[libc++] Simplify a few macros in __config

[ldionne]

Summary

Several macros were guarded with a check along the lines of:

#ifndef MACRO
#  define MACRO ...
#endif

However, some of these macros are never intended to be defined by users,
so it's pointless to make this check (i.e. the first #ifndef is always
true). This commit removes those checks.

The motivation for doing this cleanup is to remove the impression that
arbitrary configurations macros can be defined by users when including
libc++ headers, which doesn't work reliably and leads to macro spaghetti.
If one needs to be able to override a knob in the config, that's fine,
but the proper way to do that is to document the macro as being a public
facing knob in the documentation, and most likely to migrate that macro
to config_site (depending on the nature of the macro).

[ldionne]

libcxx/include/__config

493

@vitalybuka Just pinging you in case you can think of someone that might be broken by this (i.e. they would have to manually define _LIBCPP_HAS_NO_ASAN on a compiler that pretends that __has_feature(address_sanitizer) is true).

810

@EricWF In case you know someone that defines _LIBCPP_PREFERRED_OVERLOAD to something else manually?

1300

This looks like a bug to me, but I'm not sure who added those thread safety annotations or when they are used. @phosek I have a feeling I've seen you touch those at some point?

[• Quuxplusone]

libcxx/include/__config

545–547

I would strongly (but unfortunately with low authority-to-override-Louis) prefer to keep most or all of these #ifs. These #ifs seem to make it much easier to check the codegen with and without a certain feature, e.g. to compare

g++ -D_LIBCPP_HAS_NO_ASAN test.cpp -S
g++ -U_LIBCPP_HAS_NO_ASAN test.cpp -S
g++ -D_LIBCPP_NODEBUG_TYPE= test.cpp -S
g++ -D_LIBCPP_NODEBUG_TYPE='[[clang::nodebug]]' test.cpp -S

on Godbolt or something, instead of having to manually edit and rebuild the libc++ headers locally.

(I've used this same pattern for my p1144 _LIBCPP_TRIVIALLY_RELOCATABLE macro, so that you can use Godbolt to compare the codegen with -D_LIBCPP_TRIVIALLY_RELOCATABLE=[[trivially_relocatable]] against the codegen with -D_LIBCPP_TRIVIALLY_RELOCATABLE=.)
https://p1144.godbolt.org/z/h4Torssz4

[phosek]

libcxx/include/__config

1300

I added some thread annotations but this predates me, I agree that this looks like a bug.

[• Quuxplusone]

libcxx/include/__config

1300

I'll bite: In what way does this look like a bug? Am I missing something? It looks like it's just saying "If _LIBCPP_HAS_THREAD_SAFETY_ANNOTATIONS is defined from line 1294 above (or from the user), then make _LIBCPP_THREAD_SAFETY_ANNOTATION(x) do something (if the user hasn't already made it do something else); otherwise make it do nothing." That sounds to me like a reasonable bit of code.

[ldionne]

libcxx/include/__config

545–547

While I acknowledge that it makes that specific use case harder to do, I think the benefits of clarity and ease of long term evolution (since we know nobody's trying to define these macros in the wild) gives us more bang for the buck.

1300

I must agree with Arthur here - I'm not seeing anymore what I thought was a bug.

libcxx/include/__config

 #if !(__has_feature(cxx_variable_templates))
 #define _LIBCPP_HAS_NO_VARIABLE_TEMPLATES
 #endif
 
 #if !(__has_feature(cxx_noexcept))
 #define _LIBCPP_HAS_NO_NOEXCEPT
 #endif
 
-#if !defined(_LIBCPP_HAS_NO_ASAN) && !__has_feature(address_sanitizer)
+#if !__has_feature(address_sanitizer)
 #define _LIBCPP_HAS_NO_ASAN
 #endif
 
