[Bug c/42204] New: update_eliminables should be called in reload after something changes

[hutchinsonandy at gcc dot gnu dot org]

This bug was previously mentioned in email from Denis. I have confirmed this on
4.5 (after long but educational tour of reload)

http://gcc.gnu.org/ml/gcc/2006-03/msg00783.html

When stacks slots increase from zero in reload() (in my case due to
setup_save_areas() ) the register elimination conditions can change. For
example the AVR port has:

get_frame_size () > 0 

as part of frame_pointer_required_p thus FP->SP elimination can change.

New slots do restart the spill and reload loop :

      /* If we allocated another stack slot, redo elimination bookkeeping.  */
      if (starting_frame_size != get_frame_size ())
        continue;

BUT update_eliminables is never called before calculate_needs_all_insns(), so
the wrong reloads are calculated (in my case marking the FP to be spilled in
the just added caller save insn !)

As a consequence, a spill and reload failure occurs.

The solution would seem to be to add update_eliminables before
calculate_needs_all_insns (global);


-- 
           Summary: update_eliminables should be called in reload after
                    something changes
           Product: gcc
           Version: 4.5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: hutchinsonandy at gcc dot gnu dot org
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: avr-unknown-none


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42204