[Bug rtl-optimization/114664] -fno-omit-frame-pointer causes an ICE during the build of the greenlet package

["rsandifo at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114664

--- Comment #10 from Richard Sandiford <rsandifo at gcc dot gnu.org> ---
(In reply to Peter Bergner from comment #7)
> Then that would seem to indicate that mentioning the frame pointer reg in
> the asm clobber list is an error
Yeah, I agree it's an error.  The PR says “ICE”, but is there an internal
error?  The “cannot be used in ‘asm’ here” is a normal user-facing error,
albeit with bad error recovery, leading us to report the same thing multiple
times.

> but how are users supposed to know whether
> -fno-omit-frame-pointer is in effect or not?  I've looked and there is no
> pre-defined macro a user could check.
That might be a useful thing to have, but if the programmer has no control over
the build flags (i.e. cannot require/force -fomit-frame-pointer) then I think
the asm has to take care to save and restore the frame pointer itself.

Dropping "31" from the asm means that the asm must preserve the register. 
Things will go badly if the asm doesn't do that.