 // Allow for build-time disabling of unsigned integer sanitization
-#if !defined(_LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK) && __has_attribute(no_sanitize)
+#if __has_attribute(no_sanitize)
 #define _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK __attribute__((__no_sanitize__("unsigned-integer-overflow")))
 #endif
 
 #if __has_builtin(__builtin_launder)
 #define _LIBCPP_COMPILER_HAS_BUILTIN_LAUNDER
 #endif
 
 #if __has_builtin(__builtin_constant_p)

 #define _LIBCPP_HAS_NO_CXX14_CONSTEXPR
 #endif
 
 // GCC 5 supports variable templates
 #if !defined(__cpp_variable_templates) || __cpp_variable_templates < 201304L
 #define _LIBCPP_HAS_NO_VARIABLE_TEMPLATES
 #endif
 
-#if !defined(_LIBCPP_HAS_NO_ASAN) && !defined(__SANITIZE_ADDRESS__)
+#if !defined(__SANITIZE_ADDRESS__)
 #define _LIBCPP_HAS_NO_ASAN
 #endif
 
 #if _GNUC_VER >= 700
 #define _LIBCPP_COMPILER_HAS_BUILTIN_LAUNDER
 #define _LIBCPP_COMPILER_HAS_BUILTIN_CONSTANT_P
 #define _LIBCPP_HAS_UNIQUE_OBJECT_REPRESENTATIONS
 #endif
 
 #define _LIBCPP_ALWAYS_INLINE __attribute__ ((__always_inline__))
#define _LIBCPP_BEGIN_NAMESPACE_FILESYSTEM \
   _LIBCPP_BEGIN_NAMESPACE_STD namespace __fs { namespace filesystem {
 #endif
 
 #define _LIBCPP_END_NAMESPACE_FILESYSTEM \
   _LIBCPP_END_NAMESPACE_STD } }
 
 #define _VSTD_FS _VSTD::__fs::filesystem
 
-#ifndef _LIBCPP_PREFERRED_OVERLOAD
-#  if __has_attribute(__enable_if__)
-#    define _LIBCPP_PREFERRED_OVERLOAD __attribute__ ((__enable_if__(true, "")))
-#  endif
-#endif
+#if __has_attribute(__enable_if__)
+#   define _LIBCPP_PREFERRED_OVERLOAD __attribute__ ((__enable_if__(true, "")))
+#endif
 
 #ifndef _LIBCPP_HAS_NO_NOEXCEPT
 #  define _NOEXCEPT noexcept
 #  define _NOEXCEPT_(x) noexcept(x)
 #else
 #  define _NOEXCEPT throw()
 #  define _NOEXCEPT_(x)
 #endif

 // need to be used, because code correctness depends on it (several instances
 // in the <locale>). Those special declarations are declared with
 // _LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE, which is enabled even
 // when the debug mode is enabled.
 #ifndef _LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE
 # define _LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(...) extern template __VA_ARGS__;
 #endif
 
-#ifndef _LIBCPP_EXTERN_TEMPLATE_DEFINE
 #define _LIBCPP_EXTERN_TEMPLATE_DEFINE(...) template __VA_ARGS__;
-#endif
 
 #if defined(__APPLE__) || defined(__FreeBSD__) || defined(_LIBCPP_MSVCRT_LIKE) || \
     defined(__sun__) || defined(__NetBSD__) || defined(__CloudABI__)
 #define _LIBCPP_LOCALE__L_EXTENSIONS 1
 #endif
 
 #ifdef __FreeBSD__
 #define _DECLARE_C99_LDBL_MATH 1

 
 #if defined(__APPLE__)
 #  if !defined(__MAC_OS_X_VERSION_MIN_REQUIRED) && \
       defined(__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__)
 #    define __MAC_OS_X_VERSION_MIN_REQUIRED __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__
 #  endif
 #endif // defined(__APPLE__)
 
