[libcxx-commits] [PATCH] D119152: [libc++] Implement P0627R6 (Function to mark unreachable code)

[Louis Dionne via Phabricator via libcxx-commits]

ldionne added a comment.

In D119152#3309167 <https://reviews.llvm.org/D119152#3309167>, @Quuxplusone wrote:

> I don't think that's guaranteed. `__builtin_unreachable()` just means "assume false"; it doesn't necessarily translate into a `ud2` AFAIK, especially if we're talking about something that will work on both GCC and Clang.
> Even on Clang at `-O0`, it seems to just flow off the unreachable end of `main` into whatever code follows that in memory: https://godbolt.org/z/fz6hh76P5

Oh right, that's why I was seeing invalid instruction. For some reason I thought Clang was inserting something like a `__builtin_trap()`. I stand corrected.

> However, I think we //could// do a `verify.cpp` test: namely,
>
>   [[noreturn]] void f() { std::unreachable(); }
>
> should //not// trigger Clang's diagnostic `warning: function declared 'noreturn' should not return [-Winvalid-noreturn]`. If it does, that's a bug.

Yeah, I think that's the best we can do. At least we'll test that `unreachable()` is marked as `[[noreturn]]`.


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https://reviews.llvm.org/D119152