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//===- llvm/ADT/PointerUnion.h - Discriminated Union of 2 Ptrs --*- C++ -*-===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// This file defines the PointerUnion class, which is a discriminated union of
// pointer types.
#include "llvm/ADT/DenseMapInfo.h"
#include "llvm/ADT/PointerIntPair.h"
#include "llvm/Support/PointerLikeTypeTraits.h"
#include <cassert>
#include <cstddef>
#include <cstdint>
namespace llvm {
template <typename T> struct PointerUnionTypeSelectorReturn {
using Return = T;
/// Get a type based on whether two types are the same or not.
/// For:
/// \code
/// using Ret = typename PointerUnionTypeSelector<T1, T2, EQ, NE>::Return;
/// \endcode
/// Ret will be EQ type if T1 is same as T2 or NE type otherwise.
template <typename T1, typename T2, typename RET_EQ, typename RET_NE>
struct PointerUnionTypeSelector {
using Return = typename PointerUnionTypeSelectorReturn<RET_NE>::Return;
template <typename T, typename RET_EQ, typename RET_NE>
struct PointerUnionTypeSelector<T, T, RET_EQ, RET_NE> {
using Return = typename PointerUnionTypeSelectorReturn<RET_EQ>::Return;
template <typename T1, typename T2, typename RET_EQ, typename RET_NE>
struct PointerUnionTypeSelectorReturn<
PointerUnionTypeSelector<T1, T2, RET_EQ, RET_NE>> {
using Return =
typename PointerUnionTypeSelector<T1, T2, RET_EQ, RET_NE>::Return;
namespace pointer_union_detail {
/// Determine the number of bits required to store integers with values < n.
/// This is ceil(log2(n)).
constexpr int bitsRequired(unsigned n) {
return n > 1 ? 1 + bitsRequired((n + 1) / 2) : 0;
template <typename... Ts> constexpr int lowBitsAvailable() {
return std::min<int>({PointerLikeTypeTraits<Ts>::NumLowBitsAvailable...});
/// Find the index of a type in a list of types. TypeIndex<T, Us...>::Index
/// is the index of T in Us, or sizeof...(Us) if T does not appear in the
/// list.
template <typename T, typename ...Us> struct TypeIndex;
template <typename T, typename ...Us> struct TypeIndex<T, T, Us...> {
static constexpr int Index = 0;
template <typename T, typename U, typename... Us>
struct TypeIndex<T, U, Us...> {
static constexpr int Index = 1 + TypeIndex<T, Us...>::Index;
template <typename T> struct TypeIndex<T> {
static constexpr int Index = 0;
/// Find the first type in a list of types.
template <typename T, typename...> struct GetFirstType {
using type = T;
/// Provide PointerLikeTypeTraits for void* that is used by PointerUnion
/// for the template arguments.
template <typename ...PTs> class PointerUnionUIntTraits {
static inline void *getAsVoidPointer(void *P) { return P; }
static inline void *getFromVoidPointer(void *P) { return P; }
static constexpr int NumLowBitsAvailable = lowBitsAvailable<PTs...>();
/// Implement assigment in terms of construction.
template <typename Derived, typename T> struct AssignableFrom {
Derived &operator=(T t) {
return static_cast<Derived &>(*this) = Derived(t);
template <typename Derived, typename ValTy, int I, typename ...Types>
class PointerUnionMembers;
template <typename Derived, typename ValTy, int I>
class PointerUnionMembers<Derived, ValTy, I> {
ValTy Val;
PointerUnionMembers() = default;
PointerUnionMembers(ValTy Val) : Val(Val) {}
friend struct PointerLikeTypeTraits<Derived>;
template <typename Derived, typename ValTy, int I, typename Type,
typename ...Types>
class PointerUnionMembers<Derived, ValTy, I, Type, Types...>
: public PointerUnionMembers<Derived, ValTy, I + 1, Types...> {
using Base = PointerUnionMembers<Derived, ValTy, I + 1, Types...>;
using Base::Base;
PointerUnionMembers() = default;
PointerUnionMembers(Type V)
: Base(ValTy(const_cast<void *>(
I)) {}
using Base::operator=;
Derived &operator=(Type V) {
this->Val = ValTy(
const_cast<void *>(PointerLikeTypeTraits<Type>::getAsVoidPointer(V)),
return static_cast<Derived &>(*this);
/// A discriminated union of two or more pointer types, with the discriminator
/// in the low bit of the pointer.
/// This implementation is extremely efficient in space due to leveraging the
/// low bits of the pointer, while exposing a natural and type-safe API.
/// Common use patterns would be something like this:
/// PointerUnion<int*, float*> P;
/// P = (int*)0;
/// printf("%d %d",<int*>(),<float*>()); // prints "1 0"
/// X = P.get<int*>(); // ok.
/// Y = P.get<float*>(); // runtime assertion failure.
/// Z = P.get<double*>(); // compile time failure.
/// P = (float*)0;
/// Y = P.get<float*>(); // ok.
