Since you can also put noexcept(false) to indicate something throws exceptions and you didn't just forget to mark it noexcept, it's not a bad policy to say every move constructor should have a noexcept marker.

That assertion completely misses the point. The scenarios involving move constructors throwing exceptions involve objects being stuck in an inconsistent/zombie state. In fact, the whole point of a move constructors is to avoid having to allocate memory.

Folks might be using mmap with MAP_POPULATE; they might have overcommit turned off; they might be operating in an rlimit/cgroup (like most container runtimes/orchestrators configure) that limits memory; they might be on a system which doesn't have virtual memory (plenty such systems exist in 64-bit architectures); they might be using calloc on an OS that zeros pessimistically/early; and so on.

https://clang.llvm.org/extra/clang-tidy/checks/performance/n... constructor.html

Note that the way std::vector (and other STL containers) require noexcept move constructors for reallocation is by using template matching, and of course any other code might be doing this too, so having a compiler option that forced a constructor (or anything) to have a type signature different than the way it was declared would be a pretty dangerous thing to do since it'd be hard to know what the consequences would be.