[wpiutil] Upgrade to LLVM 16.0.6 (#5435)

Fixes #5332.

wpiutil/src/main/native/thirdparty/llvm/include/wpi/bit.h

@@ -0,0 +1,99 @@
+//===-- 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
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// This file implements the C++20 <bit> header.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef WPIUTIL_WPI_BIT_H
+#define WPIUTIL_WPI_BIT_H
+
+#include "wpi/Compiler.h"
+#include <cstdint>
+#include <limits>
+#include <type_traits>
+
+#if !__has_builtin(__builtin_bit_cast)
+#include <cstring>
+#endif
+
+#if defined(_MSC_VER) && !defined(_DEBUG)
+#include <cstdlib>  // for _byteswap_{ushort,ulong,uint64}
+#endif
+
+namespace wpi {
+
+// This implementation of bit_cast is different from the C++20 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 = std::enable_if_t<sizeof(To) == sizeof(From)>,
+    typename = std::enable_if_t<std::is_trivially_constructible<To>::value>,
+    typename = std::enable_if_t<std::is_trivially_copyable<To>::value>,
+    typename = std::enable_if_t<std::is_trivially_copyable<From>::value>>
+[[nodiscard]] inline To bit_cast(const From &from) noexcept {
+#if __has_builtin(__builtin_bit_cast)
+  return __builtin_bit_cast(To, from);
+#else
+  To to;
+  std::memcpy(&to, &from, sizeof(To));
+  return to;
+#endif
+}
+
+/// Reverses the bytes in the given integer value V.
+template <typename T, typename = std::enable_if_t<std::is_integral_v<T>>>
+[[nodiscard]] constexpr T byteswap(T V) noexcept {
+  if constexpr (sizeof(T) == 1) {
+    return V;
+  } else if constexpr (sizeof(T) == 2) {
+    uint16_t UV = V;
+#if defined(_MSC_VER) && !defined(_DEBUG)
+    // The DLL version of the runtime lacks these functions (bug!?), but in a
+    // release build they're replaced with BSWAP instructions anyway.
+    return _byteswap_ushort(UV);
+#else
+    uint16_t Hi = UV << 8;
+    uint16_t Lo = UV >> 8;
+    return Hi | Lo;
+#endif
+  } else if constexpr (sizeof(T) == 4) {
+    uint32_t UV = V;
+#if __has_builtin(__builtin_bswap32)
+    return __builtin_bswap32(UV);
+#elif defined(_MSC_VER) && !defined(_DEBUG)
+    return _byteswap_ulong(UV);
+#else
+    uint32_t Byte0 = UV & 0x000000FF;
+    uint32_t Byte1 = UV & 0x0000FF00;
+    uint32_t Byte2 = UV & 0x00FF0000;
+    uint32_t Byte3 = UV & 0xFF000000;
+    return (Byte0 << 24) | (Byte1 << 8) | (Byte2 >> 8) | (Byte3 >> 24);
+#endif
+  } else if constexpr (sizeof(T) == 8) {
+    uint64_t UV = V;
+#if __has_builtin(__builtin_bswap64)
+    return __builtin_bswap64(UV);
+#elif defined(_MSC_VER) && !defined(_DEBUG)
+    return _byteswap_uint64(UV);
+#else
+    uint64_t Hi = wpi::byteswap<uint32_t>(UV);
+    uint32_t Lo = wpi::byteswap<uint32_t>(UV >> 32);
+    return (Hi << 32) | Lo;
+#endif
+  } else {
+    static_assert(!sizeof(T *), "Don't know how to handle the given type.");
+    return 0;
+  }
+}
+
+} // namespace wpi
+
+#endif