/// X = P.get<int*>(); // runtime assertion failure.
template <typename... PTs>
class PointerUnion
: public pointer_union_detail::PointerUnionMembers<
void *, pointer_union_detail::bitsRequired(sizeof...(PTs)), int,
0, PTs...> {
// The first type is special because we want to directly cast a pointer to a
// default-initialized union to a pointer to the first type. But we don't
// want PointerUnion to be a 'template <typename First, typename ...Rest>'
// because it's much more convenient to have a name for the whole pack. So
// split off the first type here.
using First = typename pointer_union_detail::GetFirstType<PTs...>::type;
using Base = typename PointerUnion::PointerUnionMembers;
PointerUnion() = default;
PointerUnion(std::nullptr_t) : PointerUnion() {}
using Base::Base;
/// Test if the pointer held in the union is null, regardless of
/// which type it is.
bool isNull() const { return !this->Val.getPointer(); }
explicit operator bool() const { return !isNull(); }
/// Test if the Union currently holds the type matching T.
template <typename T> int is() const {
constexpr int Index = pointer_union_detail::TypeIndex<T, PTs...>::Index;
static_assert(Index < sizeof...(PTs),
"PointerUnion::is<T> given type not in the union");
return this->Val.getInt() == Index;
/// Returns the value of the specified pointer type.
/// If the specified pointer type is incorrect, assert.
template <typename T> T get() const {
assert(is<T>() && "Invalid accessor called");
return PointerLikeTypeTraits<T>::getFromVoidPointer(this->Val.getPointer());
/// Returns the current pointer if it is of the specified pointer type,
/// otherwises returns null.
template <typename T> T dyn_cast() const {
if (is<T>())
return get<T>();
return T();
/// If the union is set to the first pointer type get an address pointing to
/// it.
First const *getAddrOfPtr1() const {
return const_cast<PointerUnion *>(this)->getAddrOfPtr1();
/// If the union is set to the first pointer type get an address pointing to
/// it.
First *getAddrOfPtr1() {
assert(is<First>() && "Val is not the first pointer");
PointerLikeTypeTraits<First>::getAsVoidPointer(get<First>()) ==
this->Val.getPointer() &&
"Can't get the address because PointerLikeTypeTraits changes the ptr");
return const_cast<First *>(
reinterpret_cast<const First *>(this->Val.getAddrOfPointer()));
/// Assignment from nullptr which just clears the union.
const PointerUnion &operator=(std::nullptr_t) {
return *this;
/// Assignment from elements of the union.
using Base::operator=;
void *getOpaqueValue() const { return this->Val.getOpaqueValue(); }
static inline PointerUnion getFromOpaqueValue(void *VP) {
PointerUnion V;
V.Val = decltype(V.Val)::getFromOpaqueValue(VP);
return V;
template <typename ...PTs>
bool operator==(PointerUnion<PTs...> lhs, PointerUnion<PTs...> rhs) {
return lhs.getOpaqueValue() == rhs.getOpaqueValue();
template <typename ...PTs>
bool operator!=(PointerUnion<PTs...> lhs, PointerUnion<PTs...> rhs) {
return lhs.getOpaqueValue() != rhs.getOpaqueValue();
template <typename ...PTs>
bool operator<(PointerUnion<PTs...> lhs, PointerUnion<PTs...> rhs) {
return lhs.getOpaqueValue() < rhs.getOpaqueValue();
// Teach SmallPtrSet that PointerUnion is "basically a pointer", that has
// # low bits available = min(PT1bits,PT2bits)-1.
template <typename ...PTs>
struct PointerLikeTypeTraits<PointerUnion<PTs...>> {
static inline void *getAsVoidPointer(const PointerUnion<PTs...> &P) {
return P.getOpaqueValue();
static inline PointerUnion<PTs...> getFromVoidPointer(void *P) {
return PointerUnion<PTs...>::getFromOpaqueValue(P);
// The number of bits available are the min of the pointer types minus the
// bits needed for the discriminator.
static constexpr int NumLowBitsAvailable = PointerLikeTypeTraits<decltype(
/// A pointer union of three pointer types. See documentation for PointerUnion
/// for usage.
template <typename PT1, typename PT2, typename PT3>
using PointerUnion3 = PointerUnion<PT1, PT2, PT3>;
/// A pointer union of four pointer types. See documentation for PointerUnion
/// for usage.
template <typename PT1, typename PT2, typename PT3, typename PT4>
using PointerUnion4 = PointerUnion<PT1, PT2, PT3, PT4>;
// Teach DenseMap how to use PointerUnions as keys.
template <typename ...PTs> struct DenseMapInfo<PointerUnion<PTs...>> {
using Union = PointerUnion<PTs...>;
using FirstInfo =
DenseMapInfo<typename pointer_union_detail::GetFirstType<PTs...>::type>;
static inline Union getEmptyKey() { return Union(FirstInfo::getEmptyKey()); }
static inline Union getTombstoneKey() {
return Union(FirstInfo::getTombstoneKey());
static unsigned getHashValue(const Union &UnionVal) {
intptr_t key = (intptr_t)UnionVal.getOpaqueValue();
return DenseMapInfo<intptr_t>::getHashValue(key);
static bool isEqual(const Union &LHS, const Union &RHS) {
return LHS == RHS;
} // end namespace llvm