[dgrunwald]

> All noexcept does is catch any exception and immediately std::terminate.

While that's a possible implementation; the standard is a bit more relaxed: `noexcept` may also call `std::terminate` immediately when an exception is thrown, without calling destructors in the usual way a catch block would do.

https://godbolt.org/z/YTe84M5vq test1 has a ~S() destructor call if maybe_throw() throws; test2 never calls ~S().

MSVC does not appear to support this optimization, so using `noexcept` with MSVC involves overhead similar to the catch-block.

[gpderetta]

More than an optimization is a different exception handling philosophy.

AFAIK itanium ABI exception handling requires two phase unwinding: first the stack is traversed looking for a valid landing pad: if it succeeds then the stack is traversed again calling all destructors. If it fails it calls std terminate. This is actually slower as it need to traverse twice, but the big advantage is that if the program would abort, the state of the program is preserved in the core file. This is easily generalized with noexcept functions: no unwind info is generated for those, so unwind always fail.

MSVC used to do one pass unwind, but I thought they changed it when they implemented table based unwind for x64.