[ORC-RT] Add bitmask-enum and bit_ceil utilities to the ORC runtime.

bitmask_enum.h is essentially a copy of llvm/ADT/BitmaskEnum.h, with some minor
cleanup and renaming.

The bit_ceil function is a placeholder for std::bit_ceil, which we can use once
compiler-rt can use c++20.

These utilities will be used to simplify bitfield enum usage in upcoming
ORC-RT patches.

compiler-rt/lib/orc/bitmask_enum.h

@@ -0,0 +1,151 @@
+//===---- bitmask_enum.h - Enable bitmask operations on enums ---*- 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
+//
+//===----------------------------------------------------------------------===//
+//
+// This file is a part of the ORC runtime support library.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef ORC_RT_BITMASK_ENUM_H
+#define ORC_RT_BITMASK_ENUM_H
+
+#include "stl_extras.h"
+
+#include <cassert>
+#include <type_traits>
+
+namespace __orc_rt {
+
+/// ORC_RT_MARK_AS_BITMASK_ENUM lets you opt in an individual enum type so you
+/// can perform bitwise operations on it without putting static_cast everywhere.
+///
+/// \code
+///   enum MyEnum {
+///     E1 = 1, E2 = 2, E3 = 4, E4 = 8,
+///     ORC_RT_MARK_AS_BITMASK_ENUM(/* LargestValue = */ E4)
+///   };
+///
+///   void Foo() {
+///     MyEnum A = (E1 | E2) & E3 ^ ~E4; // Look, ma: No static_cast!
+///   }
+/// \endcode
+///
+/// Normally when you do a bitwise operation on an enum value, you get back an
+/// instance of the underlying type (e.g. int).  But using this macro, bitwise
+/// ops on your enum will return you back instances of the enum.  This is
+/// particularly useful for enums which represent a combination of flags.
+///
+/// The parameter to ORC_RT_MARK_AS_BITMASK_ENUM should be the largest
+/// individual value in your enum.
+///
+/// All of the enum's values must be non-negative.
+#define ORC_RT_MARK_AS_BITMASK_ENUM(LargestValue)                              \
+  ORC_RT_BITMASK_LARGEST_ENUMERATOR = LargestValue
+
+/// ORC_RT_DECLARE_ENUM_AS_BITMASK can be used to declare an enum type as a bit
+/// set, so that bitwise operation on such enum does not require static_cast.
+///
+/// \code
+///   enum MyEnum { E1 = 1, E2 = 2, E3 = 4, E4 = 8 };
+///   ORC_RT_DECLARE_ENUM_AS_BITMASK(MyEnum, E4);
+///
+///   void Foo() {
+///     MyEnum A = (E1 | E2) & E3 ^ ~E4; // No static_cast
+///   }
+/// \endcode
+///
+/// The second parameter to ORC_RT_DECLARE_ENUM_AS_BITMASK specifies the largest
+/// bit value of the enum type.
+///
+/// ORC_RT_DECLARE_ENUM_AS_BITMASK should be used in __orc_rt namespace.
+///
+/// This a non-intrusive alternative for ORC_RT_MARK_AS_BITMASK_ENUM. It allows
+/// declaring more than one non-scoped enumerations as bitmask types in the same
+/// scope. Otherwise it provides the same functionality as
+/// ORC_RT_MARK_AS_BITMASK_ENUM.
