Viewing file:  PointerEmbeddedInt.h (4.05 KB) -rw-r--r--
Select action/file-type:
 (+) |  (+) |  (+) | Code (+) | Session (+) |  (+) | SDB (+) |  (+) |  (+) |  (+) |  (+) |  (+) |
//===- llvm/ADT/PointerEmbeddedInt.h ----------------------------*- 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
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_ADT_POINTEREMBEDDEDINT_H
#define LLVM_ADT_POINTEREMBEDDEDINT_H
#include "llvm/ADT/DenseMapInfo.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/PointerLikeTypeTraits.h"
#include <cassert>
#include <climits>
#include <cstdint>
#include <type_traits>
namespace llvm {
/// Utility to embed an integer into a pointer-like type. This is specifically
/// intended to allow embedding integers where fewer bits are required than
/// exist in a pointer, and the integer can participate in abstractions along
/// side other pointer-like types. For example it can be placed into a \c
/// PointerSumType or \c PointerUnion.
///
/// Note that much like pointers, an integer value of zero has special utility
/// due to boolean conversions. For example, a non-null value can be tested for
/// in the above abstractions without testing the particular active member.
/// Also, the default constructed value zero initializes the integer.
template <typename IntT, int Bits = sizeof(IntT) * CHAR_BIT>
class PointerEmbeddedInt {
uintptr_t Value = 0;
// Note: This '<' is correct; using '<=' would result in some shifts
// overflowing their storage types.
static_assert(Bits < sizeof(uintptr_t) * CHAR_BIT,
"Cannot embed more bits than we have in a pointer!");
enum : uintptr_t {
// We shift as many zeros into the value as we can while preserving the
// number of bits desired for the integer.
Shift = sizeof(uintptr_t) * CHAR_BIT - Bits,
// We also want to be able to mask out the preserved bits for asserts.
Mask = static_cast<uintptr_t>(-1) << Bits
};
struct RawValueTag {
explicit RawValueTag() = default;
};
friend struct PointerLikeTypeTraits<PointerEmbeddedInt>;
explicit PointerEmbeddedInt(uintptr_t Value, RawValueTag) : Value(Value) {}
public:
PointerEmbeddedInt() = default;
PointerEmbeddedInt(IntT I) { *this = I; }
PointerEmbeddedInt &operator=(IntT I) {
assert((std::is_signed<IntT>::value ? isInt<Bits>(I) : isUInt<Bits>(I)) &&
"Integer has bits outside those preserved!");
Value = static_cast<uintptr_t>(I) << Shift;
return *this;
}
// Note that this implicit conversion additionally allows all of the basic
// comparison operators to work transparently, etc.
operator IntT() const {
if (std::is_signed<IntT>::value)
return static_cast<IntT>(static_cast<intptr_t>(Value) >> Shift);
return static_cast<IntT>(Value >> Shift);
}
};
// Provide pointer like traits to support use with pointer unions and sum
// types.
template <typename IntT, int Bits>
struct PointerLikeTypeTraits<PointerEmbeddedInt<IntT, Bits>> {
using T = PointerEmbeddedInt<IntT, Bits>;
static inline void *getAsVoidPointer(const T &P) {
return reinterpret_cast<void *>(P.Value);
}
static inline T getFromVoidPointer(void *P) {
return T(reinterpret_cast<uintptr_t>(P), typename T::RawValueTag());
}
static inline T getFromVoidPointer(const void *P) {
return T(reinterpret_cast<uintptr_t>(P), typename T::RawValueTag());
}
static constexpr int NumLowBitsAvailable = T::Shift;
};
// Teach DenseMap how to use PointerEmbeddedInt objects as keys if the Int type
// itself can be a key.
template <typename IntT, int Bits>
struct DenseMapInfo<PointerEmbeddedInt<IntT, Bits>> {
using T = PointerEmbeddedInt<IntT, Bits>;
using IntInfo = DenseMapInfo<IntT>;
static inline T getEmptyKey() { return IntInfo::getEmptyKey(); }
static inline T getTombstoneKey() { return IntInfo::getTombstoneKey(); }
static unsigned getHashValue(const T &Arg) {
return IntInfo::getHashValue(Arg);
}
static bool isEqual(const T &LHS, const T &RHS) { return LHS == RHS; }
};
} // end namespace llvm
#endif // LLVM_ADT_POINTEREMBEDDEDINT_H
|