Re: [PATCH 1/2] symtab: also change RTL decl name

[Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>]

On Mon, 21 Nov 2022 20:02:49 +0100
Jan Hubicka <hubicka@ucw.cz> wrote:

> > Hi Honza, Ping.
> > Regtests cleanly for c,fortran,c++,ada,d,go,lto,objc,obj-c++
> > Ok?
> > I'd need this for attribute target_clones for the Fortran FE.  
> Sorry for delay here.
> > >  void
> > > @@ -303,6 +301,10 @@ symbol_table::change_decl_assembler_name (tree decl, tree name)
> > >  	warning (0, "%qD renamed after being referenced in assembly", decl);
> > >  
> > >        SET_DECL_ASSEMBLER_NAME (decl, name);
> > > +      /* Set the new name in rtl.  */
> > > +      if (DECL_RTL_SET_P (decl))
> > > +	XSTR (XEXP (DECL_RTL (decl), 0), 0) = IDENTIFIER_POINTER (name);  
> 
> I am not quite sure how safe this is.  We generally produce DECL_RTL
> when we produce assembly file.  So if DECL_RTL is set then we probably
> already output the original function name and it is too late to change
> it.

AFAICS we make_decl_rtl in the fortran FE in trans_function_start.

> 
> Also RTL is shared so changing it in-place is going to rewrite all the
> existing RTL expressions using it.
> 
> Why the DECL_RTL is produced for function you want to rename?

I think the fortran FE sets it quite early when lowering a function.
Later, when the ME creates the target_clones, it wants to rename the
initial function to initial_fun.default for the default target.
That's where the change_decl_assembler_name is called (only on the
decl).
But nobody changes the RTL name, so the ifunc (which should be the
initial, unchanged name) is properly emitted but
assemble_start_function uses the same, unchanged, initial fnname it
later obtains by get_fnname_from_decl which fetches the (wrong) initial
name where it should use the .default target name.
See
https://gcc.gnu.org/pipermail/gcc-patches/2022-November/605081.html

I'm open to other suggestions to make this work in a different way, of
course. Maybe we're missing some magic somewhere that might share the
name between the fndecl and the RTL XSTR so the RTL is magically
updated by that single SET_ECL_ASSEMBLER_NAME in
change_decl_assembler_name? But i didn't quite see where that'd be?

thanks,

> Honza
> > > +
> > >        if (alias)
> > >  	{
> > >  	  IDENTIFIER_TRANSPARENT_ALIAS (name) = 1;  
> >