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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 https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
///
/// \file
/// This file defines the PointerUnion class, which is a discriminated union of
/// pointer types.
///
//===----------------------------------------------------------------------===//
#ifndef LLVM_ADT_POINTERUNION_H
#define LLVM_ADT_POINTERUNION_H
#include "llvm/ADT/DenseMapInfo.h"
#include "llvm/ADT/PointerIntPair.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/PointerLikeTypeTraits.h"
#include <algorithm>
#include <cassert>
#include <cstddef>
#include <cstdint>
namespace llvm {
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 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 {
public:
static inline void *getAsVoidPointer(void *P) { return P; }
static inline void *getFromVoidPointer(void *P) { return P; }
static constexpr int NumLowBitsAvailable = lowBitsAvailable<PTs...>();
};
template <typename Derived, typename ValTy, int I, typename ...Types>
class PointerUnionMembers;
template <typename Derived, typename ValTy, int I>
class PointerUnionMembers<Derived, ValTy, I> {
protected:
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...>;
public:
using Base::Base;
PointerUnionMembers() = default;
PointerUnionMembers(Type V)
: Base(ValTy(const_cast<void *>(
PointerLikeTypeTraits<Type>::getAsVoidPointer(V)),
I)) {}
using Base::operator=;
Derived &operator=(Type V) {
this->Val = ValTy(
const_cast<void *>(PointerLikeTypeTraits<Type>::getAsVoidPointer(V)),
I);
return static_cast<Derived &>(*this);
};
};
}
// This is a forward declaration of CastInfoPointerUnionImpl
// Refer to its definition below for further details
template <typename... PTs> struct CastInfoPointerUnionImpl;
/// 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", P.is<int*>(), P.is<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.
/// PointerUnion<int*, int*> Q; // compile time failure.
template <typename... PTs>
class PointerUnion
: public pointer_union_detail::PointerUnionMembers<
PointerUnion<PTs...>,
PointerIntPair<
void *, pointer_union_detail::bitsRequired(sizeof...(PTs)), int,
pointer_union_detail::PointerUnionUIntTraits<PTs...>>,
0, PTs...> {
static_assert(TypesAreDistinct<PTs...>::value,
"PointerUnion alternative types cannot be repeated");
// 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 = TypeAtIndex<0, PTs...>;
using Base = typename PointerUnion::PointerUnionMembers;
/// This is needed to give the CastInfo implementation below access
/// to protected members.
/// Refer to its definition for further details.
friend struct CastInfoPointerUnionImpl<PTs...>;
public:
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(); }
// FIXME: Replace the uses of is(), get() and dyn_cast() with
// isa<T>, cast<T> and the llvm::dyn_cast<T>
/// Test if the Union currently holds the type matching T.
template <typename T> inline bool is() const { return isa<T>(*this); }
/// Returns the value of the specified pointer type.
///
/// If the specified pointer type is incorrect, assert.
template <typename T> inline T get() const {
assert(isa<T>(*this) && "Invalid accessor called");
return cast<T>(*this);
}
/// Returns the current pointer if it is of the specified pointer type,
/// otherwise returns null.
template <typename T> inline T dyn_cast() const {
return llvm::dyn_cast_if_present<T>(*this);
}
/// 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(isa<First>(*this) && "Val is not the first pointer");
assert(
PointerLikeTypeTraits<First>::getAsVoidPointer(cast<First>(*this)) ==
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) {
this->Val.initWithPointer(nullptr);
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();
}
/// We can't (at least, at this moment with C++14) declare CastInfo
/// as a friend of PointerUnion like this:
/// ```
/// template<typename To>
/// friend struct CastInfo<To, PointerUnion<PTs...>>;
/// ```
/// The compiler complains 'Partial specialization cannot be declared as a
/// friend'.
/// So we define this struct to be a bridge between CastInfo and
/// PointerUnion.
template <typename... PTs> struct CastInfoPointerUnionImpl {
using From = PointerUnion<PTs...>;
template <typename To> static inline bool isPossible(From &F) {
return F.Val.getInt() == FirstIndexOfType<To, PTs...>::value;
}
template <typename To> static To doCast(From &F) {
assert(isPossible<To>(F) && "cast to an incompatible type!");
return PointerLikeTypeTraits<To>::getFromVoidPointer(F.Val.getPointer());
}
};
// Specialization of CastInfo for PointerUnion
template <typename To, typename... PTs>
struct CastInfo<To, PointerUnion<PTs...>>
: public DefaultDoCastIfPossible<To, PointerUnion<PTs...>,
CastInfo<To, PointerUnion<PTs...>>> {
using From = PointerUnion<PTs...>;
using Impl = CastInfoPointerUnionImpl<PTs...>;
static inline bool isPossible(From &f) {
return Impl::template isPossible<To>(f);
}
static To doCast(From &f) { return Impl::template doCast<To>(f); }
static inline To castFailed() { return To(); }
};
template <typename To, typename... PTs>
struct CastInfo<To, const PointerUnion<PTs...>>
: public ConstStrippingForwardingCast<To, const PointerUnion<PTs...>,
CastInfo<To, PointerUnion<PTs...>>> {
};
// 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(
PointerUnion<PTs...>::Val)>::NumLowBitsAvailable;
};
// 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
#endif // LLVM_ADT_POINTERUNION_H
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