+#define ORC_RT_DECLARE_ENUM_AS_BITMASK(Enum, LargestValue)                     \
+  template <> struct is_bitmask_enum<Enum> : std::true_type {};                \
+  template <> struct largest_bitmask_enum_bit<Enum> {                          \
+    static constexpr std::underlying_type_t<Enum> value = LargestValue;        \
+  }
+
+/// Traits class to determine whether an enum has been declared as a bitwise
+/// enum via ORC_RT_DECLARE_ENUM_AS_BITMASK.
+template <typename E, typename Enable = void>
+struct is_bitmask_enum : std::false_type {};
+
+template <typename E>
+struct is_bitmask_enum<
+    E, std::enable_if_t<sizeof(E::ORC_RT_BITMASK_LARGEST_ENUMERATOR) >= 0>>
+    : std::true_type {};
+
+template <typename E>
+inline constexpr bool is_bitmask_enum_v = is_bitmask_enum<E>::value;
+
+/// Traits class to deermine bitmask enum largest bit.
+template <typename E, typename Enable = void> struct largest_bitmask_enum_bit;
+
+template <typename E>
+struct largest_bitmask_enum_bit<
+    E, std::enable_if_t<sizeof(E::ORC_RT_BITMASK_LARGEST_ENUMERATOR) >= 0>> {
+  using UnderlyingTy = std::underlying_type_t<E>;
+  static constexpr UnderlyingTy value =
+      static_cast<UnderlyingTy>(E::ORC_RT_BITMASK_LARGEST_ENUMERATOR);
+};
+
+template <typename E> constexpr std::underlying_type_t<E> Mask() {
+  return bit_ceil(largest_bitmask_enum_bit<E>::value) - 1;
+}
+
+template <typename E> constexpr std::underlying_type_t<E> Underlying(E Val) {
+  auto U = static_cast<std::underlying_type_t<E>>(Val);
+  assert(U >= 0 && "Negative enum values are not allowed");
+  assert(U <= Mask<E>() && "Enum value too large (or langest val too small");
+  return U;
+}
+
+template <typename E, typename = std::enable_if_t<is_bitmask_enum_v<E>>>
+constexpr E operator~(E Val) {
+  return static_cast<E>(~Underlying(Val) & Mask<E>());
+}
+
+template <typename E, typename = std::enable_if_t<is_bitmask_enum_v<E>>>
+constexpr E operator|(E LHS, E RHS) {
+  return static_cast<E>(Underlying(LHS) | Underlying(RHS));
+}
+
+template <typename E, typename = std::enable_if_t<is_bitmask_enum_v<E>>>
+constexpr E operator&(E LHS, E RHS) {
+  return static_cast<E>(Underlying(LHS) & Underlying(RHS));
+}
+
+template <typename E, typename = std::enable_if_t<is_bitmask_enum_v<E>>>
+constexpr E operator^(E LHS, E RHS) {
+  return static_cast<E>(Underlying(LHS) ^ Underlying(RHS));
+}
+
+template <typename E, typename = std::enable_if_t<is_bitmask_enum_v<E>>>
+E &operator|=(E &LHS, E RHS) {
+  LHS = LHS | RHS;
+  return LHS;
+}
+
+template <typename E, typename = std::enable_if_t<is_bitmask_enum_v<E>>>
+E &operator&=(E &LHS, E RHS) {
+  LHS = LHS & RHS;
+  return LHS;
+}
+
+template <typename E, typename = std::enable_if_t<is_bitmask_enum_v<E>>>
+E &operator^=(E &LHS, E RHS) {
+  LHS = LHS ^ RHS;
+  return LHS;
+}
+
+} // end namespace __orc_rt
+
+#endif // ORC_RT_BITMASK_ENUM_H

