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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;
/// 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 IsFieldMutable : 1;
Descriptor *Desc;
};
/// Describes a memory block created by an allocation site.
struct Descriptor final {
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 metadata.
const InterpSize MDSize;
/// 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 {};
using MetadataSize = std::optional<InterpSize>;
static constexpr MetadataSize InlineDescMD = sizeof(InlineDescriptor);
/// 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, MetadataSize MD, bool IsConst,
bool IsTemporary, bool IsMutable);
/// Allocates a descriptor for an array of primitives.
Descriptor(const DeclTy &D, PrimType Type, MetadataSize MD, 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, MetadataSize MD,
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, MetadataSize MD, 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_if_present<ValueDecl>(asDecl());
}
const FieldDecl *asFieldDecl() const {
return dyn_cast_if_present<FieldDecl>(asDecl());
}
const RecordDecl *asRecordDecl() const {
return dyn_cast_if_present<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 size of the metadata.
unsigned getMetadataSize() const { return MDSize; }
/// 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; }
};
/// 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 initialized, the pointer to
/// this structure is 0. If the object was fully initialized, the pointer is -1.
struct InitMap final {
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();
const T *data() const;
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) const;
/// Allocates a map holding N elements.
static InitMap *allocate(unsigned N);
private:
/// Number of fields initialized.
unsigned UninitFields;
};
} // namespace interp
} // namespace clang
#endif
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