-#if !defined(_LIBCPP_HAS_NO_ALIGNED_ALLOCATION) && \
-    (defined(_LIBCPP_HAS_NO_LIBRARY_ALIGNED_ALLOCATION) || \
-    (!defined(__cpp_aligned_new) || __cpp_aligned_new < 201606))
+#if defined(_LIBCPP_HAS_NO_LIBRARY_ALIGNED_ALLOCATION) || \
+    (!defined(__cpp_aligned_new) || __cpp_aligned_new < 201606)
 #  define _LIBCPP_HAS_NO_ALIGNED_ALLOCATION
 #endif
 
 #if defined(__APPLE__) || defined(__FreeBSD__)
 #define _LIBCPP_HAS_DEFAULTRUNELOCALE
 #endif
 
 #if defined(__APPLE__) || defined(__FreeBSD__) || defined(__sun__)

 
 #if !defined(_LIBCPP_HAS_NO_CHAR8_T)
 #  define _LIBCPP_DEPRECATED_WITH_CHAR8_T _LIBCPP_DEPRECATED
 #else
 #  define _LIBCPP_DEPRECATED_WITH_CHAR8_T
 #endif
 
 // Macros to enter and leave a state where deprecation warnings are suppressed.
-#if !defined(_LIBCPP_SUPPRESS_DEPRECATED_PUSH) &&                              \
-    (defined(_LIBCPP_COMPILER_CLANG_BASED) || defined(_LIBCPP_COMPILER_GCC))
-#  define _LIBCPP_SUPPRESS_DEPRECATED_PUSH \
+#if defined(_LIBCPP_COMPILER_CLANG_BASED) || defined(_LIBCPP_COMPILER_GCC)
+#   define _LIBCPP_SUPPRESS_DEPRECATED_PUSH \
         _Pragma("GCC diagnostic push") \
         _Pragma("GCC diagnostic ignored \"-Wdeprecated\"")
-#  define _LIBCPP_SUPPRESS_DEPRECATED_POP \
+#   define _LIBCPP_SUPPRESS_DEPRECATED_POP \
         _Pragma("GCC diagnostic pop")
-#endif
-#if !defined(_LIBCPP_SUPPRESS_DEPRECATED_PUSH)
-#  define _LIBCPP_SUPPRESS_DEPRECATED_PUSH
-#  define _LIBCPP_SUPPRESS_DEPRECATED_POP
+#else
+#   define _LIBCPP_SUPPRESS_DEPRECATED_PUSH
+#   define _LIBCPP_SUPPRESS_DEPRECATED_POP
 #endif
 
 #if _LIBCPP_STD_VER <= 11
 #  define _LIBCPP_EXPLICIT_AFTER_CXX11
 #else
 #  define _LIBCPP_EXPLICIT_AFTER_CXX11 explicit
 #endif
 

 #endif
 
 #if _LIBCPP_STD_VER > 14 && defined(__cpp_inline_variables) && (__cpp_inline_variables >= 201606L)
 #  define _LIBCPP_INLINE_VAR inline
 #else
 #  define _LIBCPP_INLINE_VAR
 #endif
 
-#ifndef _LIBCPP_CONSTEXPR_IF_NODEBUG
 #if defined(_LIBCPP_DEBUG) || defined(_LIBCPP_HAS_NO_CXX14_CONSTEXPR)
-#define _LIBCPP_CONSTEXPR_IF_NODEBUG
+#   define _LIBCPP_CONSTEXPR_IF_NODEBUG
 #else
-#define _LIBCPP_CONSTEXPR_IF_NODEBUG constexpr
+#   define _LIBCPP_CONSTEXPR_IF_NODEBUG constexpr
 #endif
-#endif
 
 #if __has_attribute(no_destroy)
 #  define _LIBCPP_NO_DESTROY __attribute__((__no_destroy__))
 #else
 #  define _LIBCPP_NO_DESTROY
 #endif
 
