isLiteralType(C))
       data().HasNonLiteralTypeFieldsOrBases = true;
 
+    if (Base->isVirtual() || !BaseClassDecl->isTriviallyRelocatable())
+      data().IsNaturallyTriviallyRelocatable = false;
+
     // Now go through all virtual bases of this base and add them.
     for (const auto &VBase : BaseClassDecl->vbases()) {
       // Add this base if it's not already in the list.
@@ -570,6 +578,10 @@ bool CXXRecordDecl::hasAnyDependentBases() const {
   return !forallBases([](const CXXRecordDecl *) { return true; });
 }
 
+bool CXXRecordDecl::isTriviallyRelocatable() const {
+  return (data().IsNaturallyTriviallyRelocatable || hasAttr<TrivialABIAttr>());
+}
+
 bool CXXRecordDecl::isTriviallyCopyable() const {
   // C++0x [class]p5:
   //   A trivially copyable class is a class that:
@@ -758,6 +770,10 @@ void CXXRecordDecl::addedMember(Decl *D) {
       //    -- has no virtual functions
       data().IsStandardLayout = false;
       data().IsCXX11StandardLayout = false;
+
+      // A trivially relocatable class is a class:
+      // -- which has no virtual member functions or virtual base classes
+      data().IsNaturallyTriviallyRelocatable = false;
     }
   }
 
@@ -824,6 +840,14 @@ void CXXRecordDecl::addedMember(Decl *D) {
               ? !Constructor->isImplicit()
               : (Constructor->isUserProvided() || Constructor->isExplicit()))
         data().Aggregate = false;
+
+      // A trivially relocatable class is a class:
+      // -- where no eligible copy constructor, move constructor, copy
+      // assignment operator, move assignment operator, or destructor is
+      // user-provided,
+      if (Constructor->isUserProvided() && (Constructor->isCopyConstructor() ||
+                                            Constructor->isMoveConstructor()))
+        data().IsNaturallyTriviallyRelocatable = false;
     }
   }
 
@@ -853,11 +877,18 @@ void CXXRecordDecl::addedMember(Decl *D) {
           Method->getNonObjectParameter(0)->getType()->getAs<ReferenceType>();
       if (!ParamTy || ParamTy->getPointeeType().isConstQualified())
         data().HasDeclaredCopyAssignmentWithConstParam = true;
+
+      if (Method->isUserProvided())
+        data().IsNaturallyTriviallyRelocatable = false;
     }
 
-    if (Method->isMoveAssignmentOperator())
+    if (Method->isMoveAssignmentOperator()) {
       SMKind |= SMF_MoveAssignment;
 
+      if (Method->isUserProvided())
+        data().IsNaturallyTriviallyRelocatable = false;
+    }
+
     // Keep the list of conversion functions up-to-date.
     if (auto *Conversion = dyn_cast<CXXConversionDecl>(D)) {
       // FIXME: We use the 'unsafe' accessor for the access specifier here,
@@ -1066,6 +1097,12 @@ void CXXRecordDecl::addedMember(Decl *D) {
     } else if (!T.isCXX98PODType(Context))
       data().PlainOldData = false;
 
+    // A trivially relocatable class is a class:
+    // -- all of whose members are either of reference type or of trivially
+    // relocatable type
+    if (!T->isReferenceType() && !T.isTriviallyRelocatableType(Context))
+      data().IsNaturallyTriviallyRelocatable = false;
+
     if (T->isReferenceType()) {
       if (!Field->hasInClassInitializer())
         data().HasUninitializedReferenceMember = true;
@@ -1420,8 +1457,10 @@ void CXXRecordDecl::addedEligibleSpecialMemberFunction(const CXXMethodDecl *MD,
   // See https://github.com/llvm/llvm-project/issues/59206
 
   if (const auto *DD = dyn_cast<CXXDestructorDecl>(MD)) {
-    if (DD->isUserProvided())
+    if (DD->isUserProvided()) {
       data().HasIrrelevantDestructor = false;
+      data().IsNaturallyTriviallyRelocatable = false;
+    }
     // If the destructor is explicitly defaulted and not trivial or not public
     // or if the destructor is deleted, we clear HasIrrelevantDestructor in
     // finishedDefaultedOrDeletedMember.

