diff --git a/src/demangle/DemangleConfig.h b/src/demangle/DemangleConfig.h
index be3ea59..9d81853 100644
--- a/src/demangle/DemangleConfig.h
+++ b/src/demangle/DemangleConfig.h
@@ -1,17 +1,17 @@
-//===--- Compiler.h ---------------------------------------------*- C++ -*-===//
+//===--- DemangleConfig.h --------------------------------------*- 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 contains a subset of macros copied from
-// llvm/lib/Demangle/Compiler.h.
+// llvm/include/llvm/Demangle/DemangleConfig.h
 //===----------------------------------------------------------------------===//
 
-#ifndef LIBCXX_DEMANGLE_COMPILER_H
-#define LIBCXX_DEMANGLE_COMPILER_H
+#ifndef LIBCXXABI_DEMANGLE_DEMANGLE_CONFIG_H
+#define LIBCXXABI_DEMANGLE_DEMANGLE_CONFIG_H
 
-#include "__config"
+#include <ciso646>
 
 #ifdef _MSC_VER
 // snprintf is implemented in VS 2015
@@ -20,22 +20,78 @@
 #endif
 #endif
 
+#ifndef __has_feature
+#define __has_feature(x) 0
+#endif
+
+#ifndef __has_cpp_attribute
+#define __has_cpp_attribute(x) 0
+#endif
+
 #ifndef __has_attribute
 #define __has_attribute(x) 0
 #endif
 
-#ifndef NDEBUG
-#if __has_attribute(noinline) && __has_attribute(used)
-#define DEMANGLE_DUMP_METHOD __attribute__((noinline, used))
+#ifndef __has_builtin
+#define __has_builtin(x) 0
+#endif
+
+#ifndef DEMANGLE_GNUC_PREREQ
+#if defined(__GNUC__) && defined(__GNUC_MINOR__) && defined(__GNUC_PATCHLEVEL__)
+#define DEMANGLE_GNUC_PREREQ(maj, min, patch)                           \
+  ((__GNUC__ << 20) + (__GNUC_MINOR__ << 10) + __GNUC_PATCHLEVEL__ >=          \
+   ((maj) << 20) + ((min) << 10) + (patch))
+#elif defined(__GNUC__) && defined(__GNUC_MINOR__)
+#define DEMANGLE_GNUC_PREREQ(maj, min, patch)                           \
+  ((__GNUC__ << 20) + (__GNUC_MINOR__ << 10) >= ((maj) << 20) + ((min) << 10))
 #else
-#define DEMANGLE_DUMP_METHOD
+#define DEMANGLE_GNUC_PREREQ(maj, min, patch) 0
 #endif
 #endif
 
-#define DEMANGLE_FALLTHROUGH _LIBCPP_FALLTHROUGH()
-#define DEMANGLE_UNREACHABLE _LIBCPP_UNREACHABLE()
+#if __has_attribute(used) || DEMANGLE_GNUC_PREREQ(3, 1, 0)
+#define DEMANGLE_ATTRIBUTE_USED __attribute__((__used__))
+#else
+#define DEMANGLE_ATTRIBUTE_USED
+#endif
+
+#if __has_builtin(__builtin_unreachable) || DEMANGLE_GNUC_PREREQ(4, 5, 0)
+#define DEMANGLE_UNREACHABLE __builtin_unreachable()
+#elif defined(_MSC_VER)
+#define DEMANGLE_UNREACHABLE __assume(false)
+#else
+#define DEMANGLE_UNREACHABLE
+#endif
+
+#if __has_attribute(noinline) || DEMANGLE_GNUC_PREREQ(3, 4, 0)
+#define DEMANGLE_ATTRIBUTE_NOINLINE __attribute__((noinline))
+#elif defined(_MSC_VER)
+#define DEMANGLE_ATTRIBUTE_NOINLINE __declspec(noinline)
+#else
+#define DEMANGLE_ATTRIBUTE_NOINLINE
+#endif
+
+#if !defined(NDEBUG)
+#define DEMANGLE_DUMP_METHOD DEMANGLE_ATTRIBUTE_NOINLINE DEMANGLE_ATTRIBUTE_USED
+#else
+#define DEMANGLE_DUMP_METHOD DEMANGLE_ATTRIBUTE_NOINLINE
+#endif
+
+#if __cplusplus > 201402L && __has_cpp_attribute(fallthrough)
+#define DEMANGLE_FALLTHROUGH [[fallthrough]]
+#elif __has_cpp_attribute(gnu::fallthrough)
+#define DEMANGLE_FALLTHROUGH [[gnu::fallthrough]]
+#elif !__cplusplus
+// Workaround for llvm.org/PR23435, since clang 3.6 and below emit a spurious
+// error when __has_cpp_attribute is given a scoped attribute in C mode.
+#define DEMANGLE_FALLTHROUGH
+#elif __has_cpp_attribute(clang::fallthrough)
+#define DEMANGLE_FALLTHROUGH [[clang::fallthrough]]
+#else
+#define DEMANGLE_FALLTHROUGH
+#endif
 
 #define DEMANGLE_NAMESPACE_BEGIN namespace { namespace itanium_demangle {
 #define DEMANGLE_NAMESPACE_END } }
 
-#endif
+#endif // LIBCXXABI_DEMANGLE_DEMANGLE_CONFIG_H