Re: [PATCH v3 1/5] Improve must tail in RTL backend

[Andi Kleen <ak@linux.intel.com>]

> This results in "error: cannot tail-call: cannot tail-call: other reasons".
> So the second argument should be "other reasons" only.

Yes will fix those. Thanks.

> 
> I notice that if I don't use -O2 I also get "other reasons".  But it should be
> easy-ish to say "cannot tail-call: optimizations not enabled" or so.

It's unfortunately not easy to distinguish. It's not just -O2, but
various missing transformations make tree-tailcall not do it its job,
and they could depend on other flags. But there might be also other
reasons not related to the optimization that makes the tail call fall.
I would be uncomfortable reporting the problem is -O2 when it might 
be something else.

The right fix would be to make tree-tailcall not fail with optimization,
and for the remaining cases add errors there.  But that would
make the patch a lot bigger and it's not clear it would improve usability
that much. So I opted to just mention the problem in the documentation.

-Andi