PR97107, libgo fails to build for power10

[Segher Boessenkool]

Hi!

On Tue, Sep 22, 2020 at 09:55:12AM +0930, Alan Modra wrote:
> Calls from split-stack code to non-split-stack code need to expand
> mapped stack memory via __morestack.  Even tail calls.
> 
> __morestack is quite a surprising function on powerpc in that it calls
> back to its caller, and a tail call will continue running in the
> context of extra mapped stack.

Also known as "pure evil" :-)

> 	PR target/97107
> 	* config/rs6000/rs6000-internal.h (struct rs6000_stack): Improve
> 	calls_p comment.
> 	* config/rs6000/rs6000-logue.c (rs6000_stack_info): Likewise.
> 	(rs6000_expand_split_stack_prologue): Emit the prologue for
> 	functions that make a sibling call.

>    if (!info->push_p)
> -    return;
> +    {
> +      /* We need the -fsplit-stack prologue for functions that make
> +	 tail calls.  Tail calls don't count against crtl->is_leaf.  */
> +      for (insn = get_topmost_sequence ()->first; insn; insn = NEXT_INSN (insn))
> +	if (CALL_P (insn))
> +	  break;
> +      if (!insn)
> +	return;
> +    }

I don't think that get_topmost_sequence is correct.

Other than that this is fine for trunk (and backports).  Thanks!


Segher