clang/lib/AST/Type.cpp

@@ -2680,8 +2680,10 @@ bool QualType::isTriviallyRelocatableType(const ASTContext &Context) const {
     return false;
   } else if (!BaseElementType->isObjectType()) {
     return false;
-  } else if (const auto *RD = BaseElementType->getAsRecordDecl()) {
-    return RD->canPassInRegisters();
+  } else if (CXXRecordDecl *RD = BaseElementType->getAsCXXRecordDecl()) {
+    return RD->isTriviallyRelocatable();
+  } else if (BaseElementType.isTriviallyCopyableType(Context)) {
+    return true;
   } else {
     switch (isNonTrivialToPrimitiveDestructiveMove()) {
     case PCK_Trivial:

clang/test/SemaCXX/attr-trivial-abi.cpp

@@ -5,15 +5,7 @@ void __attribute__((trivial_abi)) foo(); // expected-warning {{'trivial_abi' att
 // Should not crash.
 template <class>
 class __attribute__((trivial_abi)) a { a(a &&); };
-#if defined(_WIN64) && !defined(__MINGW32__)
-// On Windows/MSVC, to be trivial-for-calls, an object must be trivially copyable.
-// (And it is only trivially relocatable, currently, if it is trivial for calls.)
-// In this case, it is suppressed by an explicitly defined move constructor.
-// Similar concerns apply to later tests that have #if defined(_WIN64) && !defined(__MINGW32__)
-static_assert(!__is_trivially_relocatable(a<int>), "");
-#else
 static_assert(__is_trivially_relocatable(a<int>), "");
-#endif
 
 struct [[clang::trivial_abi]] S0 {
   int a;
@@ -39,14 +31,7 @@ struct __attribute__((trivial_abi)) S3_3 { // expected-warning {{'trivial_abi' c
   S3_3(S3_3 &&);
   S3_2 s32;
 };
-#ifdef __ORBIS__
-// The ClangABI4OrPS4 calling convention kind passes classes in registers if the
-// copy constructor is trivial for calls *or deleted*, while other platforms do
-// not accept deleted constructors.
-static_assert(__is_trivially_relocatable(S3_3), "");
-#else
 static_assert(!__is_trivially_relocatable(S3_3), "");
-#endif
 
 // Diagnose invalid trivial_abi even when the type is templated because it has a non-trivial field.
 template <class T>
@@ -118,30 +103,18 @@ struct __attribute__((trivial_abi)) CopyMoveDeleted { // expected-warning {{'tri
   CopyMoveDeleted(const CopyMoveDeleted &) = delete;
   CopyMoveDeleted(CopyMoveDeleted &&) = delete;
 };
-#ifdef __ORBIS__
 static_assert(__is_trivially_relocatable(CopyMoveDeleted), "");
-#else
-static_assert(!__is_trivially_relocatable(CopyMoveDeleted), "");
-#endif
 
 struct __attribute__((trivial_abi)) S18 { // expected-warning {{'trivial_abi' cannot be applied to 'S18'}} expected-note {{copy constructors and move constructors are all deleted}}
   CopyMoveDeleted a;
 };
-#ifdef __ORBIS__
 static_assert(__is_trivially_relocatable(S18), "");
-#else
-static_assert(!__is_trivially_relocatable(S18), "");
-#endif
 
 struct __attribute__((trivial_abi)) CopyDeleted {
   CopyDeleted(const CopyDeleted &) = delete;
   CopyDeleted(CopyDeleted &&) = default;
 };
-#if defined(_WIN64) && !defined(__MINGW32__)
-static_assert(!__is_trivially_relocatable(CopyDeleted), "");
-#else
 static_assert(__is_trivially_relocatable(CopyDeleted), "");
-#endif
 
 struct __attribute__((trivial_abi)) MoveDeleted {
   MoveDeleted(const MoveDeleted &) = default;
@@ -153,19 +126,11 @@ struct __attribute__((trivial_abi)) S19 { // expected-warning {{'trivial_abi' ca
   CopyDeleted a;
   MoveDeleted b;
 };
-#ifdef __ORBIS__
 static_assert(__is_trivially_relocatable(S19), "");
-#else
-static_assert(!__is_trivially_relocatable(S19), "");
-#endif
 
 // This is fine since the move constructor isn't deleted.
 struct __attribute__((trivial_abi)) S20 {
   int &&a; // a member of rvalue reference type deletes the copy constructor.
 };
-#if defined(_WIN64) && !defined(__MINGW32__)
-static_assert(!__is_trivially_relocatable(S20), "");
-#else
 static_assert(__is_trivially_relocatable(S20), "");
-#endif
 } // namespace deletedCopyMoveConstructor

