[ADT] Add an abstraction for embedding an integer within a pointer-like

[oota-llvm.git] / include / llvm / ADT / PointerEmbeddedInt.h

diff --git a/include/llvm/ADT/PointerEmbeddedInt.h b/include/llvm/ADT/PointerEmbeddedInt.h
new file mode 100644 (file)
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+++ b/include/llvm/ADT/PointerEmbeddedInt.h
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+//===- llvm/ADT/PointerEmbeddedInt.h ----------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ADT_POINTEREMBEDDEDINT_H
+#define LLVM_ADT_POINTEREMBEDDEDINT_H
+
+#include "llvm/ADT/DenseMapInfo.h"
+#include "llvm/Support/PointerLikeTypeTraits.h"
+#include <climits>
+
+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;
+
+  static_assert(Bits < sizeof(Value) * 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(Value) * CHAR_BIT - Bits,
+
+    // We also want to be able to mask out the preserved bits for asserts.
+    Mask = static_cast<uintptr_t>(-1) << Bits
+  };
+
+  friend class PointerLikeTypeTraits<PointerEmbeddedInt>;
+
+  explicit PointerEmbeddedInt(uintptr_t Value) : Value(Value) {}
+
+public:
+  PointerEmbeddedInt() : Value(0) {}
+
+  PointerEmbeddedInt(IntT I) : Value(static_cast<uintptr_t>(I) << Shift) {
+    assert((I & Mask) == 0 && "Integer has bits outside those preserved!");
+  }
+
+  PointerEmbeddedInt &operator=(IntT I) {
+    assert((I & Mask) == 0 && "Integer has bits outside those preserved!");
+    Value = static_cast<uintptr_t>(I) << Shift;
+  }
+
+  // Note that this imilict conversion additionally allows all of the basic
+  // comparison operators to work transparently, etc.
+  operator IntT() const { return static_cast<IntT>(Value >> Shift); }
+};
+
+// Provide pointer like traits to support use with pointer unions and sum
+// types.
+template <typename IntT, int Bits>
+class PointerLikeTypeTraits<PointerEmbeddedInt<IntT, Bits>> {
+  typedef PointerEmbeddedInt<IntT, Bits> T;
+
+public:
+  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));
+  }
+  static inline T getFromVoidPointer(const void *P) {
+    return T(reinterpret_cast<uintptr_t>(P));
+  }
+
+  enum { 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>> {
+  typedef PointerEmbeddedInt<IntT, Bits> T;
+
+  typedef DenseMapInfo<IntT> IntInfo;
+
+  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; }
+};
+}
+
+#endif