 #ifndef _LIBCPP_HAS_NO_ASAN

 // CloudABI is intended for running networked services. Processes do not
 // have standard input and output channels.
 #ifdef __CloudABI__
 #define _LIBCPP_HAS_NO_STDIN
 #define _LIBCPP_HAS_NO_STDOUT
 #endif
 
 // Some systems do not provide gets() in their C library, for security reasons.
-#ifndef _LIBCPP_C_HAS_NO_GETS
-#  if defined(_LIBCPP_MSVCRT) || \
-      (defined(__FreeBSD_version) && __FreeBSD_version >= 1300043) || \
-      defined(__OpenBSD__)
-#    define _LIBCPP_C_HAS_NO_GETS
-#  endif
-#endif
+#if defined(_LIBCPP_MSVCRT) || \
+#   define _LIBCPP_C_HAS_NO_GETS
+#endif
 
 #if defined(__BIONIC__) || defined(__CloudABI__) || defined(__NuttX__) ||      \
     defined(__Fuchsia__) || defined(__wasi__) || defined(_LIBCPP_HAS_MUSL_LIBC) || \
     defined(__MVS__) || defined(__OpenBSD__)
 #define _LIBCPP_PROVIDES_DEFAULT_RUNE_TABLE
 #endif
 
 // Thread-unsafe functions such as strtok() and localtime()

 // __attribute__ are present, the processing goes awry preventing the definition
 // of the types.
 #    if !defined(_LIBCPP_OBJECT_FORMAT_COFF)
 #      define _LIBCPP_HAS_THREAD_SAFETY_ANNOTATIONS
 #    endif
 #  endif
 #endif
 
-#ifndef _LIBCPP_THREAD_SAFETY_ANNOTATION
-#  ifdef _LIBCPP_HAS_THREAD_SAFETY_ANNOTATIONS
-#    define _LIBCPP_THREAD_SAFETY_ANNOTATION(x) __attribute__((x))
-#  else
-#    define _LIBCPP_THREAD_SAFETY_ANNOTATION(x)
-#  endif
-#endif // _LIBCPP_THREAD_SAFETY_ANNOTATION
+#ifdef _LIBCPP_HAS_THREAD_SAFETY_ANNOTATIONS
+#   define _LIBCPP_THREAD_SAFETY_ANNOTATION(x) __attribute__((x))
+#else
+#   define _LIBCPP_THREAD_SAFETY_ANNOTATION(x)
+#endif
 
 #if __has_attribute(require_constant_initialization)
 #  define _LIBCPP_SAFE_STATIC __attribute__((__require_constant_initialization__))
 #else
 #  define _LIBCPP_SAFE_STATIC
 #endif
 
 #if !__has_builtin(__builtin_addressof) && _GNUC_VER < 700

 #endif
 
 #if __has_attribute(__nodebug__)
 #define _LIBCPP_NODEBUG __attribute__((__nodebug__))
 #else
 #define _LIBCPP_NODEBUG
 #endif
 
-#ifndef _LIBCPP_NODEBUG_TYPE
-#if __has_attribute(__nodebug__) && \
-    (defined(_LIBCPP_CLANG_VER) && _LIBCPP_CLANG_VER >= 900)
-#define _LIBCPP_NODEBUG_TYPE __attribute__((nodebug))
+#if __has_attribute(__nodebug__) && (defined(_LIBCPP_CLANG_VER) && _LIBCPP_CLANG_VER >= 900)
+#   define _LIBCPP_NODEBUG_TYPE __attribute__((nodebug))
 #else
-#define _LIBCPP_NODEBUG_TYPE
+#   define _LIBCPP_NODEBUG_TYPE
 #endif
-#endif // !defined(_LIBCPP_NODEBUG_TYPE)
 
 #if __has_attribute(__standalone_debug__)
 #define _LIBCPP_STANDALONE_DEBUG __attribute__((__standalone_debug__))
 #else
 #define _LIBCPP_STANDALONE_DEBUG
 #endif
 
 #if __has_attribute(__preferred_name__)