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