compiler-rt/lib/orc/stl_extras.h

@@ -28,6 +28,17 @@ template <class Ty> struct identity {
   const Ty &operator()(const Ty &self) const { return self; }
 };
 
+/// Substitute for std::bit_ceil.
+constexpr uint64_t bit_ceil(uint64_t Val) noexcept {
+  Val |= (Val >> 1);
+  Val |= (Val >> 2);
+  Val |= (Val >> 4);
+  Val |= (Val >> 8);
+  Val |= (Val >> 16);
+  Val |= (Val >> 32);
+  return Val + 1;
+}
+
 } // namespace __orc_rt
 
 #endif // ORC_RT_STL_EXTRAS

compiler-rt/lib/orc/tests/unit/CMakeLists.txt

@@ -1,5 +1,6 @@
 set(UNITTEST_SOURCES
   adt_test.cpp
+  bitmask_enum_test.cpp
   c_api_test.cpp
   endian_test.cpp
   error_test.cpp

compiler-rt/lib/orc/tests/unit/bitmask_enum_test.cpp

@@ -0,0 +1,143 @@
+//===-- adt_test.cpp ------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// This file is a part of the ORC runtime.
+//
+//===----------------------------------------------------------------------===//
+
+#include "bitmask_enum.h"
+#include "gtest/gtest.h"
+
+#include <sstream>
+#include <string>
+
+using namespace __orc_rt;
+
+namespace {
+
+enum Flags { F0 = 0, F1 = 1, F2 = 2, F3 = 4, F4 = 8 };
+
+} // namespace
+
+namespace __orc_rt {
+ORC_RT_DECLARE_ENUM_AS_BITMASK(Flags, F4);
+} // namespace __orc_rt
+
+static_assert(is_bitmask_enum<Flags>::value != 0);
+static_assert(largest_bitmask_enum_bit<Flags>::value == Flags::F4);
+
+namespace {
+
+static_assert(is_bitmask_enum<Flags>::value != 0);
+static_assert(largest_bitmask_enum_bit<Flags>::value == Flags::F4);
+
+TEST(BitmaskEnumTest, BitwiseOr) {
+  Flags f = F1 | F2;
+  EXPECT_EQ(3, f);
+
+  f = f | F3;
+  EXPECT_EQ(7, f);
+}
+
+TEST(BitmaskEnumTest, BitwiseOrEquals) {
+  Flags f = F1;
+  f |= F3;
+  EXPECT_EQ(5, f);
+
+  // |= should return a reference to the LHS.
+  f = F2;
+  (f |= F3) = F1;
+  EXPECT_EQ(F1, f);
+}
+
+TEST(BitmaskEnumTest, BitwiseAnd) {
+  Flags f = static_cast<Flags>(3) & F2;
+  EXPECT_EQ(F2, f);
+
+  f = (f | F3) & (F1 | F2 | F3);
+  EXPECT_EQ(6, f);
+}
+
+TEST(BitmaskEnumTest, BitwiseAndEquals) {
+  Flags f = F1 | F2 | F3;
+  f &= F1 | F2;
+  EXPECT_EQ(3, f);
+
+  // &= should return a reference to the LHS.
+  (f &= F1) = F3;
+  EXPECT_EQ(F3, f);
+}
+
+TEST(BitmaskEnumTest, BitwiseXor) {
+  Flags f = (F1 | F2) ^ (F2 | F3);
+  EXPECT_EQ(5, f);
+
+  f = f ^ F1;
+  EXPECT_EQ(4, f);
+}
+
+TEST(BitmaskEnumTest, BitwiseXorEquals) {
+  Flags f = (F1 | F2);
+  f ^= (F2 | F4);
+  EXPECT_EQ(9, f);
+
+  // ^= should return a reference to the LHS.
+  (f ^= F4) = F3;
+  EXPECT_EQ(F3, f);
+}
+
+TEST(BitmaskEnumTest, ConstantExpression) {
+  constexpr Flags f1 = ~F1;
+  constexpr Flags f2 = F1 | F2;
+  constexpr Flags f3 = F1 & F2;
+  constexpr Flags f4 = F1 ^ F2;
+  EXPECT_EQ(f1, ~F1);
+  EXPECT_EQ(f2, F1 | F2);
+  EXPECT_EQ(f3, F1 & F2);
+  EXPECT_EQ(f4, F1 ^ F2);
+}
+
+TEST(BitmaskEnumTest, BitwiseNot) {
+  Flags f = ~F1;
+  EXPECT_EQ(14, f); // Largest value for f is 15.
+  EXPECT_EQ(15, ~F0);
+}
+
+enum class FlagsClass {
+  F0 = 0,
+  F1 = 1,
+  F2 = 2,
+  F3 = 4,
+  ORC_RT_MARK_AS_BITMASK_ENUM(F3)
+};
+
+TEST(BitmaskEnumTest, ScopedEnum) {
+  FlagsClass f = (FlagsClass::F1 & ~FlagsClass::F0) | FlagsClass::F2;
+  f |= FlagsClass::F3;
+  EXPECT_EQ(7, static_cast<int>(f));
+}
+
+struct Container {
+  enum Flags {
+    F0 = 0,
+    F1 = 1,
+    F2 = 2,
+    F3 = 4,
+    ORC_RT_MARK_AS_BITMASK_ENUM(F3)
+  };
+
+  static Flags getFlags() {
+    Flags f = F0 | F1;
+    f |= F2;
+    return f;
+  }
+};
+
+TEST(BitmaskEnumTest, EnumInStruct) { EXPECT_EQ(3, Container::getFlags()); }
+
+} // namespace