[Bug target/85666] gcc-8.0.1 fails to build mmix target: gcc/libgcc/libgcc2.h:203:20: internal compiler error: in leaf_function_p, at final.c:4488

[hp at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85666

--- Comment #7 from Hans-Peter Nilsson <hp at gcc dot gnu.org> ---
Thank you for your interest in the MMIX port.

(In reply to Wilco from comment #3)
> (In reply to Sergei Trofimovich from comment #1)
> 
> >  #define MMIX_CFUN_NEEDS_SAVED_EH_RETURN_ADDRESS			\
> >   (flag_exceptions						\
> >    && ((reload_completed && df_regs_ever_live_p (MMIX_rJ_REGNUM))	\
> >  || !leaf_function_p ())) /// <- here
> 
> 
> Yes that looks like a bug. leaf_function_p cannot be called on a sequence as
> it will incorrectly return true on non-leaf functions. So
> MMIX_CFUN_NEEDS_SAVED_EH_RETURN_ADDRESS will randomly change its result if
> called again later. starting_frame_offset should however return a fixed
> value, so the reload_completed part also looks wrong.

Kindly refer to the comment above that macro:

/* We have no means to tell DWARF 2 about the register stack, so we need
   to store the return address on the stack if an exception can get into
   this function.  FIXME: Narrow condition.  Before any whole-function
   analysis, df_regs_ever_live_p () isn't initialized.  We know it's up-to-date
   after reload_completed; it may contain incorrect information some time
   before that.  Within a RTL sequence (after a call to start_sequence,
   such as in RTL expanders), leaf_function_p doesn't see all insns
   (perhaps any insn).  But regs_ever_live is up-to-date when
   leaf_function_p () isn't, so we "or" them together to get accurate
   information.  FIXME: Some tweak to leaf_function_p might be
   preferable.  */

So, it looks like the time has come for "some tweak to leaf_function_p",
or...some other tweak.  Yes, this was a brittle solution and someone saw fit to
pull the rug.  Maybe I'll have to compute the starting frame offset some other
way.