1 files changed, 58 insertions, 0 deletions
diff --git a/third_party/llvm-project/include/llvm/ADT/bit.h b/third_party/llvm-project/include/llvm/ADT/bit.h
new file mode 100644
index 000000000..a790d5ed2
--- /dev/null
+++ b/third_party/llvm-project/include/llvm/ADT/bit.h
@@ -0,0 +1,58 @@
+//===-- llvm/ADT/bit.h - C++20 <bit> ----------------------------*- 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 implements the C++20 <bit> header.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ADT_BIT_H
+#define LLVM_ADT_BIT_H
+
+#include "llvm/Support/Compiler.h"
+#include <cstring>
+#include <type_traits>
+
+namespace llvm {
+
+// This implementation of bit_cast is different from the C++17 one in two ways:
+//  - It isn't constexpr because that requires compiler support.
+//  - It requires trivially-constructible To, to avoid UB in the implementation.
+template <typename To, typename From
+          , typename = typename std::enable_if<sizeof(To) == sizeof(From)>::type
+#if (__has_feature(is_trivially_constructible) && defined(_LIBCPP_VERSION)) || \
+    (defined(__GNUC__) && __GNUC__ >= 5)
+          , typename = typename std::is_trivially_constructible<To>::type
+#elif __has_feature(is_trivially_constructible)
+          , typename = typename std::enable_if<__is_trivially_constructible(To)>::type
+#else
+  // See comment below.
+#endif
+#if (__has_feature(is_trivially_copyable) && defined(_LIBCPP_VERSION)) || \
+    (defined(__GNUC__) && __GNUC__ >= 5)
+          , typename = typename std::enable_if<std::is_trivially_copyable<To>::value>::type
+          , typename = typename std::enable_if<std::is_trivially_copyable<From>::value>::type
+#elif __has_feature(is_trivially_copyable)
+          , typename = typename std::enable_if<__is_trivially_copyable(To)>::type
+          , typename = typename std::enable_if<__is_trivially_copyable(From)>::type
+#else
+// This case is GCC 4.x. clang with libc++ or libstdc++ never get here. Unlike
+// llvm/Support/type_traits.h's is_trivially_copyable we don't want to
+// provide a good-enough answer here: developers in that configuration will hit
+// compilation failures on the bots instead of locally. That's acceptable
+// because it's very few developers, and only until we move past C++11.
+#endif
+>
+inline To bit_cast(const From &from) noexcept {
+  To to;
+  std::memcpy(&to, &from, sizeof(To));
+  return to;
+}
+
+} // namespace llvm
+
+#endif