[llvm] [libc] [libc] Add more functions in CPP/bit.h (PR #73814)

[Guillaume Chatelet via llvm-commits]

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@@ -1,57 +1,261 @@
-//===-- Freestanding version of bit_cast  -----------------------*- C++ -*-===//
+//===-- Implementation of the C++20 bit header  -----------------*- 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 is inspired from LLVM ADT/bit.h header.
 
 #ifndef LLVM_LIBC_SRC___SUPPORT_CPP_BIT_H
 #define LLVM_LIBC_SRC___SUPPORT_CPP_BIT_H
 
+#include "src/__support/CPP/limits.h" // numeric_limits
 #include "src/__support/CPP/type_traits.h"
 #include "src/__support/macros/attributes.h"
 #include "src/__support/macros/config.h" // LIBC_HAS_BUILTIN
 #include "src/__support/macros/sanitizer.h"
 
-namespace LIBC_NAMESPACE::cpp {
+#include <stdint.h>
 
-#if LIBC_HAS_BUILTIN(__builtin_bit_cast)
-#define LLVM_LIBC_HAS_BUILTIN_BIT_CAST
-#endif
+namespace LIBC_NAMESPACE::cpp {
 
 #if LIBC_HAS_BUILTIN(__builtin_memcpy_inline)
 #define LLVM_LIBC_HAS_BUILTIN_MEMCPY_INLINE
 #endif
 
-// This function guarantees the bitcast to be optimized away by the compiler for
-// GCC >= 8 and Clang >= 6.
-template <class To, class From>
+// This implementation of bit_cast requires trivially-constructible To, to avoid
----------------
gchatelet wrote:

No, apart from this one that I fixed https://github.com/llvm/llvm-project/pull/73804.

https://github.com/llvm/llvm-project/pull/73814