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+//===--- Descriptor.h - Types for the constexpr VM --------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// Defines descriptors which characterise allocations.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_AST_INTERP_DESCRIPTOR_H
+#define LLVM_CLANG_AST_INTERP_DESCRIPTOR_H
+
+#include "clang/AST/Decl.h"
+#include "clang/AST/Expr.h"
+
+namespace clang {
+namespace interp {
+class Block;
+class Record;
+struct Descriptor;
+enum PrimType : unsigned;
+
+using DeclTy = llvm::PointerUnion<const Decl *, const Expr *>;
+
+/// Invoked whenever a block is created. The constructor method fills in the
+/// inline descriptors of all fields and array elements. It also initializes
+/// all the fields which contain non-trivial types.
+using BlockCtorFn = void (*)(Block *Storage, char *FieldPtr, bool IsConst,
+ bool IsMutable, bool IsActive,
+ Descriptor *FieldDesc);
+
+/// Invoked when a block is destroyed. Invokes the destructors of all
+/// non-trivial nested fields of arrays and records.
+using BlockDtorFn = void (*)(Block *Storage, char *FieldPtr,
+ Descriptor *FieldDesc);
+
+/// Invoked when a block with pointers referencing it goes out of scope. Such
+/// blocks are persisted: the move function copies all inline descriptors and
+/// non-trivial fields, as existing pointers might need to reference those
+/// descriptors. Data is not copied since it cannot be legally read.
+using BlockMoveFn = void (*)(Block *Storage, char *SrcFieldPtr,
+ char *DstFieldPtr, Descriptor *FieldDesc);
+
+/// Object size as used by the interpreter.
+using InterpSize = unsigned;
+
+/// Describes a memory block created by an allocation site.
+struct Descriptor {
+private:
+ /// Original declaration, used to emit the error message.
+ const DeclTy Source;
+ /// Size of an element, in host bytes.
+ const InterpSize ElemSize;
+ /// Size of the storage, in host bytes.
+ const InterpSize Size;
+ /// Size of the allocation (storage + metadata), in host bytes.
+ const InterpSize AllocSize;
+
+ /// Value to denote arrays of unknown size.
+ static constexpr unsigned UnknownSizeMark = (unsigned)-1;
+
+public:
+ /// Token to denote structures of unknown size.
+ struct UnknownSize {};
+
+ /// Pointer to the record, if block contains records.
+ Record *const ElemRecord = nullptr;
+ /// Descriptor of the array element.
+ Descriptor *const ElemDesc = nullptr;
+ /// Flag indicating if the block is mutable.
+ const bool IsConst = false;
+ /// Flag indicating if a field is mutable.
+ const bool IsMutable = false;
+ /// Flag indicating if the block is a temporary.
+ const bool IsTemporary = false;
+ /// Flag indicating if the block is an array.
+ const bool IsArray = false;
+
+ /// Storage management methods.
+ const BlockCtorFn CtorFn = nullptr;
+ const BlockDtorFn DtorFn = nullptr;
+ const BlockMoveFn MoveFn = nullptr;
+
+ /// Allocates a descriptor for a primitive.
+ Descriptor(const DeclTy &D, PrimType Type, bool IsConst, bool IsTemporary,
+ bool IsMutable);
+
+ /// Allocates a descriptor for an array of primitives.
+ Descriptor(const DeclTy &D, PrimType Type, size_t NumElems, bool IsConst,
+ bool IsTemporary, bool IsMutable);
+
+ /// Allocates a descriptor for an array of primitives of unknown size.
+ Descriptor(const DeclTy &D, PrimType Type, bool IsTemporary, UnknownSize);
+
+ /// Allocates a descriptor for an array of composites.
+ Descriptor(const DeclTy &D, Descriptor *Elem, unsigned NumElems, bool IsConst,
+ bool IsTemporary, bool IsMutable);
+
+ /// Allocates a descriptor for an array of composites of unknown size.
+ Descriptor(const DeclTy &D, Descriptor *Elem, bool IsTemporary, UnknownSize);
+
+ /// Allocates a descriptor for a record.
