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

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

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

--- Comment #16 from Segher Boessenkool <segher at gcc dot gnu.org> ---
Yup, GPR31 is used for the emulated frame pointer, so this is user error:
saying
a fixed-purpose register is clobbered makes no sense.  You are not allowed to
use any register that the compiler uses for function calling any other way.

It is a bad idea to use -fno-omit-frame-pointer on Power, btw, just like on any
other architecture that does not have a frame pointer architecturally.  We
don't
have one in any ABI even (for C at least, who knows what other languages (or
language implementations) do).  It is a grudge for targets that do not generate
proper DWARF, or you can use it to quickly validate some (suspected!) bug is
not
in certain parts of the compiler; but we do not want to ever use it by default,
esp. because it is so costly.  Benchmark it, and quickly be dissuaded from even
thinking about ever doing this.  Progress is Good.