diff --git a/clang/docs/LanguageExtensions.rst b/clang/docs/LanguageExtensions.rst index 46f99d0bbdd06..a49e4122ffc10 100644 --- a/clang/docs/LanguageExtensions.rst +++ b/clang/docs/LanguageExtensions.rst @@ -4016,6 +4016,30 @@ Note that the `size` argument must be a compile time constant. Note that this intrinsic cannot yet be called in a ``constexpr`` context. +``__is_bitwise_cloneable`` +-------------------------- + +A type trait is used to check whether a type can be safely copied by memcpy. + +**Syntax**: + +.. code-block:: c++ + + bool __is_bitwise_cloneable(Type) + +**Description**: + +Objects of bitwise cloneable types can be bitwise copied by memcpy/memmove. The +Clang compiler warrants that this behavior is well defined, and won't be +broken by compiler optimizations and sanitizers. + +For implicit-lifetime types, the lifetime of the new object is implicitly +started after the copy. For other types (e.g., classes with virtual methods), +the lifetime isn't started, and using the object results in undefined behavior +according to the C++ Standard. + +This builtin can be used in constant expressions. + Atomic Min/Max builtins with memory ordering -------------------------------------------- diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst index 39a9013c75a41..3d54144bf9206 100644 --- a/clang/docs/ReleaseNotes.rst +++ b/clang/docs/ReleaseNotes.rst @@ -337,6 +337,9 @@ Non-comprehensive list of changes in this release ``-Winvalid-constexpr`` is not enabled for the function definition, which should result in mild compile-time performance improvements. +- Added ``__is_bitwise_cloneable`` which is used to check whether a type + can be safely copied by memcpy/memmove. + New Compiler Flags ------------------ - ``-fsanitize=implicit-bitfield-conversion`` checks implicit truncation and diff --git a/clang/include/clang/AST/Type.h b/clang/include/clang/AST/Type.h index 263b632df23ce..9eb3f6c09e3d3 100644 --- a/clang/include/clang/AST/Type.h +++ b/clang/include/clang/AST/Type.h @@ -1120,6 +1120,20 @@ class QualType { /// Return true if this is a trivially copyable type (C++0x [basic.types]p9) bool isTriviallyCopyableType(const ASTContext &Context) const; + /// Return true if the type is safe to bitwise copy using memcpy/memmove. + /// + /// This is an extension in clang: bitwise cloneable types act as trivially + /// copyable types, meaning their underlying bytes can be safely copied by + /// memcpy or memmove. After the copy, the destination object has the same + /// object representation. + /// + /// However, there are cases where it is not safe to copy: + /// - When sanitizers, such as AddressSanitizer, add padding with poison, + /// which can cause issues if those poisoned padding bits are accessed. + /// - Types with Objective-C lifetimes, where specific runtime + /// semantics may not be preserved during a bitwise copy. + bool isBitwiseCloneableType(const ASTContext &Context) const; + /// Return true if this is a trivially copyable type bool isTriviallyCopyConstructibleType(const ASTContext &Context) const; diff --git a/clang/include/clang/Basic/TokenKinds.def b/clang/include/clang/Basic/TokenKinds.def index b5a0e9df9f7ae..9c4b17465e18a 100644 --- a/clang/include/clang/Basic/TokenKinds.def +++ b/clang/include/clang/Basic/TokenKinds.def @@ -542,6 +542,8 @@ TYPE_TRAIT_2(__reference_converts_from_temporary, ReferenceConvertsFromTemporary // is not exposed to users. TYPE_TRAIT_2(/*EmptySpellingName*/, IsDeducible, KEYCXX) +TYPE_TRAIT_1(__is_bitwise_cloneable, IsBitwiseCloneable, KEYALL) + // Embarcadero Expression Traits EXPRESSION_TRAIT(__is_lvalue_expr, IsLValueExpr, KEYCXX) EXPRESSION_TRAIT(__is_rvalue_expr, IsRValueExpr, KEYCXX) diff --git a/clang/lib/AST/Type.cpp b/clang/lib/AST/Type.cpp index 2097b29b7e0b6..3f88c3441eaf6 100644 --- a/clang/lib/AST/Type.cpp +++ b/clang/lib/AST/Type.cpp @@ -2749,6 +2749,43 @@ bool QualType::isTriviallyCopyableType(const ASTContext &Context) const { /*IsCopyConstructible=*/false); } +// FIXME: each call will trigger a full computation, cache the result. +bool QualType::isBitwiseCloneableType(const ASTContext &Context) const { + auto CanonicalType = getCanonicalType(); + if (CanonicalType.hasNonTrivialObjCLifetime()) + return false; + if (CanonicalType->isArrayType()) + return Context.getBaseElementType(CanonicalType) + .isBitwiseCloneableType(Context); + + if (CanonicalType->isIncompleteType()) + return false; + const auto *RD = CanonicalType->getAsRecordDecl(); // struct/union/class + if (!RD) + return true; + + // Never allow memcpy when we're adding poisoned padding bits to the struct. + // Accessing these posioned bits will trigger false alarms on + // SanitizeAddressFieldPadding etc. + if (RD->mayInsertExtraPadding()) + return false; + + for (auto *const Field : RD->fields()) { + if (!Field->getType().isBitwiseCloneableType(Context)) + return false; + } + + if (const auto *CXXRD = dyn_cast(RD)) { + for (auto Base : CXXRD->bases()) + if (!Base.getType().isBitwiseCloneableType(Context)) + return false; + for (auto VBase : CXXRD->vbases()) + if (!VBase.getType().isBitwiseCloneableType(Context)) + return false; + } + return true; +} + bool QualType::isTriviallyCopyConstructibleType( const ASTContext &Context) const { return isTriviallyCopyableTypeImpl(*this, Context, diff --git a/clang/lib/Sema/SemaExprCXX.cpp b/clang/lib/Sema/SemaExprCXX.cpp index 4487c618862c5..eb0d987f63da5 100644 --- a/clang/lib/Sema/SemaExprCXX.cpp +++ b/clang/lib/Sema/SemaExprCXX.cpp @@ -5126,6 +5126,7 @@ static bool CheckUnaryTypeTraitTypeCompleteness(Sema &S, TypeTrait UTT, case UTT_IsStandardLayout: case UTT_IsPOD: case UTT_IsLiteral: + case UTT_IsBitwiseCloneable: // By analogy, is_trivially_relocatable and is_trivially_equality_comparable // impose the same constraints. case UTT_IsTriviallyRelocatable: @@ -5619,6 +5620,8 @@ static bool EvaluateUnaryTypeTrait(Sema &Self, TypeTrait UTT, return C.hasUniqueObjectRepresentations(T); case UTT_IsTriviallyRelocatable: return T.isTriviallyRelocatableType(C); + case UTT_IsBitwiseCloneable: + return T.isBitwiseCloneableType(C); case UTT_IsReferenceable: return T.isReferenceable(); case UTT_CanPassInRegs: diff --git a/clang/test/SemaCXX/builtin-is-bitwise-cloneable-fsanitize.cpp b/clang/test/SemaCXX/builtin-is-bitwise-cloneable-fsanitize.cpp new file mode 100644 index 0000000000000..d47a39a0754c5 --- /dev/null +++ b/clang/test/SemaCXX/builtin-is-bitwise-cloneable-fsanitize.cpp @@ -0,0 +1,34 @@ +// RUN: %clang_cc1 -triple x86_64-unknown-linux -DSANITIZER_ENABLED -fsanitize=address -fsanitize-address-field-padding=1 %s +// RUN: %clang_cc1 -triple x86_64-unknown-linux %s + +struct S { + ~S() {} + virtual void foo() {} + + int buffer[1]; + int other_field = 0; +}; + +union U { + S s; +}; + +struct Derived : S {}; + +static_assert(!__is_trivially_copyable(S)); +#ifdef SANITIZER_ENABLED +// Don't allow memcpy when the struct has poisoned padding bits. +// The sanitizer adds posion padding bits to struct S. +static_assert(sizeof(S) > 16); +static_assert(!__is_bitwise_cloneable(S)); +static_assert(sizeof(U) == sizeof(S)); // no padding bit for U. +static_assert(!__is_bitwise_cloneable(U)); +static_assert(!__is_bitwise_cloneable(S[2])); +static_assert(!__is_bitwise_cloneable(Derived)); +#else +static_assert(sizeof(S) == 16); +static_assert(__is_bitwise_cloneable(S)); +static_assert(__is_bitwise_cloneable(U)); +static_assert(__is_bitwise_cloneable(S[2])); +static_assert(__is_bitwise_cloneable(Derived)); +#endif diff --git a/clang/test/SemaCXX/builtin-is-bitwise-cloneable.cpp b/clang/test/SemaCXX/builtin-is-bitwise-cloneable.cpp new file mode 100644 index 0000000000000..1781cf48449f6 --- /dev/null +++ b/clang/test/SemaCXX/builtin-is-bitwise-cloneable.cpp @@ -0,0 +1,8 @@ +// RUN: %clang_cc1 -fsyntax-only -verify %s +// +struct DynamicClass { virtual int Foo(); }; +static_assert(!__is_trivially_copyable(DynamicClass)); +static_assert(__is_bitwise_cloneable(DynamicClass)); + +struct InComplete; // expected-note{{forward declaration}} +static_assert(!__is_bitwise_cloneable(InComplete)); // expected-error{{incomplete type 'InComplete' used in type trait expression}} diff --git a/clang/test/SemaObjCXX/arc-type-traits.mm b/clang/test/SemaObjCXX/arc-type-traits.mm index 2d30ae450f3b0..25bc8b362140a 100644 --- a/clang/test/SemaObjCXX/arc-type-traits.mm +++ b/clang/test/SemaObjCXX/arc-type-traits.mm @@ -221,3 +221,12 @@ TRAIT_IS_TRUE(__is_trivially_relocatable, HasStrong); TRAIT_IS_FALSE(__is_trivially_relocatable, HasWeak); TRAIT_IS_TRUE(__is_trivially_relocatable, HasUnsafeUnretained); + +// __is_bitwise_cloneable +TRAIT_IS_FALSE(__is_bitwise_cloneable, __strong id); +TRAIT_IS_FALSE(__is_bitwise_cloneable, __weak id); +TRAIT_IS_FALSE(__is_bitwise_cloneable, __autoreleasing id); +TRAIT_IS_TRUE(__is_trivial, __unsafe_unretained id); +TRAIT_IS_FALSE(__is_bitwise_cloneable, HasStrong); +TRAIT_IS_FALSE(__is_bitwise_cloneable, HasWeak); +TRAIT_IS_TRUE(__is_bitwise_cloneable, HasUnsafeUnretained);