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Re: CAN_ELIMINATE question
Eric Christopher <echristo@apple.com> writes:
> On Feb 13, 2006, at 7:43 AM, Denis Chertykov wrote:
>
> > Hi All.
> >
> > While I have debugging AVR target bug I found that something wrong in
> > port code or in reload.
> >
> > Is it right to use of get_frame_size() inside CAN_ELIMINATE macro
> > valid ?
> > If yes then reload have a bug.
> > If no then AVR and probably MIPS ports have invalid definitions of
> > CAN_ELIMINATE.
>
> Can you point to where you think reload is getting this wrong?
Yes.
Code fragment from reload1.c: reload()
----------------------------------------------------
if (caller_save_needed)
setup_save_areas ();
/* If we allocated another stack slot, redo elimination bookkeeping. */
if (starting_frame_size != get_frame_size ())
continue;
if (caller_save_needed)
{
save_call_clobbered_regs ();
/* That might have allocated new insn_chain structures. */
reload_firstobj = obstack_alloc (&reload_obstack, 0);
}
calculate_needs_all_insns (global);
----------------------------------------------------
Call to setup_save_areas () can change frame size but only offsets on
eliminable registers will be changed before call to calculate_needs_all_insns.
calculate_needs_all_insns will calculate wrong needs for elimination.
Example for AVR:
avr target can eliminate fp -> sp only if get_frame_size () == 0.
Before call to setup_save_areas() frame size was 0 (CAN_ELIMINATE (FP,SP) != 0)
setup_save_areas() increase frame size.
set_initial_elim_offsets() correct offsets but can_eliminate isn't changed.
save_call_clobbered_regs () emit save insn
(insn 659 161 162 16 (set (mem/c:HI (plus:HI (reg/f:HI 28 r28) # it's FP
(const_int 1 [0x1])) [29 S2 A8])
(reg:HI 24 r24)) 12 {*movhi} (nil)
(nil))
calculate_needs_all_insns() try to eliminate (reg/f:HI 28 r28) to SP.
It's wrong because get_frame_size () != 0 and CAN_ELIMINATE (FP,SP) == 0
I think that better to call update_eliminables() somewhere after
setup_save_areas()
Denis.