+ Descriptor(const DeclTy &D, Record *R, bool IsConst, bool IsTemporary,
+ bool IsMutable);
+
+ QualType getType() const;
+ SourceLocation getLocation() const;
+
+ const Decl *asDecl() const { return Source.dyn_cast<const Decl *>(); }
+ const Expr *asExpr() const { return Source.dyn_cast<const Expr *>(); }
+
+ const ValueDecl *asValueDecl() const {
+ return dyn_cast_or_null<ValueDecl>(asDecl());
+ }
+
+ const FieldDecl *asFieldDecl() const {
+ return dyn_cast_or_null<FieldDecl>(asDecl());
+ }
+
+ const RecordDecl *asRecordDecl() const {
+ return dyn_cast_or_null<RecordDecl>(asDecl());
+ }
+
+ /// Returns the size of the object without metadata.
+ unsigned getSize() const {
+ assert(!isUnknownSizeArray() && "Array of unknown size");
+ return Size;
+ }
+
+ /// Returns the allocated size, including metadata.
+ unsigned getAllocSize() const { return AllocSize; }
+ /// returns the size of an element when the structure is viewed as an array.
+ unsigned getElemSize() const { return ElemSize; }
+
+ /// Returns the number of elements stored in the block.
+ unsigned getNumElems() const {
+ return Size == UnknownSizeMark ? 0 : (getSize() / getElemSize());
+ }
+
+ /// Checks if the descriptor is of an array of primitives.
+ bool isPrimitiveArray() const { return IsArray && !ElemDesc; }
+ /// Checks if the descriptor is of an array of zero size.
+ bool isZeroSizeArray() const { return Size == 0; }
+ /// Checks if the descriptor is of an array of unknown size.
+ bool isUnknownSizeArray() const { return Size == UnknownSizeMark; }
+
+ /// Checks if the descriptor is of a primitive.
+ bool isPrimitive() const { return !IsArray && !ElemRecord; }
+
+ /// Checks if the descriptor is of an array.
+ bool isArray() const { return IsArray; }
+};
+
+/// Inline descriptor embedded in structures and arrays.
+///
+/// Such descriptors precede all composite array elements and structure fields.
+/// If the base of a pointer is not zero, the base points to the end of this
+/// structure. The offset field is used to traverse the pointer chain up
+/// to the root structure which allocated the object.
+struct InlineDescriptor {
+ /// Offset inside the structure/array.
+ unsigned Offset;
+
+ /// Flag indicating if the storage is constant or not.
+ /// Relevant for primitive fields.
+ unsigned IsConst : 1;
+ /// For primitive fields, it indicates if the field was initialized.
+ /// Primitive fields in static storage are always initialized.
+ /// Arrays are always initialized, even though their elements might not be.
+ /// Base classes are initialized after the constructor is invoked.
+ unsigned IsInitialized : 1;
+ /// Flag indicating if the field is an embedded base class.
+ unsigned IsBase : 1;
+ /// Flag indicating if the field is the active member of a union.
+ unsigned IsActive : 1;
+ /// Flag indicating if the field is mutable (if in a record).
+ unsigned IsMutable : 1;
+
+ Descriptor *Desc;
+};
+
+/// Bitfield tracking the initialisation status of elements of primitive arrays.
+/// A pointer to this is embedded at the end of all primitive arrays.
+/// If the map was not yet created and nothing was initialied, the pointer to
+/// this structure is 0. If the object was fully initialized, the pointer is -1.
+struct InitMap {
+private:
+ /// Type packing bits.
+ using T = uint64_t;
+ /// Bits stored in a single field.
+ static constexpr uint64_t PER_FIELD = sizeof(T) * CHAR_BIT;
+
+ /// Initializes the map with no fields set.
+ InitMap(unsigned N);
+
+ /// Returns a pointer to storage.
+ T *data();
+
+public:
+ /// Initializes an element. Returns true when object if fully initialized.
+ bool initialize(unsigned I);
+
+ /// Checks if an element was initialized.
+ bool isInitialized(unsigned I);
+
+ /// Allocates a map holding N elements.
+ static InitMap *allocate(unsigned N);
+
+private:
+ /// Number of fields initialized.
+ unsigned UninitFields;
+};
+
+} // namespace interp
+} // namespace clang
+
+#endif