[pclmulqdq]

The major C++ compilers are perfectly conformant with the standard. Where they can lag is after standards come out. Modules have been a challenge, but other language features get implemented within a few years. At the time of writing, all the major compilers conform with C++ 17 and aside from modules, conform with C++ 20. There absolutely is "one true C++" as set by the standard, and compiler writers have a roadmap for how to conform to it.

"The implementation is the specification" is frankly a sophomoric position. It works fine for small projects and projects of limited complexity, but Rust is neither of these.

[epage]

Looking over https://en.cppreference.com/w/cpp/compiler_support, it seems there is good conformance on C++11 and C++14 but there are gaps on C++17+ among gcc, msvc, and clang.

[gpderetta]

The gaps are on the standard library side: clang libc++ has fallen behind a bit on conformance, but you can use libstdc++ on clang as well (and it is the default for example on Linux). MSVC lags on C conformance, which is known not to be primary concern for MS (but still miles better than what it used to be).

In any cases these tables only help up to a point, even green cells often hide bugs and conformance divergences.

Still for most straightforward code compliance across compilers is very good and significantly better than the dark ages of two decades ago.

[epage]

Completely agree. I'm only calling it out because of the claim "perfectly conformant with the standard".

[pclmulqdq]

The compiler is conformant. The STL is not necessarily.