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//===- llvm/ADT/PointerUnion.h - Discriminated Union of 2 Ptrs --*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// 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/PointerIntPair.h"
namespace llvm {
/// getPointerUnionTypeNum - If the argument has type PT1* or PT2* return
/// false or true respectively.
template <typename PT1, typename PT2>
static inline bool getPointerUnionTypeNum(PT1 *P) { return false; }
template <typename PT1, typename PT2>
static inline bool getPointerUnionTypeNum(PT2 *P) { return true; }
// Enable, if we could use static_assert.
//template <typename PT1, typename PT2>
//static inline bool getPointerUnionTypeNum(...) { abort() }
/// Provide PointerLikeTypeTraits for void* that is used by PointerUnion
/// for the two template arguments.
template <typename PT1, typename PT2>
class PointerUnionUIntTraits {
public:
static inline void *getAsVoidPointer(void *P) { return P; }
static inline void *getFromVoidPointer(void *P) { return P; }
enum {
PT1BitsAv = PointerLikeTypeTraits<PT1>::NumLowBitsAvailable,
PT2BitsAv = PointerLikeTypeTraits<PT2>::NumLowBitsAvailable,
NumLowBitsAvailable = PT1BitsAv < PT2BitsAv ? PT1BitsAv : PT2BitsAv
};
};
/// PointerUnion - This implements a discriminated union of two pointer types,
/// and keeps the discriminator bit-mangled into the low bits of the pointer.
/// This allows the implementation to be extremely efficient in space, but
/// permits a very 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*>(); // does not compile.
/// P = (float*)0;
/// Y = P.get<float*>(); // ok.
/// X = P.get<int*>(); // runtime assertion failure.
template <typename PT1, typename PT2>
class PointerUnion {
public:
typedef PointerIntPair<void*, 1, bool,
PointerUnionUIntTraits<PT1,PT2> > ValTy;
private:
ValTy Val;
public:
PointerUnion() {}
PointerUnion(PT1 V) {
Val.setPointer(V);
Val.setInt(0);
}
PointerUnion(PT2 V) {
Val.setPointer(V);
Val.setInt(1);
}
/// isNull - Return true if the pointer help in the union is null,
/// regardless of which type it is.
bool isNull() const { return Val.getPointer() == 0; }
/// is<T>() return true if the Union currently holds the type matching T.
template<typename T>
int is() const {
return Val.getInt() == ::llvm::getPointerUnionTypeNum<PT1, PT2>((T*)0);
}
/// get<T>() - Return 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 static_cast<T>(Val.getPointer());
}
/// dyn_cast<T>() - If the current value is of the specified pointer type,
/// return it, otherwise return null.
template<typename T>
T dyn_cast() const {
if (is<T>()) return static_cast<T>(Val.getPointer());
return T();
}
/// Assignment operators - Allow assigning into this union from either
/// pointer type, setting the discriminator to remember what it came from.
const PointerUnion &operator=(const PT1 &RHS) {
Val.setPointer(RHS);
Val.setInt(0);
return *this;
}
const PointerUnion &operator=(const PT2 &RHS) {
Val.setPointer(RHS);
Val.setInt(1);
return *this;
}
void *getOpaqueValue() const { return Val.getOpaqueValue(); }
static PointerUnion getFromOpaqueValue(void *VP) {
PointerUnion V;
V.Val = ValTy::getFromOpaqueValue(VP);
return V;
}
};
// Teach SmallPtrSet that PointerIntPair is "basically a pointer", that has
// # low bits available = min(PT1bits,PT2bits)-1.
template<typename PT1, typename PT2>
class PointerLikeTypeTraits<PointerUnion<PT1, PT2> > {
public:
static inline void *
getAsVoidPointer(const PointerUnion<PT1, PT2> &P) {
return P.getOpaqueValue();
}
static inline PointerUnion<PT1, PT2>
getFromVoidPointer(void *P) {
return PointerUnion<PT1, PT2>::getFromOpaqueValue(P);
}
// The number of bits available are the min of the two pointer types.
enum {
NumLowBitsAvailable =
PointerUnion<PT1,PT2>::ValTy::NumLowBitsAvailable
};
};
}
#endif
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