[[musttail]] does not work in trivial noexcept functions

[chfast]

There is no way to use [[clang::musttail]] in any noexcept function.

int call(int) noexcept;

int musttail(int x) noexcept
{
    [[clang::musttail]] return call(x);
}

https://godbolt.org/z/s9vYzPbqr

<source>:5:32: error: cannot compile this tail call skipping over cleanups yet
    [[clang::musttail]] return call(x);
                               ^~~~~~~

It would be nice if clang could handle this basic case where the callee is also noexcept and the exception cleanup section is not actually needed.

[haberman]

That error comes from here:

llvm-project/clang/lib/CodeGen/CGCall.cpp

Line 5368 in 1b1c8d8

CGM.ErrorUnsupported(MustTailCall, "tail call skipping over cleanups");

It seems that there must be something on the cleanup stack that either isn't an EHCleanupScope or for which isRedundantBeforeReturn() returns false.

Unfortunately I don't know an easy way to dump the cleanup stack in Godbolt.