clang/test/SemaCXX/is-trivially-relocatable.cpp

@@ -0,0 +1,106 @@
+// RUN: %clang_cc1 -std=c++03 -fsyntax-only -verify %s -triple x86_64-windows-msvc
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify %s -triple x86_64-windows-msvc
+// RUN: %clang_cc1 -std=c++03 -fsyntax-only -verify %s -triple x86_64-apple-darwin10
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify %s -triple x86_64-apple-darwin10
+
+// expected-no-diagnostics
+
+#if __cplusplus < 201103L
+#define static_assert(...) __extension__ _Static_assert(__VA_ARGS__, "")
+// cxx98-error@-1 {{variadic macros are a C99 feature}}
+#endif
+
+template <class T>
+struct Agg {
+  T t_;
+};
+
+template <class T>
+struct Der : T {
+};
+
+template <class T>
+struct Mut {
+  mutable T t_;
+};
+
+template <class T>
+struct Non {
+  Non(); // make it a non-aggregate
+  T t_;
+};
+
+struct CompletelyTrivial {
+};
+static_assert(__is_trivially_relocatable(CompletelyTrivial));
+static_assert(__is_trivially_relocatable(Agg<CompletelyTrivial>));
+static_assert(__is_trivially_relocatable(Der<CompletelyTrivial>));
+static_assert(__is_trivially_relocatable(Mut<CompletelyTrivial>));
+static_assert(__is_trivially_relocatable(Non<CompletelyTrivial>));
+
+struct NonTrivialDtor {
+  ~NonTrivialDtor();
+};
+static_assert(!__is_trivially_relocatable(NonTrivialDtor));
+static_assert(!__is_trivially_relocatable(Agg<NonTrivialDtor>));
+static_assert(!__is_trivially_relocatable(Der<NonTrivialDtor>));
+static_assert(!__is_trivially_relocatable(Mut<NonTrivialDtor>));
+static_assert(!__is_trivially_relocatable(Non<NonTrivialDtor>));
+
+struct NonTrivialCopyCtor {
+  NonTrivialCopyCtor(const NonTrivialCopyCtor&);
+};
+static_assert(!__is_trivially_relocatable(NonTrivialCopyCtor));
+static_assert(!__is_trivially_relocatable(Agg<NonTrivialCopyCtor>));
+static_assert(!__is_trivially_relocatable(Der<NonTrivialCopyCtor>));
+static_assert(!__is_trivially_relocatable(Mut<NonTrivialCopyCtor>));
+static_assert(!__is_trivially_relocatable(Non<NonTrivialCopyCtor>));
+
+struct NonTrivialMutableCopyCtor {
+  NonTrivialMutableCopyCtor(NonTrivialMutableCopyCtor&);
+};
+static_assert(!__is_trivially_relocatable(NonTrivialMutableCopyCtor));
+static_assert(!__is_trivially_relocatable(Agg<NonTrivialMutableCopyCtor>));
+static_assert(!__is_trivially_relocatable(Der<NonTrivialMutableCopyCtor>));
+static_assert(!__is_trivially_relocatable(Mut<NonTrivialMutableCopyCtor>));
+static_assert(!__is_trivially_relocatable(Non<NonTrivialMutableCopyCtor>));
+
+#if __cplusplus >= 201103L
+struct NonTrivialMoveCtor {
+  NonTrivialMoveCtor(NonTrivialMoveCtor&&);
+};
+static_assert(!__is_trivially_relocatable(NonTrivialMoveCtor));
+static_assert(!__is_trivially_relocatable(Agg<NonTrivialMoveCtor>));
+static_assert(!__is_trivially_relocatable(Der<NonTrivialMoveCtor>));
+static_assert(!__is_trivially_relocatable(Mut<NonTrivialMoveCtor>));
+static_assert(!__is_trivially_relocatable(Non<NonTrivialMoveCtor>));
+#endif
+
+struct NonTrivialCopyAssign {
+  NonTrivialCopyAssign& operator=(const NonTrivialCopyAssign&);
+};
+static_assert(!__is_trivially_relocatable(NonTrivialCopyAssign));
+static_assert(!__is_trivially_relocatable(Agg<NonTrivialCopyAssign>));
+static_assert(!__is_trivially_relocatable(Der<NonTrivialCopyAssign>));
+static_assert(!__is_trivially_relocatable(Mut<NonTrivialCopyAssign>));
+static_assert(!__is_trivially_relocatable(Non<NonTrivialCopyAssign>));
+
+struct NonTrivialMutableCopyAssign {
+  NonTrivialMutableCopyAssign& operator=(NonTrivialMutableCopyAssign&);
+};
+static_assert(!__is_trivially_relocatable(NonTrivialMutableCopyAssign));
+static_assert(!__is_trivially_relocatable(Agg<NonTrivialMutableCopyAssign>));
+static_assert(!__is_trivially_relocatable(Der<NonTrivialMutableCopyAssign>));
+static_assert(!__is_trivially_relocatable(Mut<NonTrivialMutableCopyAssign>));
+static_assert(!__is_trivially_relocatable(Non<NonTrivialMutableCopyAssign>));
+
+#if __cplusplus >= 201103L
+struct NonTrivialMoveAssign {
+  NonTrivialMoveAssign& operator=(NonTrivialMoveAssign&&);
+};
+static_assert(!__is_trivially_relocatable(NonTrivialMoveAssign));
+static_assert(!__is_trivially_relocatable(Agg<NonTrivialMoveAssign>));
+static_assert(!__is_trivially_relocatable(Der<NonTrivialMoveAssign>));
+static_assert(!__is_trivially_relocatable(Mut<NonTrivialMoveAssign>));
+static_assert(!__is_trivially_relocatable(Non<NonTrivialMoveAssign>));
+#endif