Author: Vlad Serebrennikov Date: 2023-10-12T21:54:07+04:00 New Revision: 4c6cba31aaaa767cdb7f83ec4ca0eab9b6eae127
URL: https://github.com/llvm/llvm-project/commit/4c6cba31aaaa767cdb7f83ec4ca0eab9b6eae127 DIFF: https://github.com/llvm/llvm-project/commit/4c6cba31aaaa767cdb7f83ec4ca0eab9b6eae127.diff LOG: [clang][NFC] Specify Type and ExtQuals as having 16-byte alignment (#68377) While working on LLDB visualizer for `QualType`, I stumbled upon `Type` and `ExtQuals` defined with `alignas(8)`. Such alignment leaves only 3 lower bits available for pointer tagging, whereas `QualType` requires 4 (3 qualifiers + discriminator between `Type *` and `ExtQuals *`). Turns out `Type` and its derived classes are allocated with `TypeAlignment == 16` passed to `Allocate()`. So I'm removing misleading `alignas(8)` and fixing corresponding static asserts. Since they are already allocated with 16-byte alignment, this is a non-functional change. Added: Modified: clang/include/clang/AST/Type.h Removed: ################################################################################ diff --git a/clang/include/clang/AST/Type.h b/clang/include/clang/AST/Type.h index a78d8f60462b231..3e7e4f4f75b58b1 100644 --- a/clang/include/clang/AST/Type.h +++ b/clang/include/clang/AST/Type.h @@ -1482,7 +1482,8 @@ class ExtQualsTypeCommonBase { /// in three low bits on the QualType pointer; a fourth bit records whether /// the pointer is an ExtQuals node. The extended qualifiers (address spaces, /// Objective-C GC attributes) are much more rare. -class ExtQuals : public ExtQualsTypeCommonBase, public llvm::FoldingSetNode { +class alignas(TypeAlignment) ExtQuals : public ExtQualsTypeCommonBase, + public llvm::FoldingSetNode { // NOTE: changing the fast qualifiers should be straightforward as // long as you don't make 'const' non-fast. // 1. Qualifiers: @@ -1594,7 +1595,7 @@ enum class AutoTypeKeyword { /// /// Types, once created, are immutable. /// -class alignas(8) Type : public ExtQualsTypeCommonBase { +class alignas(TypeAlignment) Type : public ExtQualsTypeCommonBase { public: enum TypeClass { #define TYPE(Class, Base) Class, @@ -1982,9 +1983,10 @@ class alignas(8) Type : public ExtQualsTypeCommonBase { Type(TypeClass tc, QualType canon, TypeDependence Dependence) : ExtQualsTypeCommonBase(this, canon.isNull() ? QualType(this_(), 0) : canon) { - static_assert(sizeof(*this) <= 8 + sizeof(ExtQualsTypeCommonBase), + static_assert(sizeof(*this) <= + alignof(decltype(*this)) + sizeof(ExtQualsTypeCommonBase), "changing bitfields changed sizeof(Type)!"); - static_assert(alignof(decltype(*this)) % sizeof(void *) == 0, + static_assert(alignof(decltype(*this)) % TypeAlignment == 0, "Insufficient alignment!"); TypeBits.TC = tc; TypeBits.Dependence = static_cast<unsigned>(Dependence); @@ -5348,7 +5350,7 @@ class DeducedType : public Type { /// Represents a C++11 auto or C++14 decltype(auto) type, possibly constrained /// by a type-constraint. -class alignas(8) AutoType : public DeducedType, public llvm::FoldingSetNode { +class AutoType : public DeducedType, public llvm::FoldingSetNode { friend class ASTContext; // ASTContext creates these ConceptDecl *TypeConstraintConcept; @@ -5456,9 +5458,7 @@ class DeducedTemplateSpecializationType : public DeducedType, /// TemplateArguments, followed by a QualType representing the /// non-canonical aliased type when the template is a type alias /// template. -class alignas(8) TemplateSpecializationType - : public Type, - public llvm::FoldingSetNode { +class TemplateSpecializationType : public Type, public llvm::FoldingSetNode { friend class ASTContext; // ASTContext creates these /// The name of the template being specialized. This is @@ -5872,9 +5872,8 @@ class DependentNameType : public TypeWithKeyword, public llvm::FoldingSetNode { /// Represents a template specialization type whose template cannot be /// resolved, e.g. /// A<T>::template B<T> -class alignas(8) DependentTemplateSpecializationType - : public TypeWithKeyword, - public llvm::FoldingSetNode { +class DependentTemplateSpecializationType : public TypeWithKeyword, + public llvm::FoldingSetNode { friend class ASTContext; // ASTContext creates these /// The nested name specifier containing the qualifier. _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
