commit 767537a8b027bcb5807bb45b0268c5da98c2c7a0 Author: Jonathan Wakely Date: Wed Dec 16 15:54:50 2020 libstdc++: Warn if __STRICT_ANSI has been undefined Recent changes to use __int128 as an integer-like type in and to optimize std::uniform_int_distribution mean that the library relies on __int128 more heavily than in the past. The library expects that if __int128 is supported then either __GLIBCXX_TYPE_INT_N_0 is defined (and we treat is like the standard integer types), or __STRICT_ANSI__ is defined (and we need to add special handling for __int128 as a non-standard integer type). If users compile with -std=c++NN -U__STRICT_ANSI__ then it puts the library into a broken and inconsistent state, where the compiler doesn't define the __GLIBCXX_TYPE_INT_N_0 macro, but the library thinks it doesn't need special handling for __int128. What the user should do is compile with -std=gnu++NN instead. This adds a warning if it appears that __int128 is supported but neither __GLIBCXX_TYPE_INT_N_0 nor __STRICT_ANSI__ is defined. libstdc++-v3/ChangeLog: * include/bits/c++config: Warn if __STRICT_ANSI__ state is inconsistent with __GLIBCXX_TYPE_INT_N_0. diff --git a/libstdc++-v3/include/bits/c++config b/libstdc++-v3/include/bits/c++config index 155d0f46b16..cd7678eb16d 100644 --- a/libstdc++-v3/include/bits/c++config +++ b/libstdc++-v3/include/bits/c++config @@ -524,6 +524,15 @@ namespace std #define _GLIBCXX_USE_ALLOCATOR_NEW +#ifdef __SIZEOF_INT128__ +#if ! defined __GLIBCXX_TYPE_INT_N_0 && ! defined __STRICT_ANSI__ +// If __int128 is supported, we expect __GLIBCXX_TYPE_INT_N_0 to be defined +// unless the compiler is in strict mode. If it's not defined and the strict +// macro is not defined, something is wrong. +#warning "__STRICT_ANSI__ seems to have been undefined; this is not supported" +#endif +#endif + #else // !__cplusplus # define _GLIBCXX_BEGIN_EXTERN_C # define _GLIBCXX_END_EXTERN_C